Network Working Group P. Nikander Request for Comments: 5205 Ericsson Research NomadicLab Category: Experimental J. Laganier DoCoMo Euro-Labs April 2008 Host Identity Protocol (HIP) Domain Name System (DNS) Extension Status of This Memo This memo defines an Experimental Protocol for the Internet community. It does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.
AbstractThis document specifies a new resource record (RR) for the Domain Name System (DNS), and how to use it with the Host Identity Protocol (HIP). This RR allows a HIP node to store in the DNS its Host Identity (HI, the public component of the node public-private key pair), Host Identity Tag (HIT, a truncated hash of its public key), and the Domain Names of its rendezvous servers (RVSs).
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions Used in This Document . . . . . . . . . . . . . . 3 3. Usage Scenarios . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Simple Static Singly Homed End-Host . . . . . . . . . . . 5 3.2. Mobile end-host . . . . . . . . . . . . . . . . . . . . . 6 4. Overview of Using the DNS with HIP . . . . . . . . . . . . . . 8 4.1. Storing HI, HIT, and RVS in the DNS . . . . . . . . . . . 8 4.2. Initiating Connections Based on DNS Names . . . . . . . . 8 5. HIP RR Storage Format . . . . . . . . . . . . . . . . . . . . 9 5.1. HIT Length Format . . . . . . . . . . . . . . . . . . . . 9 5.2. PK Algorithm Format . . . . . . . . . . . . . . . . . . . 9 5.3. PK Length Format . . . . . . . . . . . . . . . . . . . . . 10 5.4. HIT Format . . . . . . . . . . . . . . . . . . . . . . . . 10 5.5. Public Key Format . . . . . . . . . . . . . . . . . . . . 10 5.6. Rendezvous Servers Format . . . . . . . . . . . . . . . . 10 6. HIP RR Presentation Format . . . . . . . . . . . . . . . . . . 10 7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12 8.1. Attacker Tampering with an Insecure HIP RR . . . . . . . . 12 8.2. Hash and HITs Collisions . . . . . . . . . . . . . . . . . 13 8.3. DNSSEC . . . . . . . . . . . . . . . . . . . . . . . . . . 13 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 11.1. Normative references . . . . . . . . . . . . . . . . . . . 14 11.2. Informative references . . . . . . . . . . . . . . . . . . 15
RFC1034], and how to use it with the Host Identity Protocol (HIP) [RFC5201]. This RR allows a HIP node to store in the DNS its Host Identity (HI, the public component of the node public- private key pair), Host Identity Tag (HIT, a truncated hash of its HI), and the Domain Names of its rendezvous servers (RVSs) [RFC5204]. Currently, most of the Internet applications that need to communicate with a remote host first translate a domain name (often obtained via user input) into one or more IP address(es). This step occurs prior to communication with the remote host, and relies on a DNS lookup. With HIP, IP addresses are intended to be used mostly for on-the-wire communication between end hosts, while most Upper Layer Protocols (ULP) and applications use HIs or HITs instead (ICMP might be an example of an ULP not using them). Consequently, we need a means to translate a domain name into an HI. Using the DNS for this translation is pretty straightforward: We define a new HIP resource record. Upon query by an application or ULP for a name to IP address lookup, the resolver would then additionally perform a name to HI lookup, and use it to construct the resulting HI to IP address mapping (which is internal to the HIP layer). The HIP layer uses the HI to IP address mapping to translate HIs and HITs into IP addresses and vice versa. The HIP Rendezvous Extension [RFC5204] allows a HIP node to be reached via the IP address(es) of a third party, the node's rendezvous server (RVS). An Initiator willing to establish a HIP association with a Responder served by an RVS would typically initiate a HIP exchange by sending an I1 towards the RVS IP address rather than towards the Responder IP address. Consequently, we need a means to find the name of a rendezvous server for a given host name. This document introduces the new HIP DNS resource record to store the Rendezvous Server (RVS), Host Identity (HI), and Host Identity Tag (HIT) information. RFC2119].
