draft-ietf-ace-coap-est-07.txt   draft-ietf-ace-coap-est-08.txt 
ACE P. van der Stok ACE P. van der Stok
Internet-Draft Consultant Internet-Draft Consultant
Intended status: Standards Track P. Kampanakis Intended status: Standards Track P. Kampanakis
Expires: July 13, 2019 Cisco Systems Expires: August 10, 2019 Cisco Systems
M. Richardson M. Richardson
SSW SSW
S. Raza S. Raza
RISE SICS RISE SICS
January 9, 2019 February 6, 2019
EST over secure CoAP (EST-coaps) EST over secure CoAP (EST-coaps)
draft-ietf-ace-coap-est-07 draft-ietf-ace-coap-est-08
Abstract Abstract
Enrollment over Secure Transport (EST) is used as a certificate Enrollment over Secure Transport (EST) is used as a certificate
provisioning protocol over HTTPS. Low-resource devices often use the provisioning protocol over HTTPS. Low-resource devices often use the
lightweight Constrained Application Protocol (CoAP) for message lightweight Constrained Application Protocol (CoAP) for message
exchanges. This document defines how to transport EST payloads over exchanges. This document defines how to transport EST payloads over
secure CoAP (EST-coaps), which allows constrained devices to use secure CoAP (EST-coaps), which allows constrained devices to use
existing EST functionality for provisioning certificates. existing EST functionality for provisioning certificates.
skipping to change at page 1, line 40 skipping to change at page 1, line 40
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 13, 2019. This Internet-Draft will expire on August 10, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Conformance to RFC7925 profiles . . . . . . . . . . . . . . . 6 4. Conformance to RFC7925 profiles . . . . . . . . . . . . . . . 6
5. Protocol Design . . . . . . . . . . . . . . . . . . . . . . . 7 5. Protocol Design . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Mandatory/optional EST Functions . . . . . . . . . . . . 7 5.1. Discovery and URIs . . . . . . . . . . . . . . . . . . . 8
5.2. Payload format . . . . . . . . . . . . . . . . . . . . . 8 5.2. Mandatory/optional EST Functions . . . . . . . . . . . . 10
5.2.1. Content Format application/multipart-core . . . . . . 8 5.3. Payload formats . . . . . . . . . . . . . . . . . . . . . 10
5.3. Message Bindings . . . . . . . . . . . . . . . . . . . . 9 5.4. Message Bindings . . . . . . . . . . . . . . . . . . . . 12
5.4. CoAP response codes . . . . . . . . . . . . . . . . . . . 10 5.5. CoAP response codes . . . . . . . . . . . . . . . . . . . 13
5.5. Message fragmentation . . . . . . . . . . . . . . . . . . 10 5.6. Message fragmentation . . . . . . . . . . . . . . . . . . 13
5.6. Delayed Responses . . . . . . . . . . . . . . . . . . . . 11 5.7. Delayed Responses . . . . . . . . . . . . . . . . . . . . 14
5.7. Server-side Key Generation . . . . . . . . . . . . . . . 13 5.8. Server-side Key Generation . . . . . . . . . . . . . . . 16
5.8. Deployment limits . . . . . . . . . . . . . . . . . . . . 14 6. DTLS Transport Protocol . . . . . . . . . . . . . . . . . . . 18
6. Discovery and URIs . . . . . . . . . . . . . . . . . . . . . 15 7. HTTPS-CoAPS Registrar . . . . . . . . . . . . . . . . . . . . 19
7. DTLS Transport Protocol . . . . . . . . . . . . . . . . . . . 16 8. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 21
8. HTTPS-CoAPS Registrar . . . . . . . . . . . . . . . . . . . . 18 9. Deployment limitations . . . . . . . . . . . . . . . . . . . 21
9. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 19 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 10.1. Content-Format Registry . . . . . . . . . . . . . . . . 22
10.1. Content-Format Registry . . . . . . . . . . . . . . . . 20 10.2. Resource Type registry . . . . . . . . . . . . . . . . . 22
10.2. Resource Type registry . . . . . . . . . . . . . . . . . 21 11. Security Considerations . . . . . . . . . . . . . . . . . . . 23
11. Security Considerations . . . . . . . . . . . . . . . . . . . 22 11.1. EST server considerations . . . . . . . . . . . . . . . 23
11.1. EST server considerations . . . . . . . . . . . . . . . 22 11.2. HTTPS-CoAPS Registrar considerations . . . . . . . . . . 25
11.2. HTTPS-CoAPS Registrar considerations . . . . . . . . . . 23 12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25
12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 24 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 14.1. Normative References . . . . . . . . . . . . . . . . . . 26
14.1. Normative References . . . . . . . . . . . . . . . . . . 24 14.2. Informative References . . . . . . . . . . . . . . . . . 28
14.2. Informative References . . . . . . . . . . . . . . . . . 25 Appendix A. EST messages to EST-coaps . . . . . . . . . . . . . 30
Appendix A. EST messages to EST-coaps . . . . . . . . . . . . . 28 A.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 31
A.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 28 A.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 33
A.2. csrattrs . . . . . . . . . . . . . . . . . . . . . . . . 30 A.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 35
A.3. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 31 A.4. csrattrs . . . . . . . . . . . . . . . . . . . . . . . . 37
A.4. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 33 Appendix B. EST-coaps Block message examples . . . . . . . . . . 38
Appendix B. EST-coaps Block message examples . . . . . . . . . . 35 B.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 38
B.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 36 B.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 42
B.2. enroll . . . . . . . . . . . . . . . . . . . . . . . . . 39 Appendix C. Message content breakdown . . . . . . . . . . . . . 43
Appendix C. Message content breakdown . . . . . . . . . . . . . 40 C.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 43
C.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 40 C.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 45
C.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 41 C.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 46
C.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 43 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 48
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 45
1. Change Log 1. Change Log
EDNOTE: Remove this section before publication EDNOTE: Remove this section before publication
-08
added application/pkix-cert Content-Format TBD287.
Stated that well-known/est is compulsory
Use of response codes clarified.
removed bugs: Max-Age and Content-Format Options in Request
Accept Option explained for est/skg and added in enroll example
Persistenc of DTLS connection clarified.
Minor text fixes.
-07: -07:
redone examples from scratch with openssl redone examples from scratch with openssl
Updated authors. Updated authors.
Added CoAP RST as a MAY for an equivalent to an HTTP 204 message. Added CoAP RST as a MAY for an equivalent to an HTTP 204 message.
Added serialization example of the /skg CBOR response. Added serialization example of the /skg CBOR response.
skipping to change at page 4, line 27 skipping to change at page 4, line 41
-04: -04:
Updated Delayed response section to reflect short and long delay Updated Delayed response section to reflect short and long delay
options. options.
-03: -03:
Removed observe and simplified long waits Removed observe and simplified long waits
Repaired content-format specification Repaired Content-Format specification
-02: -02:
Added parameter discussion in section 8 Added parameter discussion in section 8
Concluded content-format specification using multipart-ct draft Concluded Content-Format specification using multipart-ct draft
examples updated examples updated
-01: -01:
Editorials done. Editorials done.
Redefinition of proxy to Registrar in Section 8. Explained better Redefinition of proxy to Registrar in Section 7. Explained better
the role of https-coaps Registrar, instead of "proxy" the role of https-coaps Registrar, instead of "proxy"
Provide "observe" option examples Provide "observe" Option examples
extended block message example. extended block message example.
inserted new server key generation text in Section 5.7 and inserted new server key generation text in Section 5.8 and
motivated server key generation. motivated server key generation.
Broke down details for DTLS 1.3 Broke down details for DTLS 1.3
New media type uses CBOR array for multiple content-format
New Media-Type uses CBOR array for multiple Content-Format
payloads payloads
provided new content format tables provided new Content-Format tables
new media format for IANA new media format for IANA
-00 -00
copied from vanderstok-ace-coap-04 copied from vanderstok-ace-coap-04
2. Introduction 2. Introduction
"Classical" Enrollment over Secure Transport (EST) [RFC7030] is used "Classical" Enrollment over Secure Transport (EST) [RFC7030] is used
for authenticated/authorized endpoint certificate enrollment (and for authenticated/authorized endpoint certificate enrollment (and
optionally key provisioning) through a Certificate Authority (CA) or optionally key provisioning) through a Certificate Authority (CA) or
Registration Authority (RA). EST messages run over HTTPS. Registration Authority (RA). EST transports messages over HTTPS.
This document defines a new transport for EST based on the This document defines a new transport for EST based on the
Constrained Application Protocol (CoAP) since some Internet of Things Constrained Application Protocol (CoAP) since some Internet of Things
(IoT) devices use CoAP instead of HTTP. Therefore, this (IoT) devices use CoAP instead of HTTP. Therefore, this
specification utilizes DTLS [RFC6347], CoAP [RFC7252], and UDP specification utilizes DTLS [RFC6347], CoAP [RFC7252] and UDP instead
instead of TLS [RFC8446], HTTP [RFC7230] and TCP. of TLS [RFC8446], HTTP [RFC7230] and TCP.
EST responses can be relatively large and for this reason this EST responses can be relatively large and for this reason this
specification also uses CoAP Block-Wise Transfer [RFC7959] to offer a specification also uses CoAP Block-Wise Transfer [RFC7959] to offer a
fragmentation mechanism of EST messages at the CoAP layer. fragmentation mechanism of EST messages at the CoAP layer.
This document also profiles the use of EST to only support This document also profiles the use of EST to only support
certificate-based client authentication. HTTP Basic or Digest certificate-based client authentication. HTTP Basic or Digest
authentication (as described in Section 3.2.3 of [RFC7030] are not authentication (as described in Section 3.2.3 of [RFC7030] are not
supported. supported.
3. Terminology 3. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
Many of the concepts in this document are taken over from [RFC7030]. Many of the concepts in this document are taken from [RFC7030].
Consequently, much text is directly traceable to [RFC7030]. The same Consequently, much text is directly traceable to [RFC7030].
document structure is followed to point out the differences and
commonalities between EST and EST-coaps.
4. Conformance to RFC7925 profiles 4. Conformance to RFC7925 profiles
This section shows how EST-coaps fits into the profiles of low- This section describes how EST-coaps fits into the profiles of low-
resource devices described in [RFC7925]. EST-coaps can transport resource devices described in [RFC7925]. EST-coaps can transport
certificates and private keys. Certificates are responses to certificates and private keys. Certificates are responses to
(re-)enrollment requests or requests for a trusted certificate list. (re-)enrollment requests or requests for a trusted certificate list.
Private keys can be transported as responses to a server-side key Private keys can be transported as responses to a server-side key
generation request as described in section 4.4 of [RFC7030] snd generation request as described in section 4.4 of [RFC7030] and
discussed in Section 5.7 of this document. discussed in Section 5.8 of this document.
As per Sections 3.3 and 4.4 of [RFC7925], the mandatory cipher suite As per Sections 3.3 and 4.4 of [RFC7925], the mandatory cipher suite
for DTLS in EST-coaps is TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 for DTLS in EST-coaps is TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8
[RFC7251]. Curve secp256r1 MUST be supported [RFC8422]; this curve [RFC7251]. Curve secp256r1 MUST be supported [RFC8422]; this curve
is equivalent to the NIST P-256 curve. Crypto agility is important, is equivalent to the NIST P-256 curve. Crypto agility is important,
and the recommendations in [RFC7925] section 4.4 and any updates to and the recommendations in [RFC7925] section 4.4 and any updates to
RFC7925 concerning Curve25519 and other CFRG curves also apply. RFC7925 concerning Curve25519 and other CFRG curves also apply.
DTLS1.2 implementations MUST use the Supported Elliptic Curves and DTLS1.2 implementations MUST use the Supported Elliptic Curves and
Supported Point Formats Extensions [RFC8422]. Uncompressed point Supported Point Formats Extensions [RFC8422]. Uncompressed point
format MUST also be supported. [RFC6090] can be used as summary of format MUST also be supported. [RFC6090] is a summary of the ECC
the ECC algorithms. DTLS 1.3 [I-D.ietf-tls-dtls13] implementations algorithms. DTLS 1.3 [I-D.ietf-tls-dtls13] implementations differ
differ from DTLS 1.2 because they do not support point format from DTLS 1.2 because they do not support point format negotiation in
negotiation in favor of a single point format for each curve and thus favor of a single point format for each curve. Thus, support for
support for DTLS 1.3 does not mandate point formation extensions and DTLS 1.3 does not mandate point formation extensions and negotiation.
negotiation.
The authentication of the EST-coaps server by the EST-coaps client is The authentication of the EST-coaps server by the EST-coaps client is
based on certificate authentication in the DTLS handshake. The EST- based on certificate authentication in the DTLS handshake. The EST-
coaps client MUST be configured with at least an Implicit TA database coaps client MUST be configured with at least an Implicit TA database
from its manufacturer which will allow for the authenticating the from its manufacturer which will enable the authentication of the
server the first time before updating its trust anchor (Explicit TA) server the first time before updating its trust anchor (Explicit TA)
[RFC7030]. [RFC7030].
The authentication of the EST-coaps client is based on a client The authentication of the EST-coaps client MUST be with a client
certificate in the DTLS handshake. This can either be certificate in the DTLS handshake. This can either be
o a previously issued client certificate (e.g., an existing o a previously issued client certificate (e.g., an existing
certificate issued by the EST CA); this could be a common case for certificate issued by the EST CA); this could be a common case for
simple reenrollment of clients. simple re-enrollment of clients.
o a previously installed certificate (e.g., manufacturer-installed o a previously installed certificate (e.g., manufacturer IDevID
IDevID (IEEE 802.1AR [ieee802.1ar] certificate or a certificate [ieee802.1ar] or a certificate issued by some other party); the
issued by some other party); the server is expected to trust the server is expected to trust that certificate. IDevID's are
previously installed CA certificate in this case. IDevID's are
expected to have a very long life, as long as the device, but expected to have a very long life, as long as the device, but
under some conditions could expire. In the latter case, the under some conditions could expire. In that case, the server MAY
server MAY want to authenticate a client certificate against its want to authenticate a client certificate against its trust store
trust store although the certificate is expired (Section 11). although the certificate is expired (Section 11).
Client authentication via DTLS Client Certificate is mandatory.
5. Protocol Design 5. Protocol Design
EST-coaps uses CoAP to transfer EST messages, aided by Block-Wise EST-coaps uses CoAP to transfer EST messages, aided by Block-Wise
Transfer [RFC7959] to transport CoAP messages in blocks thus avoiding Transfer [RFC7959] to avoid (excessive) fragmentation of UDP
(excessive) fragmentation of UDP datagrams. The use of "Block" for datagrams. The use of Blocks for the transfer of larger EST messages
the transfer of larger EST messages is specified in Section 5.5. is specified in Section 5.6. Figure 1 below shows the layered EST-
Figure 1 below shows the layered EST-coaps architecture. coaps architecture.
+------------------------------------------------+ +------------------------------------------------+
| EST request/response messages | | EST request/response messages |
+------------------------------------------------+ +------------------------------------------------+
| CoAP for message transfer and signalling | | CoAP for message transfer and signaling |
+------------------------------------------------+ +------------------------------------------------+
| DTLS for transport security | | DTLS for transport security |
+------------------------------------------------+ +------------------------------------------------+
| UDP for transport | | UDP for transport |
+------------------------------------------------+ +------------------------------------------------+
Figure 1: EST-coaps protocol layers Figure 1: EST-coaps protocol layers
The EST-coaps protocol design follows closely the EST design. The The EST-coaps protocol design follows closely the EST design. The
actions supported by EST-coaps are identified by their message types: supported message types in EST-coaps are:
o CA certificate retrieval, needed to receive the complete set of CA o CA certificate retrieval, needed to receive the complete set of CA
certificates. certificates.
o Simple enroll and reenroll, for CA to sign public client-identity o Simple enroll and reenroll, for a CA to sign public client-
key. identity key.
o Certificate Signing Request (CSR) Attributes request messages, o Certificate Signing Request (CSR) Attributes messages that informs
informs the client of the fields to include in generated CSR. the client of the fields to include in generated CSR.
o Server-side key generation messages, to provide a private client- o Server-side key generation messages to provide a private client-
identity key when the client choses for an external entity to identity key when the client choses so.
generate its private key.
5.1. Mandatory/optional EST Functions 5.1. Discovery and URIs
EST-coaps is targeted for low-resource networks with small packets.
Saving header space is important and short EST-coaps URIs are
specified in this document. These URIs are shorter than the ones in
[RFC7030]. Two example EST-coaps resource path names are:
coaps://est-coaps.example.ietf.org:<port>/.well-known/est/<short-est>
coaps://est-coaps.example.ietf.org:<port>/.well-known/est/
ArbitraryLabel/<short-est>
The short-est strings are defined in Table 1. The ArbitraryLabel
path-segment, if used, SHOULD be of the shortest length possible
(Sections 3.1 and 3.2.2 of [RFC7030]. Arbitrary Labels are usually
defined and used by EST CAs in order to route client requests to the
appropriate certificate profile.
The EST-coaps server URIs, obtained through discovery of the EST-
coaps root resource(s) as shown below, are of the form:
coaps://est-coaps.example.ietf.org:<port>/<root-resource>/<short-est>
coaps://est-coaps.example.ietf.org:<port>/<root-resource>/
ArbitraryLabel/<short-est>
Figure 5 in section 3.2.2 of [RFC7030] enumerates the operations and
corresponding paths which are supported by EST. Table 1 provides the
mapping from the EST URI path to the shorter EST-coaps URI path.
