--- 1/draft-ietf-ace-coap-est-12.txt 2019-09-10 03:13:12.881207169 -0700 +++ 2/draft-ietf-ace-coap-est-13.txt 2019-09-10 03:13:12.973209484 -0700 @@ -1,23 +1,23 @@ ACE P. van der Stok Internet-Draft Consultant Intended status: Standards Track P. Kampanakis -Expires: December 7, 2019 Cisco Systems +Expires: March 13, 2020 Cisco Systems M. Richardson SSW S. Raza RISE SICS - June 5, 2019 + September 10, 2019 EST over secure CoAP (EST-coaps) - draft-ietf-ace-coap-est-12 + draft-ietf-ace-coap-est-13 Abstract Enrollment over Secure Transport (EST) is used as a certificate provisioning protocol over HTTPS. Low-resource devices often use the lightweight Constrained Application Protocol (CoAP) for message exchanges. This document defines how to transport EST payloads over secure CoAP (EST-coaps), which allows constrained devices to use existing EST functionality for provisioning certificates. @@ -29,21 +29,21 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on December 7, 2019. + This Internet-Draft will expire on March 13, 2020. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -58,56 +58,62 @@ 1. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7 4. DTLS and conformance to RFC7925 profiles . . . . . . . . . . 7 5. Protocol Design . . . . . . . . . . . . . . . . . . . . . . . 9 5.1. Discovery and URIs . . . . . . . . . . . . . . . . . . . 10 5.2. Mandatory/optional EST Functions . . . . . . . . . . . . 12 5.3. Payload formats . . . . . . . . . . . . . . . . . . . . . 13 5.4. Message Bindings . . . . . . . . . . . . . . . . . . . . 14 5.5. CoAP response codes . . . . . . . . . . . . . . . . . . . 15 - 5.6. Message fragmentation . . . . . . . . . . . . . . . . . . 15 - 5.7. Delayed Responses . . . . . . . . . . . . . . . . . . . . 16 - 5.8. Server-side Key Generation . . . . . . . . . . . . . . . 18 - 6. HTTPS-CoAPS Registrar . . . . . . . . . . . . . . . . . . . . 20 - 7. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 22 - 8. Deployment limitations . . . . . . . . . . . . . . . . . . . 22 - 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 - 9.1. Content-Format Registry . . . . . . . . . . . . . . . . . 23 - 9.2. Resource Type registry . . . . . . . . . . . . . . . . . 23 - 10. Security Considerations . . . . . . . . . . . . . . . . . . . 24 - 10.1. EST server considerations . . . . . . . . . . . . . . . 24 - 10.2. HTTPS-CoAPS Registrar considerations . . . . . . . . . . 26 - 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 26 - 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27 - 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 27 - 13.1. Normative References . . . . . . . . . . . . . . . . . . 27 - 13.2. Informative References . . . . . . . . . . . . . . . . . 28 - Appendix A. EST messages to EST-coaps . . . . . . . . . . . . . 31 - A.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 31 - A.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 33 - A.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 35 - A.4. csrattrs . . . . . . . . . . . . . . . . . . . . . . . . 37 - Appendix B. EST-coaps Block message examples . . . . . . . . . . 38 - B.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 38 - B.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 42 - Appendix C. Message content breakdown . . . . . . . . . . . . . 43 - C.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 43 + 5.6. Message fragmentation . . . . . . . . . . . . . . . . . . 16 + 5.7. Delayed Responses . . . . . . . . . . . . . . . . . . . . 17 + 5.8. Server-side Key Generation . . . . . . . . . . . . . . . 19 + 6. HTTPS-CoAPS Registrar . . . . . . . . . . . . . . . . . . . . 21 + 7. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 23 + 8. Deployment limitations . . . . . . . . . . . . . . . . . . . 23 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 + 9.1. Content-Format Registry . . . . . . . . . . . . . . . . . 24 + 9.2. Resource Type registry . . . . . . . . . . . . . . . . . 24 + 10. Security Considerations . . . . . . . . . . . . . . . . . . . 25 + 10.1. EST server considerations . . . . . . . . . . . . . . . 25 + 10.2. HTTPS-CoAPS Registrar considerations . . . . . . . . . . 27 + 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 28 + 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28 + 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 + 13.1. Normative References . . . . . . . . . . . . . . . . . . 28 + 13.2. Informative References . . . . . . . . . . . . . . . . . 30 + Appendix A. EST messages to EST-coaps . . . . . . . . . . . . . 32 + A.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 33 + A.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 34 + A.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 36 + A.4. csrattrs . . . . . . . . . . . . . . . . . . . . . . . . 38 + Appendix B. EST-coaps Block message examples . . . . . . . . . . 39 + B.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 39 + B.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 43 + Appendix C. Message content breakdown . . . . . . . . . . . . . 44 + C.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 44 C.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 45 - C.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 46 + C.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 47 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 48 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 49 1. Change Log EDNOTE: Remove this section before publication + -13 + + Updates based on AD's review and discussions + + Examples redone without password + -12 Updated section 5 based on Esko's comments and nits identified. Nits and some clarifications for Esko's new review from 5/21/2019. Nits and some clarifications for Esko's new review from 5/28/2019. -11 @@ -289,56 +295,59 @@ "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. Many of the concepts in this document are taken from [RFC7030]. Consequently, much text is directly traceable to [RFC7030]. 4. DTLS and conformance to RFC7925 profiles - This section describes how EST-coaps fits into the profiles of low- + This section describes how EST-coaps conforms to the profiles of low- resource devices described in [RFC7925]. EST-coaps can transport certificates and private keys. Certificates are responses to - (re-)enrollment requests or requests for a trusted certificate list. + (re-)enrollment requests or requests a trusted certificate list. Private keys can be transported as responses to a server-side key generation request as described in Section 4.4 of [RFC7030] and discussed in Section 5.8 of this document. EST-coaps depends on a secure transport mechanism that secures the exchanged CoAP messages. DTLS is one such secure protocol. No other changes are necessary regarding the secure transport of EST messages. +------------------------------------------------+ | EST request/response messages | +------------------------------------------------+ | CoAP for message transfer and signaling | +------------------------------------------------+ | Secure Transport | +------------------------------------------------+ Figure 1: EST-coaps protocol layers - 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 - [RFC7251]. Curve secp256r1 MUST be supported [RFC8422]; this curve - is equivalent to the NIST P-256 curve. Additionally, crypto agility - is important, and the recommendations in Section 4.4 of [RFC7925] and - any updates to it concerning Curve25519 and other curves also apply. + In accordance with 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 [RFC7251]. Curve secp256r1 MUST + be supported [RFC8422]; this curve is equivalent to the NIST P-256 + curve. Additionally, crypto agility is important, and the + recommendations in Section 4.4 of [RFC7925] and any updates to it + concerning Curve25519 and other curves also apply. DTLS 1.2 implementations must use the Supported Elliptic Curves and Supported Point Formats Extensions in [RFC8422]. Uncompressed point format must also be supported. DTLS 1.3 [I-D.ietf-tls-dtls13] implementations differ from DTLS 1.2 because they do not support point format negotiation in favor of a single point format for each curve. Thus, support for DTLS 1.3 does not mandate point format - extensions and negotiation. + extensions and negotiation. In addition, DTLS 1.3 uses the + "supported_groups" extension in contrast to Supported Elliptic Curves + used by DTLS 1.2 CoAP was designed to avoid IP fragmentation. DTLS is used to secure CoAP messages. However, fragmentation is still possible at the DTLS layer during the DTLS handshake when using ECC ciphersuites. If fragmentation is necessary, "DTLS provides a mechanism for fragmenting a handshake message over several records, each of which can be transmitted separately, thus avoiding IP fragmentation" [RFC6347]. The authentication of the EST-coaps server by the EST-coaps client is @@ -348,45 +357,44 @@ before updating its trust anchor (Explicit TA) [RFC7030]. The authentication of the EST-coaps client MUST be with a client certificate in the DTLS handshake. This can either be o a previously issued client certificate (e.g., an existing certificate issued by the EST CA); this could be a common case for simple re-enrollment of clients. o a previously installed certificate (e.g., manufacturer IDevID - [ieee802.1ar] or a certificate issued by some other party); the - server is expected to trust that certificate. IDevID's are - expected to have a very long life, as long as the device, but - under some conditions could expire. In that case, the server MAY - want to authenticate a client certificate against its trust store - although the certificate is expired (Section 10). + [ieee802.1ar] or a certificate issued by some other party). + IDevID's are expected to have a very long life, as long as the + device, but under some conditions could expire. In that case, the + server MAY want to authenticate a client certificate against its + trust store although the certificate is expired (Section 10). EST-coaps supports