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diff --git a/doc/rfc/rfc4025.txt b/doc/rfc/rfc4025.txt new file mode 100644 index 0000000..92e7f40 --- /dev/null +++ b/doc/rfc/rfc4025.txt @@ -0,0 +1,675 @@ + + + + + + +Network Working Group M. Richardson +Request for Comments: 4025 SSW +Category: Standards Track February 2005 + + + A Method for Storing IPsec Keying Material in DNS + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2005). + +Abstract + + 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 an IPsec tunnel + is established with the entity in question. + + This record replaces the functionality of the sub-type #4 of the KEY + Resource Record, which has been obsoleted by RFC 3445. + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 + 1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 2 + 1.2. Use of DNS Address-to-Name Maps (IN-ADDR.ARPA and + IP6.ARPA) . . . . . . . . . . . . . . . . . . . . . . . 3 + 1.3. Usage Criteria . . . . . . . . . . . . . . . . . . . . . 3 + 2. Storage Formats . . . . . . . . . . . . . . . . . . . . . . . 3 + 2.1. IPSECKEY RDATA Format . . . . . . . . . . . . . . . . . 3 + 2.2. RDATA Format - Precedence . . . . . . . . . . . . . . . 4 + 2.3. RDATA Format - Gateway Type . . . . . . . . . . . . . . 4 + 2.4. RDATA Format - Algorithm Type . . . . . . . . . . . . . 4 + 2.5. RDATA Format - Gateway . . . . . . . . . . . . . . . . . 5 + 2.6. RDATA Format - Public Keys . . . . . . . . . . . . . . . 5 + 3. Presentation Formats . . . . . . . . . . . . . . . . . . . . . 6 + 3.1. Representation of IPSECKEY RRs . . . . . . . . . . . . . 6 + 3.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 6 + 4. Security Considerations . . . . . . . . . . . . . . . . . . . 7 + + + +Richardson Standards Track [Page 1] + +RFC 4025 Storing IPsec Keying Material in DNS February 2005 + + + 4.1. Active Attacks Against Unsecured IPSECKEY Resource + Records . . . . . . . . . . . . . . . . . . . . . . . . 8 + 4.1.1. Active Attacks Against IPSECKEY Keying + Materials. . . . . . . . . . . . . . . . . . . . 8 + 4.1.2. Active Attacks Against IPSECKEY Gateway + Material. . . . . . . . . . . . . . . . . . . . 8 + 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 + 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 + 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 + 7.1. Normative References . . . . . . . . . . . . . . . . . . 10 + 7.2. Informative References . . . . . . . . . . . . . . . . . 10 + Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11 + Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 12 + +1. Introduction + + Suppose a host wishes (or is required by policy) to establish an + IPsec tunnel with some remote entity on the network prior to allowing + normal communication to take place. In many cases, this end system + will be able to determine the DNS name for the remote entity (either + by having the DNS name given explicitly, by performing a DNS PTR + query for a particular IP address, or through some other means, e.g., + by extracting the DNS portion of a "user@FQDN" name for a remote + entity). In these cases, the host will need to obtain a public key + 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. The IPSECKEY RR provides a + mechanism for storing such information. + + The type number for the IPSECKEY RR is 45. + + This record replaces the functionality of the sub-type #4 of the KEY + Resource Record, which has been obsoleted by RFC 3445 [11]. + +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) [1] 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 RFC 2119 [3]. + + + + + + + +Richardson Standards Track [Page 2] + +RFC 4025 Storing IPsec Keying Material in DNS February 2005 + + +1.2. Use of DNS Address-to-Name Maps (IN-ADDR.ARPA and IP6.ARPA) + + 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, frequently 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). + + The lookup is done in the fashion usual 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. + + Note: even when the IPsec function is contained in the end-host, + often only the application will know the forward name used. Although + 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. + +1.3. Usage Criteria + + An IPSECKEY resource record SHOULD be used in combination with DNSSEC + [8] 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 a need to roll over keys. + + This resource record is class independent. + +2. Storage Formats + +2.1. IPSECKEY RDATA Format + + The RDATA for an IPSECKEY RR consists of a precedence value, a + gateway type, a public key, algorithm type, and an optional gateway + address. + + + + + + + + + + + +Richardson Standards Track [Page 3] + +RFC 4025 Storing IPsec Keying Material in DNS February 2005 + + + 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. It is interpreted in + the same way as the PREFERENCE field described in section 3.3.9 of + RFC 1035 [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 - 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. (See Section 3.3 of RFC 1035 [2].) + +2.4. 