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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 4025

IPSECKEY WG                                                M. Richardson
Internet-Draft                                                       SSW
Expires: December 15, 2003                                 June 16, 2003


           A method for storing IPsec keying material in DNS.
                     draft-ietf-ipseckey-rr-04.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Drafts.

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   This Internet-Draft will expire on December 15, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document describes a new resource record for DNS.  This record
   may be used to store public keys for use in IPsec systems.

   This record replaces the functionality of the sub-type #1 of the KEY
   Resource Record, which has been obsoleted by RFC3445.










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Table of Contents

   1.    Introduction . . . . . . . . . . . . . . . . . . . . . . . .  3
   1.1   Overview . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.    Storage formats  . . . . . . . . . . . . . . . . . . . . . .  4
   2.1   IPSECKEY RDATA format  . . . . . . . . . . . . . . . . . . .  4
   2.2   RDATA format - precedence  . . . . . . . . . . . . . . . . .  4
   2.3   RDATA format - algorithm type  . . . . . . . . . . . . . . .  4
   2.4   RDATA format - gateway type  . . . . . . . . . . . . . . . .  5
   2.5   RDATA format - gateway . . . . . . . . . . . . . . . . . . .  5
   2.6   RDATA format - public keys . . . . . . . . . . . . . . . . .  5
   2.6.1 Example: RSA public keys . . . . . . . . . . . . . . . . . .  6
   3.    Presentation formats . . . . . . . . . . . . . . . . . . . .  7
   3.1   Representation of IPSECKEY RRs . . . . . . . . . . . . . . .  7
   3.2   Examples . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   4.    Security Considerations  . . . . . . . . . . . . . . . . . .  9
   4.1   Active attacks against unsecured IPSECKEY resource records .  9
   5.    IANA Considerations  . . . . . . . . . . . . . . . . . . . . 11
   6.    Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . 12
         Normative references . . . . . . . . . . . . . . . . . . . . 13
         Non-normative references . . . . . . . . . . . . . . . . . . 14
         Author's Address . . . . . . . . . . . . . . . . . . . . . . 14
         Full Copyright Statement . . . . . . . . . . . . . . . . . . 15




























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1. Introduction

   The type number for the IPSECKEY RR is TBD.

1.1 Overview

   The IPSECKEY resource record (RR) is used to publish a public key
   that is to be associated with a Domain Name System (DNS) name for use
   with the IPsec protocol suite.  This can be the  public key of a
   host, network, or application (in the case of per-port keying).

   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 [6].

   An IPSECKEY resource record SHOULD be used in combination with DNSSEC
   unless some other means of authenticating the IPSECKEY resource
   record is available.

   It is expected that there will often be multiple IPSECKEY resource
   records at the same name.  This will be due to the presence of
   multiple gateways and the need to rollover keys.

   This resource record is class independent.



























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2. Storage formats

2.1 IPSECKEY RDATA format

   The RDATA for an IPSECKEY RR consists of a precedence value, a public
   key, algorithm type, and an optional gateway address.

       0                   1                   2                   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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  precedence   | gateway type  |  algorithm  |     gateway     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------+                 +
      ~                            gateway                            ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               /
      /                          public key                           /
      /                                                               /
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|


2.2 RDATA format - precedence

   This is an 8-bit precedence for this record.  This is interpreted in
   the same way as the PREFERENCE field described in section 3.3.9 of
   RFC1035 [2].

   Gateways listed in IPSECKEY records records with  lower precedence
   are to be attempted first.  Where there is a tie in precedence, the
   order should be non-deterministic.

2.3 RDATA format - algorithm type

   RFC2535 established an IANA registry for DNS Security Algorithm
   Numbers, and subsequent documents have specified algorithms and
   associated KEY RR formats for use with DNSSEC.  Rather than respecify
   those formats, this document reuses that registry and the associated
   KEY RR formats.

   The algorithm type field identifies the public key's cryptographic
   algorithm and determines the format of the public key field.

   The public key field contains the algorithm-specific portion of the
   KEY RR RDATA, omitting the first four octets of the KEY RR RDATA.
   This is the same portion of the KEY RR that must be specified by
   documents that define a DNSSEC algorithm.  Those documents also
   specify a message digest to be used for generation of SIG RRs; that
   specification is not relevant to the IPSECKEY usage of the public key
   format.



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   A value of 0 indicates that no key is present.