the certificate types and Trust Anchors (TA) that are specified for EST in Section 3 of [RFC7030]. As described in Section 2.1 of [RFC5272] proof-of-identity refers to a value that can be used to prove that the private key corresponding - to the public key is in the possession of and can be used by an end- - entity or client. Additionally, channel-binding information can link - proof-of-identity with an established connetion. Connection-based - proof-of-possession is OPTIONAL for EST-coaps clients and servers. - When proof-of-possession is desired, a set of actions are required - regarding the use of tls-unique, described in Section 3.5 in - [RFC7030]. The tls-unique information consists of the contents of - the first "Finished" message in the (D)TLS handshake between server - and client [RFC5929]. The client adds the "Finished" message as a - ChallengePassword in the attributes section of the PKCS#10 Request - - [RFC5967] to prove that the client is indeed in control of the - private key at the time of the (D)TLS session establishment. + to the certified public key is in the possession of and can be used + by an end-entity or client. Additionally, channel-binding + information can link proof-of-identity with an established connetion. + Connection-based proof-of-possession is OPTIONAL for EST-coaps + clients and servers. When proof-of-possession is desired, a set of + actions are required regarding the use of tls-unique, described in + Section 3.5 in [RFC7030]. The tls-unique information consists of the + contents of the first "Finished" message in the (D)TLS handshake + between server and client [RFC5929]. The client adds the "Finished" + message as a ChallengePassword in the attributes section of the + PKCS#10 Request [RFC5967] to prove that the client is indeed in + control of the private key at the time of the (D)TLS session + 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 (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 @@ -404,50 +412,62 @@ security considerations apply regarding the use of the Implicit and Explicit TA database as explained in Section 10.1. Given that after a successful enrollment, it is more likely that a new EST transaction will take place after a significant amount of time, the DTLS connections SHOULD only be kept alive for EST messages that are relatively close to each other. In some cases, like NAT rebinding, keeping the state of a connection is not possible when devices sleep for extended periods of time. In such occasions, [I-D.ietf-tls-dtls-connection-id] negotiates a connection ID that can - eliminate the need for new handshake and its additional cost. + eliminate the need for new handshake and its additional cost; or DTLS + 1.3 session resumption provides a less costly alternative than re- + doing a full DTLS handshake. 5. Protocol Design EST-coaps uses CoAP to transfer EST messages, aided by Block-Wise Transfer [RFC7959] to avoid IP fragmentation. The use of Blocks for the transfer of larger EST messages is specified in Section 5.6. Figure 1 shows the layered EST-coaps architecture. The EST-coaps protocol design follows closely the EST design. The supported message types in EST-coaps are: o CA certificate retrieval needed to receive the complete set of CA certificates. - o Simple enroll and re-enroll for a CA to sign public client - identity key. + o Simple enroll and re-enroll for a CA to sign client identity + public key. - o Certificate Signing Request (CSR) attribute messages that inform + o Certificate Signing Request (CSR) attribute messages that informs the client of the fields to include in a CSR. - o Server-side key generation messages to provide a private client - identity key when the client choses so. + o Server-side key generation messages to provide a client identity + private key when the client chooses so. + + While [RFC7030] permits a number of the EST functions to be used + without authentication, this specification requires that the client + MUST be authenticated for all 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: + Two types of installations are possible (1)rigid ones where the + address and the supported functions of the EST server(s) are known, + and (2) flexible one where the EST server and it supported functions + need to be discovered. + + For both types of installations, 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://example.com:/.well-known/est/ coaps://example.com:/.well-known/est/ ArbitraryLabel/ The short-est strings are defined in Table 1. Arbitrary Labels are usually defined and used by EST CAs in order to route client requests to the appropriate certificate profile. Implementers should consider using short labels to minimize transmission overhead. @@ -455,63 +475,68 @@ coaps resource(s) as shown below, are of the form: coaps://example.com:// coaps://example.com:// ArbitraryLabel/ 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 (PKCS#7) | | /serverkeygen | /skc (application/pkix-cert) | - +------------------+-------------------------------+ + | /csrattrs | /att | + +------------------+------------------------------+ Table 1: Short EST-coaps URI path The /skg message is the EST /serverkeygen equivalent where the client - requests for a certificate in PKCS#7 format and a private key. If - the client prefers a single application/pkix-cert certificate instead - of PKCS#7, she will make an /skc request. + requests a certificate in PKCS#7 format and a private key. If the + client prefers a single application/pkix-cert certificate instead of + PKCS#7, she will make an /skc request. In both cases a private key + MUST be returned Clients and servers MUST support the short resource EST-coaps URIs. + The corresponding longer URIs from [RFC7030] MAY be supported. In the context of CoAP, the presence and location of (path to) the EST resources are discovered by sending a GET request to "/.well- known/core" including a resource type (RT) parameter with the value "ace.est*" [RFC6690]. The example below shows the discovery over CoAPS 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 ;rt="ace.est.crts";ct="281 TBD287", ;rt="ace.est.sen";ct="281 TBD287", ;rt="ace.est.sren";ct="281 TBD287", ;rt="ace.est.att";ct=285, ;rt="ace.est.skg";ct=62, ;rt="ace.est.skc";ct=62 - The first three lines of the discovery response above MUST be - returned if the server supports resource discovery. The last three - lines are only included if the corresponding EST functions are - implemented. The Content-Formats in the response allow the client to + The first three lines, describing ace.est.crts, ace.est.sen, and + ace.est.sren, of the discovery response above MUST be returned if the + server supports resource discovery. The last three lines are only + included if the corresponding EST functions are implemented (see + Table 2). The Content-Formats in the response allow the client to request one that is supported by the server. These are the values - that would be sent in the client request with an Accept option. + that would be sent in the client request with an Accept option. This + approach allows future servers to incorporate currently not specified + content-formats and resources. Discoverable port numbers can be returned in the response payload. An example response payload for non-default CoAPS server port 61617 follows below. Linefeeds are included only for readability. REQ: GET /.well-known/core?rt=ace.est* RES: 2.05 Content ;rt="ace.est.crts"; ct="281 TBD287", @@ -544,38 +569,34 @@ Table 2 specifies the mandatory-to-implement or optional implementation of the EST-coaps functions. Discovery of the existence of optional functions is described in Section 5.1. +------------------+--------------------------+ | EST Functions | EST-coaps implementation | +------------------+--------------------------+ | /cacerts | MUST | | /simpleenroll | MUST | | /simplereenroll | MUST | + | /fullcmc | Not specified | | /csrattrs | OPTIONAL | | /serverkeygen | OPTIONAL | - | /fullcmc | Not specified | +------------------+--------------------------+ Table 2: List of EST-coaps functions - While [RFC7030] permits a number of these functions to be used - without authentication, this specification requires that the client - MUST be authenticated for all functions. - 5.3. Payload formats EST-coaps is designed for low-resource devices and hence does not need to send Base64-encoded data. Simple binary is more efficient - (30% smaller payload) and well supported by CoAP. Thus, the payload - for a given Media-Type follows the ASN.1 structure of the Media-Type - and is transported in binary format. + (30% smaller payload for DER-encoded ASN.1) and well supported by + CoAP. Thus, the payload for a given Media-Type follows the ASN.1 + structure of the Media-Type and is transported in binary format. The Content-Format (HTTP Media-Type equivalent) of the CoAP message determines which EST message is transported in the CoAP payload. The Media-Types specified in the HTTP Content-Type header (Section 3.2.2 of [RFC7030]) are specified by the Content-Format Option (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 EST. The required Content-Formats for these requests and response messages are defined in Section 9.1. The CoAP response codes are defined in Section 5.5. @@ -612,32 +634,44 @@ 48 # bytes(8) FEDCBA9876543210 # "\xFE\xDC\xBA\x98vT2\x10" Multipart /skg response serialization When the client makes an /skc request the certificate returned with the private key is a single X.509 certificate (not a PKCS#7 container) with Content-Format identifier TBD287 (0x011F) instead of 281. In cases where the private key is encrypted with CMS (as explained in Section 5.8) the Content-Format identifier is 280 - (0x0118) instead of 284. The key and certificate representations are - ASN.1 encoded in binary format. An example is shown in Appendix A.3. + (0x0118) instead of 284. The content format used in the response is + summarized in Table 3. + + +----------+-----------------+-----------------+ + | Function | Response part 1 | Response part 2 | + +----------+-----------------+-----------------+ + | /skg | 284 | 281 | + | /skc | 280 | TBD287 | + +----------+-----------------+-----------------+ + + Table 3: response content formats for skg and skc + + The key and certificate representations are ASN.1 encoded in binary + format. An example is shown in Appendix A.3. 