<?xml version="1.0"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes"?>

<rfc ipr="full2026" docName="draft-ietf-ipseckey-rr-10.txt">

<front>
  <area>Security</area>
  <workgroup>IPSECKEY WG</workgroup>
  <title abbrev="Storing IPsec keying material in DNS">
     A Method for Storing IPsec Keying Material in DNS
  </title>

  <author initials="M." surname="Richardson" fullname="Michael C. Richardson">
    <organization abbrev="SSW">Sandelman Software Works</organization>
    <address>
      <postal>   
        <street>470 Dawson Avenue</street>
        <city>Ottawa</city>
        <region>ON</region>
        <code>K1Z 5V7</code>
        <country>CA</country>
      </postal>
      <email>mcr@sandelman.ottawa.on.ca</email>
      <uri>http://www.sandelman.ottawa.on.ca/</uri>
    </address>
  </author>

  <date month="March" year="2004" />

<abstract>
  <t>
This document describes a new resource record for the Domain Name System (DNS).
This record may be used to store public keys for use in IP security (IPsec)
systems. The record also includes provisions for indicating what system
should be contacted when establishing an IPsec tunnel with the entity in
question. 
</t>

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

</front>

<middle>

<section title="Introduction">
<t>
   Suppose we have a host which wishes to establish an IPsec tunnel
   with some remote entity on the network.  In many cases this end
   system will only know a DNS name for the remote entity (whether
   that DNS name be the name of the remote node, a DNS reverse tree
   name corresponding to the IP address of the remote node, or perhaps
   a the domain name portion of a "user@FQDN" name for a remote
   entity).  In these cases the host will need to obtain a public key
   in order to authenticate the remote entity, and may also need some
   guidance about whether it should contact the entity directly or use
   another node as a gateway to the target entity.
</t>
<t>
  The IPSECKEY RR provides a storage mechanism for such data as the public
key and the gateway information.
</t>
<t>
   The type number for the IPSECKEY RR is TBD.
</t>

<section title="Overview">
<t>
   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).
</t>

<t>
      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 <xref target="RFC2119" />.
</t>
</section>

<section title="Use of DNS address-to-name maps (IN-ADDR.ARPA and IP6.ARPA)">
<t>
   Often a security gateway will only have access to the IP address of
   the node with which communication is desired, and will not know any
   other name for the target node.  Because of this, it will
   frequently be the case that the best way of looking up IPSECKEY RRs
   will be by using the IP address as an index into one of the reverse
   mapping trees (IN-ADDR.ARPA for IPv4 or IP6.ARPA for IPv6).
</t>

<t>
The lookup is done in the usual fashion as for PTR records. The IP address'
octets (IPv4) or nibbles (IPv6) are reversed and looked up with the
appropriate suffix. Any CNAMEs or DNAMEs found MUST be followed.
</t>

<t>
Note: even when the IPsec function is the end-host, often only the application 
will know the forward name used. While the case where the application knows
the forward name is common, the user could easily have typed in a literal IP
address. This storage mechanism does not preclude using the forward name
when it is available, but does not require it.
</t>
</section>

<section title="Usage Criteria">
<t>
   An IPSECKEY resource record SHOULD be used in combination with DNSSEC
unless some other means of authenticating the IPSECKEY resource record
is available.
</t>

<t>  
   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.

</t>

<t>
   This resource record is class independent.
</t>
</section>
</section>

<section title="Storage formats">

<section title="IPSECKEY RDATA format">

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

<artwork><![CDATA[
    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                           /
   /                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
]]></artwork>
</section>

<section title="RDATA format - precedence">
<t>
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 <xref target="RFC1035" />. 
</t>
<t>
Gateways listed in IPSECKEY records with  lower precedence are
to be attempted first. Where there is a tie in precedence, the order
should be non-deterministic.
</t>
</section>

<section anchor="gatewaytype" title="RDATA format - gateway type">
<t>
The gateway type field indicates the format of the information that
is stored in the gateway field.
</t>

<t>
The following values are defined:
  <list style="hanging">
  <t hangText="0">No gateway is present</t>
  <t hangText="1">A 4-byte IPv4 address is present</t>
  <t hangText="2">A 16-byte IPv6 address is present</t>
  <t hangText="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. (see section 3.3 of RFC1035 <xref target="RFC1035" />).
</t>
  </list>
</t>

</section>

<section anchor="algotype" title="RDATA format - algorithm type">
<t>
The algorithm type field identifies the public key's cryptographic
algorithm and determines the format of the public key field.  
</t>

<t>
A value of 0 indicates that no key is present.
</t>

<t>
The following values are defined:
  <list style="hanging">
  <t hangText="1">A DSA key is present, in the format defined in RFC2536 <xref target="RFC2536" /></t>
  <t hangText="2">A RSA key is present, in the format defined in RFC3110 <xref target="RFC3110" /></t>
  </list>
</t>

</section>

<section title="RDATA format - gateway">
<t>
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.
</t>
<t>
There are three formats:
</t>

<t>
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
<xref target="RFC1035">RFC1035</xref>.  This is a 32-bit number in network byte order.
</t>