   The following values defined by IANA are legal:

   3  A DSA key is present, in the format defined in RFC2536 [9]

   5  A RSA key is present, in the format defined in RFC3110 [10]


2.4 RDATA format - gateway type

   The gateway type field indicates the format of the information that
   is stored in the gateway field.

   The following values are defined:

   0  No gateway is present

   1  A 4-byte IPv4 address is present

   2  A 16-byte IPv6 address is present

   3  A wire-encoded domain name is present.  The wire-encoded format is
      self-describing, so the length is implicit.  The domain name MUST
      NOT be compressed.


2.5 RDATA format - gateway

   The gateway field indicates a gateway to which an IPsec tunnel may be
   created in order to reach the entity named by this resource record.

   There are three formats:

   A 32-bit IPv4 address is present in the gateway field.  The data
   portion is an IPv4 address as described in section 3.4.1 of RFC1035
   [2].  This is a 32-bit number in network byte order.

   A 128-bit IPv6 address is present in the gateway field.  The data
   portion is an IPv6 address as described in section 3.2 of RFC1886
   [5].  This is a 128-bit number in network byte order.

   The gateway field is a normal wire-encoded domain name, as described
   in section 3.3 of RFC1035 [2].

2.6 RDATA format - public keys

   There are two defined public key formats: RSA and DSA.  No other



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   types are supported.

2.6.1 Example: RSA public keys

   Per the DNS Security Algorithm registry, an algorithm type of 5
   identifies an RSA public key, encoded as described in section 2 of
   RFC3110.  [The encoding of RSA/MD5 KEYs (type 1) specified in RFC2537
   is the same as that defined in RFC3110.  For simplicity and in
   keeping with RSA/MD5 being NOT RECOMMENDED for DNSSEC, type 1 SHOULD
   NOT be used in the IPSECKEY algorithm type.]

   The earlier definition of RSA/MD5 (algorithm type 1) in RFC2065
   limited the exponent and modulus to 2552 bits in length.  RFC3110
   extended that limit to 4096 bits for RSA/SHA1 keys (type 5).  The
   IPSECKEY RR imposes no length limit on type 5 public keys, other than
   the 65535 octet limit imposed by the two-octet length encoding.  This
   length extension is applicable only to IPSECKEY and not to KEY RRs.


































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3. Presentation formats

3.1 Representation of IPSECKEY RRs

   IPSECKEY RRs may appears in a zone data master file.  The precedence,
   gateway type and algorithm and gateway fields are REQUIRED.  The
   base64 encoded public key block is OPTIONAL; if not present, then the
   public key field of the resource record MUST be construed as being
   zero octets in length.

   If no gateway is to be indicated, then the gateway type field MUST be
   zero, and the gateway field MUST be "."

   IN     IPSECKEY ( precedence gateway-type algorithm
                     gateway base64-encoded-public-key )


3.2 Examples

   An example of a node 192.0.2.38 that will accept IPsec tunnels on its
   own behalf.

   38.2.0.192.in-addr.arpa. 7200 IN     IPSECKEY ( 10 1 5
                    192.0.2.38
                    AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )

   An example of a node, 192.0.2.38 that has published its key only.

   38.2.0.192.in-addr.arpa. 7200 IN     IPSECKEY ( 10 0 5
                    .
                    AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )

   An example of a node, 192.0.2.38 that has delegated authority to the
   node 192.0.2.3.

   38.2.0.192.in-addr.arpa. 7200 IN     IPSECKEY ( 10 1 5
                    192.0.2.3
                    AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )

   An example of a node, 192.0.1.38 that has delegated authority to the
   node with the identity "mygateway.example.com".

   38.1.0.192.in-addr.arpa. 7200 IN     IPSECKEY ( 10 3 5
                    mygateway.example.com.
                    AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )

   An example of a node, 2001:0DB8:0200:1:210:f3ff:fe03:4d0 that has
   delegated authority to the node 2001:0DB8:c000:0200:2::1



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   $ORIGIN 1.0.0.0.0.0.2.8.B.D.0.1.0.0.2.ip6.int.
   0.d.4.0.3.0.e.f.f.f.3.f.0.1.2.0 7200 IN     IPSECKEY ( 10 2 5
                    2001:0DB8:0:8002::2000:1
                    AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )















































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4. Security Considerations

   This entire memo pertains to the provision of public keying material
   for use by key management protocols such as ISAKMP/IKE (RFC2407) [7].