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 RFC 2536 [9]. + 2 A RSA key is present, in the format defined in RFC 3110 [10]. + + + + + + +Richardson Standards Track [Page 4] + +RFC 4025 Storing IPsec Keying Material in DNS February 2005 + + +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 RFC 1035 + [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 RFC 3596 + [12]. 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 RFC 1035 [2]. Compression MUST NOT be used. + +2.6. RDATA Format - Public Keys + + Both 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 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 RRs. + + 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 from the DNSSEC algorithm number) must be + assigned to it. + + The DSA key format is defined in RFC 2536 [9] + + The RSA key format is defined in RFC 3110 [10], with the following + changes: + + The earlier definition of RSA/MD5 in RFC 2065 [4] limited the + exponent and modulus to 2552 bits in length. RFC 3110 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 + + + +Richardson Standards Track [Page 5] + +RFC 4025 Storing IPsec Keying Material in DNS February 2005 + + + imposed by the two-octet length encoding. This length extension is + applicable only to IPSECKEY; it is not applicable to KEY RRs. + +3. Presentation Formats + +3.1. Representation of IPSECKEY RRs + + IPSECKEY RRs may appear in a zone data master file. The precedence, + gateway type, algorithm, and gateway fields are REQUIRED. The base64 + encoded public key block is OPTIONAL; if it is not present, the + public key field of the resource record MUST be construed to be 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 RFC 3548 [6], Section 5.2. + + The general presentation for the record is 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== ) + + + + + + + + + +Richardson Standards Track [Page 6] + +RFC 4025 Storing IPsec Keying Material in DNS February 2005 + + + 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== ) + + 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.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== ) + +4. Security Considerations + + This entire memo pertains to the provision of public keying material + for use by key management protocols such as ISAKMP/IKE (RFC 2407) + [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 defense + against both active and passive attacks. + + Any derivative specification that makes use of this resource record + MUST carefully document its trust model and why the trust model of + DNSSEC is appropriate, if that is the secure channel used. + + + + + +Richardson Standards Track [Page 7] + +RFC 4025 Storing IPsec Keying Material in DNS February 2005 + + + 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 is independent of whether the IPSECKEY RR is 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. + This section deals with the situation in which DNSSEC is not + available. This is not the recommended deployment scenario. + +4.1.1. Active Attacks Against IPSECKEY Keying Materials + + The first kind of active attack is when the attacker replaces the + keying material with either a key under its control or with garbage. + + The gateway field is either untouched or is null. The IKE + negotiation will therefore occur with the original end-system. For + this attack to succeed, the attacker must perform a man-in-the-middle + attack on the IKE negotiation. This attack requires that the + attacker be able to intercept and modify packets on the forwarding + path for the IKE and data packets. + + If the attacker is not able to perform this man-in-the-middle attack + on the IKE negotiation, then a denial of service will result, as the + IKE negotiation will fail. + + If the attacker is not only able to mount active attacks against DNS + but also in a position to perform a man-in-the-middle attack on IKE + and IPsec negotiations, then the attacker will be able 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 for + this to succeed. + +4.1.2. Active Attacks Against IPSECKEY Gateway Material + + The second kind of active attack is one in which the attacker + replaces the gateway address to point to a node under the attacker's + control. The attacker then either replaces the public key or removes + it. If the public key were removed, then the attacker could provide + an accurate public key of its own in a second record. + + This second form