draft-ietf-lamps-hash-of-root-key-cert-extn-02.txt   draft-ietf-lamps-hash-of-root-key-cert-extn-03.txt 
Network Working Group R. Housley Network Working Group R. Housley
Internet-Draft Vigil Security Internet-Draft Vigil Security
Intended status: Informational December 27, 2018 Intended status: Informational January 03, 2019
Expires: June 30, 2019 Expires: July 7, 2019
Hash Of Root Key Certificate Extension Hash Of Root Key Certificate Extension
draft-ietf-lamps-hash-of-root-key-cert-extn-02 draft-ietf-lamps-hash-of-root-key-cert-extn-03
Abstract Abstract
This document specifies the Hash Of Root Key certificate extension. This document specifies the Hash Of Root Key certificate extension.
This certificate extension is carried in the self-signed certificate This certificate extension is carried in the self-signed certificate
for a trust anchor, which is often called a Root Certification for a trust anchor, which is often called a Root Certification
Authority (CA) certificate. This certificate extension unambiguously Authority (CA) certificate. This certificate extension unambiguously
identifies the next public key that will be used by the trust anchor identifies the next public key that will be used at some point in the
at some point in the future. future as the next Root CA certificate, replacing the current one.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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 June 30, 2019. This Internet-Draft will expire on July 7, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 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.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. ASN.1 . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. ASN.1 . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Hash Of Root Key Certificate Extension . . . . . . . . . . . 4 3. Hash Of Root Key Certificate Extension . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Operational Considerations . . . . . . . . . . . . . . . . . 4 5. Operational Considerations . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6 8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 7 Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
This document specifies the Hash Of Root Key X.509 version 3 This document specifies the Hash Of Root Key X.509 version 3
certificate extension. The extension is an optional addition to the certificate extension. The extension is an optional addition to the
Internet X.509 Public Key Infrastructure Certificate and Certificate Internet X.509 Public Key Infrastructure Certificate and Certificate
Revocation List (CRL) Profile [RFC5280]. The certificate extension Revocation List (CRL) Profile [RFC5280]. The certificate extension
facilitates the orderly transition from one Root Certification facilitates the orderly transition from one Root Certification
Authority (CA) public key to the next. It does so by publishing the Authority (CA) public key to the next. It does so by publishing the
hash value of the next generation public key in the current self- hash value of the next generation public key in the current self-
signed certificate. This allows a relying party to unambiguously signed certificate. This hash value is a commitment to a particular
recognize the next generation public key when it becomes available, public key in the next generation self-signed certificate. This
install that public key in the trust anchor store, and remove the commitment allows a relying party to unambiguously recognize the next
previous public key from the trust anchor store. generation self-signed certificate when it becomes available, install
the new self-signed certificate in the trust anchor store, and remove
the previous one from the trust anchor store.
A Root CA Certificate MAY include the Hashed Root Key certificate A Root CA Certificate MAY include the Hashed Root Key certificate
extension to provide the hash value of the next public key that will extension to provide the hash value of the next public key that will
be used by the Root CA. be used by the Root CA.
1.1. Terminology 1.1. 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
14 [RFC2119][RFC8174] when, and only when, they appear in all BCP 14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
1.2. ASN.1 1.2. ASN.1
Certificates [RFC5280] are generated using ASN.1 [X680]; certificates Certificates [RFC5280] are generated using ASN.1 [X680]; certificates
are always encoded with the Distinguished Encoding Rules (DER) are always encoded with the Distinguished Encoding Rules (DER)
[X690]. [X690].
2. Overview 2. Overview
Before the initial deployment of the Root CA, the following are Before the initial deployment of the Root CA, the following are
generated: generated:
R1 = The initial Root key pair R1 = The initial Root key pair
C1 = Self-signed certificate for R1, which also contains H2
R2 = The second generation Root key pair R2 = The second generation Root key pair
H2 = Thumbprint (hash) of the public key of R2 H2 = Thumbprint (hash) of the public key of R2
C1 = Self-signed certificate for R1, which also contains H2
C1 is a self-signed certificate, and it contains H2 within the C1 is a self-signed certificate, and it contains H2 within the
HashOfRootKey extension. C1 is distributed as part of the initial HashOfRootKey extension. C1 is distributed as part of the initial
the system deployment. The HashOfRootKey certificate extension is the system deployment. The HashOfRootKey certificate extension is
described in Section 3. described in Section 3.