   The IPSECKEY resource record contains information that SHOULD be
   communicated to the end client in an integral fashion - i.e.  free
   from modification.  The form of this channel is up to the consumer of
   the data - there must be a trust relationship between the end
   consumer of this resource record and the server.  This relationship
   may be end-to-end DNSSEC validation, a TSIG or SIG(0) channel to
   another secure source, a secure local channel on the host, or some
   combination of the above.

   The keying material provided by the IPSECKEY resource record is not
   sensitive to passive attacks.  The keying material may be freely
   disclosed to any party without any impact on the security properties
   of the resulting IPsec session: IPsec and IKE provide for defense
   against both active and passive attacks.

   Any user of this resource record MUST carefully document their trust
   model, and why the trust model of DNSSEC is appropriate, if that is
   the secure channel used.

4.1 Active attacks against unsecured IPSECKEY resource records

   This section deals with active attacks against the DNS.  These
   attacks require that DNS requests and responses be intercepted and
   changed.  DNSSEC is designed to defend against attacks of this kind.

   The first kind of active attack is when the attacker replaces the
   keying material with either a key under its control or with garbage.

   If the attacker is not able to mount a subsequent man-in-the-middle
   attack on the IKE negotiation after replacing the public key, then
   this will result in a denial of service, as the authenticator used by
   IKE would fail.

   If the attacker is able to both to mount active attacks against DNS
   and is also in a position to perform a man-in-the-middle attack on
   IKE and IPsec negotiations, then the attacker will be in a position
   to compromise the resulting IPsec channel.  Note that an attacker
   must be able to perform active DNS attacks on both sides of the IKE
   negotiation in order for this to succeed.

   The second kind of active attack is one in which the attacker
   replaces the the gateway address to point to a node under the
   attacker's control.  The attacker can then either replace the public



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   key or remove it, thus providing an IPSECKEY record of its own to
   match the gateway address.

   This later form creates a simple man-in-the-middle since the attacker
   can then create a second tunnel to the real destination.  Note that,
   as before, this requires that the attacker also mount an active
   attack against the responder.

   Note that the man-in-the-middle can not just forward cleartext
   packets to the original destination.  While the destination may be
   willing to speak in the clear, replying to the original sender, the
   sender will have already created a policy expecting ciphertext.
   Thus, the attacker will need to intercept traffic from both sides.

   Note that the danger here only applies to cases where the gateway
   field of the IPSECKEY RR indicates a different entity than the owner
   name of the IPSECKEY RR.  In cases where the end-to-end integrity of
   the IPSECKEY RR is suspect, the end client MUST restrict its use of
   the IPSECKEY RR to cases where the RR owner name matches the content
   of the gateway field.































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5. IANA Considerations

   This document updates the IANA Registry for DNS Resource Record Types
   by assigning type X to the IPSECKEY record.

   The values for the algorithm type field in the IPSECKEY record are
   inherited from the DNS Security Algorithm Numbers registry, and this
   document makes no changes to that registry.











































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6. Acknowledgments

   My thanks to Paul Hoffman, Sam Weiler, Jean-Jacques Puig, and Olafur
   Gurmundsson who reviewed this document carefully.  Additional thanks
   to Olafur Gurmundsson for a reference implementation.














































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Normative references

   [1]  Mockapetris, P., "Domain names - concepts and facilities", STD
        13, RFC 1034, November 1987.

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

   [3]  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
        9, RFC 2026, October 1996.

   [4]  Eastlake, D. and C. Kaufman, "Domain Name System Security
        Extensions", RFC 2065, January 1997.






































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Non-normative references

   [5]   Thomson, S. and C. Huitema, "DNS Extensions to support IP
         version 6", RFC 1886, December 1995.

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

   [7]   Piper, D., "The Internet IP Security Domain of Interpretation
         for ISAKMP", RFC 2407, November 1998.

   [8]   Eastlake, D., "Domain Name System Security Extensions", RFC
         2535, March 1999.

   [9]   Eastlake, D., "DSA KEYs and SIGs in the Domain Name System
         (DNS)", RFC 2536, March 1999.

   [10]  Eastlake, D., "RSA/SHA-1 SIGs and RSA KEYs in the Domain Name
         System (DNS)", RFC 3110, May 2001.

   [11]  Massey, D. and S. Rose, "Limiting the Scope of the KEY Resource
         Record (RR)", RFC 3445, December 2002.


Author's Address

   Michael C. Richardson
   Sandelman Software Works
   470 Dawson Avenue
   Ottawa, ON  K1Z 5V7
   CA

   EMail: mcr@sandelman.ottawa.on.ca
   URI:   http://www.sandelman.ottawa.on.ca/

















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Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
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   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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