A DANE Record and DNSSEC Authentication Chain Extension for TLS
draft-shore-tls-dnssec-chain-extension-01

TLS                                                             M. Shore
Internet-Draft                                      No Mountain Software
Intended status: Standards Track                               R. Barnes
Expires: January 7, 2016                                         Mozilla
                                                                S. Huque
                                                           Verisign Labs
                                                               W. Toorop
                                                              NLNet Labs
                                                            July 6, 2015

    A DANE Record and DNSSEC Authentication Chain Extension for TLS
               draft-shore-tls-dnssec-chain-extension-01

Abstract

   This draft describes a new TLS extension for transport of a DNS
   record set serialized with the DNSSEC signatures needed to
   authenticate that record set.  The intent of this proposal is to
   allow TLS clients to perform DANE authentication of a TLS server
   certificate without needing to perform additional DNS record lookups.
   It will typically not be used for general DNSSEC validation of TLS
   endpoint names.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 January 7, 2016.

Copyright Notice

   Copyright (c) 2015 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

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   (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
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   described in the Simplified BSD License.

Table of Contents

   1.  Requirements Notation . . . . . . . . . . . . . . . . . . . .   2
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  DNSSEC Authentication Chain Extension . . . . . . . . . . . .   3
     3.1.  Protocol  . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  DNSSEC Authentication Chain Data  . . . . . . . . . . . .   4
   4.  Construction of Serialized Authentication Chains  . . . . . .   5
   5.  Caching and Regeneration of the Authentication Chain  . . . .   6
   6.  Verification  . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Trust Anchor Maintenance  . . . . . . . . . . . . . . . . . .   7
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   7
   11. Test Vectors  . . . . . . . . . . . . . . . . . . . . . . . .   8
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     12.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Appendix A.  Pseudocode example . . . . . . . . . . . . . . . . .  10
   Appendix B.  Test vector  . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  Introduction

   This draft describes a new TLS [RFC5246] extension for transport of a
   DNS record set serialized with the DNSSEC signatures [RFC4034] needed
   to authenticate that record set.  The intent of this proposal is to
   allow TLS clients to perform DANE authentication [RFC6698] of a TLS
   server certificate without performing perform additional DNS record
   lookups and incurring the associated latency penalty.  It also
   provides the ability to avoid potential problems with TLS clients
   being unable to look up DANE records because of an interfering or
   broken middlebox on the path between the endpoint and a DNS server.
   And lastly, it allows a TLS client to validate DANE records itself

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   without needing access to a validating DNS resolver to which it has a
   secure connection.  It will typically not be used for general DNSSEC
   validation of endpoint names, but is more appropriate for validation
   of DANE records such as TLSA, SMIMEA, etc.

   This mechanism is useful for TLS applications that need to address
   the problems described above, typically web browsers or VoIP and XMPP
   services.  It may not be relevant for many other applications.  For
   example, SMTP MTAs are usually located in data centers, may tolerate
   extra DNS lookup latency, are on servers where it is easier to
   provision a validating resolver, and are less likely to experience
   traffic interference from misconfigured middleboxes.  Furthermore,
   SMTP MTAs usually employ Opportunistic Security [RFC7435], in which
   the presence of the DNS TLSA records is used to determine whether to
   enforce an authenticated TLS connection.  Hence DANE authentication
   of SMTP MTAs [DANESMTP] should not use this mechanism.

   The extension described here allows a TLS client to request in the
   client hello message that the DNS validation chain be returned in the
   (extended) server hello message.  If the server is configured for
   DANE authentication, then it performs the appropriate DNS queries,
   builds the validation chain, and returns it to the client.  The
   server will usually use a previously cached authentication chain, but
   it will need to rebuild it periodically as described in Section 5.
   The client then authenticates the chain using a pre-configured trust
   anchor.

   This specification is based on Adam Langley's original proposal for
   serializing DNSSEC authentication chains [AGL] and it incorporates
   his ideas and some of his text.  It modifies his approach by using
   DNS wire formats and assumes that in implementation, the serialized
   DNSSEC object will be prepared by a DNS-specific module and the
   validation actions on serialized DNSSEC will also be carried out by a
   DNS-specific module.  An appendix (empty in the 00 version) provides
   a Python code example of interfacing with a DNS-specific module.

3.  DNSSEC Authentication Chain Extension

3.1.  Protocol

   A client MAY include an extension of type "dnssec_chain" in the
   (extended) ClientHello.  The "extension_data" field of this extension
   MUST be empty.

   [Placeholder: an upcoming revision of this specification will support
   the ability for the client to include a set of unexpired cached
   records it possesses, and correspondingly allow the server to return
   an authentication chain with those records omitted.]