When the time comes to replace the initial Root CA certificate, R1, When the time comes to replace the initial Root CA certificate, R1,
the following are generated: the following are generated:
R3 = The third generation Root key pair R3 = The third generation Root key pair
H3 = Thumbprint (hash) the public key of R3 H3 = Thumbprint (hash) the public key of R3
C2 = Self-signed certificate for R2, which contains H3 C2 = Self-signed certificate for R2, which contains H3
This is an iterative process. That is, R4 and H4 are generated when This is an iterative process. That is, R4 and H4 are generated when
it is time for C3 to replace C2. And so on. it is time for C3 to replace C2. And so on.
The successors to the Root CA self-signed certificate can be The successor to the Root CA self-signed certificate can be delivered
delivered by any means. Whenever a new Root CA certificate is by any means. Whenever a new Root CA certificate is received, the
received, the recipient is able to verify that the potential Root CA recipient is able to verify that the potential Root CA certificate
certificate links back to a previously authenticated Root CA links back to a previously authenticated Root CA certificate with the
certificate with the hashOfRootKey certificate extension. That is, hashOfRootKey certificate extension. That is, the recipient verifies
verify the signature on the self-signed certificate and verify that the signature on the self-signed certificate and verifies that the
the hash of the DER-encoded SubjectPublicKeyInfo from the potential hash of the DER-encoded SubjectPublicKeyInfo from the potential Root
Root CA certificate matches the value from the HashOfRootKey CA certificate matches the value from the HashOfRootKey certificate
certificate extension of the current Root CA certificate. Checking extension of the current Root CA certificate. Checking the self-
the self-signed certificate signature ensures that the certificate signed certificate signature ensures that the certificate contains
contains the subject name that the key owner intends, which is the subject name, public key algorithm identifier, and public key
important for path validation. Checking the hash of the algorithm parameters intended by the key owner intends; these are
important inputs to certification path validation as defined in
Section 6 of [RFC5280]. Checking the hash of the
SubjectPublicKeyInfo ensures that the certificate contains the SubjectPublicKeyInfo ensures that the certificate contains the
intended public key. If either check fails, then potential Root CA intended public key. If either check fails, then potential Root CA
certificate is not a valid replacement, and the recipient continues certificate is not a valid replacement, and the recipient continues
to use the current Root CA certificate. to use the current Root CA certificate.
3. Hash Of Root Key Certificate Extension 3. Hash Of Root Key Certificate Extension
The HashOfRootKey certificate extension MUST NOT be critical. The HashOfRootKey certificate extension MUST NOT be critical.
The following ASN.1 [X680][X690] syntax defines the HashOfRootKey The following ASN.1 [X680][X690] syntax defines the HashOfRootKey
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5. Operational Considerations 5. Operational Considerations
Guidance on the transition from one trust anchor to another is Guidance on the transition from one trust anchor to another is
available in [RFC2510]. In particular, the oldWithNew and newWithOld available in [RFC2510]. In particular, the oldWithNew and newWithOld
advice ensures that relying parties are able to validate certificates advice ensures that relying parties are able to validate certificates
issued under the current Root CA certificate and the next generation issued under the current Root CA certificate and the next generation
Root CA certificate throughout the transition. Further, this Root CA certificate throughout the transition. Further, this
technique avoids the need for all relying parties to make the technique avoids the need for all relying parties to make the
transition at the same time. transition at the same time.
The Root CA must securely back up the yet-to-be-deployed key pair.
If the Root CA stores the key pair in a hardware security module, and
that module fails, the Root CA remains committed to the now
unavailable key pair. The remedy is to deploy a new self-signed
certificate that contains a newly-generated key pair in the same
manner as the initial self-signed certificate, thus loosing the
benefits of the Hash Of Root Key certificate extension altogether.
6. Security Considerations 6. Security Considerations
The security considerations from [RFC5280] apply, especially the The security considerations from [RFC5280] apply, especially the
discussion of self-issued certificates. discussion of self-issued certificates.
