IPSECKEY WG M. Richardson
Internet-Draft SSW
Expires: March 4, 2004 September 4, 2003
A method for storing IPsec keying material in DNS.
draft-ietf-ipseckey-rr-07.txt
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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
1.2 Usage Criteria . . . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . 4
2.5 RDATA format - gateway . . . . . . . . . . . . . . . . . . . . 5
2.6 RDATA format - public keys . . . . . . . . . . . . . . . . . . 5
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 [8].
1.2 Usage Criteria
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 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
The algorithm type field identifies the public key's cryptographic
algorithm and determines the format of the public key field.
A value of 0 indicates that no key is present.
The following values are defined:
1 A DSA key is present, in the format defined in RFC2536 [11]
2 A RSA key is present, in the format defined in RFC3110 [12]
2.4 RDATA format - gateway type
The gateway type field indicates the format of the information that
is stored in the gateway field.
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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 2.2 of RFC1886
[7]. 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]. Compression MUST NOT be used.
2.6 RDATA format - public keys
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.
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
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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.
The DSA key format is defined in RFC2536 [11]
The RSA key format is defined in RFC3110 [12], with the following
changes:
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.
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3. Presentation formats
3.1 Representation of IPSECKEY RRs
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.
The algorithm field is an unsigned integer. No mnemonics are
defined.
If no gateway is to be indicated, then the gateway type field MUST be
zero, and the gateway field MUST be "."
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 RFC1521 [3] Section 5.2.
The general presentation for the record as as follows:
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 2
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 2
.
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 2
192.0.2.3
AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )
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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 2
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
$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 2
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) [9].
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.
In some cases, the attacker may be able to accomplish the full
intercept by use of Network Addresss/Port Translation (NAT/NAPT)
technology.
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.
This document creates an IANA registry for the algorithm type field.
Values 0, 1 and 2 are defined in Section 2.3. Algorithm numbers 3
through 255 can be assigned by IETF Consensus (see RFC2434 [6]).
This document creates an IANA registry for the gateway type field.
Values 0, 1, 2 and 3 are defined in Section 2.4. Algorithm numbers 4
through 255 can be assigned by Standards Action (see RFC2434 [6]).
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6. Acknowledgments
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.
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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] Borenstein, N. and N. Freed, "MIME (Multipurpose Internet Mail
Extensions) Part One: Mechanisms for Specifying and Describing
the Format of Internet Message Bodies", RFC 1521, September
1993.
[4] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
[5] Eastlake, D. and C. Kaufman, "Domain Name System Security
Extensions", RFC 2065, January 1997.
[6] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
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Non-normative references
[7] Thomson, S. and C. Huitema, "DNS Extensions to support IP
version 6", RFC 1886, December 1995.
[8] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[9] Piper, D., "The Internet IP Security Domain of Interpretation
for ISAKMP", RFC 2407, November 1998.
[10] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
[11] Eastlake, D., "DSA KEYs and SIGs in the Domain Name System
(DNS)", RFC 2536, March 1999.
[12] Eastlake, D., "RSA/SHA-1 SIGs and RSA KEYs in the Domain Name
System (DNS)", RFC 3110, May 2001.
[13] 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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