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   Servers receiving a "dnssec_chain" extension in the client hello
   SHOULD return a serialized authentication chain in the extended
   ServerHello message, using the format described below.  If a server
   is unable to return a authentication chain, or does not wish to
   return a authentication chain, it does not include a dnssec_chain
   extension.  As with all TLS extensions, if the server does not
   support this extension it will not return any authentication chain.

3.2.  DNSSEC Authentication Chain Data

   The "extension_data" field of the "dnssec_chain" extension represents
   a sequence of DNS resource record sets, which provide a chain from
   the DANE record being provided to a trust anchor chosen by the
   server.  The "extension_data" field MUST contain a DNSSEC
   Authentication Chain encoded in the following form:

             struct {
               opaque rrset<0..2^16-1>;
               opaque rrsig<0..2^16-1>;
             } RRset

             RRset AuthenticationChain<0..2^16-1>;

   Each RRset in the authentication chain encodes an RRset along with a
   signature on that RRset.  The "rrsig" field contains the RDATA for
   the RRSIG record, defined in Section 3.1 of RFC 4034 [RFC4034].  The
   "rrset" field contains the covered resource records, in the format
   defined in Section 3.1.8.1 of RFC 4034 [RFC4034]:

             signature = sign(RRSIG_RDATA | RR(1) | RR(2)... )

             RR(i) = owner | type | class | TTL | RDATA length | RDATA

   The first RRset in the chain MUST contain the DANE records being
   presented.  The subsequent RRsets MUST be an sequence of DNSKEY and
   DS RRsets, starting with a DNSKEY RRset.  Each RRset MUST
   authenticate the preceding RRset:

      For a DNSKEY RRset, one of the covered DNSKEY RRs MUST be the
      public key used to verify the previous RRset.

      For a DS RRset, the set of key hashes MUST overlap with the
      preceding set of DNSKEY records.

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   In addition, a DNSKEY RRset followed by a DS RRset MUST be self-
   signed, in the sense that its RRSIG MUST verify under one of the keys
   in the DNSKEY RRSET.

   The final RRset in the authentication chain, representing the trust
   anchor, SHOULD be omitted.  In this case, the client MUST verify that
   the key tag and owner name in the final RRSIG record correspond to a
   trust anchor.

   For example, for an HTTPS server at www.example.com, where there are
   zone cuts at "com." and "example.com.", the AuthenticationChain
   structure would comprise the following RRsets (and their
   corresponding RRSIG signatures):

             _443._tcp.www.example.com. TLSA
             example.com. DNSKEY
             example.com. DS
             com. DNSKEY
             com. DS
             . DNSKEY

   [Some names involving CNAME and DNAMEs may involve multiple branches
   of the DNS tree.  The authors are contemplating enhancements to the
   AuthenticationChain structure to accommodate these for a future
   revision of the draft.]

4.  Construction of Serialized Authentication Chains

   This section describes a possible procedure for the server to use to
   build the serialized DNSSEC chain.

   When the goal is to perform DANE authentication [RFC6698] of the
   server's X.509 certificate, the DNS record set to be serialized is a
   TLSA record set corresponding to the server's domain name.

   The domain name of the server MUST be that included in the TLS Server
   Name Indication extension [RFC6066] when present.  If the Server Name
   Indication extension is not present, or if the server does not
   recognize the provided name and wishes to proceed with the handshake
   rather than aborting the connection, the server uses the domain name
   associated with the server IP address to which the connection has
   been established.

   The TLSA record to be queried is constructed by prepending the _port
   and _transport labels to the domain name as described in [RFC6698],
   where "port" is the port number associated with the TLS server.  The
   transport is "tcp" for TLS servers, and "udp" for DTLS servers.  The

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   port number label is the left-most label, followed by the transport,
   followed by the base domain name.

   The components of the authentication chain are built by starting at
   the target record and its corresponding RRSIG.  Then traversing the
   DNS tree upwards towards the trust anchor zone (normally the DNS
   root), for each zone cut, the DS and DNSKEY RRsets and their
   signatures are added.

   In order to meet these formatting requirements, the server must
   perform some preprocessing on the resource records it receives.  It
   must first compute the uncompressed representation of the RRs,
   removing DNS name compression [RFC1035], if present.  It then
   extracts the relevant fields from the resource records and assembles
   them into an RRset.

5.  Caching and Regeneration of the Authentication Chain

   DNS records have Time To Live (TTL) parameters, and DNSSEC signatures
   have validity periods (specifically signature expiration times).
   After the TLS server constructs the serialized authentication chain,
   it can cache and reuse it in multiple TLS connection handshakes.
   However, it should keep track of the TTLs and signature validity
   periods, and requery the records and rebuild the authentication chain
   as needed.  A server implementation could carefully track these
   parameters and requery the chain correspondingly.  Alternatively, it
   could be configured to rebuild the chain at some predefined periodic
   interval that does not exceed the DNS TTLs or signature validity
   periods of the component records in the chain.

