IPSECKEY WG M. Richardson Internet-Draft SSW Expires: November 21, 2003 May 23, 2003 A method for storing IPsec keying material in DNS. draft-ietf-ipseckey-rr-02.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 other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on November 21, 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. Richardson Expires November 21, 2003 [Page 1] Internet-Draft ipsecrr May 2003 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 - RSA public key . . . . . . . . . . . . . . . . 5 2.7 RDATA format - DSA public key . . . . . . . . . . . . . . . . 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 Richardson Expires November 21, 2003 [Page 2] Internet-Draft ipsecrr May 2003 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 MUST 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 node. This will be due to the presence of multiple gateways and the need to rollover keys. This resource record is class independent. Richardson Expires November 21, 2003 [Page 3] Internet-Draft ipsecrr May 2003 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, they order should be non-deterministic. 2.3 RDATA format - algorithm type The algorithm field indicates the type of key that is present in the public key field. A positive number larger than 0 identifies an algorithm type. The following values, which have been previously defined by IANA, are useful (see RFC2535 [8]). A value of 0 indicates that no key is present. The following values defined by IANA are useful: 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] Richardson Expires November 21, 2003 [Page 4] Internet-Draft ipsecrr May 2003 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 - RSA public key If the algorithm type has the value 5, then public key portion contains an RSA public key, encoded as described in secion 2 of RFC3110 [10]. RFC2065 limited the exponent and modulus to 2552 bits in length, and RFC3110 limits them to 4096 bits. No such limit is specified here for the purposes of encoding and decoding. The length in octets of the public exponent length is represented as one octet if it is in the range of 1 to 255, and by a zero octet Richardson Expires November 21, 2003 [Page 5] Internet-Draft ipsecrr May 2003 followed by a two octet unsigned length if it is longer than 255 bytes. The public key modulus field is a multiprecision unsigned integer. The length of the modulus can be determined from the RDLENGTH and the preceding RDATA fields including the exponent. Leading zero bytes are prohibited in the exponent and modulus. 2.7 RDATA format - DSA public key If the algorithm type has the value 3, then public key portion contains an DSA public key, encoded as described in RFC2536 [9]. Richardson Expires November 21, 2003 [Page 6] Internet-Draft ipsecrr May 2003 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. There base64 encoded public key block is OPTIONAL; if not present, then the public key field of the resource record MUST be contrued being zero octets in length. If no gateway is to be indicated, then the gateway type field MUST be zero, and the gateway type 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 AQOrXJxB56Q28iOO43Va36elIFFKc/QB2orIeL94BdC5X4idFQZjSpsZ Th48wKVXUE9xjwUkwR4R4/+1vjNN7KFp9fcqa2OxgjsoGqCn+3OPR8La 