+------------------+-----------+
| EST | EST-coaps |
+------------------+-----------+
| /cacerts | /crts |
| /simpleenroll | /sen |
| /simplereenroll | /sren |
| /csrattrs | /att |
| /serverkeygen | /skg |
+------------------+-----------+
Table 1: Table 1: Short EST-coaps URI path
Clients and servers MUST support the short resource URIs. The
corresponding longer URIs from [RFC7030] MAY be supported.
In the context of CoAP, the presence and location of (path to) the
management data are discovered by sending a GET request to "/.well-
known/core" including a resource type (RT) parameter with the value
"ace.est" [RFC6690]. Upon success, the return payload will contain
the root resource of the EST resources. The example below shows the
discovery of the presence and location of EST-coaps resources.
Linefeeds are included only for readability.
REQ: GET /.well-known/core?rt=ace.est*
RES: 2.05 Content
</est>; rt="ace.est",
</est/crts>;rt="ace.est.crts";ct="281 TBD287",
</est/sen>;rt="ace.est.sen";ct="281 TBD287",
</est/sren>;rt="ace.est.sren";ct="281 TBD287",
</est/att>;rt="ace.est.att";ct=285,
</est/skg>;rt="ace.est.skg";ct="62 280 284 281 TBD287"
The first line of the discovery response above MUST be included. The
five consecutive lines after the first MAY be included. The return
of the content types allows the client to choose the most appropriate
one.
Port numbers, not returned in the example, are assumed to be the
default numbers 5683 and 5684 for CoAP and CoAPS respectively
(Sections 12.6 and 12.7 of [RFC7252]). Discoverable port numbers MAY
be returned in the <href> of the payload
[I-D.ietf-core-resource-directory]. An example response payload for
non-default CoAPS server port 61617 follows below. Linefeeds were
included only for readability.
REQ: GET /.well-known/core?rt=ace.est*
RES: 2.05 Content
<coap://[2001:db8:3::123]:61617/est>;rt="ace.est";
anchor="coap://[2001:db8:3::123]:61617",
<coap://[2001:db8:3::123]:61617/est/crts>;rt="ace.est.crts";
ct="281 TBD287";anchor="coap://[2001:db8:3::123]:61617",
<coap://[2001:db8:3::123]:61617/est/sen>;rt="ace.est.sen";
ct="281 TBD287";anchor="coap://[2001:db8:3::123]:61617",
<coap://[2001:db8:3::123]:61617/est/sren>;rt="ace.est.sren";
ct="281 TBD287";anchor="coap://[2001:db8:3::123]:61617",
<coap://[2001:db8:3::123]:61617/est/att>;rt="ace.est.att";
ct="285";anchor="coap://[2001:db8:3::123]:61617",
<coap://[2001:db8:3::123]:61617/est/skg>;rt="ace.est.skg";
ct="62 280 284 281 TBD287";anchor="coap://[2001:db8:3::123]:61617"
The server MUST support the default /.well-known/est server root
resource and port 5684. Resource discovery is necessary when the IP
address of the server is unknown to the client. Resource discovery
SHOULD be employed when non-default URIs (like /est or /est/
ArbitraryLabel) or ports are supported by the server, when the client
is unaware of what EST-coaps resources are available or if the client
considers sending two Uri-Path Options to convey the resource is
wasteful.
It is up to the implementation to choose its root resource;
throughout this document the example root resource /est is used.
5.2. Mandatory/optional EST Functions
This specification contains a set of required-to-implement functions, This specification contains a set of required-to-implement functions,
optional functions, and not specified functions. The latter ones are optional functions, and not specified functions. The latter ones are
deemed too expensive for low-resource devices in payload and deemed too expensive for low-resource devices in payload and
calculation times. calculation times.
Table 1 specifies the mandatory-to-implement or optional Table 2 specifies the mandatory-to-implement or optional
implementation of the est-coaps functions. implementation of the est-coaps functions.
+------------------+--------------------------+ +------------------+--------------------------+
| EST Functions | EST-coaps implementation | | EST Functions | EST-coaps implementation |
+------------------+--------------------------+ +------------------+--------------------------+
| /cacerts | MUST | | /cacerts | MUST |
| /simpleenroll | MUST | | /simpleenroll | MUST |
| /simplereenroll | MUST | | /simplereenroll | MUST |
| /fullcmc | Not specified | | /fullcmc | Not specified |
| /serverkeygen | OPTIONAL | | /serverkeygen | OPTIONAL |
| /csrattrs | OPTIONAL | | /csrattrs | OPTIONAL |
+------------------+--------------------------+ +------------------+--------------------------+
Table 1: Table 1: List of EST-coaps fuctions Table 2: Table 2: List of EST-coaps functions
While [RFC7030] permits a number of these functions to be used While [RFC7030] permits a number of these functions to be used
without authentication, this specification requires authentication without authentication, this specification requires that the client
for all functions. MUST be authenticated for all functions.
5.2. Payload format 5.3. Payload formats
The content-format (media type equivalent) of the CoAP message The Content-Format (HTTP Media-Type equivalent) of the CoAP message
determines which EST message is transported in the CoAP payload. The determines which EST message is transported in the CoAP payload. The
media types specified in the HTTP Content-Type header (section 3.2.2 Media-Types specified in the HTTP Content-Type header (section 3.2.2
of [RFC7030]) are in EST-coaps specified by the Content-Format Option of [RFC7030]) are in EST-coaps specified by the Content-Format Option
(12) of CoAP. The combination of URI path and content-format in EST- (12) of CoAP. The combination of URI-Path and Content-Format in EST-
coaps MUST map to an allowed combination of URI and media type in coaps MUST map to an allowed combination of URI and Media-Type in
EST. The required content-formats for these requests and response EST. The required Content-Formats for these requests and response
messages are defined in Section 10.1. The CoAP response codes are messages are defined in Section 10.1. The CoAP response codes are
defined in Section 5.4. defined in Section 5.5.
EST-coaps is designed for use between low-resource devices and hence Content-Format TBD287 can be used in place of 281 to carry a single
does not need to send Base64-encoded data. Simple binary is more certificate instead of a PKCS#7 container in a /crts, /sen, /sren or
efficient (30% smaller payload) and well supported by CoAP. Thus, /skg response. Content-Format 281 MUST be supported by EST-coaps
the payload for a given media type follows the ASN.1 structure of the servers. Servers MAY also support Content-Format TBD287. It is up
media-type and is transported in binary DER format. Section 5.2.1 to the client to support only Content-Format 281, TBD287 or both.
specifies the payload structure when multiple media types are present The client is expected to use an COAP Accept Option in the request to
in the payload. express the preferred response Content-Format. If an Accept Option
is not included in the request, the client is not expressing any
preference and the server SHOULD choose format 281. If the preferred
Content-Format cannot be returned, the server MUST send a 4.06 (Not
Acceptable) response, unless another error code takes precedence for
the response [RFC7252].
5.2.1. Content Format application/multipart-core Content-Format 286 is used in /sen, /sren and /skg requests and 285
in /att responses.
A representation with content format ID 62 contains a collection of EST-coaps is designed for low-resource devices and hence does not
representations along with their respective content format. The need to send Base64-encoded data. Simple binary is more efficient
content-format identifies the media-type application/multipart-core (30% smaller payload) and well supported by CoAP. Thus, the payload
specified in [I-D.ietf-core-multipart-ct]. for a given Media-Type follows the ASN.1 structure of the Media-Type
and is transported in binary format.
*application/multipart-core*
A representation with Content-Format identifier 62 contains a
collection of representations along with their respective Content-
Format. The Content-Format identifies the Media-Type application/
multipart-core specified in [I-D.ietf-core-multipart-ct].
The collection is encoded as a CBOR array [RFC7049] with an even The collection is encoded as a CBOR array [RFC7049] with an even
number of elements. The second, fourth, sixth, etc. element is a number of elements. The second, fourth, sixth, etc. element is a
binary string containing a representation. The first, third, fifth, binary string containing a representation. The first, third, fifth,
etc. element is an unsigned integer specifying the content format ID etc. element is an unsigned integer specifying the Content-Format
of the consecutive representation. For example, a collection identifier of the consecutive representation. For example, a
containing two representations in response to a server-side key collection containing two representations in response to a EST-coaps
generation request, could include a private key in PKCS#8 [RFC5958] server-side key generation request, could include a private key in
with content format ID 284 (0x011C) and a certificate with content PKCS#8 [RFC5958] with Content-Format identifier 284 (0x011C) and a
format ID 281 (0x0119). Such a collection would look like single certificate in a PKCS#7 container with Content-Format
identifier 281 (0x0119). Such a collection would look like
[284,h'0123456789abcdef', 281,h'fedcba9876543210'] in diagnostic CBOR [284,h'0123456789abcdef', 281,h'fedcba9876543210'] in diagnostic CBOR
notation. The serialization of such CBOR content would be notation. The serialization of such CBOR content would be
84 # array(4) 84 # array(4)
19 011C # unsigned(284) 19 011C # unsigned(284)
48 # bytes(8) 48 # bytes(8)
0123456789ABCDEF # "\x01#Eg\x89\xAB\xCD\xEF" 0123456789ABCDEF # "\x01#Eg\x89\xAB\xCD\xEF"
19 0119 # unsigned(281) 19 0119 # unsigned(281)
48 # bytes(8) 48 # bytes(8)
FEDCBA9876543210 # "\xFE\xDC\xBA\x98vT2\x10" FEDCBA9876543210 # "\xFE\xDC\xBA\x98vT2\x10"
Multipart /skg response serialization Multipart /skg response serialization
skipping to change at page 9, line 22 skipping to change at page 12, line 14
84 # array(4) 84 # array(4)
19 011C # unsigned(284) 19 011C # unsigned(284)
48 # bytes(8) 48 # bytes(8)
0123456789ABCDEF # "\x01#Eg\x89\xAB\xCD\xEF" 0123456789ABCDEF # "\x01#Eg\x89\xAB\xCD\xEF"
19 0119 # unsigned(281) 19 0119 # unsigned(281)
48 # bytes(8) 48 # bytes(8)
FEDCBA9876543210 # "\xFE\xDC\xBA\x98vT2\x10" FEDCBA9876543210 # "\xFE\xDC\xBA\x98vT2\x10"
Multipart /skg response serialization Multipart /skg response serialization
The PKCS#8 key and X.509 certificate representations are ASN.1 When the returned certificate is a single X.509 certificate (not a
encoded in binary DER format. An example is shown in Appendix A.4. PKCS#7 container) the Content-Format identifier is TBD287 (0x011F)
instead of 281. In cases where the private key is encrypted with CMS
In cases where the private key is further encrypted with CMS (as (as explained in Section 5.8) the Content-Format identifier is 280
explained in Section 5.7) the content format ID is 280 (0x0118). (0x0118) instead of 284. The key and certificate representations are
ASN.1 encoded in binary format. An example is shown in Appendix A.3.
5.3. Message Bindings 5.4. Message Bindings
The general EST CoAP message characteristics are: The general EST-coaps message characteristics are:
o All EST-coaps messages expect a response from the server, thus the o All EST-coaps messages expect a response from the server, thus the
client MUST send the requests over confirmable CON CoAP messages. client MUST send the requests over confirmable CON CoAP messages.
o The Ver, TKL, Token, and Message ID values of the CoAP header are o The Ver, TKL, Token, and Message ID values of the CoAP header are
not affected by EST. not affected by EST.
o The CoAP options used are Uri-Host, Uri-Path, Uri-Port, Content- o The CoAP Options used are Uri-Host, Uri-Path, Uri-Port, Content-
Format, and Location-Path. These CoAP Options are used to Format, Accept and Location-Path. These CoAP Options are used to
communicate the HTTP fields specified in the EST REST messages. communicate the HTTP fields specified in the EST REST messages.
The Uri-Host and Uri-Port Options are optional. They are usually
omitted as the DTLS destination and port are sufficient. Explicit
Uri-Host and Uri-Port Options are typically used when an endpoint
hosts multiple virtual servers and uses the Options to route the
requests accordingly. Alternatively, if a UDP port to a server is
blocked, someone could send the DTLS packets to a known open port
on the server and use the Uri-Port to convey the intended port he
is attempting to reach.
o EST URLs are HTTPS based (https://), in CoAP these are assumed to o EST URLs are HTTPS based (https://), in CoAP these are assumed to
be translated to coaps (coaps://) be translated to CoAPS (coaps://)
Appendix A includes some practical examples of EST messages Table 1 provides the mapping from the EST URI path to the EST-coaps
translated to CoAP. URI path. Appendix A includes some practical examples of EST
messages translated to CoAP.
5.4. CoAP response codes 5.5. CoAP response codes
Section 5.9 of [RFC7252] and Section 7 of [RFC8075] specify the Section 5.9 of [RFC7252] and Section 7 of [RFC8075] specify the
mapping of HTTP response codes to CoAP response codes. Every time mapping of HTTP response codes to CoAP response codes. Every time
the HTTP response code 200 is specified in [RFC7030] in response to a the HTTP response code 200 is specified in [RFC7030] in response to a
GET request (/cacerts, /csrattrs), in EST-coaps the equivalent CoAP GET request (/cacerts, /csrattrs), in EST-coaps the equivalent CoAP
response code 2.05 or 2.03 MUST be used. Similarly, 2.01, 2.02 or response code 2.05 or 2.03 MUST be used. Similarly, 2.01, 2.02 or
2.04 MUST be used in response to HTTP POST EST requests 2.04 MUST be used in response to EST POST requests (/simpleenroll,
(/simpleenroll, /simplereenroll, /serverkeygen ). Response code HTTP /simplereenroll, /serverkeygen).
202 Retry-After that existed in EST has no equivalent in CoAP.
Section 5.6 specifies how EST requests over CoAP handle delayed Response code HTTP 202 Retry-After that existed in EST has no
equivalent in CoAP. Retry-After is used in EST for delayed server
responses. Section 5.7 specifies how EST-coaps handles delayed
messages. messages.
EST makes use of HTTP 204 and 404 responses when a resource is not EST makes use of HTTP 204 and 404 responses when a resource is not
available for the client. The equivalent CoAP error code to use in available for the client. The equivalent CoAP codes to use in an
an EST-coaps responses are 2.04 and 4.04. Additionally, EST's HTTP EST-coaps responses are 2.04 and 4.04. Additionally, EST's HTTP 401
401 error translates to 4.01 in EST-coaps. Other EST HTTP error error translates to 4.01 in EST-coaps. Other EST HTTP error messages
messages are 400, 423 and 503. Their equivalent CoAP errors are are 400, 423 and 503. Their equivalent CoAP errors are 4.00, 4.03
4.00, 4.03 and 5.03 respectively. In case a required COAP option and 5.03 respectively. In case a CoAP Option is unrecognized and
(i.e Content-Format) is omitted, the server is expected to return a critical, the server is expected to return a 4.02 (Bad Option).
4.02. Moreover, if the Content-Format requested in the client Accept
Option, is not supported the server MUST return a 4.06 (Not
Acceptable), unless another error code takes precedence for the
response.
5.5. Message fragmentation 5.6. Message fragmentation
DTLS defines fragmentation only for the handshake and not for secure DTLS defines fragmentation only for the handshake and not for secure
data exchange (DTLS records). [RFC6347] states that to avoid using data exchange (DTLS records). [RFC6347] states that to avoid using
IP fragmentation, which involves error-prone datagram reconstitution, IP fragmentation, which involves error-prone datagram reconstitution,
invokers of the DTLS record layer SHOULD size DTLS records so that invokers of the DTLS record layer SHOULD size DTLS records so that
they fit within any Path MTU estimates obtained from the record they fit within any Path MTU estimates obtained from the record
layer. In addition, invokers residing on a 6LoWPAN over IEEE layer. In addition, invokers residing on a 6LoWPAN over IEEE
802.15.4 [ieee802.15.4] network SHOULD attempt to size CoAP messages 802.15.4 [ieee802.15.4] network SHOULD attempt to size CoAP messages
such that each DTLS record will fit within one or two IEEE 802.15.4 such that each DTLS record will fit within one or two IEEE 802.15.4
frames. frames.
That is not always possible in EST-coaps. Even though ECC That is not always possible in EST-coaps. Even though ECC
certificates are small in size, they can vary greatly based on certificates are small in size, they can vary greatly based on
signature algorithms, key sizes, and OID fields used. For 256-bit signature algorithms, key sizes, and Object Identifier (OID) fields
curves, common ECDSA cert sizes are 500-1000 bytes which could used. For 256-bit curves, common ECDSA cert sizes are 500-1000 bytes
fluctuate further based on the algorithms, OIDs, SANs and cert which could fluctuate further based on the algorithms, OIDs, Subject
fields. For 384-bit curves, ECDSA certs increase in size and can Alternative Names (SAN) and cert fields. For 384-bit curves, ECDSA
sometimes reach 1.5KB. Additionally, there are times when the EST certificates increase in size and can sometimes reach 1.5KB.
cacerts response from the server can include multiple certs that Additionally, there are times when the EST cacerts response from the
amount to large payloads. Section 4.6 of CoAP [RFC7252] describes server can include multiple certificates that amount to large
the possible payload sizes: "if nothing is known about the size of payloads. Section 4.6 of CoAP [RFC7252] describes the possible
the headers, good upper bounds are 1152 bytes for the message size payload sizes: "if nothing is known about the size of the headers,
and 1024 bytes for the payload size". Section 4.6 of [RFC7252] also good upper bounds are 1152 bytes for the message size and 1024 bytes
suggests that IPv4 implementations may want to limit themselves to for the payload size". Section 4.6 of [RFC7252] also suggests that
more conservative IPv4 datagram sizes such as 576 bytes. Even with IPv4 implementations may want to limit themselves to more
ECC certs, EST-coaps messages can still exceed MTU sizes on the conservative IPv4 datagram sizes such as 576 bytes. Even with ECC,
Internet or 6LoWPAN [RFC4919] (Section 2 of [RFC7959]). EST-coaps EST-coaps messages can still exceed MTU sizes on the Internet or
needs to be able to fragment messages into multiple DTLS datagrams. 6LoWPAN [RFC4919] (Section 2 of [RFC7959]). EST-coaps needs to be
able to fragment messages into multiple DTLS datagrams.