6.  Verification

   A TLS client making use of this specification, and which receives a
   DNSSEC authentication chain extension from a server, SHOULD use this
   information to perform DANE authentication of the server certificate.
   In order to do this, it uses the mechanism specified by the DNSSEC
   protocol [RFC4035].  This mechanism is sometimes implemented in a
   DNSSEC validation engine or library.

   If the authentication chain is correctly verified, the client then
   performs DANE authentication of the server according to the DANE TLS
   protocol [RFC6698], and the additional protocol requirements outlined
   in [DANEOPS].

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7.  Trust Anchor Maintenance

   The trust anchor may change periodically, e.g. when the operator of
   the trust anchor zone performs a DNSSEC key rollover.  Managed key
   rollovers typically use a process that can be tracked by verifiers
   allowing them to automatically update their trust anchors, as
   described in [RFC5011].  TLS clients using this specification are
   also expected to use such a mechanism to keep their trust anchors
   updated.  Some operating systems may have a system-wide service to
   maintain and keep up-to-date the root trust anchor.  It may be
   possible for the TLS client application to simply reference that as
   its trust anchor, periodically checking whether it has changed.

8.  Security Considerations

   The security considerations of the normatively referenced RFCs (1035,
   4034, 4035, 5246, 6066, 6698) all pertain to this extension.  Since
   the server is delivering a chain of DNS records and signatures to the
   client, it must take care to rebuild the chain in accordance with TTL
   and signature expiration of the chain components as described in
   Section 5.  TLS clients need roughly accurate time in order to
   properly authenticate these signatures.  This could be achieved by
   running a time synchronization protocol like NTP [RFC5905] or SNTP
   [RFC4330], which are already widely used today.  TLS clients must
   support a mechanism to track and rollover the trust anchor key as
   described in Section 7.

9.  IANA Considerations

   This extension requires the registration of a new value in the TLS
   ExtensionsType registry.  The value requested from IANA is 53.  If
   the draft is adopted by the WG, the authors expect to make an early
   allocation request as specified in [RFC7120].

10.  Acknowledgments

   Many thanks to Adam Langley for laying the groundwork for this
   extension.  The original idea is his but our acknowledgment in no way
   implies his endorsement.  This document also benefited from
   discussions with and review from the following people: Allison
   Mankin, Duane Wessels, Jeff Hodges, Patrick McManus, and Gowri
   Visweswaran.  We are particularly grateful to Viktor Dukhovni for his
   detailed review.

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11.  Test Vectors

   [TO BE ADDED LATER.  THE ORIGINAL CONTENT WAS OBSOLETE.]

12.  References

12.1.  Normative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, March 2005.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, March 2005.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC6066]  Eastlake, D., "Transport Layer Security (TLS) Extensions:
              Extension Definitions", RFC 6066, January 2011.

   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", RFC 6698, August 2012.

12.2.  Informative References

   [RFC4330]  Mills, D., "Simple Network Time Protocol (SNTP) Version 4
              for IPv4, IPv6 and OSI", RFC 4330, January 2006.

   [RFC5011]  StJohns, M., "Automated Updates of DNS Security (DNSSEC)
              Trust Anchors", STD 74, RFC 5011, September 2007.

   [RFC5905]  Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
              Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, June 2010.

   [RFC7120]  Cotton, M., "Early IANA Allocation of Standards Track Code
              Points", BCP 100, RFC 7120, January 2014.

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   [RFC7435]  Dukhovni, V., "Opportunistic Security: Some Protection
              Most of the Time", RFC 7435, December 2014.

   [AGL]      Langley, A., "Serializing DNS Records with DNSSEC
              Authentication", <https://tools.ietf.org/id/draft-agl-
              dane-serializechain-01.txt>.

   [DANESMTP]
              Dukhovni, V. and W. Hardaker, "SMTP Security via
              opportunistic DANE TLS", <https://tools.ietf.org/html/
              draft-ietf-dane-smtp-with-dane-19>.

   [DANEOPS]  Dukhovni, V., "Updates to and Operational Guidance for the
              DANE Protocol", <https://tools.ietf.org/html/draft-ietf-
              dane-ops>.

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Appendix A.  Pseudocode example

   [code goes here]

Appendix B.  Test vector

   [data go here]

Authors' Addresses

   Melinda Shore
   No Mountain Software

   EMail: melinda.shore@nomountain.net

   Richard Barnes
   Mozilla

   EMail: rlb@ipv.sx

   Shumon Huque
   Verisign Labs

   EMail: shuque@verisign.com

   Willem Toorop
   NLNet Labs

   EMail: willem@nlnetlabs.nl

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