The Hash Of Root Key certificate extension facilitates the orderly The Hash Of Root Key certificate extension facilitates the orderly
transition from one Root CA public key to the next by publishing the transition from one Root CA public key to the next by publishing the
hash value of the next generation public key in the current hash value of the next generation public key in the current
certificate. This allows a relying party to unambiguously recognize certificate. This allows a relying party to unambiguously recognize
the next generation public key when it becomes available; however, the next generation public key when it becomes available; however,
the full public key is not disclosed until the Root CA releases the the full public key is not disclosed until the Root CA releases the
next generation certificate. In this way, attackers cannot begin to next generation certificate. In this way, attackers cannot begin to
analyze the public key before the next generation Root CA certificate analyze the public key before the next generation Root CA self-signed
is released. certificate is released.
The Root CA needs to ensure that the public key in the next The Root CA needs to ensure that the public key in the next
generation certificate is as strong or stronger than the key that it generation certificate is as strong or stronger than the key that it
is replacing. is replacing. Of course, a significant advance in cryptoanalytic
capability can break the yet-to-be-deployed key pair. Such advances
are rare and difficult to predict. If such an advance occurs, the
Root CA remains committed to the now broken key. The remedy is to
deploy a new public key and algorithm in the same manner as the
initial Root CA self-signed certificate, thus loosing the benefits of
the Hash Of Root Key certificate extension altogether.
The Root CA needs to employ a hash function that is resistant to The Root CA needs to employ a hash function that is resistant to
preimage attacks [RFC4270]. A first-preimage attack against the hash preimage attacks [RFC4270]. A first-preimage attack against the hash
function would allow an attacker to find another input that results function would allow an attacker to find another input that results
published hash value. For the attack to be successful, the input published hash value. For the attack to be successful, the input
would have to be a valid SubjectPublicKeyInfo that contains the would have to be a valid SubjectPublicKeyInfo that contains the
public key that corresponds to a private key known to the attacker. public key that corresponds to a private key known to the attacker.
A second-preimage attack becomes possible once the Root CA releases A second-preimage attack becomes possible once the Root CA releases
the next generation public key, which makes the input to the hash the next generation public key, which makes the input to the hash
function becomes available to the attacker and everyone else. Again, function becomes available to the attacker and everyone else. Again,
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The Secure Electronic Transaction (SET) [SET] specification published The Secure Electronic Transaction (SET) [SET] specification published
by MasterCard and VISA in 1997 includes a very similar certificate by MasterCard and VISA in 1997 includes a very similar certificate
extension. The SET certificate extension has essentially the same extension. The SET certificate extension has essentially the same
semantics, but the syntax fairly different. semantics, but the syntax fairly different.
CTIA - The Wireless Association is developing a public key CTIA - The Wireless Association is developing a public key
infrastructure that will make use of the certificate extension infrastructure that will make use of the certificate extension
described in this document. described in this document.
Many thanks to Jim Schaad and Stefan Santesson. Their review and Many thanks to Jim Schaad, Stefan Santesson, and Paul Hoffman. Their
comments have greatly improved the document, especially the review and comments have greatly improved the document, especially
Operational Considerations and Security Considerations sections. the Operational Considerations and Security Considerations sections.
8. References 8. References
8.1. Normative References 8.1. Normative References
[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>.
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HashAlgorithmId ::= AlgorithmIdentifier {DIGEST-ALGORITHM,{ ... }} HashAlgorithmId ::= AlgorithmIdentifier {DIGEST-ALGORITHM,{ ... }}
id-ce-hashOfRootKey OBJECT IDENTIFIER ::= { 1 3 6 1 4 1 51483 2 1 } id-ce-hashOfRootKey OBJECT IDENTIFIER ::= { 1 3 6 1 4 1 51483 2 1 }
END END
Author's Address Author's Address
Russ Housley Russ Housley
Vigil Security Vigil Security
918 Spring Knoll Drive 516 Dranesville Road
Herndon, VA 20170 Herndon, VA 20170
US US
Email: housley@vigilsec.com Email: housley@vigilsec.com
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