5.4. Message Bindings The general EST-coaps message characteristics are: o EST-coaps servers sometimes need to provide delayed responses - which are conveyed with an empty ACK or an ACK containing response - code 5.03 as explained in Section 5.7. Thus, it is RECOMMENDED - for implementers to send EST-coaps requests in confirmable CON - CoAP messages. + which are preceded by an immediately returned empty ACK or an ACK + containing response code 5.03 as explained in Section 5.7. Thus, + it is RECOMMENDED for implementers to send EST-coaps requests in + confirmable CON CoAP messages. o The CoAP Options used are Uri-Host, Uri-Path, Uri-Port, Content- Format, Block1, Block2, and Accept. These CoAP Options are used to communicate the HTTP fields specified in the EST REST messages. The Uri-host and Uri-Port Options can be omitted from the COAP message sent on the wire. When omitted, they are logically assumed to be the transport protocol destination address and port respectively. 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. Other COAP @@ -663,46 +697,46 @@ POST (/sen, /sren, /skg, /skc). 4.04 is used when the resource is not available for the client. HTTP response code 202 with a Retry-After header in [RFC7030] has no equivalent in CoAP. HTTP 202 with Retry-After is used in EST for delayed server responses. Section 5.7 specifies how EST-coaps handles delayed messages with 5.03 responses with a Max-Age Option. Additionally, EST's HTTP 400, 401, 403, 404 and 503 status codes have their equivalent CoAP 4.00, 4.01, 4.03, 4.04 and 5.03 response codes - in EST-coaps. Table 3 summarizes the EST-coaps response codes. + in EST-coaps. Table 4 summarizes the EST-coaps response codes. +-----------------+-----------------+-------------------------------+ | operation | EST-coaps | Description | | | response code | | +-----------------+-----------------+-------------------------------+ | /crts, /att | 2.05 | Success. Certs included in | | | | the response payload. | | | 4.xx / 5.xx | Failure. | | /sen, /skg, | 2.04 | Success. Cert included in the | | /sren, /skc | | response payload. | | | 5.03 | Retry in Max-Age Option time. | | | 4.xx / 5.xx | Failure. | +-----------------+-----------------+-------------------------------+ - Table 3: EST-coaps response codes + Table 4: EST-coaps response codes 5.6. Message fragmentation DTLS defines fragmentation only for the handshake and not for secure data exchange (DTLS records). [RFC6347] states that to avoid using IP fragmentation, which involves error-prone datagram reconstitution, invokers of the DTLS record layer should size DTLS records so that they fit within any Path MTU estimates obtained from the record 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 are recommended to size CoAP messages such that each DTLS record will fit within one or two IEEE 802.15.4 frames. That is not always possible in EST-coaps. Even though ECC certificates are small in size, they can vary greatly based on signature algorithms, key sizes, and Object Identifier (OID) fields used. For 256-bit curves, common ECDSA cert sizes are 500-1000 bytes which could fluctuate further based on the algorithms, OIDs, Subject Alternative Names (SAN) and cert fields. For 384-bit curves, ECDSA certificates increase in size and can sometimes reach 1.5KB. @@ -735,33 +769,35 @@ Examples of fragmented EST-coaps messages are shown in Appendix B. 5.7. Delayed Responses Server responses can sometimes be delayed. According to Section 5.2.2 of [RFC7252], a slow server can acknowledge the request and respond later with the requested resource representation. In particular, a slow server can respond to an EST-coaps enrollment request with an empty ACK with code 0.00, before sending the certificate to the client after a short delay. If the certificate - response is large, the server will need more than one Block2 blocks - to transfer it. + response is large, the server will need more than one Block2 block to + transfer it. This situation is shown in Figure 2. The client sends an enrollment request that uses N1+1 Block1 blocks. The server uses an empty 0.00 ACK to announce the delayed response which is provided later with 2.04 messages containing N2+1 Block2 Options. The first 2.04 is a confirmable message that is acknowledged by the client. Onwards, having received the first 256 bytes in the first Block2 block, the client asks for a block reduction to 128 bytes in a confirmable enrollment request and acknowledges the Block2 blocks sent up to that point. + The notation of Figure 2 is explained in Appendix B.1. + POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR (frag# 1)} --> <-- (ACK) (1:0/1/256) (2.31 Continue) POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR (frag# 2)} --> <-- (ACK) (1:1/1/256) (2.31 Continue) . . . POST [2001:db8::2:1]:61616/est/sen(CON)(1:N1/0/256){CSR (frag# N1+1)}--> <-- (0.00 empty ACK) | @@ -772,42 +808,41 @@ POST [2001:db8::2:1]:61616/est/sen (CON)(2:1/0/128) --> <-- (ACK) (2:1/1/128) (2.04 Changed) {Cert resp (frag# 2)} . . . POST [2001:db8::2:1]:61616/est/sen (CON)(2:N2/0/128) --> <-- (ACK) (2:N2/0/128) (2.04 Changed) {Cert resp (frag# N2+1)} Figure 2: EST-COAP enrollment with short wait - If the server is very slow (i.e. minutes) in providing the response - (i.e. when a manual intervention is needed), he SHOULD respond with + If the server is very slow (i.e., minutes) in providing the response + (i.e., when a manual intervention is needed), he SHOULD respond with an ACK containing response code 5.03 (Service 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, the client SHOULD resend the identical CSR to the server. As long as the server responds with response code 5.03 (Service Unavailable) with a Max-Age Option, the client SHOULD keep resending the enrollment request until the server - responds with the certificate or the client abandons for other - reasons. + responds with the certificate or the client abandons the request for + other reasons. To demonstrate this scenario, Figure 3 shows a client sending an enrollment request that uses N1+1 Block1 blocks to send the CSR to the server. The server needs N2+1 Block2 blocks to respond, but also needs to take a long delay (minutes) to provide the response. - Consequently, the server uses a 5.03 ACK response with a Max-Age Option. The client waits for a period of Max-Age as many times as she receives the same 5.03 response and retransmits the enrollment request until she receives a certificate in a fragmented 2.04 - response. Note that the server asks for a decrease in the block size - when acknowledging the first Block2. + response. Note that the client asks again for a decrease in the + block size when acknowledging the first Block2. POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR (frag# 1)} --> <-- (ACK) (1:0/1/256) (2.31 Continue) POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR (frag# 2)} --> <-- (ACK) (1:1/1/256) (2.31 Continue) . . . POST [2001:db8::2:1]:61616/est/sen(CON)(1:N1/0/256){CSR (frag# N1+1)}--> <-- (ACK) (1:N1/0/256) (5.03 Service Unavailable) (Max-Age) @@ -817,102 +852,111 @@ | | POST [2001:db8::2:1]:61616/est/sen(CON)(1:N1/0/256){CSR (frag# 1)}--> <-- (ACK) (1:0/1/256) (2.31 Continue) POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR (frag# 2)} --> <-- (ACK) (1:1/1/256) (2.31 Continue) . . . POST [2001:db8::2:1]:61616/est/sen(CON)(1:N1/0/256){CSR (frag# N1+1)}--> + | + ... Immediate response when certificate is ready ... + | <-- (ACK) (1:N1/0/256) (2:0/1/128) (2.04 Changed){Cert resp (frag# 1)} POST [2001:db8::2:1]:61616/est/sen (CON)(2:1/0/128) --> <-- (ACK) (2:1/1/128) (2.04 Changed) {Cert resp (frag# 2)} . . . POST [2001:db8::2:1]:61616/est/sen (CON)(2:N2/0/128) --> <-- (ACK) (2:N2/0/128) (2.04 Changed) {Cert resp (frag# N2+1)} Figure 3: EST-COAP enrollment with long wait 5.8. Server-side Key Generation In scenarios where it is desirable that the server generates the - private key, server-side key generation should be used. Such - scenarios could be when it is considered more secure to generate at - the server the long-lived random private key that identifies the - client, or when the resources spent to generate a random private key - at the client are considered scarce, or when the security policy - requires that the certificate public and corresponding private keys - are centrally generated and controlled. Of course, that does not - eliminate the need for proper random numbers in various protocols - like (D)TLS (Section 10.1). + private key, server-side key generation is available. Such scenarios + could be when it is considered more secure to generate at the server + the long-lived random private key that identifies the client, or when + the resources spent to generate a random private key at the client + are considered scarce, or when the security policy requires that the + certificate public and corresponding private keys are centrally + generated and controlled. Of course, that does not eliminate the + need for proper random numbers in various protocols like (D)TLS + (Section 10.1). When requesting server-side key generation, the client asks for the server or proxy to generate the private key and the certificate which are transferred back to the client in the server-side key generation - response. In all respects, the server 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 key values and signature in - the CSR. These are included in the request only to allow re-use of + response. In all respects, the server treats the CSR as it would + treat any enroll or re-enroll CSR; the only distinction here is that + the server MUST ignore the public key values and signature in the + CSR. These are included in the request only to allow re-use of existing codebases for generating and parsing such requests. The client /skg request is for a certificate in a PKCS#7 container and private key in two application/multipart-core elements. Respectively, an /skc request is for a single application/pkix-cert certificate and a private key. The private key Content-Format - requested by the client is depicted in the PKCS#10 CSR request. If + requested by the client is indicated in the PKCS#10 CSR request. If the request contains SMIMECapabilities and DecryptKeyIdentifier or AsymmetricDecryptKeyIdentifier the client is expecting Content-Format 280 for the private key. Then the private key is encrypted symmetrically or asymmetrically as per [RFC7030]. The symmetric key or the asymmetric keypair establishment method is out of scope of the specification. A /skg or /skc request with a CSR without SMIMECapabilities expects an application/multipart-core with an unencrypted PKCS#8 private key with Content-Format 284. The EST-coaps server-side key generation response is returned with Content-Format application/multipart-core [I-D.ietf-core-multipart-ct] containing a CBOR array with four items (Section 5.3) . The two representations (each consisting of two CBOR - array items) do not have to be in a particular order since each - representation is preceded by its Content-Format ID. The private key - can be in unprotected PKCS#8 [RFC5958] format (Content-Format 284) or - protected inside of CMS SignedData (Content-Format 280). The - SignedData is signed by the party that generated the private key, - which may be the EST server or the EST CA. The SignedData is further - protected by placing it inside of a CMS EnvelopedData as explained in - Section 4.4.2 of [RFC7030]. In summary, the symmetrically encrypted - key is included in the encryptedKey attribute in a KEKRecipientInfo - structure. In the case where the asymmetric encryption key is - suitable for transport key operations the generated private key is - encrypted with a symmetric 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. + array items) are preceded by its Content-Format ID. Dependent on the + contents of the CSR, the private key can be in unprotected PKCS#8 + [RFC5958] format (Content-Format 284) or protected inside of CMS + SignedData (Content-Format 280). The SignedData, placed in the + outermost container, is signed by the party that generated the + private key, which may be the EST server or the EST CA. SignedData + placed within the Enveloped Data does not need additional signing as + explained in Section 4.4.2 of [RFC7030]. In summary, the + symmetrically encrypted key is included in the encryptedKey attribute + in a KEKRecipientInfo structure. In the case where the asymmetric + encryption key is suitable for transport key operations the generated + private key is encrypted with a symmetric 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 key is encrypted with a symmetric key which is encrypted by the client defined (in the CSR) asymmetric public key and is carried in an recipientEncryptedKeys attribute in a KeyAgreeRecipientInfo. [RFC7030] recommends the use of additional encryption of the returned private key. For the context of this specification, clients and servers that choose to support server-side key generation MUST support unprotected (PKCS#8) private keys (Content-Format 284). Symmetric or asymmetric encryption of the private key (CMS EnvelopedData, Content-Format 280) SHOULD be supported for deployments where end-to-end encryption needs to be provided between the client and a server. Such cases could include architectures where an entity between the client and the CA terminates the DTLS connection (Registrar in Figure 4). + Following [RFC7030]: "It is strongly RECOMMENDED that the clients + request that the returned private key be afforded the additional + security of the Cryptographic Message Syntax (CMS) EnvelopedData in + addition to the TLS-provided security to protect against unauthorized + disclosure." + 6. HTTPS-CoAPS Registrar In real-world deployments, the EST server will not always reside within the CoAP boundary. The EST server can exist outside the constrained network in which case it will support TLS/HTTP instead of CoAPS. In such environments EST-coaps is used by the client within the CoAP boundary and TLS is used to transport the EST messages outside the CoAP boundary. A Registrar at the edge is required to operate between the CoAP environment and the external HTTP network as shown in Figure 4. @@ -927,100 +971,101 @@ |Server|over TLS | Registrar | '-----------' || '------' '-----------------' || || || |'--------------------------'| '----------------------------' Figure 4: EST-coaps-to-HTTPS Registrar at the CoAP boundary. The EST-coaps-to-HTTPS Registrar MUST terminate EST-coaps downstream and initiate EST connections over TLS upstream. The Registrar MUST - authenticate and OPTIONALLY authorize the clients and it MUST be - authenticated by the EST server or CA. The trust relationship - between the Registrar and the EST server SHOULD be pre-established - for the Registrar to proxy these connections on behalf of various - clients. + authenticate and optionally authorize the client requests while it + MUST be authenticated by the EST server or CA. The trust + relationship between the Registrar and the EST server SHOULD be pre- + established for the Registrar to proxy these connections on behalf of + various 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 is used to prove that the private key corresponding to the public key is in the possession of the client and was used to establish the connection as explained in Section 4. - The POP linking information is lost between the EST-coaps client and + The PoP linking information is lost between the EST-coaps client and the EST server when a Registrar is present. The EST server becomes aware of the presence of a Registrar from its TLS client certificate that includes id-kp-cmcRA [RFC6402] extended key usage extension - (EKU). As explained in Section 3.7 of [RFC7030], the EST server + (EKU). As explained in Section 3.7 of [RFC7030], the "EST server SHOULD apply an authorization policy consistent with a Registrar - client. For example, it could be configured to accept POP linking + client. For example, it could be configured to accept PoP linking information that does not match the current TLS session because the authenticated EST client Registrar has verified this information when - acting as an EST server. + acting as an EST server". For some use cases, clients that leverage server-side key generation might prefer for the enrolled keys to be generated by the Registrar - if the CA does not support server-side key generation. Such + if the CA does not support server-side key generation. Such a Registrar is responsible for generating a new CSR signed by a new key which will be returned to the client along with the certificate from - the CA. In these cases, the Registrar MUST support random number - generation using proper entropy. + the CA. In these cases, the Registrar MUST use random number + generation with proper entropy. Table 1 contains the URI mappings between EST-coaps and EST that the Registrar MUST adhere to. Section 5.5 of this specification and Section 7 of [RFC8075] define the mappings between EST-coaps and HTTP response codes, that determine how the Registrar MUST translate CoAP response codes from/to HTTP status codes. The mapping from CoAP Content-Format to HTTP Media-Type is defined in Section 9.1. Additionally, a conversion from CBOR major type 2 to Base64 encoding - MUST take place at the Registrar when server-side key generation is - supported. If CMS end-to-end encryption is employed for the private - key, the encrypted CMS EnvelopedData blob MUST be converted to binary - in CBOR type 2 downstream to the client. + MUST take place at the Registrar. If CMS end-to-end encryption is + employed for the private key, the encrypted CMS EnvelopedData blob + MUST be converted at the Registrar to binary CBOR type 2 downstream + to the client. Due to fragmentation of large messages into blocks, an EST-coaps-to- HTTP Registrar MUST reassemble the BLOCKs before translating the binary content to Base64, and consecutively relay the message upstream. The EST-coaps-to-HTTP Registrar MUST support resource discovery - according to the rules in Section 5.1. Section 5.1. + according to the rules in Section 5.1. 7. Parameters This section addresses transmission parameters described in sections 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 - to be tuned to the CoAP parameter values. + the CoAP parameters in [RFC7252], but the setting of the CoAP + parameter values may have consequence for the setting of the EST + parameter values. It is recommended, based on experiments, to follow the default CoAP configuration parameters ([RFC7252]). However, depending on the implementation scenario, retransmissions and timeouts can also occur on other networking layers, governed by other configuration - 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. + parameters. When a change in a server parameter has been + effectuated, the parameter values in the communicating endpoints MUST + be adjusted when necessary. Some further comments about some specific parameters, mainly from Table 2 in [RFC7252]: o NSTART: A parameter that controls the number of simultaneous outstanding interactions that a client maintains to a given - server. An EST-coaps client is not expected to interact with more - than one servers at the same time, which is the default NSTART - value defined in [RFC7252]. + server. An EST-coaps client is expected to control at most one + interaction with a given server, which is the default NSTART value + defined in [RFC7252]. o DEFAULT_LEISURE: This setting is only relevant in multicast scenarios, outside the scope of EST-coaps. o PROBING_RATE: A parameter which specifies the rate of re-sending - non-confirmable messages. The EST messages are defined to be sent - as CoAP confirmable messages, hence this setting is not - applicable. + non-confirmable messages. In the rare situations that non- + confirmable messages are used, the default PROBING_RATE value + defined in [RFC7252] applies. Finally, the Table 3 parameters in [RFC7252] are mainly derived from Table 2. Directly changing parameters on one table would affect parameters on the other. 