To perform fragmentation in CoAP, [RFC7959] specifies the "Block1" To perform fragmentation in CoAP, [RFC7959] specifies the Block1
option for fragmentation of the request payload and the "Block2" Option for fragmentation of the request payload and the Block2 Option
option for fragmentation of the return payload of a CoAP flow. As for fragmentation of the return payload of a CoAP flow. As explained
explained in Section 1 of [RFC7959], blockwise transfers SHOULD be in Section 1 of [RFC7959], block-wise transfers should be used in
used in Confirmable CoAP messages to avoid the exacerbation of lost Confirmable CoAP messages to avoid the exacerbation of lost blocks.
blocks. [RFC7959] defines SZX in the block option fields. SZX is The EST-coaps client and server MUST support Block2. Block1 MUST be
used to convey the size of the blocks in the requests or responses. supported for EST-coaps enrollment requests that exceed the Path MTU.
The CoAP client MAY specify the Block1 size and MAY also specify the
Block2 size. The CoAP server MAY specify the Block2 size, but not
the Block1 size.
[RFC7959] also defines Size1 and Size2 options to provide size [RFC7959] also defines Size1 and Size2 Options to provide size
information about the resource representation in a request and information about the resource representation in a request and
response. The Size1 response MAY be parsed by the client as a size response. EST-client and server MAY support Size1 and Size2 Options.
indication of the Block2 resource in the server response or by the
server as a request for a size estimate by the client. Similarly,
the Size2 option defined in BLOCK should be parsed by the server as
an indication of the size of the resource carried in Block1 options
and by the client as a maximum size expected in the 4.13 (Request
Entity Too Large) response to a request.
Examples of fragmented EST messages are shown in Appendix B. Examples of fragmented EST-coaps messages are shown in Appendix B.
5.6. Delayed Responses 5.7. Delayed Responses
Server responses can sometimes be delayed. According to section Server responses can sometimes be delayed. According to section
5.2.2 of [RFC7252], a slow server can acknowledge the request with a 5.2.2 of [RFC7252], a slow server can acknowledge the request and
2.31 code and respond later with the requested resource respond later with the requested resource representation. In
representation. In particular, a slow server can respond to an particular, a slow server can respond to an EST-coaps enrollment
enrollment request with an empty ACK with code 0.00, before sending request with an empty ACK with code 0.00, before sending the
the certificate to the server after a short delay. If the certificate to the server after a short delay. If the certificate
certificate response is large, the server will need more than one response is large, the server will need more than one Block2 blocks
"Block2" blocks to transfer it. This situation is shown in Figure 2 to transfer it. This situation is shown in Figure 2. The client
where a client sends an enrollment request that uses more than one sends an enrollment request that uses N1+1 Block1 blocks. The server
"Block1" blocks. The server uses an empty 0.00 ACK to announce the uses an empty 0.00 ACK to announce the delayed response which is
delayed response which is provided later with 2.04 messages provided later with 2.04 messages containing N2+1 Block2 Options.
containing "Block2" options. Having received the first 256 bytes in The first 2.04 is a confirmable message that is acknowledged by the
the first "block2" block, the client asks for a block reduction to client with an ACK. Onwards, having received the first 256 bytes in
128 bytes in all following "block2" blocks, starting with the second the first Block2 block, the client asks for a block reduction to 128
block (NUM=1). bytes in a confirmable enrollment request Uri-Path and acknowledges
the Block2 blocks sent up to that point.
POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR req} --> POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR req} -->
<-- (ACK) (1:0/1/256) (2.31 Continue) <-- (ACK) (1:0/1/256) (2.31 Continue)
POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR req} --> POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR req} -->
<-- (ACK) (1:1/1/256) (2.31 Continue) <-- (ACK) (1:1/1/256) (2.31 Continue)
. .
. .
. .
POST [2001:db8::2:1]:61616/est/sen (CON)(1:N1/0/256){CSR req} --> POST [2001:db8::2:1]:61616/est/sen (CON)(1:N1/0/256){CSR req} -->
<-- (0.00 empty ACK) <-- (0.00 empty ACK)
skipping to change at page 12, line 27 skipping to change at page 15, line 27
<-- (CON) (1:N1/0/256)(2:0/1/256)(2.04 Changed) {Cert resp} <-- (CON) (1:N1/0/256)(2:0/1/256)(2.04 Changed) {Cert resp}
(ACK) --> (ACK) -->
POST [2001:db8::2:1]:61616/est/sen (CON)(2:1/0/128) --> POST [2001:db8::2:1]:61616/est/sen (CON)(2:1/0/128) -->
<-- (ACK) (2:1/1/128) (2.04 Changed) {Cert resp} <-- (ACK) (2:1/1/128) (2.04 Changed) {Cert resp}
. .
. .
. .
POST [2001:db8::2:1]:61616/est/sen (CON)(2:N2/0/128) --> POST [2001:db8::2:1]:61616/est/sen (CON)(2:N2/0/128) -->
<-- (ACK) (2:N2/0/128) (2.04 Changed) {Cert resp} <-- (ACK) (2:N2/0/128) (2.04 Changed) {Cert resp}
Figure 2: EST-COAP enrolment with short wait Figure 2: EST-COAP enrollment with short wait
If the server is very slow (i.e. minutes) in providing the response If the server is very slow (i.e. minutes) in providing the response
(i.e. when a manual intervention is needed), the server SHOULD (i.e. when a manual intervention is needed), the server SHOULD
respond with an ACK containing response code 5.03 (Service respond with an ACK containing response code 5.03 (Service
unavailable) and a Max-Age option to indicate the time the client unavailable) and a Max-Age Option to indicate the time the client
SHOULD wait to request the content later. After a delay of Max-Age, SHOULD wait to request the content later. After a delay of Max-Age,
the client SHOULD resend the identical CSR to the server. As long as the client SHOULD resend the identical CSR to the server. As long as
the server responds with response code 5.03 (Service Unavailable) the server responds with response code 5.03 (Service Unavailable)
with a Max-Age option, the client can resend the enrolment request with a Max-Age Option, the client SHOULD keep resending the
until the server responds with the certificate or the client abandons enrollment request until the server responds with the certificate or
for other reasons. the client abandons for other reasons.
To demonstrate this scenario, Figure 3 shows a client sending an To demonstrate this scenario, Figure 3 shows a client sending an
enrolment request that uses more than one "Block1" blocks to send the enrollment request that uses N1+1 Block1 blocks to send the CSR to
CSR to the server. The server needs more than one "Block2" blocks to the server. The server needs N2+1 Block2 blocks to respond, but also
respond, but also needs to take a long delay (minutes) to provide the needs to take a long delay (minutes) to provide the response.
response. Consequently, the server uses a 5.03 ACK response with a Consequently, the server uses a 5.03 ACK response with a Max-Age
Max-Age option. The client waits for a period of Max-Age as many Option. The client waits for a period of Max-Age as many times as he
times as he receives the same 5.03 response and retransmits the receives the same 5.03 response and retransmits the enrollment
enrollment request until he receives a certificate. Note that in the request until he receives a certificate in a fragmented 2.01
example below the server asks for a decrease in the block size when response. Note that the server asks for a decrease in the block size
acknowledging the first Block2. when acknowledging the first Block2.
POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR req} --> POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR req} -->
<-- (ACK) (1:0/1/256) (2.31 Continue) <-- (ACK) (1:0/1/256) (2.31 Continue)
POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR req} --> POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR req} -->
<-- (ACK) (1:1/1/256) (2.31 Continue) <-- (ACK) (1:1/1/256) (2.31 Continue)
. .
. .
POST [2001:db8::2:1]:61616/est/sen (CON)(1:N1/0/256){CSR req} --> POST [2001:db8::2:1]:61616/est/sen (CON)(1:N1/0/256){CSR req} -->
<-- (ACK) (1:N1/0/256) (2:0/0/128) (5.03 Service Unavailable) <-- (ACK) (1:N1/0/256) (2:0/0/128)(5.03 Service Unavailable)
(Max-Age) (Max-Age)
| |
| |
Client tries one or more times after Max-Age with identical payload Client tries one or more times after Max-Age with identical payload
| |
| |
POST [2001:db8::2:1]:61616/est/sen (CON)(1:N1/0/256){CSR req} --> POST [2001:db8::2:1]:61616/est/sen (CON)(1:N1/0/256){CSR req} -->
<-- (ACK) (1:N1/0/256) (2:0/1/128) (2.04 Changed){Cert resp} <-- (ACK) (1:N1/0/256) (2:0/1/128) (2.01 Created){Cert resp}
POST [2001:db8::2:1]:61616/est/sen (CON)(2:1/0/128) --> POST [2001:db8::2:1]:61616/est/sen (CON)(2:1/0/128) -->
<-- (ACK) (2:1/1/128) (2.04 Changed) {Cert resp} <-- (ACK) (2:1/1/128) (2.01 Created) {Cert resp}
. .
. .
. .
POST [2001:db8::2:1]:61616/est/sen (CON)(2:N2/0/128) --> POST [2001:db8::2:1]:61616/est/sen (CON)(2:N2/0/128) -->
<-- (ACK) (2:N2/0/128) (2.04 Changed) {Cert resp} <-- (ACK) (2:N2/0/128) (2.01 Created) {Cert resp}
Figure 3: EST-COAP enrolment with long wait Figure 3: EST-COAP enrollment with long wait
5.7. Server-side Key Generation 5.8. Server-side Key Generation
Constrained devices sometimes do not have the necessary hardware to Constrained devices sometimes do not have the necessary hardware to
generate statistically random numbers for private keys and DTLS generate statistically random numbers for private keys and DTLS
ephemeral keys. Past experience has also shown that low-resource ephemeral keys. Past experience has also shown that low-resource
endpoints sometimes generate numbers which could allow someone to endpoints sometimes generate numbers which could allow someone to
decrypt the communication or guess the private key and impersonate as decrypt the communication or guess the private key and impersonate as
the device [PsQs] [RSAorig]. the device [PsQs] [RSAorig]. Additionally, random number key
generation is costly, thus energy draining. Even though the random
Additionally, random number key generation is costly, thus energy numbers that constitute the identity/cert do not get generated often,
draining. Even though the random numbers that constitute the an endpoint may not want to spend time and energy generating
identity/cert do not get generated often, an endpoint may not want to keypairs, and just ask for one from the server.
spend time and energy generating keypairs, and just ask for one from
the server.
In these scenarios, server-side key generation can be used. The In these scenarios, server-side key generation can be used. The
client asks for the server or proxy to generate the private key and client asks for the server or proxy to generate the private key and
the certificate which is transferred back to the client in the the certificate which are transferred back to the client in the
server-side key generation response. In all respects, the server server-side key generation response. In all respects, the server
SHOULD treat the CSR as it would treat any enroll or re-enroll CSR; SHOULD treat the CSR as it would treat any enroll or re-enroll CSR;
the only distinction here is that the server MUST ignore the public the only distinction here is that the server MUST ignore the public
key values and signature in the CSR. These are included in the key values and signature in the CSR. These are included in the
request only to allow re-use of existing codebases for generating and request only to allow re-use of existing codebases for generating and
parsing such requests. parsing such requests.
[RFC7030] recommends the private key returned by the server to be The client /skg request needs to communicate to the server the
encrypted. This specification provides two methods to encrypt the Content-Format of the application/multipart-core elements. The key
generated key, symmetric and asymmetric. The methods are signalled Content-Format requested by the client is depicted in the PKCS#10
by the client by using the relevant attributes (SMIMECapabilities and request. If the request contains SMIMECapabilities the client is
expecting Content-Format 280. Otherwise he expects a PKCS#8 key in
Content-Format 284. The client expresses the preferred certificate
Content-Format in his /skg request by using an Accept Option. The
Accept Option is 281 when preferring a certificate in a PKCS#7
container or TBD287 when preferring a single X.509 certificate.
[RFC7030] provides two methods, symmetric and asymmetric, to
optionally encrypt the generated key. The methods are signaled by
the client by using the relevant attributes (SMIMECapabilities and
DecryptKeyIdentifier or AsymmetricDecryptKeyIdentifier) in the CSR DecryptKeyIdentifier or AsymmetricDecryptKeyIdentifier) in the CSR
request. The symmetric key or the asymmetric keypair establishment request. The symmetric key or the asymmetric keypair establishment
method is out of scope of this specification. method is out of scope of the specification.
The sever-side key generation response is returned using a CBOR array The EST-coaps server-side key generation response is returned with
Section 5.2.1. The certificate part exactly matches the response Content-Format application/multipart-core
from an enrollment response. The private key can be in unprotected [I-D.ietf-core-multipart-ct] containing a CBOR array with four items
PKCS#8 [RFC5958] format (content type 281) or protected inside of CMS Section 5.3. The certificate part exactly matches the response from
SignedData (content type 280). The SignedData is signed by the party an enrollment response. The private key can be in unprotected PKCS#8
that generated the private key, which may or may not be the EST [RFC5958] format (Content-Format 284) or protected inside of CMS
server or the EST CA. The SignedData is further protected by placing SignedData (Content-Format 280). The SignedData is signed by the
it inside of a CMS EnvelopedData as explained in Section 4.4.2 of party that generated the private key, which may be the EST server or
[RFC7030]. In summary, the symmetricly encrypted key is included in the EST CA. The SignedData is further protected by placing it inside
the encryptedKey attribute in a KEKRecipientInfo structure. In the of a CMS EnvelopedData as explained in Section 4.4.2 of [RFC7030].
case where the asymmetric encryption key is suitable for transport In summary, the symmetrically encrypted key is included in the
key operations the generated private key is encrypted with a encryptedKey attribute in a KEKRecipientInfo structure. In the case
symmetric key which is encrypted by using the client defined (in the where the asymmetric encryption key is suitable for transport key
CSR) asymmetric public key and is carried in an encryptedKey operations the generated private key is encrypted with a symmetric
attribute in a KeyTransRecipientInfo. Finally, if the asymmetric key which is encrypted by the client defined (in the CSR) asymmetric
public key and is carried in an encryptedKey attribute in a
KeyTransRecipientInfo structure. Finally, if the asymmetric
encryption key is suitable for key agreement, the generated private encryption key is suitable for key agreement, the generated private
key is encrypted with a symmetric key which is encrypted by using the key is encrypted with a symmetric key which is encrypted by the
client defined (in the CSR) asymmetric public key and is carried in client defined (in the CSR) asymmetric public key and is carried in
an recipientEncryptedKeys attribute in a KeyAgreeRecipientInfo. an recipientEncryptedKeys attribute in a KeyAgreeRecipientInfo.
[RFC7030] recommends the use of additional encryption of the returned [RFC7030] recommends the use of additional encryption of the returned
private key. For the context of this specification, clients and private key. For the context of this specification, clients and
servers that choose to support server-side key generation MUST servers that choose to support server-side key generation MUST
support unprotected (PKCS#8) private keys (content type 281). support unprotected (PKCS#8) private keys (Content-Format 284).
Symmetric or asymmetric encryption of the private key (CMS Symmetric or asymmetric encryption of the private key (CMS
EnvelopedData, content type 280) SHOULD be supported for deployments EnvelopedData, Content-Format 280) SHOULD be supported for
where end-to-end encryption needs to be provided between the client deployments where end-to-end encryption needs to be provided between
and a server. Such cases could include architectures where an entity the client and a server. Such cases could include architectures
between the client and the CA terminates the DTLS connection where an entity between the client and the CA terminates the DTLS
(Registrar in Figure 4). connection (Registrar in Figure 4).
5.8. Deployment limits
Although EST-coaps paves the way for the utilization of EST by
constrained devices in constrained networks, some classes of devices
[RFC7228] will not have enough resources to handle the large payloads
that come with EST-coaps. The specification of EST-coaps is intended
to ensure that EST works for networks of constrained devices that
choose to limit their communications stack to UDP/DTLS/CoAP. It is
up to the network designer to decide which devices execute the EST
protocol and which do not.
6. Discovery and URIs
EST-coaps is targeted for low-resource networks with small packets.
Saving header space is important and short EST-coaps URIs are
specified in this document. These URIs are shorter than the ones in
[RFC7030]. The EST-coaps resource path names are:
coaps://example.com:<port>/.well-known/est/<short-est>
coaps://example.com:<port>/.well-known/est/ArbitraryLabel/<short-est>
The short-est strings are defined in Table 2. The ArbitraryLabel
Path-Segment, if used, SHOULD be of the shortest length possible
(Sections 3.1 and 3.2.2 of [RFC7030]. Following [RFC7030] discovery
is not needed when the client is preconfigured with the /.well-known/
est server URI and the coaps port 5684.
