Network Working Group R. Housley Internet-Draft Vigil Security Intended status: Informational November 07, 2018 Expires: May 11, 2019 Hash Of Root Key Certificate Extension draft-ietf-lamps-hash-of-root-key-cert-extn-01 Abstract This document specifies the Hash Of Root Key certificate extension. This certificate extension is carried in the self-signed certificate for a trust anchor, which is often called a Root Certification Authority (CA) certificate. This certificate extension unambiguously identifies the next public key that will be used by the trust anchor at some point in the future. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. 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 May 11, 2019. Copyright Notice Copyright (c) 2018 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 carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Housley Expires May 11, 2019 [Page 1] Internet-Draft Hash Of Root Key Extension November 2018 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 1.2. ASN.1 . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Hash Of Root Key Certificate Extension . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 5. Operational Considerations . . . . . . . . . . . . . . . . . 4 6. Security Considerations . . . . . . . . . . . . . . . . . . . 4 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 8.1. Normative References . . . . . . . . . . . . . . . . . . 6 8.2. Informative References . . . . . . . . . . . . . . . . . 7 Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction This document specifies the Hash Of Root Key X.509 version 3 certificate extension. The extension is an optional addition to the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile [RFC5280]. The certificate extension facilitates the orderly transition from one Root Certification 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- signed certificate. This allows a relying party to unambiguously recognize the next generation public key when it becomes available, install that public key in the trust anchor store, and remove the previous public key from the trust anchor store. A Root CA Certificate MAY include the Hashed Root Key certificate extension to provide the hash value of the next public key that will be used by the Root CA. 1.1. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "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. Housley Expires May 11, 2019 [Page 2] Internet-Draft Hash Of Root Key Extension November 2018 1.2. ASN.1 Certificates [RFC5280] are generated using ASN.1 [X680]; certificates are always encoded with the Distinguished Encoding Rules (DER) [X690]. 2. Overview Before the initial deployment of the Root CA, the following are generated: R1 = The initial Root key pair C1 = Self-signed certificate for R1, which also contains H2 R2 = The second generation Root key pair H2 = Thumbprint (hash) of the public key of R2 C1 is a self-signed certificate, and it contains H2 within the HashOfRootKey extension. C1 is distributed as part of the initial the system deployment. The HashOfRootKey certificate extension is described in Section 3. When the time comes to replace the initial Root CA certificate, R1, the following are generated: R3 = The third generation Root key pair H3 = Thumbprint (hash) the public key of R3 C2 = Self-signed certificate for R2, which contains H3 This is an iterative process. That is, R4 and H4 are generated when it is time for C3 to replace C2. And so on. The successors to the Root CA self-signed certificate can be delivered by any means. Whenever a new Root CA certificate is received, the recipient is able to verify that the potential Root CA certificate links back to a previously authenticated Root CA certificate with the hashOfRootKey certificate extension. That is, validate the self-signed signature and verify that the hash of the DER-encoded SubjectPublicKeyInfo from the potential Root CA certificate matches the value from the HashOfRootKey certificate extension of the current Root CA certificate. If the signature does not validate or the hash values do not match, then potential Root CA certificate is not a valid replacement, and the recipient continues to use the current Root CA certificate. Housley Expires May 11, 2019 [Page 3] Internet-Draft Hash Of Root Key Extension November 2018 3. Hash Of Root Key Certificate Extension The HashOfRootKey certificate extension MUST NOT be critical. The following ASN.1 [X680][X690] syntax defines the HashOfRootKey certificate extension: ext-HashOfRootKey EXTENSION ::= { -- Only in Root CA certificates SYNTAX HashedRootKey IDENTIFIED BY id-ce-hashOfRootKey CRITICALITY {FALSE} } HashedRootKey ::= SEQUENCE { hashAlg AlgorithmIdentifier, -- Hash algorithm used hashValue OCTET STRING } -- Hash of DER-encoded -- SubjectPublicKeyInfo id-ce-hashOfRootKey ::= OBJECT IDENTIFIER { 1 3 6 1 4 1 51483 2 1 } The definitions of EXTENSION and HashAlgorithm can be found in [RFC5912]. The hashAlg indicates the one-way hash algorithm that was used to compute the hash value. The hashValue contains the hash value computed from the next generation public key. The public key is DER-encoded SubjectPublicKeyInfo as defined in [RFC5280]. 