8. 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 payloads that @@ -1028,201 +1073,203 @@ ensure that EST works for networks of constrained devices that choose to limit their communications stack to DTLS/CoAP. It is up to the network designer to decide which devices execute the EST protocol and which do not. 9. IANA Considerations 9.1. Content-Format Registry Additions to the sub-registry "CoAP Content-Formats", within the - "CoRE Parameters" registry [COREparams] are specified in Table 4. + "CoRE Parameters" registry [COREparams] are specified in Table 5. These have been registered provisionally in the IETF Review or IESG Approval range (256-9999). +------------------------------+-------+----------------------------+ | HTTP Media-Type | ID | Reference | +------------------------------+-------+----------------------------+ | application/pkcs7-mime; | 280 | [RFC7030] [I-D.ietf-lamps- | - | smime-type=server-generated- | | rfc5751-bis] | + | smime-type=server-generated- | | rfc5751-bis] [ThisRFC] | | key | | | | application/pkcs7-mime; | 281 | [I-D.ietf-lamps-rfc5751-bi | - | smime-type=certs-only | | s] | + | smime-type=certs-only | | s] [ThisRFC] | | application/pkcs8 | 284 | [RFC5958] [I-D.ietf-lamps- | - | | | rfc5751-bis] | - | application/csrattrs | 285 | [RFC7030] [RFC7231] | + | | | rfc5751-bis] [ThisRFC] | + | application/csrattrs | 285 | [RFC7030] | | application/pkcs10 | 286 | [RFC5967] [I-D.ietf-lamps- | - | | | rfc5751-bis] | - | application/pkix-cert | TBD28 | [RFC2585] | + | | | rfc5751-bis] [ThisRFC] | + | application/pkix-cert | TBD28 | [RFC2585] [ThisRFC] | | | 7 | | +------------------------------+-------+----------------------------+ - Table 4: New CoAP Content-Formats + Table 5: New CoAP Content-Formats It is suggested that 287 is allocated to TBD287. 9.2. Resource Type registry This memo registers new Resource Type (rt=) Link Target Attributes in the "Resource Type (rt=) Link Target Attribute Values" subregistry under the "Constrained RESTful Environments (CoRE) Parameters" registry. o rt="ace.est.crts". This resource depicts the support of EST get cacerts. o rt="ace.est.sen". This resource depicts the support of EST simple enroll. o rt="ace.est.sren". This resource depicts the support of EST simple reenroll. - o rt="ace.est.att". This resource depicts the support of EST CSR - attributes. + o rt="ace.est.att". This resource depicts the support of EST get + CSR attributes. o rt="ace.est.skg". This resource depicts the support of EST server-side key generation with the returned certificate in a PKCS#7 container. o rt="ace.est.skc". This resource depicts the support of EST server-side key generation with the returned certificate in application/pkix-cert format. 10. Security Considerations 10.1. EST server considerations The security considerations of Section 6 of [RFC7030] are only partially valid for the purposes of this document. As HTTP Basic Authentication is not supported, the considerations expressed for - using passwords do not apply. + using passwords do not apply. The other portions of the security + considerations of [RFC7030] continue to apply. Modern security protocols require random numbers to be available - during the protocol run, for example for nonces, ephemeral (EC) + during the protocol run, for example for nonces and ephemeral (EC) Diffie-Hellman key generation. This capability to generate random numbers is also needed when the constrained device generates the private key (that corresponds to the public key enrolled in the CSR). When server-side key generation is used, the constrained device depends on the server to generate the private key randomly, but it still needs locally generated random numbers for use in security protocols, as explained in Section 12 of [RFC7925]. Additionally, the transport of keys generated at the server is inherently risky. - Analysis SHOULD be done to establish whether server-side key - generation increases or decreases the probability of digital identity - theft. + For those deploying server-side key generation, analysis SHOULD be + done to establish whether server-side key generation increases or + decreases the probability of digital identity theft. It is important to note that sources contributing to the randomness pool used to generate random numbers on laptops or desktop PCs are not available on many constrained devices, such as mouse movement, - timing of keystrokes, air turbulence on the movement of hard drive + timing of keystrokes, or air turbulence on the movement of hard drive heads, as pointed out in [PsQs]. Other sources have to be used or dedicated hardware has to be added. Selecting hardware for an IoT device that is capable of producing high-quality random numbers is therefore important [RSAfact]. It is also RECOMMENDED that the Implicit Trust Anchor database used for EST server authentication is carefully managed to reduce the chance of a third-party CA with poor certification practices jeopardizing authentication. Disabling the Implicit Trust Anchor database after successfully receiving the Distribution of CA certificates response (Section 4.1.3 of [RFC7030]) limits any risk to the first DTLS exchange. Alternatively, in a case where a /sen request immediately follows a /crts, a client MAY choose to keep the connection authenticated by the Implicit TA open for efficiency - reasons (Section 4). A client that pipelines EST-coaps /crts request - with other requests in the same DTLS connection SHOULD revalidate the - server certificate chain against the updated Explicit TA from the - /crts 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. + reasons (Section 4). A client that interleaves EST-coaps /crts + request with other requests in the same DTLS connection SHOULD + revalidate the server certificate chain against the updated Explicit + TA from the /crts 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 the server MAY still authenticate the client because IDevIDs are expected to live as long as the device itself (Section 4). In such occasions, checking the certificate revocation status or authorizing the client using another method is important for the server to ensure that the client is to be trusted. In accordance with [RFC7030], TLS cipher suites that include "_EXPORT_" and "_DES_" in their names MUST NOT be used. More information about recommendations of TLS and DTLS are included in [RFC7525]. As described in CMC, Section 6.7 of [RFC5272], "For keys that can be 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 the TLS proof-of-identity. This implies but does not prove that only the authenticated client currently has access to the private key. - What's more, POP linking uses tls-unique as it is defined in + What's more, CMC PoP linking uses tls-unique as it is defined in [RFC5929]. The 3SHAKE attack [tripleshake] poses a risk by allowing a man-in-the-middle to leverage session resumption and renegotiation to inject himself between a client and server even when channel - 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 a channel binding - value generated from an exporter would break backwards compatibility. - Thus, in this specification we still depend on the tls-unique - mechanism defined in [RFC5929], especially since a 3SHAKE attack does - not expose messages exchanged with EST-coaps. + binding is in use. 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]) value in place of the tls-unique value in + the CSR. Such mechanism has not been standardized yet. Adopting a + channel binding value generated from an exporter would break + backwards compatibility for an RA that proxies through to a classic + EST server. Thus, in this specification we still depend on the tls- + unique mechanism defined in [RFC5929], especially since a 3SHAKE + attack does not expose messages exchanged with EST-coaps. Regarding the Certificate Signing Request (CSR), an EST-coaps server is expected to be able to recover from improper CSR requests. Interpreters of ASN.1 structures should be aware of the use of invalid ASN.1 length fields and should take appropriate measures to guard against buffer overflows, stack overruns in particular, and malicious content in general. 10.2. HTTPS-CoAPS Registrar considerations The Registrar proposed in Section 6 must be deployed with care, and - only when the recommended connections are impossible. When POP - linking is used the Registrar terminating the TLS connection - 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. - The EST server could be configured to accept POP linking information - that does not match the current TLS session because the authenticated - EST Registrar client has verified this information when acting as an - EST server. + only when direct client-server connections are not possible. When + PoP linking is used the Registrar terminating the DTLS connection + establishes a new TLS connection with the upstream CA. Thus, it is + impossible for PoP linking to be enforced end-to-end for the EST + transaction. The EST server could be configured to accept PoP + linking information that does not match the current TLS session + because the authenticated EST Registrar is assumed to have verified + PoP linking downstream to 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. - 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 - client uses the Implicit TA database for certificate validation, she - SHOULD confirm if the server is acting as an RA by the presence of - the id-kp-cmcRA EKU [RFC6402] in the server certificate. + can authenticate the Registrar using its implicit or explicit TA + database. 