RFC1035] and AAAA [RFC3596] RR sets (RRSets [RFC2181]). o A Host Identity (HI), Host Identity Tag (HIT), and possibly a set of rendezvous servers (RVS) through HIP RRs. When a HIP node wants to initiate communication with another HIP node, it first needs to perform a HIP base exchange to set up a HIP association towards its peer. Although such an exchange can be initiated opportunistically, i.e., without prior knowledge of the Responder's HI, by doing so both nodes knowingly risk man-in-the- middle attacks on the HIP exchange. To prevent these attacks, it is recommended that the Initiator first obtain the HI of the Responder, and then initiate the exchange. This can be done, for example, through manual configuration or DNS lookups. Hence, a new HIP RR is introduced. When a HIP node is frequently changing its IP address(es), the natural DNS latency for propagating changes may prevent it from publishing its new IP address(es) in the DNS. For solving this problem, the HIP Architecture [RFC4423] introduces rendezvous servers (RVSs) [RFC5204]. A HIP host uses a rendezvous server as a rendezvous point to maintain reachability with possible HIP initiators while moving [RFC5206]. Such a HIP node would publish in the DNS its RVS domain name(s) in a HIP RR, while keeping its RVS up- to-date with its current set of IP addresses. When a HIP node wants to initiate a HIP exchange with a Responder, it will perform a number of DNS lookups. Depending on the type of implementation, the order in which those lookups will be issued may vary. For instance, implementations using HIT in APIs may typically first query for HIP resource records at the Responder FQDN, while
those using an IP address in APIs may typically first query for A and/or AAAA resource records. In the following, we assume that the Initiator first queries for HIP resource records at the Responder FQDN. If the query for the HIP type was responded to with a DNS answer with RCODE=3 (Name Error), then the Responder's information is not present in the DNS and further queries for the same owner name SHOULD NOT be made. In case the query for the HIP records returned a DNS answer with RCODE=0 (No Error) and an empty answer section, it means that no HIP information is available at the responder name. In such a case, if the Initiator has been configured with a policy to fallback to opportunistic HIP (initiating without knowing the Responder's HI) or plain IP, it would send out more queries for A and AAAA types at the Responder's FQDN. Depending on the combinations of answers, the situations described in Section 3.1 and Section 3.2 can occur. Note that storing HIP RR information in the DNS at an FQDN that is assigned to a non-HIP node might have ill effects on its reachability by HIP nodes.
o QNAME=www.example.com, QTYPE=A QNAME=www.example.com, QTYPE=AAAA Which returns DNS packets with RCODE=0 and one or more A or AAAA RRs containing IP address(es) of the Responder (e.g., IP-R) in the answer section. Caption: In the remainder of this document, for the sake of keeping diagrams simple and concise, several DNS queries and answers are represented as one single transaction, while in fact there are several queries and answers flowing back and forth, as described in the textual examples. [HIP? A? ] [www.example.com] +-----+ +-------------------------------->| | | | DNS | | +-------------------------------| | | | [HIP? A? ] +-----+ | | [www.example.com] | | [HIP HIT-R HI-R ] | | [A IP-R ] | v +-----+ +-----+ | |--------------I1------------->| | | I |<-------------R1--------------| R | | |--------------I2------------->| | | |<-------------R2--------------| | +-----+ +-----+ Static Singly Homed Host The Initiator would then send an I1 to the Responder's IP addresses (IP-R).
Which returns a DNS packet with RCODE=0 and one or more HIP RRs with the HIT, HI, and RVS domain name(s) (e.g., HIT-R, HI-R, and rvs.example.com) of the Responder in the answer section. o QNAME=rvs.example.com, QTYPE=A QNAME=www.example.com, QTYPE=AAAA Which returns DNS packets with RCODE=0 and one or more A or AAAA RRs containing IP address(es) of the Responder's RVS (e.g., IP-RVS) in the answer section. [HIP? ] [www.example.com] [A? ] [rvs.example.com] +-----+ +----------------------------------------->| | | | DNS | | +----------------------------------------| | | | [HIP? ] +-----+ | | [www.example.com ] | | [HIP HIT-R HI-R rvs.example.com] | | | | [A? ] | | [rvs.example.com] | | [A IP-RVS ] | | | | +-----+ | | +------I1----->| RVS |-----I1------+ | | | +-----+ | | | | | | | | | | v | v +-----+ +-----+ | |<---------------R1------------| | | I |----------------I2----------->| R | | |<---------------R2------------| | +-----+ +-----+ Mobile End-Host The Initiator would then send an I1 to the RVS IP address (IP-RVS). Following, the RVS will relay the I1 up to the mobile node's IP address (IP-R), which will complete the HIP exchange.