4. IANA Considerations This document makes no requests of the IANA. 5. Operational Considerations Guidance on the transition from one trust anchor to another is available in [RFC2510]. In particular, the oldWithNew and newWithOld advice ensures that relying parties are able to validate certificates issued under the current Root CA certificate and the next generation Root CA certificate throughout the transition. Further, this technique ovoids the need for all relying parties to make the transition at the same time. 6. Security Considerations The security considerations from [RFC5280] apply, especially the discussion of self-issued certificates. Housley Expires May 11, 2019 [Page 4] Internet-Draft Hash Of Root Key Extension November 2018 The Hash Of Root Key certificate extension facilitates the orderly transition from one Root CA public key to the next by publishing the hash value of the next generation public key in the current certificate. This allows a relying party to unambiguously recognize the next generation public key when it becomes available; however, the full public key is not disclosed until the Root CA releases the next generation certificate. In this way, attackers cannot begin to analyze the public key before the next generation Root CA certificate is released. 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 is replacing. The Root CA needs to employ a hash function that is resistant to preimage attacks [RFC4270]. A first-preimage attack against the hash function would allow an attacker to find another input that results published hash value. For the attack to be successful, the input would have to be a valid SubjectPublicKeyInfo that contains the public key that corresponds to a private key known to the attacker. A second-preimage attack becomes possible once the Root CA releases the next generation public key, which makes the input to the hash function becomes available to the attacker and everyone else. Again, the attacker needs to find a valid SubjectPublicKeyInfo that contains the public key that corresponds to a private key known to the attacker. If an early release of the next generation public key occurs and the Root CA is concerned that attackers were given too much lead time to analyze that public key, then the Root CA can transition to a freshly generated key pair by rapidly performing two transitions. The first transition takes the Root CA to the key pair that suffered the early release, and it causes the Root CA to generate the subsequent Root key pair. The second transition occurs when the Root CA is confident that the population of relying parties have completed the first transition, and it takes the Root CA to the freshly generated key pair. Of course, the second transition also causes the Root CA to generate the Root key pair for future use. 7. Acknowledgements The Secure Electronic Transaction (SET) [SET] specification published by MasterCard and VISA in 1997 includes a very similar certificate extension. The SET certificate extension has essentially the same semantics, but the syntax fairly different. Housley Expires May 11, 2019 [Page 5] Internet-Draft Hash Of Root Key Extension November 2018 CTIA - The Wireless Association is developing a public key infrastructure that will make use of the certificate extension described in this document. Many thanks to Jim Schaad and Stefan Santesson. Their review and comments have greatly improved the document, especially the Operational Considerations and Security Considerations sections. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC2510] Adams, C. and S. Farrell, "Internet X.509 Public Key Infrastructure Certificate Management Protocols", RFC 2510, DOI 10.17487/RFC2510, March 1999, . [RFC4270] Hoffman, P. and B. Schneier, "Attacks on Cryptographic Hashes in Internet Protocols", RFC 4270, DOI 10.17487/RFC4270, November 2005, . [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, . [RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the Public Key Infrastructure Using X.509 (PKIX)", RFC 5912, DOI 10.17487/RFC5912, June 2010, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [X680] ITU-T, "Information technology -- Abstract Syntax Notation One (ASN.1): Specification of basic notation", ITU-T Recommendation X.680, 2015. Housley Expires May 11, 2019 [Page 6] Internet-Draft Hash Of Root Key Extension November 2018 [X690] ITU-T, "Information Technology -- ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)", ITU-T Recommendation X.690, 2015. 8.2. Informative References [SET] MasterCard and VISA, "SET Secure Electronic Transaction Specification -- Book 2: Programmer's Guide, Version 1.0", May 1997. Appendix A. ASN.1 Module The following ASN.1 module provides the complete definition of the HashOfRootKey certificate extension. Housley Expires May 11, 2019 [Page 7] Internet-Draft Hash Of Root Key Extension November 2018 HashedRootKeyCertExtn { 1 3 6 1 4 1 51483 0 1 } DEFINITIONS IMPLICIT TAGS ::= BEGIN -- EXPORTS All IMPORTS AlgorithmIdentifier{}, DIGEST-ALGORITHM FROM AlgorithmInformation-2009 -- [RFC5912] { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-algorithmInformation-02(58) } EXTENSION FROM PKIX-CommonTypes-2009 { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-pkixCommon-02(57) } ; -- -- Expand the certificate extensions list in [RFC5912] -- CertExtensions EXTENSION ::= { ext-HashOfRootKey, ... } -- -- HashOfRootKey Certificate Extension -- ext-HashOfRootKey EXTENSION ::= { -- Only in Root CA certificates SYNTAX HashedRootKey IDENTIFIED BY id-ce-hashOfRootKey CRITICALITY {FALSE} } HashedRootKey ::= SEQUENCE { hashAlg HashAlgorithmId, -- Hash algorithm used hashValue OCTET STRING } -- Hash of DER-encoded -- SubjectPublicKeyInfo HashAlgorithmId ::= AlgorithmIdentifier {DIGEST-ALGORITHM,{ ... }} id-ce-hashOfRootKey OBJECT IDENTIFIER ::= { 1 3 6 1 4 1 51483 2 1 } END Housley Expires May 11, 2019 [Page 8] Internet-Draft Hash Of Root Key Extension November 2018 Author's Address Russ Housley Vigil Security 918 Spring Knoll Drive Herndon, VA 20170 US Email: housley@vigilsec.com Housley Expires May 11, 2019 [Page 9]