Signaling Cryptographic Algorithm Understanding in DNS Security Extensions (DNSSEC)
RFC 6975

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Internet Engineering Task Force (IETF)                        S. Crocker
Request for Comments: 6975                                 Shinkuro Inc.
Category: Standards Track                                        S. Rose
ISSN: 2070-1721                                                     NIST
                                                               July 2013

           Signaling Cryptographic Algorithm Understanding in
                    DNS Security Extensions (DNSSEC)

Abstract

   The DNS Security Extensions (DNSSEC) were developed to provide origin
   authentication and integrity protection for DNS data by using digital
   signatures.  These digital signatures can be generated using
   different algorithms.  This document specifies a way for validating
   end-system resolvers to signal to a server which digital signature
   and hash algorithms they support.  The extensions allow the signaling
   of new algorithm uptake in client code to allow zone administrators
   to know when it is possible to complete an algorithm rollover in a
   DNSSEC-signed zone.

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
   Internet 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/rfc6975.

Crocker & Rose               Standards Track                    [Page 1]
RFC 6975                    Algorithm-Signal                   July 2013

Copyright Notice

   Copyright (c) 2013 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
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . . . 4
   3.  Signaling DNSSEC Algorithm Understood (DAU), DS Hash
       Understood (DHU), and NSEC3 Hash Understood (N3U) Using EDNS  . 4
   4.  Client Considerations . . . . . . . . . . . . . . . . . . . . . 5
     4.1.  Stub Resolvers  . . . . . . . . . . . . . . . . . . . . . . 5
       4.1.1.  Validating Stub Resolvers . . . . . . . . . . . . . . . 5
       4.1.2.  Non-validating Stub Resolvers . . . . . . . . . . . . . 6
     4.2.  Recursive Resolvers . . . . . . . . . . . . . . . . . . . . 6
       4.2.1.  Validating Recursive Resolvers  . . . . . . . . . . . . 6
       4.2.2.  Non-validating Recursive Resolvers  . . . . . . . . . . 6
   5.  Intermediate System Considerations  . . . . . . . . . . . . . . 6
   6.  Server Considerations . . . . . . . . . . . . . . . . . . . . . 7
   7.  Traffic Analysis Considerations . . . . . . . . . . . . . . . . 7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
   9.  Security Considerations . . . . . . . . . . . . . . . . . . . . 8
   10. Normative References  . . . . . . . . . . . . . . . . . . . . . 8

Crocker & Rose               Standards Track                    [Page 2]
RFC 6975                    Algorithm-Signal                   July 2013

1.  Introduction

   The DNS Security Extensions (DNSSEC), [RFC4033], [RFC4034], and
   [RFC4035], were developed to provide origin authentication and
   integrity protection for DNS data by using digital signatures.  Each
   digital signature (RRSIG) Resource Record (RR) contains an algorithm
   code number that corresponds to a DNSSEC public key (DNSKEY) RR.
   These algorithm codes tell validators which cryptographic algorithm
   was used to generate the digital signature.

   Likewise, the Delegation Signer (DS) RRs and Hashed Authenticated
   Denial of Existence (NSEC3) RRs use a hashed value as part of their
   resource record data (RDATA) and, like digital signature algorithms,
   these hash algorithms have code numbers.  All three algorithm codes
   (RRSIG/DNSKEY, DS, and NSEC3) are maintained in unique IANA
   registries.

   This document sets specifies a way for validating end-system
   resolvers to tell a server in a DNS query which digital signature
   and/or hash algorithms they support.  This is done using the new
   Extension Mechanisms for DNS (EDNS0) options specified below in