<t>A 128-bit IPv6 address is present in the gateway field.
The data portion is an IPv6 address as described in section 2.2 of
<xref target="RFC3596">RFC3596</xref>. This is a 128-bit number in network byte order. 
</t>

<t>
The gateway field is a normal wire-encoded domain name, as described
in section 3.3 of RFC1035 <xref target="RFC1035" />. Compression MUST NOT be used. 
</t>

</section>

<section title="RDATA format - public keys">
<t>
Both of the public key types defined in this document (RSA and DSA)
inherit their public key formats from the corresponding KEY RR formats. 
Specifically, the public key field contains the algorithm-specific
portion of the KEY RR RDATA, which is all of the KEY RR DATA after the
first four octets.  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 for IPSECKEY RR.
</t>

<t>
Future algorithms, if they are to be used by both DNSSEC (in the KEY
RR) and IPSECKEY, are likely to use the same public key encodings in
both records.  Unless otherwise specified, the IPSECKEY public key
field will contain the algorithm-specific portion of the KEY RR RDATA
for the corresponding algorithm.  The algorithm must still be
designated for use by IPSECKEY, and an IPSECKEY algorithm type number
(which might be different than the DNSSEC algorithm number) must be
assigned to it.
</t>

<t>The DSA key format is defined in RFC2536 <xref target="RFC2536" /></t>.

<t>The RSA key format is defined in RFC3110 <xref target="RFC3110" />,
with the following changes:</t>

<t>
The earlier definition of RSA/MD5 in RFC2065 limited the exponent and
modulus to 2552 bits in length.  RFC3110 extended that limit to 4096
bits for RSA/SHA1 keys.  The IPSECKEY RR imposes no length limit on
RSA 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. 
</t>

</section>

</section>



<section title="Presentation formats">

<section title="Representation of IPSECKEY RRs">
<t>
   IPSECKEY RRs may appear 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.
</t>
<t>
   The algorithm field is an unsigned integer. No mnemonics are defined.
</t>
<t>
   If no gateway is to be indicated, then the gateway type field MUST
   be zero, and the gateway field MUST be "."
</t>

<t>
   The Public Key field is represented as a Base64 encoding of the
   Public Key.  Whitespace is allowed within the Base64 text.  For a
   definition of Base64 encoding, see
<xref target="RFC3548">RFC3548</xref> Section 5.2.
</t>

   
<t>
   The general presentation for the record as as follows:
<artwork><![CDATA[
IN     IPSECKEY ( precedence gateway-type algorithm
                  gateway base64-encoded-public-key )
]]></artwork>
</t>
</section>


<section title="Examples">
<t> 
An example of a node 192.0.2.38 that will accept IPsec tunnels on its
own behalf.
<artwork><![CDATA[
38.2.0.192.in-addr.arpa. 7200 IN     IPSECKEY ( 10 1 2 
                 192.0.2.38
                 AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )
]]></artwork>
</t>

<t> 
An example of a node, 192.0.2.38 that has published its key only.
<artwork><![CDATA[
38.2.0.192.in-addr.arpa. 7200 IN     IPSECKEY ( 10 0 2
                 .
                 AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )
]]></artwork>
</t>

<t> 
An example of a node, 192.0.2.38 that has delegated authority to the node
192.0.2.3.
<artwork><![CDATA[
38.2.0.192.in-addr.arpa. 7200 IN     IPSECKEY ( 10 1 2
                 192.0.2.3
                 AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )
]]></artwork>
</t>

<t> 
An example of a node, 192.0.1.38 that has delegated authority to the node
with the identity "mygateway.example.com".
<artwork><![CDATA[
38.1.0.192.in-addr.arpa. 7200 IN     IPSECKEY ( 10 3 2
                 mygateway.example.com.
                 AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )
]]></artwork>
</t>

<t> 
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
<artwork><![CDATA[
$ORIGIN 1.0.0.0.0.0.2.8.B.D.0.1.0.0.2.ip6.arpa.
0.d.4.0.3.0.e.f.f.f.3.f.0.1.2.0 7200 IN     IPSECKEY ( 10 2 2
                 2001:0DB8:0:8002::2000:1
                 AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )
]]></artwork>
</t>

</section>
</section>

<section title="Security Considerations">
<t>
   This entire memo pertains to the provision of public keying material
   for use by key management protocols such as ISAKMP/IKE (RFC2407)
   <xref target="RFC2407" />.
</t>

<t>
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.
</t>

<t>
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.
</t>

<t>
   Any derivative specification that makes use 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.
</t>

<section title="Active attacks against unsecured IPSECKEY resource records">
<t>
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.
</t>

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

<t>
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.  
</t>

<t>
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. 
</t>

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

<t>
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. 
</t>

<t>
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. In some
cases, the attacker may be able to accomplish the full intercept by use
of Network Addresss/Port Translation (NAT/NAPT) technology.
</t>

<t>
Note that risk of a man-in-the-middle attack mediated by the IPSECKEY
RR only applies to cases where the gateway field of the IPSECKEY RR
indicates a different entity than the owner name of the IPSECKEY RR.
</t>
<t>
An active attack on the DNS that caused the wrong IP address to be retrieved
(via forged address), and therefore the wrong QNAME to be queried would also
result in a man-in-the-middle attack. This situation exists independantly
of whether or not the IPSECKEY RR is used.
</t>