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 client uses the Implicit TA database for certificate + validation, she SHOULD confirm if the server is acting as an RA by + the presence of the id-kp-cmcRA EKU [RFC6402] in the server + certificate. 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 man-in-the-middle. Thus, the client puts its trust on the Registrar not exposing the private key. Clients that leverage server-side key generation without end-to-end encryption of the private key (Section 5.8) have no knowledge if the Registrar will be generating the private key and enrolling the certificates with the CA or if the CA will be responsible for generating the key. In such cases, the existence of a Registrar - requires the client to put its trust on the registrar doing the right - thing if it is generating the private key. + requires the client to put its trust on the registrar when it is + generating the private key. 11. Contributors Martin Furuhed contributed to the EST-coaps specification by providing feedback based on the Nexus EST over CoAPS server implementation that started in 2015. Sandeep Kumar kick-started this specification and was instrumental in drawing attention to the importance of the subject. 12. Acknowledgements @@ -1241,44 +1288,54 @@ Camezind, Bjorn Elmers and Joel Hoglund. Robert Moskowitz provided code to create the examples. 13. References 13.1. Normative References [I-D.ietf-core-multipart-ct] Fossati, T., Hartke, K., and C. Bormann, "Multipart - Content-Format for CoAP", draft-ietf-core-multipart-ct-03 - (work in progress), March 2019. + Content-Format for CoAP", draft-ietf-core-multipart-ct-04 + (work in progress), August 2019. + + [I-D.ietf-lamps-rfc5751-bis] + Schaad, J., Ramsdell, B., and S. Turner, "Secure/ + Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 + Message Specification", draft-ietf-lamps-rfc5751-bis-12 + (work in progress), September 2018. [I-D.ietf-tls-dtls13] Rescorla, E., Tschofenig, H., and N. Modadugu, "The Datagram Transport Layer Security (DTLS) Protocol Version - 1.3", draft-ietf-tls-dtls13-31 (work in progress), March + 1.3", draft-ietf-tls-dtls13-32 (work in progress), July 2019. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [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, . [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008, . + [RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958, + DOI 10.17487/RFC5958, August 2010, + . + [RFC5967] Turner, S., "The application/pkcs10 Media Type", RFC 5967, DOI 10.17487/RFC5967, August 2010, . [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January 2012, . [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, @@ -1287,60 +1344,72 @@ [RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed., "Enrollment over Secure Transport", RFC 7030, DOI 10.17487/RFC7030, October 2013, . [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, . + [RFC7925] Tschofenig, H., Ed. and T. Fossati, "Transport Layer + Security (TLS) / Datagram Transport Layer Security (DTLS) + Profiles for the Internet of Things", RFC 7925, + DOI 10.17487/RFC7925, July 2016, + . + [RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in the Constrained Application Protocol (CoAP)", RFC 7959, DOI 10.17487/RFC7959, August 2016, . + [RFC8075] Castellani, A., Loreto, S., Rahman, A., Fossati, T., and + E. Dijk, "Guidelines for Mapping Implementations: HTTP to + the Constrained Application Protocol (CoAP)", RFC 8075, + DOI 10.17487/RFC8075, February 2017, + . + [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . + [RFC8422] Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic + Curve Cryptography (ECC) Cipher Suites for Transport Layer + Security (TLS) Versions 1.2 and Earlier", RFC 8422, + DOI 10.17487/RFC8422, August 2018, + . + [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . 13.2. Informative References [COREparams] "Constrained RESTful Environments (CoRE) Parameters", - . - - [I-D.ietf-lamps-rfc5751-bis] - Schaad, J., Ramsdell, B., and S. Turner, "Secure/ - Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 - Message Specification", draft-ietf-lamps-rfc5751-bis-12 - (work in progress), September 2018. + . [I-D.ietf-tls-dtls-connection-id] Rescorla, E., Tschofenig, H., and T. Fossati, "Connection Identifiers for DTLS 1.2", draft-ietf-tls-dtls-connection- - id-05 (work in progress), May 2019. + id-06 (work in progress), July 2019. [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] Moskowitz, R., Birkholz, H., Xia, L., and M. Richardson, "Guide for building an ECC pki", draft-moskowitz-ecdsa- - pki-05 (work in progress), March 2019. + pki-07 (work in progress), August 2019. [ieee802.15.4] "IEEE Standard 802.15.4-2006", 2006. [ieee802.1ar] "IEEE 802.1AR Secure Device Identifier", December 2009. [PsQs] "Mining Your Ps and Qs: Detection of Widespread Weak Keys in Network Devices", USENIX Security Symposium 2012 ISBN 978-931971-95-9, August 2012. @@ -1356,97 +1425,75 @@ . [RFC5705] Rescorla, E., "Keying Material Exporters for Transport Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705, March 2010, . [RFC5929] Altman, J., Williams, N., and L. Zhu, "Channel Bindings for TLS", RFC 5929, DOI 10.17487/RFC5929, July 2010, . - [RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958, - DOI 10.17487/RFC5958, August 2010, - . - [RFC6402] Schaad, J., "Certificate Management over CMS (CMC) Updates", RFC 6402, DOI 10.17487/RFC6402, November 2011, . [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May 2014, . [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7230, DOI 10.17487/RFC7230, June 2014, . - [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer - Protocol (HTTP/1.1): Semantics and Content", RFC 7231, - DOI 10.17487/RFC7231, June 2014, - . - [RFC7251] McGrew, D., Bailey, D., Campagna, M., and R. Dugal, "AES- CCM Elliptic Curve Cryptography (ECC) Cipher Suites for TLS", RFC 7251, DOI 10.17487/RFC7251, June 2014, . + [RFC7299] Housley, R., "Object Identifier Registry for the PKIX + Working Group", RFC 7299, DOI 10.17487/RFC7299, July 2014, + . + [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, "Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 2015, . - [RFC7925] Tschofenig, H., Ed. and T. Fossati, "Transport Layer - Security (TLS) / Datagram Transport Layer Security (DTLS) - Profiles for the Internet of Things", RFC 7925, - DOI 10.17487/RFC7925, July 2016, - . - - [RFC8075] Castellani, A., Loreto, S., Rahman, A., Fossati, T., and - E. Dijk, "Guidelines for Mapping Implementations: HTTP to - the Constrained Application Protocol (CoAP)", RFC 8075, - DOI 10.17487/RFC8075, February 2017, - . - - [RFC8422] Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic - Curve Cryptography (ECC) Cipher Suites for Transport Layer - Security (TLS) Versions 1.2 and Earlier", RFC 8422, - DOI 10.17487/RFC8422, August 2018, - . - [RSAfact] "Factoring RSA keys from certified smart cards: - Coppersmith in the wild", Advances in Cryptology - - ASIACRYPT 2013, August 2013. + Coppersmith in the wild", Advances in Cryptology + - ASIACRYPT 2013, August 2013. [tripleshake] "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 This section shows similar examples to the ones presented in Appendix A of [RFC7030]. The payloads in the examples are the hex encoded binary, generated with 'xxd -p', of the PKI certificates created following [I-D.moskowitz-ecdsa-pki]. Hex is used for visualization purposes because a binary representation cannot be rendered well in text. The hexadecimal representations would not be transported in hex, but in binary. The payloads are shown unencrypted. In practice the message content would be transferred - over an encrypted DTLS tunnel. + over an encrypted DTLS channel. The certificate responses included in the examples contain Content- Format 281 (application/pkcs7). If the client had requested Content- Format TBD287 (application/pkix-cert) by querying /est/skc, the - server would respond with a single DER binary certificate. + server would respond with a single DER binary certificate in the + multipart-core container. These examples assume a short resource path of "/est". Even though omitted from the examples for brevity, before making the EST-coaps requests, a client would learn about the server supported EST-coaps resources with a GET request for /.well-known/core?rt=ace.est* as explained in Section 5.1. The corresponding CoAP headers are only shown in Appendix A.1. Creating CoAP headers is assumed to be generally understood. @@ -1462,33 +1509,33 @@ The corresponding CoAP header fields are shown below. The use of block and DTLS are worked out in Appendix B. Ver = 1 T = 0 (CON) Code = 0x01 (0.01 is GET) Token = 0x9a (client generated) Options Option (Uri-Host) Option Delta = 0x3 (option# 3) - Option Length = 0xD + Option Length = 0xB Option Value = "example.com" Option (Uri-Port) Option Delta = 0x4 (option# 3+4=7) - Option Length = 0x4 + Option Length = 0x2 Option Value = 9085 Option (Uri-Path) Option Delta = 0x4 (option# 7+4=11) - Option Length = 0x5 + Option Length = 0x3 Option Value = "est" Option (Uri-Path) Option Delta = 0x0 (option# 11+0=11) - Option Length = 0x6 + Option Length = 0x4 Option Value = "crts" Option (Accept) Option Delta = 0x6 (option# 11+6=17) Option Length = 0x2 Option Value = 281 Payload = [Empty] The Uri-Host and Uri-Port Options can be omitted if they coincide with the transport protocol destination address and port respectively. Explicit Uri-Host and Uri-Port Options are typically @@ -1509,52 +1557,52 @@ Option (Content-Format) Option Delta = 0xC (option# 12) Option Length = 0x2 Option Value = 281 [ 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. ] Payload = - 3082027b06092a864886f70d010702a082026c308202680201013100300b - 06092a864886f70d010701a082024e3082024a308201f0a0030201020209 - 009189bcdf9c99244b300a06082a8648ce3d0403023067310b3009060355 - 040613025553310b300906035504080c024341310b300906035504070c02 - 4c4131143012060355040a0c0b4578616d706c6520496e63311630140603 - 55040b0c0d63657274696669636174696f6e3110300e06035504030c0752 - 6f6f74204341301e170d3139303130373130343034315a170d3339303130 - 323130343034315a3067310b3009060355040613025553310b3009060355 - 04080c024341310b300906035504070c024c4131143012060355040a0c0b - 4578616d706c6520496e6331163014060355040b0c0d6365727469666963 - 6174696f6e3110300e06035504030c07526f6f742043413059301306072a - 8648ce3d020106082a8648ce3d03010703420004814994082b6e8185f3df - 53f5e0bee698973335200023ddf78cd17a443ffd8ddd40908769c55652ac - 2ccb75c4a50a7c7ddb7c22dae6c85cca538209fdbbf104c9a38184308181 - 301d0603551d0e041604142495e816ef6ffcaaf356ce4adffe33cf492abb - a8301f0603551d230418301680142495e816ef6ffcaaf356ce4adffe33cf - 492abba8300f0603551d130101ff040530030101ff300e0603551d0f0101 - ff040403020106301e0603551d1104173015811363657274696679406578 - 616d706c652e636f6d300a06082a8648ce3d0403020348003045022100da - e37c96f154c32ec0b4af52d46f3b7ecc9687ddf267bcec368f7b7f135327 - 2f022047a28ae5c7306163b3c3834bab3c103f743070594c089aaa0ac870 - cd13b902caa1003100 + 3082027a06092a864886f70d010702a082026b308202670201013100300b + 06092a864886f70d010701a082024d30820249308201efa0030201020208 + 0b8bb0fe604f6a1e300a06082a8648ce3d0403023067310b300906035504 + 0613025553310b300906035504080c024341310b300906035504070c024c + 4131143012060355040a0c0b4578616d706c6520496e6331163014060355 + 040b0c0d63657274696669636174696f6e3110300e06035504030c07526f + 6f74204341301e170d3139303133313131323730335a170d333930313236 + 3131323730335a3067310b3009060355040613025553310b300906035504 + 080c024341310b300906035504070c024c4131143012060355040a0c0b45 + 78616d706c6520496e6331163014060355040b0c0d636572746966696361 + 74696f6e3110300e06035504030c07526f6f742043413059301306072a86 + 48ce3d020106082a8648ce3d030107034200040c1b1e82ba8cc72680973f + 97edb8a0c72ab0d405f05d4fe29b997a14ccce89008313d09666b6ce375c + 595fcc8e37f8e4354497011be90e56794bd91ad951ab45a3818430818130 + 1d0603551d0e041604141df1208944d77b5f1d9dcb51ee244a523f3ef5de + 301f0603551d230418301680141df1208944d77b5f1d9dcb51ee244a523f + 3ef5de300f0603551d130101ff040530030101ff300e0603551d0f0101ff + 040403020106301e0603551d110417301581136365727469667940657861 + 6d706c652e636f6d300a06082a8648ce3d040302034800304502202b891d + d411d07a6d6f621947635ba4c43165296b3f633726f02e51ecf464bd4002 + 2100b4be8a80d08675f041fbc719acf3b39dedc85dc92b3035868cb2daa8 + f05db196a1003100 The breakdown of the payload is shown in Appendix C.1. A.2. enroll / reenroll During the (re-)enroll exchange the EST-coaps client uses a CSR (Content-Format 286) request in the POST request payload. The Accept option tells the server that the client is expecting Content-Format 281 (PKCS#7) in the response. As shown in Appendix C.2, the CSR - contains a ChallengePassword which is used for POP linking + contains a ChallengePassword which is used for PoP linking (Section 4). POST [2001:db8::2:321]:61616/est/sen (Token: 0x45) (Accept: 281) (Content-Format: 286) [ 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. ] @@ -1614,64 +1662,65 @@ In a serverkeygen exchange the CoAP POST request looks like POST 192.0.2.1:8085/est/skg (Token: 0xa5) (Accept: 62) (Content-Format: 286) [ 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. ] - 3081cf3078020100301631143012060355040a0c0b736b67206578616d70 - 6c653059301306072a8648ce3d020106082a8648ce3d030107034200041b - b8c1117896f98e4506c03d70efbe820d8e38ea97e9d65d52c8460c5852c5 - 1dd89a61370a2843760fc859799d78cd33f3c1846e304f1717f8123f1a28 - 4cc99fa000300a06082a8648ce3d04030203470030440220387cd4e9cf62 - 8d4af77f92ebed4890d9d141dca86cd2757dd14cbd59cdf6961802202f24 - 5e828c77754378b66660a4977f113cacdaa0cc7bad7d1474a7fd155d090d + 3081d03078020100301631143012060355040a0c0b736b67206578616d70 + 6c653059301306072a8648ce3d020106082a8648ce3d03010703420004c8 + b421f11c25e47e3ac57123bf2d9fdc494f028bc351cc80c03f150bf50cff + 958d75419d81a6a245dffae790be95cf75f602f9152618f816a2b23b5638 + e59fd9a000300a06082a8648ce3d040302034800304502207c553981b1fe + 349249d8a3f50a0346336b7dfaa099cf74e1ec7a37a0a760485902210084 + 79295398774b2ff8e7e82abb0c17eaef344a5088fa69fd63ee611850c34b + 0a The response would follow [I-D.ietf-core-multipart-ct] and could look like 2.04 Changed (Token: 0xa5) (Content-Format: 62) [ The hexadecimal representations below would NOT be transported in hex, but in binary. Hex is used because a binary representation cannot be rendered well in text. ] 84 # array(4) 19 011C # unsigned(284) 58 8A # bytes(138) 308187020100301306072a8648ce3d020106082a8648ce3d030107046d30 - 6b02010104200b9a67785b65e07360b6d28cfc1d3f3925c0755799deeca7 - 45372b01697bd8a6a144034200041bb8c1117896f98e4506c03d70efbe82 - 0d8e38ea97e9d65d52c8460c5852c51dd89a61370a2843760fc859799d78 - cd33f3c1846e304f1717f8123f1a284cc99f + 6b020101042061336a86ac6e7af4a96f632830ad4e6aa0837679206094d7 + 679a01ca8c6f0c37a14403420004c8b421f11c25e47e3ac57123bf2d9fdc + 494f028bc351cc80c03f150bf50cff958d75419d81a6a245dffae790be95 + cf75f602f9152618f816a2b23b5638e59fd9 19 0119 # unsigned(281) 59 01D3 # bytes(467) 308201cf06092a864886f70d010702a08201c0308201bc0201013100300b - 06092a864886f70d010701a08201a23082019e30820143a0030201020208 - 126de8571518524b300a06082a8648ce3d04030230163114301206035504 - 0a0c0b736b67206578616d706c65301e170d313930313039303835373038 - 5a170d3339303130343038353730385a301631143012060355040a0c0b73 - 6b67206578616d706c653059301306072a8648ce3d020106082a8648ce3d - 030107034200041bb8c1117896f98e4506c03d70efbe820d8e38ea97e9d6 - 5d52c8460c5852c51dd89a61370a2843760fc859799d78cd33f3c1846e30 - 4f1717f8123f1a284cc99fa37b307930090603551d1304023000302c0609 - 6086480186f842010d041f161d4f70656e53534c2047656e657261746564 - 204365727469666963617465301d0603551d0e04160414494be598dc8dbc - 0dbc071c486b777460e5cce621301f0603551d23041830168014494be598 - dc8dbc0dbc071c486b777460e5cce621300a06082a8648ce3d0403020349 - 003046022100a4b167d0f9add9202810e6bf6a290b8cfdfc9b9c9fea2cc1 - c8fc3a464f79f2c202210081d31ba142751a7b4a34fd1a01fcfb08716b9e - b53bdaadc9ae60b08f52429c0fa1003100 + 06092a864886f70d010701a08201a23082019e30820144a0030201020209 + 00b3313e8f3fc9538e300a06082a8648ce3d040302301631143012060355 + 040a0c0b736b67206578616d706c65301e170d3139303930343037343430 + 335a170d3339303833303037343430335a301631143012060355040a0c0b + 736b67206578616d706c653059301306072a8648ce3d020106082a8648ce + 3d03010703420004c8b421f11c25e47e3ac57123bf2d9fdc494f028bc351 + cc80c03f150bf50cff958d75419d81a6a245dffae790be95cf75f602f915 + 2618f816a2b23b5638e59fd9a37b307930090603551d1304023000302c06 + 096086480186f842010d041f161d4f70656e53534c2047656e6572617465 + 64204365727469666963617465301d0603551d0e0416041496600d8716bf + 7fd0e752d0ac760777ad665d02a0301f0603551d2304183016801496600d + 8716bf7fd0e752d0ac760777ad665d02a0300a06082a8648ce3d04030203 + 48003045022100e95bfa25a08976652246f2d96143da39fce0dc4c9b26b9 + cce1f24164cc2b12b602201351fd8eea65764e3459d324e4345ff5b2a915 + 38c04976111796b3698bf6379ca1003100 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 A.4. csrattrs Below is a csrattrs exchange REQ: @@ -1709,78 +1758,77 @@ The payloads are shown unencrypted. In practice the message contents would be binary formatted and transferred over an encrypted DTLS tunnel. The corresponding CoAP headers are only shown in Appendix B.1. Creating CoAP headers is assumed to be generally known. B.1. cacerts This section provides a detailed example of the messages using DTLS - and BLOCK option Block2. The minimum PMTU is 1280 bytes, which is - the example value assumed for the DTLS datagram size. The example - block length is taken as 64 which gives an SZX value of 2. + and BLOCK option Block2. The example 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 content length of the cacerts response in appendix A.1 of [RFC7030] - contains 639 bytes in binary. The CoAP message adds around 10 bytes, - 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 - 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 - tenth packet of 63 bytes. The client sends an IPv6 packet containing - the UDP datagram with the DTLS record that encapsulates the CoAP - request 10 times. The server returns an IPv6 packet containing the - UDP datagram with the DTLS record that encapsulates the CoAP - response. The CoAP request-response exchange with block option is - shown below. Block Option is shown in a decomposed way (block- - 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 - 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 - used with SZX=2 to avoid IP fragmentation. The CoAP Request is sent - confirmable (CON) and the Content-Format of the response, even though - not shown, is 281 (application/pkcs7-mime; smime-type=certs-only). - The transfer of the 10 blocks with partially filled block NUM=9 is - shown below + contains 639 bytes in binary in this example. The CoAP message adds + around 10 bytes in this exmple, the DTLS record around 29 bytes. To + avoid IP fragmentation, the CoAP Block 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 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 a UDP datagram + with the DTLS record that encapsulates a CoAP request 10 times. The + server returns an IPv6 packet containing a UDP datagram with a DTLS + record that encapsulates the CoAP response. The CoAP request- + response exchange with block option is shown below. Block Option is + shown in a decomposed way (block-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 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 used with SZX=2. The CoAP + Request is sent confirmable (CON) and the Content-Format of the + response, even though not shown, is 281 (application/pkcs7-mime; + smime-type=certs-only). The transfer of the 10 blocks with partially + filled block NUM=9 is shown below GET example.com:9085/est/crts (2:0/0/64) --> <-- (2:0/1/64) 2.05 Content GET example.com:9085/est/crts (2:1/0/64) --> <-- (2:1/1/64) 2.05 Content | | | GET example.com:9085/est/crts (2:9/0/64) --> <-- (2:9/0/64) 2.05 Content The header of the GET request looks like Ver = 1 T = 0 (CON) Code = 0x01 (0.1 GET) Token = 0x9a (client