creates a simple man-in-the-middle attacks 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. + + + +Richardson Standards Track [Page 8] + +RFC 4025 Storing IPsec Keying Material in DNS February 2005 + + + Note that the man-in-the-middle cannot 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 + already have created a policy expecting ciphertext. Thus, the + attacker will need to intercept traffic in both directions. In some + cases, the attacker may be able to accomplish the full intercept by + use of Network Address/Port Translation (NAT/NAPT) technology. + + This attack is easier than the first one because the attacker does + NOT need to be on the end-to-end forwarding path. The attacker need + only be able to modify DNS replies. This can be done by packet + modification, by various kinds of race attacks, or through methods + that pollute DNS caches. + + If 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. As the RR owner + name is assumed when the gateway field is null, a null gateway field + is considered a match. + + Thus, any records obtained under unverified conditions (e.g., no + DNSSEC or trusted path to source) that have a non-null gateway field + MUST be ignored. + + This restriction eliminates attacks against the gateway field, which + are considered much easier, as the attack does not need to be on the + forwarding path. + + In the case of an IPSECKEY RR with a value of three in its gateway + type field, the gateway field contains a domain name. The subsequent + query required to translate that name into an IP address or IPSECKEY + RR will also be subject to man-in-the-middle attacks. If the + end-to-end integrity of this second query is suspect, then the + provisions above also apply. The IPSECKEY RR MUST be ignored + whenever the resulting gateway does not match the QNAME of the + original IPSECKEY RR query. + +5. IANA Considerations + + This document updates the IANA Registry for DNS Resource Record Types + by assigning type 45 to the IPSECKEY record. + + This document creates two new IANA registries, both specific to the + IPSECKEY Resource Record: + + This document creates an IANA registry for the algorithm type field. + + + + + +Richardson Standards Track [Page 9] + +RFC 4025 Storing IPsec Keying Material in DNS February 2005 + + + Values 0, 1, and 2 are defined in Section 2.4. Algorithm numbers 3 + through 255 can be assigned by IETF Consensus (see RFC 2434 [5]). + + This document creates an IANA registry for the gateway type field. + + Values 0, 1, 2, and 3 are defined in Section 2.3. Gateway type + numbers 4 through 255 can be assigned by Standards Action (see RFC + 2434 [5]). + +6. Acknowledgements + + My thanks to Paul Hoffman, Sam Weiler, Jean-Jacques Puig, Rob + Austein, and Olafur Gudmundsson, who reviewed this document + carefully. Additional thanks to Olafur Gurmundsson for a reference + implementation. + +7. References + +7.1. 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., "Key words for use in RFCs to Indicate Requirement + Levels", BCP 14, RFC 2119, March 1997. + + [4] Eastlake 3rd, D. and C. Kaufman, "Domain Name System Security + Extensions", RFC 2065, January 1997. + + [5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA + Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. + + [6] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", + RFC 3548, July 2003. + +7.2. Informative References + + [7] Piper, D., "The Internet IP Security Domain of Interpretation + for ISAKMP", RFC 2407, November 1998. + + [8] Eastlake 3rd, D., "Domain Name System Security Extensions", RFC + 2535, March 1999. + + [9] Eastlake 3rd, D., "DSA KEYs and SIGs in the Domain Name System + (DNS)", RFC 2536, March 1999. + + + +Richardson Standards Track [Page 10] + +RFC 4025 Storing IPsec Keying Material in DNS February 2005 + + + [10] Eastlake 3rd, 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. + + [12] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi, "DNS + Extensions to Support IP Version 6", RFC 3596, October 2003. + +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 Standards Track [Page 11] + +RFC 4025 Storing IPsec Keying Material in DNS February 2005 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2005). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights 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; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the IETF's procedures with respect to rights in IETF Documents can + be found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat 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 implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at ietf- + ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + +Richardson Standards Track [Page 12] + |