The EST-coaps server URIs, obtained through discovery of the EST-
coaps root resource(s) as shown below, are of the form:
coaps://example.com:<port>/<root-resource>/<short-est>
coaps://example.com:<port>/<root-resource>/ArbitraryLabel/<short-est>
Figure 5 in section 3.2.2 of [RFC7030] enumerates the operations and
corresponding paths which are supported by EST. Table 2 provides the
mapping from the EST URI path to the shorter EST-coaps URI path.
+------------------+-----------+
| EST | EST-coaps |
+------------------+-----------+
| /cacerts | /crts |
| /simpleenroll | /sen |
| /simplereenroll | /sren |
| /csrattrs | /att |
| /serverkeygen | /skg |
+------------------+-----------+
Table 2: Table 2: Short EST-coaps URI path
Clients and servers MUST support the short resource URIs. The
corresponding longer URIs from [RFC7030] MAY be supported.
In the context of CoAP, the presence and location of (path to) the
management data are discovered by sending a GET request to "/.well-
known/core" including a resource type (RT) parameter with the value
"ace.est" [RFC6690]. Upon success, the return payload will contain
the root resource of the EST resources. The server MAY return all
available resource paths and the used content types. This is useful
when multiple content types are supported by the EST-coaps server and
optional functions are available. The example below shows the
discovery of the presence and location of EST-coaps resources.
Linefeeds are included only for readability.
REQ: GET /.well-known/core?rt=ace.est*
RES: 2.05 Content
</est>; rt="ace.est",
</est/crts>;rt="ace.est.crts";ct=281,
</est/sen>;rt="ace.est.sen";ct=281 286,
</est/sren>;rt="ace.est.sren";ct=281 286,
</est/att>;rt="ace.est.att";ct=285,
</est/skg>;rt="ace.est.skg";ct=280 286 62
The first line of the discovery response above MUST be included. The
five consecutive lines after the first MAY be included. The return
of the content-types allows the client to choose the most appropriate
one from multiple content types.
Port numbers, not returned in the example, are assumed to be the
default numbers 5683 and 5684 for coap and coaps respectively
(Sections 12.6 and 12.7 of [RFC7252]). Discoverable port numbers MAY
be returned in the <href> of the payload.
It is up to the implementation to choose its root resource;
throughout this document the example root resource /est is used.
7. DTLS Transport Protocol 6. DTLS Transport Protocol
EST-coaps depends on a secure transport mechanism over UDP that EST-coaps depends on a secure transport mechanism over UDP that
secures the exchanged CoAP messages. DTLS is one such secure secures the exchanged CoAP messages. DTLS is one such secure
protocol. Where TLS is used in the context of EST, it is understood protocol. EST depended in TLS. No other changes are necessary
that EST-coaps uses DTLS instead. No other changes are necessary regarding the secure transport of EST messages.
regarding the secure transport of EST messages (all provisional modes
etc. are the same as in TLS).
CoAP was designed to avoid fragmentation. DTLS is used to secure CoAP was designed to avoid fragmentation. DTLS is used to secure
CoAP messages. However, fragmentation is still possible at the DTLS CoAP messages. However, fragmentation is still possible at the DTLS
layer during the DTLS handshake when using ECC ciphersuites. If layer during the DTLS handshake when using ECC ciphersuites. If
fragmentation is necessary, "DTLS provides a mechanism for fragmentation is necessary, "DTLS provides a mechanism for
fragmenting a handshake message over several records, each of which fragmenting a handshake message over several records, each of which
can be transmitted separately, thus avoiding IP fragmentation" can be transmitted separately, thus avoiding IP fragmentation"
[RFC6347]. [RFC6347].
The DTLS handshake is authenticated by using certificates. EST-coaps The DTLS handshake is authenticated by using certificates. EST-coaps
supports the certificate types and Trust Anchors (TA) that are supports the certificate types and Trust Anchors (TA) that are
specified for EST in Section 3 of [RFC7030]. specified for EST in Section 3 of [RFC7030].
CoAP and DTLS can provide proof-of-identity for EST-coaps clients and CoAP and DTLS can provide proof-of-identity for EST-coaps clients and
servers with simple PKI messages as descrbed in Section 3.1 of servers with simple PKI messages as described in Section 3.1 of
[RFC5272]. Moreover, channel-binding information for linking proof- [RFC5272]. Moreover, channel-binding information for linking proof-
of-identity with connection-based proof-of-possession is OPTIONAL for of-identity with connection-based proof-of-possession is OPTIONAL for
EST-coaps. When proof-of-possession is desired, a set of actions are EST-coaps. When proof-of-possession is desired, a set of actions are
required regarding the use of tls-unique, described in section 3.5 in required regarding the use of tls-unique, described in section 3.5 in
[RFC7030]. The tls-unique information consists of the contents of [RFC7030]. The tls-unique information consists of the contents of
the first "Finished" message in the (D)TLS handshake between server the first "Finished" message in the (D)TLS handshake between server
and client [RFC5929]. The client is supposed to add this "Finished" and client [RFC5929]. The client adds the "Finished" message as a
message as a ChallengePassword in the attributes section of the ChallengePassword in the attributes section of the PKCS#10 Request
PKCS#10 Request [RFC5967] Info to prove that the client is indeed in [RFC5967] to prove that the client is indeed in control of the
control of the private key at the time of the (D)TLS session private key at the time of the (D)TLS session establishment.
establishment. In the case of EST-coaps, the same operations can be
performed during the DTLS handshake. For DTLS 1.2, in the event of
handshake message fragmentation, the Hash of the handshake messages
used in the MAC calculation of the Finished message MUST be computed
as if each handshake message had been sent as a single fragment
[RFC6347]. The Finished message is calculated as:
PRF(master_secret, finished_label, Hash(handshake_messages))
[0..verify_data_length-1];
Similarly, for DTLS 1.3, the Finished message MUST be computed as if
each handshake message had been sent as a single fragment following
the algorithm described in 4.4.4 of [RFC8446]. The Finished message
is calculated as:
HMAC(finished_key,
Transcript-Hash(Handshake Context,
Certificate*, CertificateVerify*))
* Only included if present. In the case of EST-coaps, the same operations can be performed during
the DTLS handshake. For DTLS 1.2, in the event of handshake message
fragmentation, the Hash of the handshake messages used in the MAC
calculation of the Finished message MUST be computed as if each
handshake message had been sent as a single fragment (Section 4.2.6
of [RFC6347]). The Finished message is calculated as shown in
Section 7.4.9 of [RFC5246]. Similarly, for DTLS 1.3, the Finished
message MUST be computed as if each handshake message had been sent
as a single fragment (Section 5.8 of [I-D.ietf-tls-dtls13]) following
the algorithm described in 4.4.4 of [RFC8446].
In a constrained CoAP environment, endpoints can't afford to In a constrained CoAP environment, endpoints can't always afford to
establish a DTLS connection for every EST transaction. establish a DTLS connection for every EST transaction.
Authenticating and negotiating DTLS keys requires resources on low- Authenticating and negotiating DTLS keys requires resources on low-
end endpoints and consumes valuable bandwidth. The DTLS connection end endpoints and consumes valuable bandwidth. To alleviate this
SHOULD remain open for sequential EST transactions. For example, an situation, an EST-coaps DTLS connection MAY remain open for
EST cacerts request that is followed by a simpleenroll request can sequential EST transactions. For example, an EST csrattrs request
use the same authenticated DTLS connection. However, some additional that is followed by a simpleenroll request can use the same
authenticated DTLS connection. However, when a cacerts request is
included in the set of sequential EST transactions, some additional
security considerations apply regarding the use of the Implicit and security considerations apply regarding the use of the Implicit and
Explicit TA database (Section 11.1) Explicit TA database as explained in Section 11.1.
Given that after a successful enrollment, it is more likely that a Given that after a successful enrollment, it is more likely that a
new EST transaction will take place after a significant amount of new EST transaction will take place after a significant amount of
time, the DTLS connections SHOULD only be kept alive for EST messages time, the DTLS connections SHOULD only be kept alive for EST messages
that are relatively close to each other. In some cases like NAT that are relatively close to each other. In some cases, like NAT
rebinding, keeping the state of a connection is not possible when rebinding, keeping the state of a connection is not possible when
devices sleep for extended periods of time. In such occasions, devices sleep for extended periods of time. In such occasions,
[I-D.rescorla-tls-dtls-connection-id] negotiates a connection ID that [I-D.ietf-tls-dtls-connection-id] negotiates a connection ID that can
can eliminate the need for new handshake and its additional cost. eliminate the need for new handshake and its additional cost.
8. HTTPS-CoAPS Registrar 7. HTTPS-CoAPS Registrar
In real-world deployments, the EST server will not always reside In real-world deployments, the EST server will not always reside
within the CoAP boundary. The EST server can exist outside the within the CoAP boundary. The EST server can exist outside the
constrained network that supports TLS/HTTP. In such environments constrained network in which case it will support TLS/HTTP instead of
EST-coaps is used by the client within the CoAP boundary and TLS is CoAPS. In such environments EST-coaps is used by the client within
used to transport the EST messages outside the CoAP boundary. A the CoAP boundary and TLS is used to transport the EST messages
Registrar at the edge is required to operate between the CoAP outside the CoAP boundary. A Registrar at the edge is required to
environment and the external HTTP network as shown in Figure 4. operate between the CoAP environment and the external HTTP network as
shown in Figure 4.
Constrained Network Constrained Network
.------. .----------------------------. .------. .----------------------------.
| CA | |.--------------------------.| | CA | |.--------------------------.|
'------' || || '------' || ||
| || || | || ||
.------. HTTP .-----------------. CoAPS .-----------. || .------. HTTP .-----------------. CoAPS .-----------. ||
| EST |<------->|EST-coaps-to-HTTPS|<------->| EST Client| || | EST |<------->|EST-coaps-to-HTTPS|<------->| EST Client| ||
|Server|over TLS | Registrar | '-----------' || |Server|over TLS | Registrar | '-----------' ||
'------' '-----------------' || '------' '-----------------' ||
skipping to change at page 18, line 50 skipping to change at page 20, line 14
The EST-coaps-to-HTTPS Registrar MUST terminate EST-coaps downstream The EST-coaps-to-HTTPS Registrar MUST terminate EST-coaps downstream
and initiate EST connections over TLS upstream. The Registrar MUST and initiate EST connections over TLS upstream. The Registrar MUST
authenticate and OPTIONALLY authorize the clients and it MUST be authenticate and OPTIONALLY authorize the clients and it MUST be
authenticated by the EST server or CA. The trust relationship authenticated by the EST server or CA. The trust relationship
between the Registrar and the EST server SHOULD be pre-established between the Registrar and the EST server SHOULD be pre-established
for the Registrar to proxy these connections on behalf of various for the Registrar to proxy these connections on behalf of various
clients. clients.
When enforcing Proof-of-Possession (POP) linking, the DTLS tls-unique When enforcing Proof-of-Possession (POP) linking, the DTLS tls-unique
value of the (D)TLS session needs to be used to prove that the value of the (D)TLS session is used to prove that the private key
private key corresponding to the public key is in the possession of corresponding to the public key is in the possession of and was used
and was used to establish the connection by the client as explained to establish the connection by the client as explained in Section 6).
in Section 7). The POP linking information is lost between the EST- The POP linking information is lost between the EST-coaps client and
coaps client and the EST server when a Registrar is present. The EST the EST server when a Registrar is present. The EST server becomes
server becomes aware of the presence of a Registrar from its TLS aware of the presence of a Registrar from its TLS client certificate
client certificate that includes id-kp-cmcRA [RFC6402] extended key that includes id-kp-cmcRA [RFC6402] extended key usage extension
usage extension (EKU). As explained in Section 3.7 of [RFC7030], the (EKU). As explained in Section 3.7 of [RFC7030], the EST server
EST server SHOULD apply an authorization policy consistent with a SHOULD apply an authorization policy consistent with a Registrar
Registrar client. For example, it could be configured to accept POP client. For example, it could be configured to accept POP linking
linking information that does not match the current TLS session information that does not match the current TLS session because the
because the authenticated EST client Registrar has verified this authenticated EST client Registrar has verified this information when
information when acting as an EST server. acting as an EST server.
For some use cases, clients that leverage server-side key generation For some use cases, clients that leverage server-side key generation
might prefer for the enrolled keys to be generated by the Registrar might prefer for the enrolled keys to be generated by the Registrar
if the CA does not support server-side key generation. In these if the CA does not support server-side key generation. In these
cases the Registrar MUST support random number generation using cases, the Registrar MUST support random number generation using
proper entropy. Such Registrar is responsible for generating a new proper entropy. Such Registrar is responsible for generating a new
CSR signed by a new key which will be returned to the client along CSR signed by a new key which will be returned to the client along
with the certificate from the CA. with the certificate from the CA.
Table 2 contains the URI mappings between EST-coaps and EST that the Table 1 contains the URI mappings between EST-coaps and EST that the
Registrar MUST adhere to. Section 5.4 of this specification and Registrar MUST adhere to. Section 5.5 of this specification and
Section 7 of [RFC8075] define the mappings between EST-coaps and HTTP Section 7 of [RFC8075] define the mappings between EST-coaps and HTTP
response codes, that determine how the Registrar MUST translate CoAP response codes, that determine how the Registrar MUST translate CoAP
response codes from/to HTTP status codes. The mapping from CoAP response codes from/to HTTP status codes. The mapping from CoAP
Content-Type to HTTP Media-Type is defined in Section 10.1. Content-Format to HTTP Media-Type is defined in Section 10.1.
Additionally, a conversion from CBOR major type 2 to Base64 encoding Additionally, a conversion from CBOR major type 2 to Base64 encoding
MUST take place at the Registrar when server-side key generation is MUST take place at the Registrar when server-side key generation is
supported. If CMS end-to-end encryption is employed for the private supported. If CMS end-to-end encryption is employed for the private
key, the encrypted CMS EnvelopedData blob should be included in key, the encrypted CMS EnvelopedData blob MUST be converted to binary
binary in CBOR type 2 downstream to the client. in CBOR type 2 downstream to the client.
Due to fragmentation of large messages into blocks, an EST-coaps-to- Due to fragmentation of large messages into blocks, an EST-coaps-to-
HTTP Registrar MUST reassemble the BLOCKs before translating the HTTP Registrar MUST reassemble the BLOCKs before translating the
binary content to Base64, and consecutively relay the message binary content to Base64, and consecutively relay the message
upstream. upstream.
For the discovery of the EST server by the EST client in the CoAP For the discovery of the EST server by the EST client in the CoAP
environment, the EST-coaps-to-HTTP Registrar MUST announce itself environment, the EST-coaps-to-HTTP Registrar MUST announce itself
according to the rules in Section 6. The available actions of the according to the rules in Section 5.1. The available actions of the
Registrars MUST be announced with as many resource paths necessary. Registrars MUST be announced with as many resource paths necessary.
.
9. Parameters 8. Parameters
This section addresses transmission parameters described in sections This section addresses transmission parameters described in sections
4.7 and 4.8 of [RFC7252]. 4.7 and 4.8 of [RFC7252]. EST does not impose any unique values on
the CoAP parameters in [RFC7252], but the EST parameter values need
ACK_TIMEOUT | 2 seconds | to be tuned to the CoAP parameter values.
ACK_RANDOM_FACTOR | 1.5 |
MAX_RETRANSMIT | 4 |
NSTART | 1 |
DEFAULT_LEISURE | 5 seconds |
PROBING_RATE | 1 byte/second |
EST does not impose any unique parameters that affect the CoAP
parameters But the CoAP ones could be affecting EST. For example,
the processing delay of CAs could be less then 2s, but in this case
the EST-coaps server should be sending a CoAP ACK every 2s while
processing.
The main recommendation, based on experiments, is to follow the It is RECOMMENDED, based on experiments, to follow the default CoAP
default CoAP configuration parameters. However, depending on the configuration parameters ([RFC7252]). However, depending on the
implementation scenario, retransmissions and timeouts can also occur implementation scenario, retransmissions and timeouts can also occur
on other networking layers, governed by other configuration on other networking layers, governed by other configuration
parameters. parameters. A change in a server parameter MUST ensure the adjusted
value is also available to all the endpoints with which these
adjusted values are to be used to communicate.
Some further comments about some specific parameters, mainly from Some further comments about some specific parameters, mainly from
Table 2 in [RFC7252]: Table 2 in [RFC7252]:
o NSTART: Limit the number of simultaneous outstanding interactions o NSTART: Limit the number of simultaneous outstanding interactions
that a client maintains to a given server. EST-coaps clients that a client maintains to a given server. EST-coaps clients
SHOULD use 1, which is the default. A EST-coaps client is not SHOULD use 1, which is the default. A EST-coaps client is not
expected to interact with more than one servers at the same time. expected to interact with more than one servers at the same time.
o DEFAULT_LEISURE: This setting is only relevant in multicast o DEFAULT_LEISURE: This setting is only relevant in multicast
skipping to change at page 20, line 44 skipping to change at page 21, line 45
o PROBING_RATE: A parameter which specifies the rate of re-sending o PROBING_RATE: A parameter which specifies the rate of re-sending
non-confirmable messages. The EST messages are defined to be sent non-confirmable messages. The EST messages are defined to be sent
as CoAP confirmable messages, hence this setting is not as CoAP confirmable messages, hence this setting is not
applicable. applicable.
Finally, the Table 3 parameters in [RFC7252] are mainly derived from Finally, the Table 3 parameters in [RFC7252] are mainly derived from
Table 2. Directly changing parameters on one table would affect Table 2. Directly changing parameters on one table would affect
parameters on the other. parameters on the other.