<t>
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.
</t>
</section>

</section>

<section title="IANA Considerations">
<t>
This document updates the IANA Registry for DNS Resource Record Types
by assigning type X to the IPSECKEY record.  
</t>

<t>
This document creates two new IANA registries, both specific to the
IPSECKEY Resource Record:
</t>

<t>
This document creates an IANA registry for the algorithm type field.
</t>
<t>
Values 0, 1 and 2 are defined in <xref target="algotype" />. Algorithm numbers
3 through 255 can be assigned by IETF Consensus (<xref target="RFC2434">see RFC2434</xref>).
</t>

<t>
This document creates an IANA registry for the gateway type field.
</t>
<t>
Values 0, 1, 2 and 3 are defined in <xref target="gatewaytype" />.
Gateway type numbers 4 through 255 can be assigned by
Standards Action (<xref target="RFC2434">see RFC2434</xref>).
</t>



</section>

<section title="Intellectual Property Claims">
<t>
The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.
</t>

<t>
   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.
</t>
</section>


<section title="Acknowledgments">
<t>
My thanks to Paul Hoffman, Sam Weiler, Jean-Jacques Puig, Rob Austein,
and Olafur Gurmundsson who reviewed this document carefully.
Additional thanks to Olafur Gurmundsson for a reference implementation.
</t>
</section>

</middle>

<back>
<references title="Normative references">
<!-- DNSSEC -->
<?rfc include="reference.RFC.1034" ?>
<?rfc include="reference.RFC.1035" ?>
<?rfc include="reference.RFC.2026" ?>
<?rfc include="reference.RFC.2065" ?>
<?rfc include="reference.RFC.2434" ?>
<?rfc include="reference.RFC.3548" ?>
</references>

<references title="Non-normative references">
<?rfc include="reference.RFC.2119" ?>
<?rfc include="reference.RFC.2407" ?>
<?rfc include="reference.RFC.2535" ?>
<?rfc include="reference.RFC.2536" ?>
<?rfc include="reference.RFC.3110" ?>
<?rfc include="reference.RFC.3445" ?>
<?rfc include="reference.RFC.3596" ?>
</references>
</back>
</rfc>
<!--
  $Id: draft-richardson-ipsec-rr.xml,v 1.24 2004/03/25 16:18:34 mcr Exp $

  $Log: draft-richardson-ipsec-rr.xml,v $
  Revision 1.24  2004/03/25 16:18:34  mcr
  	new revisions to IPSECKEY.

  Revision 1.23  2003/09/04 23:26:09  mcr
  	more nits.

  Revision 1.22  2003/08/16 15:55:35  mcr
  	fixed version to -06.

  Revision 1.21  2003/08/16 15:52:32  mcr
  	Sam's comments on IANA considerations.

  Revision 1.20  2003/07/27 22:57:54  mcr
  	updated document with new text about a seperate registry
  	for the algorithm type.

  Revision 1.19  2003/06/30 01:51:50  mcr
  	minor typo fixes.

  Revision 1.18  2003/06/16 17:45:00  mcr
  	adjusted date on rev-04.

  Revision 1.17  2003/06/16 17:41:30  mcr
  	revision -04

  Revision 1.16  2003/06/16 17:39:20  mcr
  	adjusted typos, and adjusted IANA considerations.

  Revision 1.15  2003/05/26 19:31:23  mcr
  	updates to drafts - IPSEC RR - SC versions, and RFC3526
  	reference in OE draft.

  Revision 1.14  2003/05/23 13:57:40  mcr
  	updated draft ##.

  Revision 1.13  2003/05/23 13:54:45  mcr
  	updated month on draft.

  Revision 1.12  2003/05/21 15:42:49  mcr
  	new SC section with comments from Rob Austein.

  Revision 1.11  2003/05/20 20:52:22  mcr
  	new security considerations section.

  Revision 1.10  2003/05/20 19:07:47  mcr
  	rewrote Security Considerations.

  Revision 1.9  2003/05/20 18:17:09  mcr
  	nits from Rob Austein.

  Revision 1.8  2003/04/29 00:44:59  mcr
  	updates according to WG consensus: restored three-way
  	gateway field type.

  Revision 1.7  2003/03/30 17:00:29  mcr
  	updates according to community feedback.

  Revision 1.6  2003/03/19 02:20:24  mcr
  	updated draft based upon comments from working group

  Revision 1.5  2003/02/23 22:39:22  mcr
  	updates to IPSECKEY draft.

  Revision 1.4  2003/02/21 04:39:04  mcr
  	updated drafts, and added crosscompile.html

  Revision 1.3  2003/01/17 16:26:34  mcr
  	updated IPSEC KEY draft with restrictions.

  Revision 1.2  2002/08/26 18:20:54  mcr
  	updated documents

  Revision 1.1  2002/08/10 20:05:33  mcr
  	document proposing IPSECKEY Resource Record


!>
