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Versions: 00

Network Working Group                                           D. Zhang
Internet-Draft                                                    Huawei
Intended status: Experimental                              July 22, 2014
Expires: January 23, 2015


  Certificate Transparency for Domain Name System Security Extensions
                     draft-zhang-ct-dnssec-trans-00

Abstract

   In draft-ietf-trans-rfc6962-bis, a solution is proposed for publicly
   logging the existence of Transport Layer Security (TLS) certificates
   using Merkle Hash Trees.  This document tries to use this idea in
   DNSSEC and publicly logging the existence of keys used in securing
   DNS resource records.

Requirements Language

   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 RFC 2119 [RFC2119].

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 http://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 January 23, 2015.

Copyright Notice

   Copyright (c) 2014 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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Cryptographic Components  of Certificate Transparency . . . .   3
   3.  Log Format and Operation  . . . . . . . . . . . . . . . . . .   3
     3.1.  Log Entries . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Including the Signed Certificate Timestamp into DNS Security
       Extensions  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  SCT RR  . . . . . . . . . . . . . . . . . . . . . . . . .   4
       4.1.1.  The Key Tag Field . . . . . . . . . . . . . . . . . .   4
       4.1.2.  The Algorithm Field . . . . . . . . . . . . . . . . .   5
       4.1.3.  The Digest Type Field . . . . . . . . . . . . . . . .   5
       4.1.4.  The Digest Field  . . . . . . . . . . . . . . . . . .   5
       4.1.5.  The SCT Field . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Operations  . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
     6.1.  Logging other types of RRs  . . . . . . . . . . . . . . .   6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   [I-D.ietf-trans-rfc6962-bis] specifies a Certificate Transparency
   (CT) mechanism to disclosing TLS certificates into public logs so as
   to benefit the public to monitor the operations in issuing
   certificates.  The logs do not prevent mis-issuing behavior, but the
   provided public audibility can increase the possibility in detecting
   certain mis-behaviors of issuers.  The logs are constructed with
   Merkle Hash Trees to ensure the append-only property, and thus enable
   anyone to verify the correctness of each log and to monitor when new
   certificates are added to it.  Note that CT is a common mechanism
   although [I-D.ietf-trans-rfc6962-bis] only describe its usage in
   publishing TLS server certificates issued by public certificate
   authorities (CAs).

   This document discusses the application of CT to publicly logging the
   public keys used by DNSSEC.  DNSSEC distributes public keys to
   provide origin authentication and integrity protection for DNS
   resource records.  In order to prove the validity of keys used for



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   signing DNS data, DNSSEC uses DNS public key (DNSKEY) RRsets and
   Delegation Signer (DS) RRsets to form authentication chains for the
   signed data, with each link in the chains vouching for the next.  If
   an authentication chain can be eventually connected to the a trsuted
   public key, the client can then ensure the key for signing the data
   is valid.

   The application of CT to publish the existence of (DNSKEY) RRsets and
   (DS) RRsets can benefit the detection of misissurance of DNSSEC keys.
   For instance, if the owner of foo.example.com finds that its parent
   zone (example.com) publish a DS RR for its zone which however does
   not point to any legal zone signing keys or key signing keys, the
   owner can claim that a mississuance event occures.

   This work re-use some text in [I-D.ietf-trans-rfc6962-bis].

2.  Cryptographic Components of Certificate Transparency

   The introduce of cryptographic components of CT is in Section 2 of
   [I-D.ietf-trans-rfc6962-bis].  When applying CT for NDSSEC, a log is
   a single, ever-growing, append-only Merkle Tree of DNSKEY and DS RRs.

3.  Log Format and Operation

   When generating a new DNSKEY RR or a DS RR (i.e., during the
   publication of a KSK or a zone authentication key), a zone owner will
   publish the RR to the CT logs.  Because a key will not be trusted by
   clients unless logged, it is expected that a zone owner will usually
   deliver the RRs (keys) for audit purposes.

   Identical to what is specified in [I-D.ietf-trans-rfc6962-bis],when a
   valid DNSKEY RR or a valid DS RR is submitted to a log, the log MUST
   immediately return a Signed Certificate Timestamp (SCT).  The SCT is
   the log's promise to incorporate the RR in the Merkle Tree within a
   fixed amount of time known as the Maximum Merge Delay (MMD).  If the
   log has previously seen the certificate, it MAY return the same SCT
   as it returned before.  DNS servers MUST provide an SCT from one or
   more logs to the client within a SCT RR.  DNS clients MUST NOT trust
   a key that does not have a valid SCT.