9. Deployment limitations
Although EST-coaps paves the way for the utilization of EST by
constrained devices in constrained networks, some classes of devices
[RFC7228] will not have enough resources to handle the large payloads
that come with EST-coaps. The specification of EST-coaps is intended
to ensure that EST works for networks of constrained devices that
choose to limit their communications stack to UDP/DTLS/CoAP. It is
up to the network designer to decide which devices execute the EST
protocol and which do not.
10. IANA Considerations 10. IANA Considerations
10.1. Content-Format Registry 10.1. Content-Format Registry
Additions to the sub-registry "CoAP Content-Formats", within the Additions to the sub-registry "CoAP Content-Formats", within the
"CoRE Parameters" registry [COREparams] are specified in Table 3. "CoRE Parameters" registry [COREparams] are specified in Table 3.
These have been registered temporarily in the Expert Review range These have been registered provisionally in the Expert Review range
(0-255). (0-255).
+-------------------------------+-----+-----------------------------+ +------------------------------+-------+----------------------------+
| HTTP Media-Type | ID | Reference | | HTTP Media-Type | ID | Reference |
+-------------------------------+-----+-----------------------------+ +------------------------------+-------+----------------------------+
| application/pkcs7-mime; | 280 | [I-D.ietf-lamps-rfc5751-bis | | application/pkcs7-mime; | 280 | [RFC7030] [I-D.ietf-lamps- |
| smime-type=server-generated- | | ] [RFC7030] | | smime-type=server-generated- | | rfc5751-bis] |
| key | | | | key | | |
| application/pkcs7-mime; | 281 | [I-D.ietf-lamps-rfc5751-bis | | application/pkcs7-mime; | 281 | [I-D.ietf-lamps-rfc5751-bi |
| smime-type=certs-only | | ] | | smime-type=certs-only | | s] |
| application/pkcs7-mime; | 282 | [I-D.ietf-lamps-rfc5751-bis | | application/pkcs7-mime; | 282 | [RFC5273] [I-D.ietf-lamps- |
| smime-type=CMC-request | | ] [RFC5273] | | smime-type=CMC-request | | rfc5751-bis] |
| application/pkcs7-mime; | 283 | [I-D.ietf-lamps-rfc5751-bis | | application/pkcs7-mime; | 283 | [RFC5273] [I-D.ietf-lamps- |
| smime-type=CMC-response | | ] [RFC5273] | | smime-type=CMC-response | | rfc5751-bis] |
| application/pkcs8 | 284 | [I-D.ietf-lamps-rfc5751-bis | | application/pkcs8 | 284 | [RFC5958] [I-D.ietf-lamps- |
| | | ] [RFC5958] | | | | rfc5751-bis] |
| application/csrattrs | 285 | [RFC7030] [RFC7231] | | application/csrattrs | 285 | [RFC7030] [RFC7231] |
| application/pkcs10 | 286 | [I-D.ietf-lamps-rfc5751-bis | | application/pkcs10 | 286 | [RFC5967] [I-D.ietf-lamps- |
| | | ] [RFC5967] | | | | rfc5751-bis] |
+-------------------------------+-----+-----------------------------+ | application/pkix-cert | TBD28 | [RFC2585] |
| | 7 | |
+------------------------------+-------+----------------------------+
Table 3: New CoAP Content-Formats Table 3: Table 3: New CoAP Content-Formats
The Content-Formats 281 to 286 have been the subject of an earlier
temporary allocation. It is suggested that 287 is allocated to
TBD287.
10.2. Resource Type registry 10.2. Resource Type registry
This memo registers a new Resource Type (rt=) Link Target Attributes This memo registers a new Resource Type (rt=) Link Target Attributes
in the "Resource Type (rt=) Link Target Attribute Values" subregistry in the "Resource Type (rt=) Link Target Attribute Values" subregistry
under the "Constrained RESTful Environments (CoRE) Parameters" under the "Constrained RESTful Environments (CoRE) Parameters"
registry. registry.
o rt="ace.est". This EST resource is used to query and return the o rt="ace.est". This EST resource is used to query and return the
supported EST resources of a CoAP server. supported EST resources of a CoAP server.
skipping to change at page 22, line 18 skipping to change at page 23, line 33
The security considerations of Section 6 of [RFC7030] are only The security considerations of Section 6 of [RFC7030] are only
partially valid for the purposes of this document. As HTTP Basic partially valid for the purposes of this document. As HTTP Basic
Authentication is not supported, the considerations expressed for Authentication is not supported, the considerations expressed for
using passwords do not apply. using passwords do not apply.
Given that the client has only limited resources and may not be able Given that the client has only limited resources and may not be able
to generate sufficiently random keys to encrypt its identity, it is to generate sufficiently random keys to encrypt its identity, it is
possible that the client uses server generated private/public keys. possible that the client uses server generated private/public keys.
The transport of these keys is inherently risky. Analysis SHOULD be The transport of these keys is inherently risky. Analysis SHOULD be
done to establish whether server side key generation enhances or done to establish whether server-side key generation enhances or
decreases the probability of identity stealing. decreases the probability of identity stealing.
It is also RECOMMENDED that the Implicit Trust Anchor database used It is also RECOMMENDED that the Implicit Trust Anchor database used
for EST server authentication be carefully managed to reduce the for EST server authentication is carefully managed to reduce the
chance of a third-party CA with poor certification practices from chance of a third-party CA with poor certification practices
being trusted. Disabling the Implicit Trust Anchor database after jeopardizing authentication. Disabling the Implicit Trust Anchor
successfully receiving the Distribution of CA certificates response database after successfully receiving the Distribution of CA
(Section 4.1.3 of [RFC7030]) limits any risk to the first DTLS certificates response (Section 4.1.3 of [RFC7030]) limits any risk to
exchange. Alternatively, in a persistent DTLS connection where a the first DTLS exchange. Alternatively, in a case where a /sen
/sen request follows a /crt in the same connection, a client MAY request immediately follows a /crt, a client MAY choose to keep the
choose to keep the connection already authenticated by the Implicit connection authenticated by the Implicit TA open for efficiency
TA open for efficiency reasons (Section 7) by assuming that the reasons (Section 6). A client that pipelines EST-coaps /crt request
identity of the server is to be trusted. In that case then the with other requests in the same DTLS connection SHOULD revalidate the
Explicit TA MUST be used starting from the next DTLS connection. server certificate chain against the updated Explicit TA from the
/crt response before proceeding with the subsequent requests. If the
server certificate chain does not authenticate against the database,
the client SHOULD close the connection without completing the rest of
the requests. The updated Explicit TA MUST continue to be used in
new DTLS connections.
In cases where the IDevID used to authenticate the client is expired In cases where the IDevID used to authenticate the client is expired
the server MAY still authenticate the client because IDevIDs are the server MAY still authenticate the client because IDevIDs are
expected to live as long as the device itself (Section 4). In such expected to live as long as the device itself (Section 4). In such
occasions, checking the certificate revocation status or authorizing occasions, checking the certificate revocation status or authorizing
the client using another method is important for the server to ensure the client using another method is important for the server to ensure
that the client is to be trusted. that the client is to be trusted.
In accordance with [RFC7030], TLS cipher suites that include In accordance with [RFC7030], TLS cipher suites that include
"_EXPORT_" and "_DES_" in their names MUST NOT be used. More "_EXPORT_" and "_DES_" in their names MUST NOT be used. More
information about recommendations of TLS and DTLS are included in information about recommendations of TLS and DTLS are included in
[RFC7525]. [RFC7525].
As described in CMC, Section 6.7 of [RFC5272], "For keys that can be As described in CMC, Section 6.7 of [RFC5272], "For keys that can be
used as signature keys, signing the certification request with the used as signature keys, signing the certification request with the
private key serves as a POP on that key pair". The inclusion of tls- private key serves as a POP on that key pair". The inclusion of tls-
unique in the certificate request links the proof-of-possession to unique in the certificate request links the proof-of-possession to
the TLS proof-of-identity. This implies but does not prove that only the TLS proof-of-identity. This implies but does not prove that only
the authenticated client currently has access to the private key. the authenticated client currently has access to the private key.
Regarding the Certificate Signing Request (CSR), an adversary could What's more, POP linking uses tls-unique as it is defined in
exclude attributes that a server may want, include attributes that a [RFC5929]. The 3SHAKE attack [tripleshake] poses a risk by allowing
server may not want, and render meaningless other attributes that a a man-in-the-middle to leverage session resumption and renegotiation
server may want. The CA is expected to be able to enforce policies to inject himself between a client and server even when channel
to recover from improper CSR requests. binding is in use. The attack was possible because of certain (D)TLS
implementation imperfections. In the context of this specification,
an attacker could invalidate the purpose of the POP linking
ChallengePassword in the client request by resuming an EST-coaps
connection. Even though the practical risk of such an attack to EST-
coaps is not devastating, we would rather use a more secure channel
binding mechanism. Such a mechanism could include an updated tls-
unique value generation like the tls-unique-prf defined in
[I-D.josefsson-sasl-tls-cb] by using a TLS exporter [RFC5705] in TLS
1.2 or TLS 1.3's updated exporter (Section 7.5 of [RFC8446]). Such
mechanism has not been standardized yet. Adopting in this document a
channel binding value generated from an exporter would break
backwards compatibility. Thus, in this specification we still depend
in the tls-unique mechanism defined in [RFC5929], especially since
the practicality of such an attack would not expose any messages
exchanged with EST-coaps.
Regarding the Certificate Signing Request (CSR), a CA is expected to
be able to enforce policies to recover from improper CSR requests.
Interpreters of ASN.1 structures should be aware of the use of Interpreters of ASN.1 structures should be aware of the use of
invalid ASN.1 length fields and should take appropriate measures to invalid ASN.1 length fields and should take appropriate measures to
guard against buffer overflows, stack overruns in particular, and guard against buffer overflows, stack overruns in particular, and
malicious content in general. malicious content in general.
11.2. HTTPS-CoAPS Registrar considerations 11.2. HTTPS-CoAPS Registrar considerations
The Registrar proposed in Section 8 must be deployed with care, and The Registrar proposed in Section 7 must be deployed with care, and
only when the recommended connections are impossible. When POP only when the recommended connections are impossible. When POP
linking is used the Registrar terminating the TLS connection linking is used the Registrar terminating the TLS connection
establishes a new one with the upstream CA. Thus, it is impossible establishes a new one with the upstream CA. Thus, it is impossible
for POP linking to be enforced end-to-end for the EST transaction. for POP linking to be enforced end-to-end for the EST transaction.
The EST server could be configured to accept POP linking information The EST server could be configured to accept POP linking information
that does not match the current TLS session because the authenticated that does not match the current TLS session because the authenticated
EST Registrar client has verified this information when acting as an EST Registrar client has verified this information when acting as an
EST server. EST server.
The introduction of an EST-coaps-to-HTTP Registrar assumes the client The introduction of an EST-coaps-to-HTTP Registrar assumes the client
can trust the registrar using its implicit or explicit TA database. can trust the registrar using its implicit or explicit TA database.
It also assumes the Registrar has a trust relationship with the It also assumes the Registrar has a trust relationship with the
upstream EST server in order to act on behalf of the clients. When a upstream EST server in order to act on behalf of the clients. When a
client uses the Implicit TA database for certificate validation, he client uses the Implicit TA database for certificate validation, he
SHOULD confirm if the server is acting as an RA by the presence of SHOULD confirm if the server is acting as an RA by the presence of
the id-kp-cmcRA [RFC6402] EKU in the server certificate. If the the id-kp-cmcRA [RFC6402] EKU in the server certificate. If the
server certificate does not include the EKU, it is RECOMMENDED that server certificate does not include the EKU, it is RECOMMENDED that
the client includes "Linking Identity and POP Information" the client includes "Linking Identity and POP Information"
(Section 7) in requests. (Section 6) in requests.
In a server-side key generation case, if no end-to-end encryption is In a server-side key generation case, if no end-to-end encryption is
used, the Registrar may be able see the private key as it acts as a used, the Registrar may be able see the private key as it acts as a
man-in-the-middle. Thus, the client puts its trust on the Registrar man-in-the-middle. Thus, the client puts its trust on the Registrar
not exposing the private key. not exposing the private key.
Clients that leverage server-side key generation without end-to-end Clients that leverage server-side key generation without end-to-end
encryption of the private key (Section 5.7 have no knowledge if the encryption of the private key (Section 5.8) have no knowledge if the
Registrar will be generating the private key and enrolling the Registrar will be generating the private key and enrolling the
certificates with the CA or if the CA will be responsible for certificates with the CA or if the CA will be responsible for
generating the key. In such cases, the existence of a Registrar generating the key. In such cases, the existence of a Registrar
requires the client to put its trust on the registrar doing the right requires the client to put its trust on the registrar doing the right
thing if it is generating the private key. thing if it is generating the private key.
12. Contributors 12. Contributors
Martin Furuhed contributed to the EST-coaps specification by Martin Furuhed contributed to the EST-coaps specification by
providing feedback based on the Nexus EST over CoAPs server providing feedback based on the Nexus EST over CoAPS server
implementation that started in 2015. Sandeep Kumar kick-started this implementation that started in 2015. Sandeep Kumar kick-started this
specification and was instrumental in drawing attention to the specification and was instrumental in drawing attention to the
importance of the subject. importance of the subject.
13. Acknowledgements 13. Acknowledgements
The authors are very grateful to Klaus Hartke for his detailed The authors are very grateful to Klaus Hartke for his detailed
explanations on the use of Block with DTLS and his support for the explanations on the use of Block with DTLS and his support for the
content-format specification. The authors would like to thank Esko Content-Format specification. The authors would like to thank Esko
Dijk and Michael Verschoor for the valuable discussions that helped Dijk and Michael Verschoor for the valuable discussions that helped
in shaping the solution. They would also like to thank Peter in shaping the solution. They would also like to thank Peter
Panburana for his feedback on technical details of the solution. Panburana for his feedback on technical details of the solution.
Constructive comments were received from Benjamin Kaduk, Eliot Lear, Constructive comments were received from Benjamin Kaduk, Eliot Lear,
Jim Schaad, Hannes Tschofenig, Julien Vermillard, John Manuel, Oliver Jim Schaad, Hannes Tschofenig, Julien Vermillard, John Manuel, Oliver
Pfaff and Pete Beal. Pfaff and Pete Beal.
Interop tests were done by Oliver Pfaff, Thomas Werner, Oskar Interop tests were done by Oliver Pfaff, Thomas Werner, Oskar
Camezind, Bjorn Elmers and Joel Hoglund. Camezind, Bjorn Elmers and Joel Hoglund.
skipping to change at page 24, line 50 skipping to change at page 26, line 42
Rescorla, E., Tschofenig, H., and N. Modadugu, "The Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version Datagram Transport Layer Security (DTLS) Protocol Version
1.3", draft-ietf-tls-dtls13-30 (work in progress), 1.3", draft-ietf-tls-dtls13-30 (work in progress),
November 2018. November 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC2585] Housley, R. and P. Hoffman, "Internet X.509 Public Key
Infrastructure Operational Protocols: FTP and HTTP",
RFC 2585, DOI 10.17487/RFC2585, May 1999,
<https://www.rfc-editor.org/info/rfc2585>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC5967] Turner, S., "The application/pkcs10 Media Type", RFC 5967, [RFC5967] Turner, S., "The application/pkcs10 Media Type", RFC 5967,
DOI 10.17487/RFC5967, August 2010, DOI 10.17487/RFC5967, August 2010,
<https://www.rfc-editor.org/info/rfc5967>. <https://www.rfc-editor.org/info/rfc5967>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>. January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
skipping to change at page 25, line 42 skipping to change at page 27, line 46
[RFC8075] Castellani, A., Loreto, S., Rahman, A., Fossati, T., and [RFC8075] Castellani, A., Loreto, S., Rahman, A., Fossati, T., and
E. Dijk, "Guidelines for Mapping Implementations: HTTP to E. Dijk, "Guidelines for Mapping Implementations: HTTP to
the Constrained Application Protocol (CoAP)", RFC 8075, the Constrained Application Protocol (CoAP)", RFC 8075,
DOI 10.17487/RFC8075, February 2017, DOI 10.17487/RFC8075, February 2017,
<https://www.rfc-editor.org/info/rfc8075>. <https://www.rfc-editor.org/info/rfc8075>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
14.2. Informative References 14.2. Informative References
[COREparams] [COREparams]
IANA, "Constrained RESTful Environments (CoRE) IANA, "Constrained RESTful Environments (CoRE)
Parameters", <https://www.iana.org/assignments/core- Parameters", <https://www.iana.org/assignments/core-
parameters/core-parameters.xhtml>. parameters/core-parameters.xhtml>.
[I-D.ietf-core-resource-directory]
Shelby, Z., Koster, M., Bormann, C., Stok, P., and C.
Amsuess, "CoRE Resource Directory", draft-ietf-core-
resource-directory-19 (work in progress), January 2019.
[I-D.ietf-lamps-rfc5751-bis] [I-D.ietf-lamps-rfc5751-bis]
Schaad, J., Ramsdell, B., and S. Turner, "Secure/ Schaad, J., Ramsdell, B., and S. Turner, "Secure/
Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
Message Specification", draft-ietf-lamps-rfc5751-bis-12 Message Specification", draft-ietf-lamps-rfc5751-bis-12
(work in progress), September 2018. (work in progress), September 2018.
