PROPOSED STANDARD

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Internet Engineering Task Force (IETF) O. Sury Request for Comments: 6594 CZ.NIC Category: Standards Track April 2012 ISSN: 2070-1721 Use of the SHA-256 Algorithm with RSA, Digital Signature Algorithm (DSA), and Elliptic Curve DSA (ECDSA) in SSHFP Resource Records Abstract This document updates the IANA registries in RFC 4255, which defines SSHFP, a DNS Resource Record (RR) that contains a standard Secure Shell (SSH) key fingerprint used to verify SSH host keys using DNS Security Extensions (DNSSEC). This document defines additional options supporting SSH public keys applying the Elliptic Curve Digital Signature Algorithm (ECDSA) and the implementation of fingerprints computed using the SHA-256 message digest algorithm in SSHFP Resource Records. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the fInternet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6594. Copyright Notice Copyright (c) 2012 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 (http://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 Sury Standards Track [Page 1]

RFC 6594 ECDSA and SHA-256 Algorithms for SSHFP April 2012 1. Introduction ....................................................3 2. Requirements Language ...........................................4 3. SSHFP Resource Records ..........................................4 3.1. SSHFP Fingerprint Type Specification .......................4 3.1.1. SHA-256 SSHFP Fingerprint Type Specification ........4 3.2. SSHFP Algorithm Number Specification .......................4 3.2.1. ECDSA SSHFP Algorithm Number Specification ..........4 4. Implementation Considerations ...................................4 4.1. Support for SHA-256 Fingerprints ...........................4 4.2. Support for ECDSA ..........................................4 5. Examples ........................................................5 5.1. RSA Public Key .............................................5 5.1.1. RSA Public Key with SHA1 Fingerprint ................5 5.1.2. RSA Public Key with SHA-256 Fingerprint .............5 5.2. DSA Public Key .............................................6 5.2.1. DSA Public Key with SHA1 Fingerprint ................6 5.2.2. DSA Public Key with SHA-256 Fingerprint .............6 5.3. ECDSA Public Key ...........................................6 5.3.1. ECDSA Public Key with SHA1 Fingerprint ..............7 5.3.2. ECDSA Public Key with SHA-256 Fingerprint ...........7 6. IANA Considerations .............................................7 6.1. SSHFP RR Types for Public Key Algorithms ...................7 6.2. SSHFP RR Types for Fingerprint Types .......................7 7. Security Considerations .........................................8 8. References ......................................................8 8.1. Normative References .......................................8 8.2. Informative References .....................................9 Sury Standards Track [Page 2]

RFC 6594 ECDSA and SHA-256 Algorithms for SSHFP April 2012 1 . Introduction RFC 4253 [RFC4253] defines Public Key Algorithms for the Secure Shell server public keys. The DNS has been extended to store fingerprints in a DNS Resource Record named SSHFP [RFC4255], which provides out-of-band verification by looking up a fingerprint of the server public key in the DNS [RFC1034][RFC1035] and using Domain Name System Security Extensions (DNSSEC) [RFC4033][RFC4034][RFC4035] to verify the lookup. RFC 4255 [RFC4255] describes how to store the cryptographic fingerprint of SSH public keys in SSHFP Resource Records. SSHFP Resource Records contain the fingerprint and two index numbers identifying the cryptographic algorithms used: 1. to link the fingerprinted public key with the corresponding private key, and 2. to derive the message digest stored as the fingerprint in the record. RFC 4255 [RFC4255] then specifies lists of cryptographic algorithms and the corresponding index numbers used to identify them in SSHFP Resource Records. This document updates the IANA registry "SSHFP RR Types for public key algorithms" and "SSHFP RR types for fingerprint types" [SSHFPVALS] by adding a new option in each list: o the Elliptic Curve Digital Signature Algorithm (ECDSA) [RFC6090], which has been added to the Secure Shell Public Key list by RFC 5656 [RFC5656] in the public key algorithms list, and o the SHA-256 algorithm [FIPS.180-3.2008] in the SSHFP fingerprint type list. Familiarity with DNSSEC, SSH Protocol [RFC4251][RFC4253][RFC4250], SSHFP [RFC4255], and the SHA-2 [FIPS.180-3.2008] family of algorithms is assumed in this document. Sury Standards Track [Page 3]

RFC 6594 ECDSA and SHA-256 Algorithms for SSHFP April 2012 5 . Examples 5.1 . RSA Public Key RFC4716] would appear as follows: ---- BEGIN SSH2 PUBLIC KEY ---- AAAAB3NzaC1yc2EAAAADAQABAAABAQDCUR4JOhxTinzq7QO3bQXW4jmPCCulFsnh 8Yi7MKwpMnd96+T7uV7nEwy+6+GWYu98IxFJByIjFXX/a6BXDp3878wezH1DZ2tN D/tu/eudz6ErpTFYmnVLyEDARYSzVBNQuIK1UDqvvB6KffJcyt78FpwW27euGkqE kam7GaurPRAgwXehDB/gMwRtXVRZ+13zYWkAmAY+5OAWVmdXuQVm5kjlvcNzto2H 3m3nqJtD4J9L1lKPuSVVqwJr4/6hibXJkQEvWpUvdOAUw3frKpNwa932fXFk3ke4 rsDjQ/W8GyleMtK3Tx8tE4z1wuowXtYe6Ba8q3LAPs/m2S4pUscx ---- END SSH2 PUBLIC KEY ---- 5.1.1 . RSA Public Key with SHA1 Fingerprint 5.1.2 . RSA Public Key with SHA-256 Fingerprint Sury Standards Track [Page 5]

RFC 6594 ECDSA and SHA-256 Algorithms for SSHFP April 2012 5.2 . DSA Public Key 5.2.1 . DSA Public Key with SHA1 Fingerprint 5.2.2 . DSA Public Key with SHA-256 Fingerprint 5.3 . ECDSA Public Key Sury Standards Track [Page 6]

RFC 6594 ECDSA and SHA-256 Algorithms for SSHFP April 2012 5.3.1 . ECDSA Public Key with SHA1 Fingerprint 5.3.2 . ECDSA Public Key with SHA-256 Fingerprint 6 . IANA Considerations SSHFPVALS]. 6.1 . SSHFP RR Types for Public Key Algorithms 6.2 . SSHFP RR Types for Fingerprint Types Sury Standards Track [Page 7]