3.1.  Log Entries

   A zone owner can submit a DNSKEY or DS RR to any log before
   publishing the RR.  In order to enable attribution of each logged RR
   to its issuer, the log SHALL publish a list of acceptable zone
   signing public keys (or hashes of public keys) of root zones or
   islands of security.  Each submitted RR MUST be accompanied by all
   additional RRs (DNSKEY RRs, DS RRs, and RRSIG RRs) which construct an



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   authentication chain to an accepted root public key.  Note that the
   NSEC RR is not provided since the existence of this type of RR
   indicates the broken of an authentication chain.

   A typical authentication chain is Public
   Key->[DS->(DNSKEY)*->DNSKEY]*->RRset, where "*" denotes zero or more
   subchains.  (DNSKEY)* indicates that DNSSEC permits additional layers
   of DNSKEY RRs signing other DNSKEY RRs within a zone.  Each DNSKEY/DS
   RR in the chain is authenticated by a RRSIG RR.  In practice, a RRSIG
   RR may be used to sign a DS/DNSKEY RRset rather than a single RR.  In
   this case, not only the DS/DNSKEY RR on the authentication chain but
   also other records in the RRset SHOULD be provided to the log the
   verification purpose.  Otherwise, the log may have to consult DNS
   again in order to verify the authentication chains.

4.  Including the Signed Certificate Timestamp into DNS Security
    Extensions

4.1.  SCT RR

   The SCT associated with a DNSKEY/ DS RR is stored within a STC RR.

   The type number for the DS record is TBD1.

   The DS resource record is class independent.

   The DS RR has no special TTL requirements.

                           1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Key Tag             |  Algorithm    |  Digest Type  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                                                               /
      /                            Digest                             /
      /                                                               /
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /                                                               /
      /                              STC                              /
      /                                                               /
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.1.1.  The Key Tag Field

   The Key Tag field lists the key tag of the DNSKEY RR referred to by
   the SCT record, in network byte order.  Appendix B of [RFC4034]
   describes how to compute a Key Tag.




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4.1.2.  The Algorithm Field

   The Algorithm field lists the algorithm number of the DNSKEY RR
   referred to by the SCT record.  Appendix A.1 of [RFC4034] lists the
   algorithm number types.

4.1.3.  The Digest Type Field

   The Digest Type field identifies the algorithm used to construct the
   digest used to identify the DNSKEY RR that the SCT RR refers to.
   Appendix A.2 of [RFC4034] lists the possible digest algorithm types.

4.1.4.  The Digest Field

   The method of calculating digest is identical to what is specified in
   Section 5.1.4 of [RFC4034]

4.1.5.  The SCT Field

   This field contains the SCT got from the log.

4.2.  Operations

   After introducing the SCT RR, the verification procedures of DNS data
   specified in DNSSEC[RFC4305] do not change a lot.  However, the
   correctness of CTS needs to be assessed during checking the validity
   of a NDSKEY/DS RR.

   A NDSKEY/DS RR needs to be associated with a CTS RR which contains a
   valid CTS and signed with a proper public key.  Otherwise, the
   NDSKEY/DS RR will not be used to construct the authentication chain.
   The signatures of NDSKEY/DS RR and its CTS RR should be stored in
   different RRSIG RR respectively.  In addition, a DNS server will
   sends CTS RRs and the associated RRSIG RRs to a resolver only when it
   indicates the support of CT in the request.

5.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.

6.  Security Considerations







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6.1.  Logging other types of RRs

   The above section tries to propose a solution to disclose keys for
   DNSSEC in logs for the public to audit.  However, it may be valuable
   to also log the RRs specified in [RFC1035].  For instance, assume
   there is an attacker which has compromised the zone authentication
   key and is able to perform the MITM attack between a resolver and the
   DNS server of the zone.  It is possible for an attacker to transfer a
   forged RR which is signed with the compromised key.  The current
   solution cannot benefit the detection of this attack in this
   scenario.  However, if the RR is also required to be uploaded to
   public logs, the condition is changed.  If the attacker does not
   publish the RR to a log, it cannot get the SCT.  When the attacker
   tries to publish the RR to the log, the owner of the zone may detect
   the problem even if the attacker can provide keys to convince the log
   to accept the RR.

7.  Acknowledgements

8.  Normative References

   [I-D.ietf-trans-rfc6962-bis]
              Laurie, B., Langley, A., Kasper, E., and R. Stradling,
              "Certificate Transparency", draft-ietf-trans-
              rfc6962-bis-04 (work in progress), July 2014.

   [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.

   [RFC4305]  Eastlake, D., "Cryptographic Algorithm Implementation
              Requirements for Encapsulating Security Payload (ESP) and
              Authentication Header (AH)", RFC 4305, December 2005.

Author's Address

   Dacheng Zhang
   Huawei

   Email: zhangdacheng@huawei.com





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