generated) Options Option (Uri-Host) Option Delta = 0x3 (option# 3) - Option Length = 0xD + Option Length = 0xB Option Value = "example.com" Option (Uri-Port) Option Delta = 0x4 (option# 3+4=7) - Option Length = 0x4 + Option Length = 0x2 Option Value = 9085 Option (Uri-Path) Option Delta = 0x4 (option# 7+4=11) - Option Length = 0x5 + Option Length = 0x3 Option Value = "est" Option (Uri-Path)Uri-Path) Option Delta = 0x0 (option# 11+0=11) - Option Length = 0x6 + Option Length = 0x4 Option Value = "crts" Option (Accept) Option Delta = 0x6 (option# 11+6=17) Option Length = 0x2 Option Value = 281 Payload = [Empty] The Uri-Host and Uri-Port Options can be omitted if they coincide with the transport protocol destination address and port respectively. Explicit Uri-Host and Uri-Port Options are typically @@ -1863,98 +1911,100 @@ 003100 B.2. enroll / reenroll In this example, the requested Block2 size of 256 bytes, required by 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 notation for block numbering is the same as in Appendix B.1. The header fields and the payload are omitted for brevity. - POST [2001:db8::2:321]:61616/est/sen (CON)(1:0/1/256) {CSR req} --> +POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR (frag# 1)} --> + <-- (ACK) (1:0/1/256) (2.31 Continue) - POST [2001:db8::2:321]:61616/est/sen (CON)(1:1/1/256) {CSR req} --> +POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR (frag# 2)} --> <-- (ACK) (1:1/1/256) (2.31 Continue) . . . - POST [2001:db8::2:321]:61616/est/sen (CON)(1:N1/0/256){CSR req} --> - <-- (ACK) (1:N1/0/256)(2:0/1/256)(2.04 Changed){Cert resp} - POST [2001:db8::2:321]:61616/est/sen (CON)(2:1/0/256) --> - <-- (ACK) (2:1/1/256)(2.04 Changed) {Cert resp} +POST [2001:db8::2:1]:61616/est/sen (CON)(1:N1/0/256){CSR(frag# N1+1)}--> + | + ...........Immediate response ......... + | + <-- (ACK) (1:N1/0/256)(2:0/1/256)(2.04 Changed){Cert resp (frag# 1)} +POST [2001:db8::2:1]:61616/est/sen (CON)(2:1/0/256) --> + <-- (ACK) (2:1/1/256)(2.04 Changed) {Cert resp (frag# 2)} . . . POST [2001:db8::2:321]: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 (frag# N2+1)} Figure 5: EST-COAP enrollment with multiple blocks N1+1 blocks have been transferred from client to the server and N2+1 blocks have been transferred from server to client. Appendix C. Message content breakdown This appendix presents the breakdown of the hexadecimal dumps of the binary payloads shown in Appendix A. C.1. cacerts The breakdown of cacerts response containing one root CA certificate is Certificate: Data: Version: 3 (0x2) - Serial Number: - 91:89:bc:df:9c:99:24:4b + Serial Number: 831953162763987486 (0xb8bb0fe604f6a1e) Signature Algorithm: ecdsa-with-SHA256 Issuer: C=US, ST=CA, L=LA, O=Example Inc, OU=certification, CN=Root CA Validity - Not Before: Jan 7 10:40:41 2019 GMT - Not After : Jan 2 10:40:41 2039 GMT + Not Before: Jan 31 11:27:03 2019 GMT + Not After : Jan 26 11:27:03 2039 GMT Subject: C=US, ST=CA, L=LA, O=Example Inc, OU=certification, CN=Root CA Subject Public Key Info: Public Key Algorithm: id-ecPublicKey Public-Key: (256 bit) pub: - 04:81:49:94:08:2b:6e:81:85:f3:df:53:f5:e0:be: - e6:98:97:33:35:20:00:23:dd:f7:8c:d1:7a:44:3f: - fd:8d:dd:40:90:87:69:c5:56:52:ac:2c:cb:75:c4: - a5:0a:7c:7d:db:7c:22:da:e6:c8:5c:ca:53:82:09: - fd:bb:f1:04:c9 + 04:0c:1b:1e:82:ba:8c:c7:26:80:97:3f:97:ed:b8: + a0:c7:2a:b0:d4:05:f0:5d:4f:e2:9b:99:7a:14:cc: + ce:89:00:83:13:d0:96:66:b6:ce:37:5c:59:5f:cc: + 8e:37:f8:e4:35:44:97:01:1b:e9:0e:56:79:4b:d9: + 1a:d9:51:ab:45 ASN1 OID: prime256v1 NIST CURVE: P-256 X509v3 extensions: X509v3 Subject Key Identifier: - 24:95:E8:16:EF:6F:FC:AA:F3:56:CE:4A:DF:FE:33:CF:49:2A:BB:A8 + 1D:F1:20:89:44:D7:7B:5F:1D:9D:CB:51:EE:24:4A:52:3F:3E:F5:DE X509v3 Authority Key Identifier: keyid: - 24:95:E8:16:EF:6F:FC:AA:F3:56:CE:4A:DF:FE:33:CF:49:2A:BB:A8 + 1D:F1:20:89:44:D7:7B:5F:1D:9D:CB:51:EE:24:4A:52:3F:3E:F5:DE X509v3 Basic Constraints: critical CA:TRUE X509v3 Key Usage: critical Certificate Sign, CRL Sign X509v3 Subject Alternative Name: email:certify@example.com Signature Algorithm: ecdsa-with-SHA256 - 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: - 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 + 30:45:02:20:2b:89:1d:d4:11:d0:7a:6d:6f:62:19:47:63:5b: + a4:c4:31:65:29:6b:3f:63:37:26:f0:2e:51:ec:f4:64:bd:40: + 02:21:00:b4:be:8a:80:d0:86:75:f0:41:fb:c7:19:ac:f3:b3: + 9d:ed:c8:5d:c9:2b:30:35:86:8c:b2:da:a8:f0:5d:b1:96 C.2. enroll / reenroll The breakdown of the enrollment request is - Certificate Request: Data: Version: 0 (0x0) Subject: C=US, ST=CA, L=LA, O=example Inc, OU=IoT/serialNumber=Wt1234 Subject Public Key Info: Public Key Algorithm: id-ecPublicKey Public-Key: (256 bit) pub: 04:c8:b4:21:f1:1c:25:e4:7e:3a:c5:71:23:bf:2d: @@ -1958,41 +2008,43 @@ Public-Key: (256 bit) pub: 04:c8:b4:21:f1:1c:25:e4:7e:3a:c5:71:23:bf:2d: 9f:dc:49:4f:02:8b:c3:51:cc:80:c0:3f:15:0b:f5: 0c:ff:95:8d:75:41:9d:81:a6:a2:45:df:fa:e7:90: be:95:cf:75:f6:02:f9:15:26:18:f8:16:a2:b2:3b: 56:38:e5:9f:d9 ASN1 OID: prime256v1 NIST CURVE: P-256 Attributes: - challengePassword : <256-bit POP linking value> + challengePassword: <256-bit PoP linking value> Requested Extensions: X509v3 Subject Alternative Name: othername: Signature Algorithm: ecdsa-with-SHA256 30:45:02:21:00:92:56:3a:54:64:63:bd:9e:cf:f1:70:d0:fd: 1f:2e:f0:d3:d0:12:16:0e:5e:e9:0c:ff:ed:ab:ec:9b:9a:38: 92:02:20:17:9f:10:a3:43:61:09:05:1a:ba:d1:75:90:a0:9b: 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 - (Section 4). + The CSR contains a ChallengePassword which is used for PoP linking + (Section 4). The CSR also contains an id-on-hardwareModuleName + hardware identifier to customize the returned certificate to the + requesting device (See [RFC7299] and [I-D.moskowitz-ecdsa-pki]). The breakdown of the issued certificate is Certificate: Data: Version: 3 (0x2) Serial Number: 9112578475118446130 (0x7e7661d7b54e4632) Signature Algorithm: ecdsa-with-SHA256 - Issuer: C=US, ST=CA, O=Example Inc, OU=certification, - CN=802.1AR CA + Issuer: C=US, ST=CA, O=Example Inc, + OU=certification, CN=802.1AR CA Validity Not Before: Jan 31 11:29:16 2019 GMT Not After : Dec 31 23:59:59 9999 GMT Subject: C=US, ST=CA, L=LA, O=example Inc, OU=IoT/serialNumber=Wt1234 Subject Public Key Info: Public Key Algorithm: id-ecPublicKey Public-Key: (256 bit) pub: 04:c8:b4:21:f1:1c:25:e4:7e:3a:c5:71:23:bf:2d: @@ -2028,92 +2079,93 @@ request. Certificate Request: Data: Version: 0 (0x0) Subject: O=skg example Subject Public Key Info: Public Key Algorithm: id-ecPublicKey Public-Key: (256 bit) pub: - 04:1b:b8:c1:11:78:96:f9:8e:45:06:c0:3d:70:ef: - be:82:0d:8e:38:ea:97:e9:d6:5d:52:c8:46:0c:58: - 52:c5:1d:d8:9a:61:37:0a:28:43:76:0f:c8:59:79: - 9d:78:cd:33:f3:c1:84:6e:30:4f:17:17:f8:12:3f: - 1a:28:4c:c9:9f + 04:c8:b4:21:f1:1c:25:e4:7e:3a:c5:71:23:bf:2d: + 9f:dc:49:4f:02:8b:c3:51:cc:80:c0:3f:15:0b:f5: + 0c:ff:95:8d:75:41:9d:81:a6:a2:45:df:fa:e7:90: + be:95:cf:75:f6:02:f9:15:26:18:f8:16:a2:b2:3b: + 56:38:e5:9f:d9 ASN1 OID: prime256v1 NIST CURVE: P-256 Attributes: a0:00 Signature Algorithm: ecdsa-with-SHA256 - 30:44:02:20:38:7c:d4:e9:cf:62:8d:4a:f7:7f:92:eb:ed:48: - 90:d9:d1:41:dc:a8:6c:d2:75:7d:d1:4c:bd:59:cd:f6:96:18: - 02:20:2f:24:5e:82:8c:77:75:43:78:b6:66:60:a4:97:7f:11: - 3c:ac:da:a0:cc:7b:ad:7d:14:74:a7:fd:15:5d:09:0d + 30:45:02:20:7c:55:39:81:b1:fe:34:92:49:d8:a3:f5:0a:03: + 46:33:6b:7d:fa:a0:99:cf:74:e1:ec:7a:37:a0:a7:60:48:59: + 02:21:00:84:79:29:53:98:77:4b:2f:f8:e7:e8:2a:bb:0c:17: + ea:ef:34:4a:50:88:fa:69:fd:63:ee:61:18:50:c3:4b:0a Following is the breakdown of the private key content of the server- side key generation response. Private-Key: (256 bit) priv: - 0b:9a:67:78:5b:65:e0:73:60:b6:d2:8c:fc:1d:3f: - 39:25:c0:75:57:99:de:ec:a7:45:37:2b:01:69:7b: - d8:a6 + 61:33:6a:86:ac:6e:7a:f4:a9:6f:63:28:30:ad:4e: + 6a:a0:83:76:79:20:60:94:d7:67:9a:01:ca:8c:6f: + 0c:37 pub: - 04:1b:b8:c1:11:78:96:f9:8e:45:06:c0:3d:70:ef: - be:82:0d:8e:38:ea:97:e9:d6:5d:52:c8:46:0c:58: - 52:c5:1d:d8:9a:61:37:0a:28:43:76:0f:c8:59:79: - 9d:78:cd:33:f3:c1:84:6e:30:4f:17:17:f8:12:3f: - 1a:28:4c:c9:9f + 04:c8:b4:21:f1:1c:25:e4:7e:3a:c5:71:23:bf:2d: + 9f:dc:49:4f:02:8b:c3:51:cc:80:c0:3f:15:0b:f5: + 0c:ff:95:8d:75:41:9d:81:a6:a2:45:df:fa:e7:90: + be:95:cf:75:f6:02:f9:15:26:18:f8:16:a2:b2:3b: + 56:38:e5:9f:d9 ASN1 OID: prime256v1 NIST CURVE: P-256 The following is the breakdown of the certificate in the server-side key generation response payload. Certificate: Data: Version: 3 (0x2) - Serial Number: 1327972925857878603 (0x126de8571518524b) + Serial Number: + b3:31:3e:8f:3f:c9:53:8e Signature Algorithm: ecdsa-with-SHA256 Issuer: O=skg example Validity - Not Before: Jan 9 08:57:08 2019 GMT - Not After : Jan 4 08:57:08 2039 GMT + Not Before: Sep 4 07:44:03 2019 GMT + Not After : Aug 30 07:44:03 2039 GMT Subject: O=skg example Subject Public Key Info: Public Key Algorithm: id-ecPublicKey Public-Key: (256 bit) pub: - 04:1b:b8:c1:11:78:96:f9:8e:45:06:c0:3d:70:ef: - be:82:0d:8e:38:ea:97:e9:d6:5d:52:c8:46:0c:58: - 52:c5:1d:d8:9a:61:37:0a:28:43:76:0f:c8:59:79: - 9d:78:cd:33:f3:c1:84:6e:30:4f:17:17:f8:12:3f: - 1a:28:4c:c9:9f + 04:c8:b4:21:f1:1c:25:e4:7e:3a:c5:71:23:bf:2d: + 9f:dc:49:4f:02:8b:c3:51:cc:80:c0:3f:15:0b:f5: + 0c:ff:95:8d:75:41:9d:81:a6:a2:45:df:fa:e7:90: + be:95:cf:75:f6:02:f9:15:26:18:f8:16:a2:b2:3b: + 56:38:e5:9f:d9 ASN1 OID: prime256v1 NIST CURVE: P-256 X509v3 extensions: X509v3 Basic Constraints: CA:FALSE Netscape Comment: OpenSSL Generated Certificate 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: keyid: - 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 Signature Algorithm: ecdsa-with-SHA256 - 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: - 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 + 30:45:02:21:00:e9:5b:fa:25:a0:89:76:65:22:46:f2:d9:61: + 43:da:39:fc:e0:dc:4c:9b:26:b9:cc:e1:f2:41:64:cc:2b:12: + b6:02:20:13:51:fd:8e:ea:65:76:4e:34:59:d3:24:e4:34:5f: + f5:b2:a9:15:38:c0:49:76:11:17:96:b3:69:8b:f6:37:9c Authors' Addresses Peter van der Stok Consultant Email: consultancy@vanderstok.org Panos Kampanakis Cisco Systems