9uyvZg0OBuSTj3qkbh/2HacAUJ7vqvjQ3W8Wj6sMXtTueR8NNcdSzJh1 49ch3zqfiXrxxna8+8UEDQaRR9KOPiSvXb2KjnuDan6hDKOT4qTZRRRC MWwnNQ9zPIMNbLBp0rNcZ+ZGFg2ckWtWh5yhv1iXYLV2vmd9DB6d4Dv8 cW7scc3rPmDXpYR6APqPBRHlcbenfHCt+oCkEWse8OQhMM56KODIVQq3 fejrfi1H ) 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 . AQOrXJxB56Q28iOO43Va36elIFFKc/QB2orIeL94BdC5X4idFQZjSpsZ Th48wKVXUE9xjwUkwR4R4/+1vjNN7KFp9fcqa2OxgjsoGqCn+3OPR8La 9uyvZg0OBuSTj3qkbh/2HacAUJ7vqvjQ3W8Wj6sMXtTueR8NNcdSzJh1 49ch3zqfiXrxxna8+8UEDQaRR9KOPiSvXb2KjnuDan6hDKOT4qTZRRRC MWwnNQ9zPIMNbLBp0rNcZ+ZGFg2ckWtWh5yhv1iXYLV2vmd9DB6d4Dv8 cW7scc3rPmDXpYR6APqPBRHlcbenfHCt+oCkEWse8OQhMM56KODIVQq3 fejrfi1H ) 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 5 1 Richardson Expires November 21, 2003 [Page 7] Internet-Draft ipsecrr May 2003 192.0.2.3 AQOrXJxB56Q28iOO43Va36elIFFKc/QB2orIeL94BdC5X4idFQZjSpsZ Th48wKVXUE9xjwUkwR4R4/+1vjNN7KFp9fcqa2OxgjsoGqCn+3OPR8La 9uyvZg0OBuSTj3qkbh/2HacAUJ7vqvjQ3W8Wj6sMXtTueR8NNcdSzJh1 49ch3zqfiXrxxna8+8UEDQaRR9KOPiSvXb2KjnuDan6hDKOT4qTZRRRC MWwnNQ9zPIMNbLBp0rNcZ+ZGFg2ckWtWh5yhv1iXYLV2vmd9DB6d4Dv8 cW7scc3rPmDXpYR6APqPBRHlcbenfHCt+oCkEWse8OQhMM56KODIVQq3 fejrfi1H ) 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. AQOrXJxB56Q28iOO43Va36elIFFKc/QB2orIeL94BdC5X4idFQZjSpsZ Th48wKVXUE9xjwUkwR4R4/+1vjNN7KFp9fcqa2OxgjsoGqCn+3OPR8La 9uyvZg0OBuSTj3qkbh/2HacAUJ7vqvjQ3W8Wj6sMXtTueR8NNcdSzJh1 49ch3zqfiXrxxna8+8UEDQaRR9KOPiSvXb2KjnuDan6hDKOT4qTZRRRC MWwnNQ9zPIMNbLBp0rNcZ+ZGFg2ckWtWh5yhv1iXYLV2vmd9DB6d4Dv8 cW7scc3rPmDXpYR6APqPBRHlcbenfHCt+oCkEWse8OQhMM56KODIVQq3 fejrfi1H ) 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 5 2001:0DB8:0:8002::2000:1 AQOrXJxB56Q28iOO43Va36elIFFKc/QB2orIeL94BdC5X4idFQZjSpsZ Th48wKVXUE9xjwUkwR4R4/+1vjNN7KFp9fcqa2OxgjsoGqCn+3OPR8La 9uyvZg0OBuSTj3qkbh/2HacAUJ7vqvjQ3W8Wj6sMXtTueR8NNcdSzJh1 49ch3zqfiXrxxna8+8UEDQaRR9KOPiSvXb2KjnuDan6hDKOT4qTZRRRC MWwnNQ9zPIMNbLBp0rNcZ+ZGFg2ckWtWh5yhv1iXYLV2vmd9DB6d4Dv8 cW7scc3rPmDXpYR6APqPBRHlcbenfHCt+oCkEWse8OQhMM56KODIVQq3 fejrfi1H ) Richardson Expires November 21, 2003 [Page 8] Internet-Draft ipsecrr May 2003 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 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. 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 Richardson Expires November 21, 2003 [Page 9] Internet-Draft ipsecrr May 2003 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. Richardson Expires November 21, 2003 [Page 10] Internet-Draft ipsecrr May 2003 5. IANA Considerations IANA is asked to assign a resource record type number from the normal resource record number space. The algorithm field does not require any IANA action, as it is inherited from DNS KEY algorithm values. Richardson Expires November 21, 2003 [Page 11] Internet-Draft ipsecrr May 2003 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. Richardson Expires November 21, 2003 [Page 12] Internet-Draft ipsecrr May 2003 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. Richardson Expires November 21, 2003 [Page 13] Internet-Draft ipsecrr May 2003 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/ Richardson Expires November 21, 2003 [Page 14] Internet-Draft ipsecrr May 2003 Full Copyright Statement Copyright (C) The Internet Society (2003). All Rights Reserved. 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