[I-D.ietf-tls-dtls-connection-id]
Rescorla, E., Tschofenig, H., Fossati, T., and T. Gondrom,
"Connection Identifiers for DTLS 1.2", draft-ietf-tls-
dtls-connection-id-02 (work in progress), October 2018.
[I-D.josefsson-sasl-tls-cb]
Josefsson, S., "Channel Bindings for TLS based on the
PRF", draft-josefsson-sasl-tls-cb-03 (work in progress),
March 2015.
[I-D.moskowitz-ecdsa-pki] [I-D.moskowitz-ecdsa-pki]
Moskowitz, R., Birkholz, H., Xia, L., and M. Richardson, Moskowitz, R., Birkholz, H., Xia, L., and M. Richardson,
"Guide for building an ECC pki", draft-moskowitz-ecdsa- "Guide for building an ECC pki", draft-moskowitz-ecdsa-
pki-04 (work in progress), September 2018. pki-04 (work in progress), September 2018.
[I-D.rescorla-tls-dtls-connection-id]
Rescorla, E., Tschofenig, H., Fossati, T., and T. Gondrom,
"The Datagram Transport Layer Security (DTLS) Connection
Identifier", draft-rescorla-tls-dtls-connection-id-02
(work in progress), November 2017.
[ieee802.15.4] [ieee802.15.4]
Institute of Electrical and Electronics Engineers, "IEEE Institute of Electrical and Electronics Engineers, "IEEE
Standard 802.15.4-2006", 2006. Standard 802.15.4-2006", 2006.
[ieee802.1ar] [ieee802.1ar]
Institute of Electrical and Electronics Engineers, "IEEE Institute of Electrical and Electronics Engineers, "IEEE
802.1AR Secure Device Identifier", December 2009. 802.1AR Secure Device Identifier", December 2009.
[PsQs] Nadia Heninger, Zakir Durumeric, Eric Wustrow, J. Alex [PsQs] Nadia Heninger, Zakir Durumeric, Eric Wustrow, J. Alex
Halderman, "Mining Your Ps and Qs: Detection of Widespread Halderman, "Mining Your Ps and Qs: Detection of Widespread
skipping to change at page 26, line 50 skipping to change at page 29, line 20
[RFC5272] Schaad, J. and M. Myers, "Certificate Management over CMS [RFC5272] Schaad, J. and M. Myers, "Certificate Management over CMS
(CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008, (CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008,
<https://www.rfc-editor.org/info/rfc5272>. <https://www.rfc-editor.org/info/rfc5272>.
[RFC5273] Schaad, J. and M. Myers, "Certificate Management over CMS [RFC5273] Schaad, J. and M. Myers, "Certificate Management over CMS
(CMC): Transport Protocols", RFC 5273, (CMC): Transport Protocols", RFC 5273,
DOI 10.17487/RFC5273, June 2008, DOI 10.17487/RFC5273, June 2008,
<https://www.rfc-editor.org/info/rfc5273>. <https://www.rfc-editor.org/info/rfc5273>.
[RFC5705] Rescorla, E., "Keying Material Exporters for Transport
Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705,
March 2010, <https://www.rfc-editor.org/info/rfc5705>.
[RFC5929] Altman, J., Williams, N., and L. Zhu, "Channel Bindings [RFC5929] Altman, J., Williams, N., and L. Zhu, "Channel Bindings
for TLS", RFC 5929, DOI 10.17487/RFC5929, July 2010, for TLS", RFC 5929, DOI 10.17487/RFC5929, July 2010,
<https://www.rfc-editor.org/info/rfc5929>. <https://www.rfc-editor.org/info/rfc5929>.
[RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958, [RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958,
DOI 10.17487/RFC5958, August 2010, DOI 10.17487/RFC5958, August 2010,
<https://www.rfc-editor.org/info/rfc5958>. <https://www.rfc-editor.org/info/rfc5958>.
[RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic [RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
Curve Cryptography Algorithms", RFC 6090, Curve Cryptography Algorithms", RFC 6090,
skipping to change at page 28, line 11 skipping to change at page 30, line 33
Profiles for the Internet of Things", RFC 7925, Profiles for the Internet of Things", RFC 7925,
DOI 10.17487/RFC7925, July 2016, DOI 10.17487/RFC7925, July 2016,
<https://www.rfc-editor.org/info/rfc7925>. <https://www.rfc-editor.org/info/rfc7925>.
[RFC8422] Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic [RFC8422] Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic
Curve Cryptography (ECC) Cipher Suites for Transport Layer Curve Cryptography (ECC) Cipher Suites for Transport Layer
Security (TLS) Versions 1.2 and Earlier", RFC 8422, Security (TLS) Versions 1.2 and Earlier", RFC 8422,
DOI 10.17487/RFC8422, August 2018, DOI 10.17487/RFC8422, August 2018,
<https://www.rfc-editor.org/info/rfc8422>. <https://www.rfc-editor.org/info/rfc8422>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RSAorig] Petr Svenda, Matus Nemec, Peter Sekan, Rudolf Kvasnovsky, [RSAorig] Petr Svenda, Matus Nemec, Peter Sekan, Rudolf Kvasnovsky,
David Formanek, David Komarek, Vashek Matyas, "The David Formanek, David Komarek, Vashek Matyas, "The
Million-Key Question - Investigating the Origins of RSA Million-Key Question - Investigating the Origins of RSA
Public Keys", USENIX Security Symposium 2016 ISBN Public Keys", USENIX Security Symposium 2016 ISBN
978-1-931971-32-4, August 2016. 978-1-931971-32-4, August 2016.
[tripleshake]
Karthikeyan Bhargavan, Antoine Delignat-Lavaud, Cedric
Fournet, Alfredo Pironti, Pierre-Yves Strub, "Triple
Handshakes and Cookie Cutters: Breaking and Fixing
Authentication over TLS", IEEE Security and Privacy ISBN
978-1-4799-4686-0, May 2014.
Appendix A. EST messages to EST-coaps Appendix A. EST messages to EST-coaps
This section shows similar examples to the ones presented in This section shows similar examples to the ones presented in
Appendix A of [RFC7030]. The payloads in the examples are the hex Appendix A of [RFC7030]. The payloads in the examples are the hex
encoded DER binary, generated with 'xxd -p', of the PKI certificates encoded binary, generated with 'xxd -p', of the PKI certificates
created following [I-D.moskowitz-ecdsa-pki]. The payloads are shown created following [I-D.moskowitz-ecdsa-pki]. The payloads are shown
unencrypted. In practice the message content would be binary DER unencrypted. In practice the message content would be binary
formatted and transferred over an encrypted DTLS tunnel. The formatted and transferred over an encrypted DTLS tunnel. The
hexadecimal representations in the examples below would NOT be hexadecimal representations in the examples below would NOT be
transported in hex, but in binary DER. Hex is used for visualization transported in hex, but in binary. Hex is used for visualization
purposes because a binary representation cannot be rendered well in purposes because a binary representation cannot be rendered well in
text. text.
The message content breakdown is presented in Appendix C. The certificate responses included in the examples contain Content-
Format 281 (application/pkcs7). If the client had requested Content-
Format TBD287 (application/pkix-cert) with an Accept Option, the
server would respond a single DER binary certificate.
These examples assume that the resource discovery, returned a short
base path of "/est".
The corresponding CoAP headers are only shown in Appendix A.1. The corresponding CoAP headers are only shown in Appendix A.1.
Creating CoAP headers is assumed to be generally understood. Creating CoAP headers is assumed to be generally understood.
These examples assume that the resource discovery, returned a short The message content breakdown is presented in Appendix C.
base path of "/est".
A.1. cacerts A.1. cacerts
In EST-coaps, a coaps cacerts message can be: In EST-coaps, a cacerts message can be:
GET coaps://192.0.2.1:8085/est/crts GET coaps://est-coaps.example.ietf.org:9085/est/crts
(Accept: 281)
The corresponding CoAP header fields are shown below. The use of The corresponding CoAP header fields are shown below. The use of
block and DTLS are worked out in Appendix B. block and DTLS are worked out in Appendix B.
Ver = 1 Ver = 1
T = 0 (CON) T = 0 (CON)
Code = 0x01 (0.01 is GET) Code = 0x01 (0.01 is GET)
Token = 0x9a (client generated) Token = 0x9a (client generated)
Options Options
Option [optional] Option (Uri-Host) [optional]
Option Delta = 0x3 (option# 3 Uri-Host) Option Delta = 0x3 (option# 3)
Option Length = 0x9 Option Length = 0x9
Option Value = 192.0.2.1 Option Value = est-coaps.example.ietf.org
Option [optional] Option (Uri-Port) [optional]
Option Delta = 0x4 (option# 3+4=7 Uri-Port) Option Delta = 0x4 (option# 3+4=7)
Option Length = 0x4 Option Length = 0x4
Option Value = 8085 Option Value = 9085
Option Option (Uri-Path)
Option Delta = 0x4 (option# 7+4=11 Uri-Path) Option Delta = 0x4 (option# 7+4=11)
Option Length = 0x5 Option Length = 0x5
Option Value = "est" Option Value = "est"
Option Option (Uri-Path)
Option Delta = 0x0 (option# 11+0=11 Uri-Path) Option Delta = 0x0 (option# 11+0=11)
Option Length = 0x6 Option Length = 0x6
Option Value = "crts" Option Value = "crts"
Option Option (Accept)
Option Delta = 0x3 (option# 11+3=14 Max-Age) Option Delta = 0x6 (option# 11+6=17)
Option Length = 0x1 Option Length = 0x2
Option Value = 0x1 (1 minute) Option Value = 281
Payload = [Empty] Payload = [Empty]
The Uri-Host and Uri-Port Options are optional. They are usually
omitted as the DTLS destination and port are sufficient. Explicit
Uri-Host and Uri-Port Options are typically used when an endpoint
hosts multiple virtual servers and uses the Options to route the
requests accordingly. Alternatively, if a UDP port to a server is
blocked, someone could send the DTLS packets to a known open port on
the server and use the Uri-Port to convey the intended port he is
attempting to reach.
A 2.05 Content response with a cert in EST-coaps will then be A 2.05 Content response with a cert in EST-coaps will then be
2.05 Content (Content-Format: 281) 2.05 Content (Content-Format: 281)
{payload with certificate in binary DER format} {payload with certificate in binary format}
with CoAP fields with CoAP fields
Ver = 1 Ver = 1
T = 2 (ACK) T = 2 (ACK)
Code = 0x45 (2.05 Content) Code = 0x45 (2.05 Content)
Token = 0x9a (copied from request by server) Token = 0x9a (copied from request by server)
Options Options
Option Option (Content-Format)
Option Delta = 0xC (option# 12 Content-Format) Option Delta = 0xC (option# 12)
Option Length = 0x2 Option Length = 0x2
Option Value = 281 Option Value = 281
[ The hexadecimal representation below would NOT be transported [ The hexadecimal representation below would NOT be transported
in hex, but in DER. Hex is used because a binary representation in hex, but in binary. Hex is used because a binary representation
cannot be rendered well in text. ] cannot be rendered well in text. ]
Payload = Payload =
3082027b06092a864886f70d010702a082026c308202680201013100300b 3082027b06092a864886f70d010702a082026c308202680201013100300b
06092a864886f70d010701a082024e3082024a308201f0a0030201020209 06092a864886f70d010701a082024e3082024a308201f0a0030201020209
009189bcdf9c99244b300a06082a8648ce3d0403023067310b3009060355 009189bcdf9c99244b300a06082a8648ce3d0403023067310b3009060355
040613025553310b300906035504080c024341310b300906035504070c02 040613025553310b300906035504080c024341310b300906035504070c02
4c4131143012060355040a0c0b4578616d706c6520496e63311630140603 4c4131143012060355040a0c0b4578616d706c6520496e63311630140603
55040b0c0d63657274696669636174696f6e3110300e06035504030c0752 55040b0c0d63657274696669636174696f6e3110300e06035504030c0752
6f6f74204341301e170d3139303130373130343034315a170d3339303130 6f6f74204341301e170d3139303130373130343034315a170d3339303130
skipping to change at page 30, line 44 skipping to change at page 33, line 44
a8301f0603551d230418301680142495e816ef6ffcaaf356ce4adffe33cf a8301f0603551d230418301680142495e816ef6ffcaaf356ce4adffe33cf
492abba8300f0603551d130101ff040530030101ff300e0603551d0f0101 492abba8300f0603551d130101ff040530030101ff300e0603551d0f0101
ff040403020106301e0603551d1104173015811363657274696679406578 ff040403020106301e0603551d1104173015811363657274696679406578
616d706c652e636f6d300a06082a8648ce3d0403020348003045022100da 616d706c652e636f6d300a06082a8648ce3d0403020348003045022100da
e37c96f154c32ec0b4af52d46f3b7ecc9687ddf267bcec368f7b7f135327 e37c96f154c32ec0b4af52d46f3b7ecc9687ddf267bcec368f7b7f135327
2f022047a28ae5c7306163b3c3834bab3c103f743070594c089aaa0ac870 2f022047a28ae5c7306163b3c3834bab3c103f743070594c089aaa0ac870
cd13b902caa1003100 cd13b902caa1003100
The breakdown of the payload is shown in Appendix C.1. The breakdown of the payload is shown in Appendix C.1.
A.2. csrattrs A.2. enroll / reenroll
In the following csrattrs exchange, the CoAP GET request looks like
REQ:
GET coaps://[2001:db8::2:1]:61616/est/att
(Content-Format: 285)
[ The hexadecimal representation below would NOT be transported
in hex, but in DER. Hex is used because a binary representation
cannot be rendered well in text. ]
307c06072b06010101011630220603883701311b131950617273652053455
420617320322e3939392e31206461746106092a864886f70d010907302c06
0388370231250603883703060388370413195061727365205345542061732
0322e3939392e32206461746106092b240303020801010b06096086480165
03040202
A 2.05 Content response should contain attributes which are relevant
for the authenticated client. This example is copied from section
A.2 in [RFC7030], where the base64 representation is replaced with a
hexadecimal representation of the equivalent binary DER format. The
EST-coaps server returns attributes that the client can ignore if
they are unknown to him.
A.3. enroll / reenroll
During the (re-)enroll exchange the EST-coaps client uses a CSR During the (re-)enroll exchange the EST-coaps client uses a CSR
(Content-Format 286) request in the POST request payload. As shown (Content-Format 286) request in the POST request payload. The Accept
in Appendix C.2, the CSR contains a ChallengePassword which is used option tells the server that the client is expecting Content-Format
for POP linking (Section 7). 281 (PKCS#7) in the response. As shown in Appendix C.2, the CSR
contains a ChallengePassword which is used for POP linking
(Section 6).
POST [2001:db8::2:1]:61616/est/sen POST [2001:db8::2:1]:61616/est/sen
(token 0x45) (Token: 0x45)
(Accept: 281)
(Content-Format: 286) (Content-Format: 286)
[ The hexadecimal representation below would NOT be transported [ The hexadecimal representation below would NOT be transported
in hex, but in DER. Hex is used because a binary representation in hex, but in binary. Hex is used because a binary representation
cannot be rendered well in text. ] cannot be rendered well in text. ]
308201853082012c0201003070310b3009060355040613025553310b3009 3082018b30820131020100305c310b3009060355040613025553310b3009
06035504080c024341310b300906035504070c024c413114301206035504 06035504080c024341310b300906035504070c024c413114301206035504
0a0c0b6578616d706c6520496e63310c300a060355040b0c03496f543112 0a0c0b6578616d706c6520496e63310c300a060355040b0c03496f54310f
301006035504030c09436c69656e74205241310f300d0603550405130657 300d060355040513065774313233343059301306072a8648ce3d02010608
74313233343059301306072a8648ce3d020106082a8648ce3d0301070342 2a8648ce3d03010703420004c8b421f11c25e47e3ac57123bf2d9fdc494f
00041bb8c1117896f98e4506c03d70efbe820d8e38ea97e9d65d52c8460c 028bc351cc80c03f150bf50cff958d75419d81a6a245dffae790be95cf75
5852c51dd89a61370a2843760fc859799d78cd33f3c1846e304f1717f812 f602f9152618f816a2b23b5638e59fd9a073303406092a864886f70d0109
3f1a284cc99fa05a301b06092a864886f70d010907310e0c0c6461746e69 0731270c2576437630292a264a4b4a3bc3a2c280c2992f3e3c2e2c3d6b6e
65746465657274303b06092a864886f70d01090e312e302c302a0603551d 7634332323403d204e787e60303b06092a864886f70d01090e312e302c30
1104233021a01f06082b06010505070804a013301106092b06010401b43b 2a0603551d1104233021a01f06082b06010505070804a013301106092b06
0a01040401020304300a06082a8648ce3d040302034700304402201f82c6 010401b43b0a01040401020304300a06082a8648ce3d0403020348003045
868a654e2dec43cff50aebd6cbbe20dc8242a20a806684f2b8545d008902 02210092563a546463bd9ecff170d0fd1f2ef0d3d012160e5ee90cffedab
20668de2c306df1768105a781e49b1cdc42a2a7f41d6b71d928789547d61 ec9b9a38920220179f10a3436109051abad17590a09bc87c4dce5453a6fc
b2b7cf 1135a1e84eed754377
After verification of the CSR by the server, a 2.01 Content response After verification of the CSR by the server, a 2.01 Content response
with the issued certificate will be returned to the client. As with the issued certificate will be returned to the client.
described in Section 5.6, if the server is not able to provide a
response immediately, it sends an empty ACK with response code 5.03
(Service Unavailable) and the Max-Age option. See Figure 3 for an
example exchange.
RET:
(Content-Format: 281)(token =0x45)
2.01 Created 2.01 Created
(Token: 0x45)
(Content-Format: 281)
[ The hexadecimal representation below would NOT be transported [ The hexadecimal representation below would NOT be transported
in hex, but in DER. Hex is used because a binary representation in hex, but in binary. Hex is used because a binary representation
cannot be rendered well in text. ] cannot be rendered well in text. ]
3082028206092a864886f70d010702a08202733082026f0201013100300b 3082026e06092a864886f70d010702a082025f3082025b0201013100300b
06092a864886f70d010701a082025530820251308201f7a0030201020209 06092a864886f70d010701a08202413082023d308201e2a0030201020208
00ce06119a0fd27ca9300a06082a8648ce3d040302305d310b3009060355 7e7661d7b54e4632300a06082a8648ce3d040302305d310b300906035504
040613025553310b300906035504080c02434131143012060355040a0c0b 0613025553310b300906035504080c02434131143012060355040a0c0b45
4578616d706c6520496e6331163014060355040b0c0d6365727469666963 78616d706c6520496e6331163014060355040b0c0d636572746966696361
6174696f6e3113301106035504030c0a3830322e3141522043413020170d 74696f6e3113301106035504030c0a3830322e3141522043413020170d31
3139303130373130343832345a180f39393939313233313233353935395a 39303133313131323931365a180f39393939313233313233353935395a30
3070310b3009060355040613025553310b300906035504080c024341310b 5c310b3009060355040613025553310b300906035504080c024341310b30
300906035504070c024c4131143012060355040a0c0b6578616d706c6520 0906035504070c024c4131143012060355040a0c0b6578616d706c652049
496e63310c300a060355040b0c03496f543112301006035504030c09436c 6e63310c300a060355040b0c03496f54310f300d06035504051306577431
69656e74205241310f300d06035504051306577431323334305930130607 3233343059301306072a8648ce3d020106082a8648ce3d03010703420004
2a8648ce3d020106082a8648ce3d030107034200041bb8c1117896f98e45 c8b421f11c25e47e3ac57123bf2d9fdc494f028bc351cc80c03f150bf50c
06c03d70efbe820d8e38ea97e9d65d52c8460c5852c51dd89a61370a2843 ff958d75419d81a6a245dffae790be95cf75f602f9152618f816a2b23b56
760fc859799d78cd33f3c1846e304f1717f8123f1a284cc99fa3818a3081 38e59fd9a3818a30818730090603551d1304023000301d0603551d0e0416
8730090603551d1304023000301d0603551d0e04160414494be598dc8dbc 041496600d8716bf7fd0e752d0ac760777ad665d02a0301f0603551d2304
0dbc071c486b777460e5cce621301f0603551d23041830168014d344161b 183016801468d16551f951bfc82a431d0d9f08bc2d205b1160300e060355
ff1fa5343015958577dd33507be6b29b300e0603551d0f0101ff04040302 1d0f0101ff0404030205a0302a0603551d1104233021a01f06082b060105
05a0302a0603551d1104233021a01f06082b06010505070804a013301106 05070804a013301106092b06010401b43b0a01040401020304300a06082a
092b06010401b43b0a01040401020304300a06082a8648ce3d0403020348 8648ce3d0403020349003046022100c0d81996d2507d693f3c48eaa5ee94
003045022100a8073d6c1f9abb40739fc85a3773378568544036d8cd24f0 91bda6db214099d98117c63b361374cd86022100a774989f4c321a5cf25d
1d4b34cb61d9602c022008cc77f8dd5ca7c2fcf95ffc94fdc341e2b61080 832a4d336a08ad67df20f1506421188a0ade6d349236a1003100
118a9576c09e88d2fbd8a921a1003100
The breakdown of the request and response is shown in Appendix C.2. The breakdown of the request and response is shown in Appendix C.2.
A.4. serverkeygen As described in Section 5.7, if the server is not able to provide a
response immediately, it sends an empty ACK with response code 5.03
(Service Unavailable) and the Max-Age Option. See Figure 3 for an
example exchange.
In a serverkeygen exchange the CoAP GET request looks like A.3. serverkeygen
In a serverkeygen exchange the CoAP POST request looks like
POST coaps://192.0.2.1:8085/est/skg POST coaps://192.0.2.1:8085/est/skg
(token 0xa5) (Token: 0xa5)
(Content-Format: 286)(Max-Age=120) (Accept: 281)
(Content-Format: 286)
[ The hexadecimal representation below would NOT be transported [ The hexadecimal representation below would NOT be transported
in hex, but in DER. Hex is used because a binary representation in hex, but in binary. Hex is used because a binary representation
cannot be rendered well in text. ] cannot be rendered well in text. ]
3081cf3078020100301631143012060355040a0c0b736b67206578616d70 3081cf3078020100301631143012060355040a0c0b736b67206578616d70
6c653059301306072a8648ce3d020106082a8648ce3d030107034200041b 6c653059301306072a8648ce3d020106082a8648ce3d030107034200041b
b8c1117896f98e4506c03d70efbe820d8e38ea97e9d65d52c8460c5852c5 b8c1117896f98e4506c03d70efbe820d8e38ea97e9d65d52c8460c5852c5
1dd89a61370a2843760fc859799d78cd33f3c1846e304f1717f8123f1a28 1dd89a61370a2843760fc859799d78cd33f3c1846e304f1717f8123f1a28
4cc99fa000300a06082a8648ce3d04030203470030440220387cd4e9cf62 4cc99fa000300a06082a8648ce3d04030203470030440220387cd4e9cf62
8d4af77f92ebed4890d9d141dca86cd2757dd14cbd59cdf6961802202f24 8d4af77f92ebed4890d9d141dca86cd2757dd14cbd59cdf6961802202f24
5e828c77754378b66660a4977f113cacdaa0cc7bad7d1474a7fd155d090d 5e828c77754378b66660a4977f113cacdaa0cc7bad7d1474a7fd155d090d
The response would follow [I-D.ietf-core-multipart-ct] and could The response would follow [I-D.ietf-core-multipart-ct] and could look
looke like like
RET: 2.01 Content
2.01 Content (Content-Format: 62) (Token: 0xa5)
(token=0xa5) (Content-Format: 62)
[ The hexadecimal representations below would NOT be transported [ The hexadecimal representations below would NOT be transported
in hex, but in DER. Hex is used because a binary representation in hex, but in binary. Hex is used because a binary representation
cannot be rendered well in text. ] cannot be rendered well in text. ]
84 # array(4) 84 # array(4)
19 011C # unsigned(284) 19 011C # unsigned(284)
58 8A # bytes(138) 58 8A # bytes(138)
308187020100301306072a8648ce3d020106082a8648ce3d030107046d30 308187020100301306072a8648ce3d020106082a8648ce3d030107046d30
6b02010104200b9a67785b65e07360b6d28cfc1d3f3925c0755799deeca7 6b02010104200b9a67785b65e07360b6d28cfc1d3f3925c0755799deeca7
45372b01697bd8a6a144034200041bb8c1117896f98e4506c03d70efbe82 45372b01697bd8a6a144034200041bb8c1117896f98e4506c03d70efbe82
0d8e38ea97e9d65d52c8460c5852c51dd89a61370a2843760fc859799d78 0d8e38ea97e9d65d52c8460c5852c51dd89a61370a2843760fc859799d78
cd33f3c1846e304f1717f8123f1a284cc99f cd33f3c1846e304f1717f8123f1a284cc99f
skipping to change at page 35, line 39 skipping to change at page 37, line 39
5d52c8460c5852c51dd89a61370a2843760fc859799d78cd33f3c1846e30 5d52c8460c5852c51dd89a61370a2843760fc859799d78cd33f3c1846e30
4f1717f8123f1a284cc99fa37b307930090603551d1304023000302c0609 4f1717f8123f1a284cc99fa37b307930090603551d1304023000302c0609
6086480186f842010d041f161d4f70656e53534c2047656e657261746564 6086480186f842010d041f161d4f70656e53534c2047656e657261746564
204365727469666963617465301d0603551d0e04160414494be598dc8dbc 204365727469666963617465301d0603551d0e04160414494be598dc8dbc
0dbc071c486b777460e5cce621301f0603551d23041830168014494be598 0dbc071c486b777460e5cce621301f0603551d23041830168014494be598
dc8dbc0dbc071c486b777460e5cce621300a06082a8648ce3d0403020349 dc8dbc0dbc071c486b777460e5cce621300a06082a8648ce3d0403020349
003046022100a4b167d0f9add9202810e6bf6a290b8cfdfc9b9c9fea2cc1 003046022100a4b167d0f9add9202810e6bf6a290b8cfdfc9b9c9fea2cc1
c8fc3a464f79f2c202210081d31ba142751a7b4a34fd1a01fcfb08716b9e c8fc3a464f79f2c202210081d31ba142751a7b4a34fd1a01fcfb08716b9e
b53bdaadc9ae60b08f52429c0fa1003100 b53bdaadc9ae60b08f52429c0fa1003100
The private key in the response above is without CMS EnvelopedData
and has no additional encryption beyond DTLS (Section 5.8).
The breakdown of the request and response is shown in Appendix C.3 The breakdown of the request and response is shown in Appendix C.3
A.4. csrattrs
Below is a csrattrs exchange
REQ:
GET coaps://[2001:db8::2:1]:61616/est/att
RES:
2.05 Content
(Content-Format: 285)
[ The hexadecimal representation below would NOT be transported
in hex, but in binary. Hex is used because a binary representation
cannot be rendered well in text. ]
307c06072b06010101011630220603883701311b131950617273652053455
420617320322e3939392e31206461746106092a864886f70d010907302c06
0388370231250603883703060388370413195061727365205345542061732
0322e3939392e32206461746106092b240303020801010b06096086480165
03040202
A 2.05 Content response should contain attributes which are relevant
for the authenticated client. This example is copied from section
A.2 in [RFC7030], where the base64 representation is replaced with a
hexadecimal representation of the equivalent binary format. The EST-
coaps server returns attributes that the client can ignore if they
are unknown to him.
Appendix B. EST-coaps Block message examples Appendix B. EST-coaps Block message examples
Two examples are presented in this section: Two examples are presented in this section:
1. a cacerts exchange shows the use of Block2 and the block headers 1. a cacerts exchange shows the use of Block2 and the block headers
2. an enroll exchange shows the Block1 and Block2 size negotiation 2. an enroll exchange shows the Block1 and Block2 size negotiation
for request and response payloads. for request and response payloads.
The payloads are shown unencrypted. In practice the message contents The payloads are shown unencrypted. In practice the message contents
would be binary DER formatted and transferred over an encrypted DTLS would be binary formatted and transferred over an encrypted DTLS
tunnel. The corresponding CoAP headers are only shown in tunnel. The corresponding CoAP headers are only shown in
Appendix B.1. Creating CoAP headers are assumed to be generally Appendix B.1. Creating CoAP headers are assumed to be generally
known. known.
B.1. cacerts B.1. cacerts
This section provides a detailed example of the messages using DTLS This section provides a detailed example of the messages using DTLS
and BLOCK option Block2. The minimum PMTU is 1280 bytes, which is and BLOCK option Block2. The minimum PMTU is 1280 bytes, which is
the example value assumed for the DTLS datagram size. The example the example value assumed for the DTLS datagram size. The example
block length is taken as 64 which gives an SZX value of 2. block length is taken as 64 which gives an SZX value of 2.
The following is an example of a cacerts exchange over DTLS. The The following is an example of a cacerts exchange over DTLS. The
content length of the cacerts response in appendix A.1 of [RFC7030] content length of the cacerts response in appendix A.1 of [RFC7030]
contains 639 bytes in binary. The CoAP message adds around 10 bytes, contains 639 bytes in binary. The CoAP message adds around 10 bytes,
the DTLS record 29 bytes. To avoid IP fragmentation, the CoAP block the DTLS record 29 bytes. To avoid IP fragmentation, the CoAP Block
option is used and an MTU of 127 is assumed to stay within one IEEE Option is used and an MTU of 127 is assumed to stay within one IEEE
802.15.4 packet. To stay below the MTU of 127, the payload is split 802.15.4 packet. To stay below the MTU of 127, the payload is split
in 9 packets with a payload of 64 bytes each, followed by a last in 9 packets with a payload of 64 bytes each, followed by a last
tenth packet of 63 bytes. The client sends an IPv6 packet containing tenth packet of 63 bytes. The client sends an IPv6 packet containing
the UDP datagram with the DTLS record that encapsulates the CoAP the UDP datagram with the DTLS record that encapsulates the CoAP
request 10 times. The server returns an IPv6 packet containing the request 10 times. The server returns an IPv6 packet containing the
UDP datagram with the DTLS record that encapsulates the CoAP UDP datagram with the DTLS record that encapsulates the CoAP
response. The CoAP request-response exchange with block option is response. The CoAP request-response exchange with block option is
shown below. Block option is shown in a decomposed way (block- shown below. Block Option is shown in a decomposed way (block-
option:NUM/M/size) indicating the kind of Block option (2 in this option:NUM/M/size) indicating the kind of Block Option (2 in this
case) followed by a colon, and then the block number (NUM), the more case) followed by a colon, and then the block number (NUM), the more
bit (M = 0 in Block2 response means it is last block), and block size bit (M = 0 in Block2 response means it is last block), and block size
with exponent (2**(SZX+4)) separated by slashes. The Length 64 is with exponent (2**(SZX+4)) separated by slashes. The Length 64 is
used with SZX=2 to avoid IP fragmentation. The CoAP Request is sent used with SZX=2 to avoid IP fragmentation. The CoAP Request is sent
with confirmable (CON) option and the content format of the response, confirmable (CON) and the Content-Format of the response, even though
even though not shown, is 281 (application/pkcs7-mime; smime- not shown, is 281 (application/pkcs7-mime; smime-type=certs-only).
type=certs-only). The transer of the 11 blocks with partially filled The transfer of the 10 blocks with partially filled block NUM=9 is
block NUM=10 is shown below shown below
GET /192.0.2.1:8085/est/crts (2:0/0/64) --> GET coaps://est-coaps.example.ietf.org:9085/est/crts (2:0/0/64) -->
<-- (2:0/1/64) 2.05 Content <-- (2:0/1/64) 2.05 Content
GET /192.0.2.1:8085/est/crts (2:1/0/64) --> GET coaps://est-coaps.example.ietf.org:9085/est/crts (2:1/0/64) -->
<-- (2:1/1/64) 2.05 Content <-- (2:1/1/64) 2.05 Content
| |
| |
| |
GET /192.0.2.1:8085/est/crts (2:10/0/64) --> GET coaps://est-coaps.example.ietf.org:9085/est/crts (2:9/0/64) -->
<-- (2:9/0/64) 2.05 Content <-- (2:9/0/64) 2.05 Content
The header of the GET request looks like The header of the GET request looks like
Ver = 1 Ver = 1
T = 0 (CON) T = 0 (CON)
Code = 0x01 (0.1 GET) Code = 0x01 (0.1 GET)
Token = 0x9a (client generated) Token = 0x9a (client generated)
Options Options
Option [optional] Option (Uri-Host) [optional]
Option Delta = 0x3 (option# 3 Uri-Host) Option Delta = 0x3 (option# 3)
Option Length = 0x9 Option Length = 0x9
Option Value = 192.0.2.1 Option Value = est-coaps.example.ietf.org
Option [optional] Option (Uri-Port) [optional]
Option Delta = 0x4 (option# 3+4=7 Uri-Port) Option Delta = 0x4 (option# 3+4=7)
Option Length = 0x4 Option Length = 0x4
Option Value = 8085 Option Value = 9085
Option Option (Uri-Path)
Option Delta = 0x4 (option# 7+4=11 Uri-Path) Option Delta = 0x4 (option# 7+4=11)
Option Length = 0x5 Option Length = 0x5
Option Value = "est" Option Value = "est"
Option4 Option (Uri-Path)Uri-Path)
Option Delta = 0x0 (option# 11+0=11 Uri-Path) Option Delta = 0x0 (option# 11+0=11)
Option Length = 0x6 Option Length = 0x6
Option Value = "crts" Option Value = "crts"
Option (Accept)
Option Delta = 0x6 (option# 11+6=17)
Option Length = 0x2
Option Value = 281
Payload = [Empty] Payload = [Empty]
The Uri-Host and Uri-Port Options are optional. They are usually
omitted as the DTLS destination and port are sufficient. Explicit
Uri-Host and Uri-Port Options are typically used when an endpoint
hosts multiple virtual servers and uses the Options to route the
requests accordingly. Alternatively, if a UDP port to a server is
blocked, someone could send the DTLS packets to a known open port on
the server and use the Uri-Port to convey the intended port he is
attempting to reach.
For further detailing the CoAP headers, the first two and the last For further detailing the CoAP headers, the first two and the last
blocks are written out below. The header of the first Block2 blocks are written out below. The header of the first Block2
response looks like response looks like
Ver = 1 Ver = 1
T = 2 (ACK) T = 2 (ACK)
Code = 0x45 (2.05 Content) Code = 0x45 (2.05 Content)
Token = 0x9a (copied from request by server) Token = 0x9a (copied from request by server)
Options Options
Option Option
Option Delta = 0xC (option# 12 Content-Format) Option Delta = 0xC (option# 12 Content-Format)
Option Length = 0x2 Option Length = 0x2
Option Value = 281 Option Value = 281
Option Option
Option Delta = 0xB (option# 12+11=23 Block2) Option Delta = 0xB (option# 12+11=23 Block2)
Option Length = 0x1 Option Length = 0x1
Option Value = 0x0A (block#=0, M=1, SZX=2) Option Value = 0x0A (block#=0, M=1, SZX=2)
[ The hexadecimal representation below would NOT be transported [ The hexadecimal representation below would NOT be transported
in hex, but in DER. Hex is used because a binary representation in hex, but in binary. Hex is used because a binary representation
cannot be rendered well in text. ] cannot be rendered well in text. ]
Payload = Payload =
3082027b06092a864886f70d010702a082026c308202680201013100300b 3082027b06092a864886f70d010702a082026c308202680201013100300b
06092a864886f70d010701a082024e3082024a308201f0a0030201020209 06092a864886f70d010701a082024e3082024a308201f0a0030201020209
009189bc 009189bc
The second Block2: The second Block2:
Ver = 1 Ver = 1
skipping to change at page 38, line 44 skipping to change at page 41, line 44
Option Option
Option Delta = 0xC (option# 12 Content-Format) Option Delta = 0xC (option# 12 Content-Format)
Option Length = 0x2 Option Length = 0x2
Option Value = 281 Option Value = 281
Option Option
Option Delta = 0xB (option 12+11=23 Block2) Option Delta = 0xB (option 12+11=23 Block2)
Option Length = 0x1 Option Length = 0x1
Option Value = 0x1A (block#=1, M=1, SZX=2) Option Value = 0x1A (block#=1, M=1, SZX=2)
[ The hexadecimal representation below would NOT be transported [ The hexadecimal representation below would NOT be transported
in hex, but in DER. Hex is used because a binary representation in hex, but in binary. Hex is used because a binary representation
cannot be rendered well in text. ] cannot be rendered well in text. ]
Payload = Payload =
df9c99244b300a06082a8648ce3d0403023067310b300906035504061302 df9c99244b300a06082a8648ce3d0403023067310b300906035504061302
5553310b300906035504080c024341310b300906035504070c024c413114 5553310b300906035504080c024341310b300906035504070c024c413114
30120603 30120603
The 11th and final Block2: The 10th and final Block2:
Ver = 1 Ver = 1
T = 2 (means ACK) T = 2 (means ACK)
Code = 0x45 (2.05 Content) Code = 0x45 (2.05 Content)
Token = 0x9a (copied from request by server) Token = 0x9a (copied from request by server)
Options Options
Option Option
Option Delta = 0xC (option# 12 Content-Format) Option Delta = 0xC (option# 12 Content-Format)
Option Length = 0x2 Option Length = 0x2
Option Value = 281 Option Value = 281
Option Option
Option Delta = 0xB (option# 12+11=23 Block2 ) Option Delta = 0xB (option# 12+11=23 Block2 )
Option Length = 0x2 Option Length = 0x2
Option Value = 0x92 (block#=9, M=0, SZX=2) Option Value = 0x92 (block#=9, M=0, SZX=2)
[ The hexadecimal representation below would NOT be transported [ The hexadecimal representation below would NOT be transported
in hex, but in DER. Hex is used because a binary representation in hex, but in binary. Hex is used because a binary representation
cannot be rendered well in text. ] cannot be rendered well in text. ]
Payload = Payload =
2ec0b4af52d46f3b7ecc9687ddf267bcec368f7b7f1353272f022047a28a 2ec0b4af52d46f3b7ecc9687ddf267bcec368f7b7f1353272f022047a28a
e5c7306163b3c3834bab3c103f743070594c089aaa0ac870cd13b902caa1 e5c7306163b3c3834bab3c103f743070594c089aaa0ac870cd13b902caa1
003100 003100
B.2. enroll B.2. enroll / reenroll
In this example the requested Block2 size of 256 bytes, required by In this example the requested Block2 size of 256 bytes, required by
the client, is transferred to the server in the very first request the client, is transferred to the server in the very first request
message. The block size 256=(2**(SZX+4)) which gives SZX=4. The message. The block size 256=(2**(SZX+4)) which gives SZX=4. The
notation for block numbering is the same as in Appendix B.1. It is notation for block numbering is the same as in Appendix B.1. It is
assumed that CSR takes N1+1 blocks and the cert response takes N2+1 assumed that CSR takes N1+1 blocks and the cert response takes N2+1
blocks. The header fields and the payload are omitted for brevity. blocks. The header fields and the payload are omitted for brevity.
POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR req} --> POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR req} -->
<-- (ACK) (1:0/1/256) (2.31 Continue) <-- (ACK) (1:0/1/256) (2.31 Continue)
POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR req} --> POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR req} -->
<-- (ACK) (1:1/1/256) (2.31 Continue) <-- (ACK) (1:1/1/256) (2.31 Continue)
. .
. .
. .
POST [2001:db8::2:1]:61616/est/sen (CON)(1:N1/0/256){CSR req} --> POST [2001:db8::2:1]:61616/est/sen (CON)(1:N1/0/256){CSR req} -->
<-- (ACK) (1:N1/0/256) (2:0/1/256) (2.04 Changed){Cert resp} <-- (ACK) (1:N1/0/256)(2:0/1/256)(2.04 Changed){Cert resp}
POST [2001:db8::2:1]:61616/est/sen (CON)(2:1/0/256) --> POST [2001:db8::2:1]:61616/est/sen (CON)(2:1/0/256) -->
<-- (ACK) (2:1/1/256) (2.04 Changed) {Cert resp} <-- (ACK) (2:1/1/256)(2.04 Changed) {Cert resp}
. .
. .
. .
POST [2001:db8::2:1]:61616/est/sen (CON)(2:N2/0/256) --> POST [2001:db8::2:1]:61616/est/sen (CON)(2:N2/0/256) -->
<-- (ACK) (2:N2/0/256) (2.04 Changed) {Cert resp} <-- (ACK) (2:N2/0/256) (2.04 Changed) {Cert resp}
Figure 5: EST-COAP enrolment with multiple blocks Figure 5: EST-COAP enrollment with multiple blocks
N1+1 blocks have been transferred from client to the server and N2+1 N1+1 blocks have been transferred from client to the server and N2+1
blocks have been transferred from server to client. blocks have been transferred from server to client.
Appendix C. Message content breakdown Appendix C. Message content breakdown
This appendix presents the breakdown of the hexadecimal dumps of the This appendix presents the breakdown of the hexadecimal dumps of the
binary payloads shown in Appendix A. binary payloads shown in Appendix A.
C.1. cacerts C.1. cacerts
skipping to change at page 42, line 4 skipping to change at page 45, line 8
email:certify@example.com email:certify@example.com
Signature Algorithm: ecdsa-with-SHA256 Signature Algorithm: ecdsa-with-SHA256
30:45:02:21:00:da:e3:7c:96:f1:54:c3:2e:c0:b4:af:52:d4: 30:45:02:21:00:da:e3:7c:96:f1:54:c3:2e:c0:b4:af:52:d4:
6f:3b:7e:cc:96:87:dd:f2:67:bc:ec:36:8f:7b:7f:13:53:27: 6f:3b:7e:cc:96:87:dd:f2:67:bc:ec:36:8f:7b:7f:13:53:27:
2f:02:20:47:a2:8a:e5:c7:30:61:63:b3:c3:83:4b:ab:3c:10: 2f:02:20:47:a2:8a:e5:c7:30:61:63:b3:c3:83:4b:ab:3c:10:
3f:74:30:70:59:4c:08:9a:aa:0a:c8:70:cd:13:b9:02:ca 3f:74:30:70:59:4c:08:9a:aa:0a:c8:70:cd:13:b9:02:ca
C.2. enroll / reenroll C.2. enroll / reenroll
The breakdown of the request is The breakdown of the request is
Certificate Request: Certificate Request:
Data: Data:
Version: 0 (0x0) Version: 0 (0x0)
Subject: C=US, ST=CA, L=LA, O=example Inc, Subject: C=US, ST=CA, L=LA, O=example Inc,
OU=IoT, CN=Client RA/serialNumber=Wt1234 OU=IoT/serialNumber=Wt1234
Subject Public Key Info: Subject Public Key Info:
Public Key Algorithm: id-ecPublicKey Public Key Algorithm: id-ecPublicKey
Public-Key: (256 bit) Public-Key: (256 bit)
pub: pub:
04:1b:b8:c1:11:78:96:f9:8e:45:06:c0:3d:70:ef: 04:c8:b4:21:f1:1c:25:e4:7e:3a:c5:71:23:bf:2d:
be:82:0d:8e:38:ea:97:e9:d6:5d:52:c8:46:0c:58: 9f:dc:49:4f:02:8b:c3:51:cc:80:c0:3f:15:0b:f5:
52:c5:1d:d8:9a:61:37:0a:28:43:76:0f:c8:59:79: 0c:ff:95:8d:75:41:9d:81:a6:a2:45:df:fa:e7:90:
9d:78:cd:33:f3:c1:84:6e:30:4f:17:17:f8:12:3f: be:95:cf:75:f6:02:f9:15:26:18:f8:16:a2:b2:3b:
1a:28:4c:c9:9f 56:38:e5:9f:d9
ASN1 OID: prime256v1 ASN1 OID: prime256v1
NIST CURVE: P-256 NIST CURVE: P-256
Attributes: Attributes:
challengePassword :datnietdeert challengePassword : <256-bit POP linking value>
Requested Extensions: Requested Extensions:
X509v3 Subject Alternative Name: X509v3 Subject Alternative Name:
othername:<unsupported> othername:<unsupported>
Signature Algorithm: ecdsa-with-SHA256 Signature Algorithm: ecdsa-with-SHA256
30:44:02:20:1f:82:c6:86:8a:65:4e:2d:ec:43:cf:f5:0a:eb: 30:45:02:21:00:92:56:3a:54:64:63:bd:9e:cf:f1:70:d0:fd:
d6:cb:be:20:dc:82:42:a2:0a:80:66:84:f2:b8:54:5d:00:89: 1f:2e:f0:d3:d0:12:16:0e:5e:e9:0c:ff:ed:ab:ec:9b:9a:38:
02:20:66:8d:e2:c3:06:df:17:68:10:5a:78:1e:49:b1:cd:c4: 92:02:20:17:9f:10:a3:43:61:09:05:1a:ba:d1:75:90:a0:9b:
2a:2a:7f:41:d6:b7:1d:92:87:89:54:7d:61:b2:b7:cf c8:7c:4d:ce:54:53:a6:fc:11:35:a1:e8:4e:ed:75:43:77
The CSR contained a ChallengePassword which is used for POP linking The CSR contained a ChallengePassword which is used for POP linking
(Section 7) (Section 6).
The breakdown of the issued certificate response is The breakdown of the issued certificate response is
Certificate: Certificate:
Data: Data:
Version: 3 (0x2) Version: 3 (0x2)
Serial Number: Serial Number: 9112578475118446130 (0x7e7661d7b54e4632)
ce:06:11:9a:0f:d2:7c:a9
Signature Algorithm: ecdsa-with-SHA256 Signature Algorithm: ecdsa-with-SHA256
Issuer: C=US, ST=CA, O=Example Inc, Issuer: C=US, ST=CA, O=Example Inc, OU=certification,
OU=certification, CN=802.1AR CA CN=802.1AR CA
Validity Validity
Not Before: Jan 7 10:48:24 2019 GMT Not Before: Jan 31 11:29:16 2019 GMT
Not After : Dec 31 23:59:59 9999 GMT Not After : Dec 31 23:59:59 9999 GMT
Subject: C=US, ST=CA, L=LA, O=example Inc, Subject: C=US, ST=CA, L=LA, O=example Inc,
OU=IoT, CN=Client RA/serialNumber=Wt1234 OU=IoT/serialNumber=Wt1234
Subject Public Key Info: Subject Public Key Info:
Public Key Algorithm: id-ecPublicKey Public Key Algorithm: id-ecPublicKey
Public-Key: (256 bit) Public-Key: (256 bit)
pub: pub:
04:1b:b8:c1:11:78:96:f9:8e:45:06:c0:3d:70:ef: 04:c8:b4:21:f1:1c:25:e4:7e:3a:c5:71:23:bf:2d:
be:82:0d:8e:38:ea:97:e9:d6:5d:52:c8:46:0c:58: 9f:dc:49:4f:02:8b:c3:51:cc:80:c0:3f:15:0b:f5:
52:c5:1d:d8:9a:61:37:0a:28:43:76:0f:c8:59:79: 0c:ff:95:8d:75:41:9d:81:a6:a2:45:df:fa:e7:90:
9d:78:cd:33:f3:c1:84:6e:30:4f:17:17:f8:12:3f: be:95:cf:75:f6:02:f9:15:26:18:f8:16:a2:b2:3b:
1a:28:4c:c9:9f 56:38:e5:9f:d9
ASN1 OID: prime256v1 ASN1 OID: prime256v1
NIST CURVE: P-256 NIST CURVE: P-256
X509v3 extensions: X509v3 extensions:
X509v3 Basic Constraints: X509v3 Basic Constraints:
CA:FALSE CA:FALSE
X509v3 Subject Key Identifier: X509v3 Subject Key Identifier:
49:4B:E5:98:DC:8D:BC:0D:BC:07:1C:48:6B:77:74:60:E5:CC:E6:21 96:60:0D:87:16:BF:7F:D0:E7:52:D0:AC:76:07:77:AD:66:5D:02:A0
X509v3 Authority Key Identifier: X509v3 Authority Key Identifier:
keyid: keyid:
D3:44:16:1B:FF:1F:A5:34:30:15:95:85:77:DD:33:50:7B:E6:B2:9B 68:D1:65:51:F9:51:BF:C8:2A:43:1D:0D:9F:08:BC:2D:20:5B:11:60
X509v3 Key Usage: critical X509v3 Key Usage: critical
Digital Signature, Key Encipherment Digital Signature, Key Encipherment
X509v3 Subject Alternative Name: X509v3 Subject Alternative Name:
othername:<unsupported> othername:<unsupported>
Signature Algorithm: ecdsa-with-SHA256 Signature Algorithm: ecdsa-with-SHA256
30:45:02:21:00:a8:07:3d:6c:1f:9a:bb:40:73:9f:c8:5a:37: 30:46:02:21:00:c0:d8:19:96:d2:50:7d:69:3f:3c:48:ea:a5:
73:37:85:68:54:40:36:d8:cd:24:f0:1d:4b:34:cb:61:d9:60: ee:94:91:bd:a6:db:21:40:99:d9:81:17:c6:3b:36:13:74:cd:
2c:02:20:08:cc:77:f8:dd:5c:a7:c2:fc:f9:5f:fc:94:fd:c3: 86:02:21:00:a7:74:98:9f:4c:32:1a:5c:f2:5d:83:2a:4d:33:
41:e2:b6:10:80:11:8a:95:76:c0:9e:88:d2:fb:d8:a9:21 6a:08:ad:67:df:20:f1:50:64:21:18:8a:0a:de:6d:34:92:36
C.3. serverkeygen C.3. serverkeygen
The followng is the breakdown of the request example used. The following is the breakdown of the request example used.
Certificate Request: Certificate Request:
Data: Data:
Version: 0 (0x0) Version: 0 (0x0)
Subject: O=skg example Subject: O=skg example
Subject Public Key Info: Subject Public Key Info:
Public Key Algorithm: id-ecPublicKey Public Key Algorithm: id-ecPublicKey
Public-Key: (256 bit) Public-Key: (256 bit)
pub: pub:
04:1b:b8:c1:11:78:96:f9:8e:45:06:c0:3d:70:ef: 04:1b:b8:c1:11:78:96:f9:8e:45:06:c0:3d:70:ef:
skipping to change at page 45, line 43 skipping to change at page 48, line 43
X509v3 Authority Key Identifier: X509v3 Authority Key Identifier:
keyid: keyid:
49:4B:E5:98:DC:8D:BC:0D:BC:07:1C:48:6B:77:74:60:E5:CC:E6:21 49:4B:E5:98:DC:8D:BC:0D:BC:07:1C:48:6B:77:74:60:E5:CC:E6:21
Signature Algorithm: ecdsa-with-SHA256 Signature Algorithm: ecdsa-with-SHA256
30:46:02:21:00:a4:b1:67:d0:f9:ad:d9:20:28:10:e6:bf:6a: 30:46:02:21:00:a4:b1:67:d0:f9:ad:d9:20:28:10:e6:bf:6a:
29:0b:8c:fd:fc:9b:9c:9f:ea:2c:c1:c8:fc:3a:46:4f:79:f2: 29:0b:8c:fd:fc:9b:9c:9f:ea:2c:c1:c8:fc:3a:46:4f:79:f2:
c2:02:21:00:81:d3:1b:a1:42:75:1a:7b:4a:34:fd:1a:01:fc: c2:02:21:00:81:d3:1b:a1:42:75:1a:7b:4a:34:fd:1a:01:fc:
fb:08:71:6b:9e:b5:3b:da:ad:c9:ae:60:b0:8f:52:42:9c:0f fb:08:71:6b:9e:b5:3b:da:ad:c9:ae:60:b0:8f:52:42:9c:0f
The private key in the response above is without CMS EnvelopedData
and has no additional encryption beyond DTLS (Section 5.7).
Authors' Addresses Authors' Addresses
Peter van der Stok Peter van der Stok
Consultant Consultant
Email: consultancy@vanderstok.org Email: consultancy@vanderstok.org
Panos Kampanakis Panos Kampanakis
Cisco Systems Cisco Systems
Email: pkampana@cisco.com Email: pkampana@cisco.com
 End of changes. 195 change blocks. 
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