Section 3 of the HIP specification [RFC5201]. Upon return of a HIP RR, a host MUST always calculate the HI- derivative HIT to be used in the HIP exchange, as specified in Section 3 of the HIP specification [RFC5201], while the HIT possibly embedded along SHOULD only be used as an optimization (e.g., table lookup). The HIP resource record may also contain one or more domain name(s) of rendezvous server(s) towards which HIP I1 packets might be sent to trigger the establishment of an association with the entity named by this resource record [RFC5204]. The rendezvous server field of the HIP resource record stored at a given owner name MAY include the owner name itself. A semantically equivalent situation occurs if no rendezvous server is present in the HIP resource record stored at that owner name. Such situations occur in two cases: o The host is mobile, and the A and/or AAAA resource record(s) stored at its host name contain the IP address(es) of its rendezvous server rather than its own one. o The host is stationary, and can be reached directly at the IP address(es) contained in the A and/or AAAA resource record(s) stored at its host name. This is a degenerated case of rendezvous service where the host somewhat acts as a rendezvous server for itself. An RVS receiving such an I1 would then relay it to the appropriate Responder (the owner of the I1 receiver HIT). The Responder will then complete the exchange with the Initiator, typically without ongoing help from the RVS.
RFC4025]. The DSA key format is defined in RFC 2536 [RFC2536]. The RSA key format is defined in RFC 3110 [RFC3110] and the RSA key size limit (4096 bits) is relaxed in the IPSECKEY RR [RFC4025] specification. Section 3.3 of RFC 1035 [RFC1035]. The wire-encoded format is self- describing, so the length is implicit. The domain names MUST NOT be compressed. The rendezvous server(s) are listed in order of preference (i.e., first rendezvous server(s) are preferred), defining an implicit order amongst rendezvous servers of a single RR. When multiple HIP RRs are present at the same owner name, this implicit order of rendezvous servers within an RR MUST NOT be used to infer a preference order between rendezvous servers stored in different RRs. RFC4648] (a.k.a. hex or hexadecimal) of the HIT. The encoding MUST NOT contain whitespaces to distinguish it from the public key field.
The Public Key field is represented as the Base64 encoding [RFC4648] of the public key. The encoding MUST NOT contain whitespace(s) to distinguish it from the Rendezvous Servers field. The PK length field is not represented, as it is implicitly known thanks to the Public key field representation containing no whitespaces. The Rendezvous Servers field is represented by one or more domain name(s) separated by whitespace(s). The complete representation of the HPIHI record is: IN HIP ( pk-algorithm base16-encoded-hit base64-encoded-public-key rendezvous-server ... rendezvous-server[n] ) When no RVSs are present, the representation of the HPIHI record is: IN HIP ( pk-algorithm base16-encoded-hit base64-encoded-public-key )
Example of a node with a HI, HIT, and two RVSs: www.example.com. IN HIP ( 2 200100107B1A74DF365639CC39F1D578 AwEAAbdxyhNuSutc5EMzxTs9LBPCIkOFH8cIvM4p 9+LrV4e19WzK00+CI6zBCQTdtWsuxKbWIy87UOoJTwkUs7lBu+Upr1gsNrut79ryra+bSRGQ b1slImA8YVJyuIDsj7kwzG7jnERNqnWxZ48AWkskmdHaVDP4BcelrTI3rMXdXF5D rvs1.example.com. rvs2.example.com. ) RFC4025], the HIP DNS Extension allows for the provision of two HIP nodes with the public keying material (HI) of their peer. These HIs will be subsequently used in a key exchange between the peers. Hence, the HIP DNS Extension introduces the same kind of threats that IPSECKEY does, plus threats caused by the possibility given to a HIP node to initiate or accept a HIP exchange using "opportunistic" or "unpublished Initiator HI" modes. A HIP node SHOULD obtain HIP RRs from a trusted party trough a secure channel ensuring data integrity and authenticity of the RRs. DNSSEC [RFC4033] [RFC4034] [RFC4035] provides such a secure channel. However, it should be emphasized that DNSSEC only offers data integrity and authenticity guarantees to the channel between the DNS server publishing a zone and the HIP node. DNSSEC does not ensure that the entity publishing the zone is trusted. Therefore, the RRSIG signature of the HIP RRSet MUST NOT be misinterpreted as a certificate binding the HI and/or the HIT to the owner name. In the absence of a proper secure channel, both parties are vulnerable to MitM and DoS attacks, and unrelated parties might be subject to DoS attacks as well. These threats are described in the following sections.
The HIP RR may contain a rendezvous server domain name resolved into a destination IP address where the named peer is reachable by an I1, as per the HIP Rendezvous Extension [RFC5204]. Thus, an attacker able to tamper with this RR is able to redirect I1 packets sent to the named peer to a chosen IP address for DoS or MitM attacks. Note that this kind of attack is not specific to HIP and exists independently of whether or not HIP and the HIP RR are used. Such an attacker might tamper with A and AAAA RRs as well. An attacker might obviously use these two attacks in conjunction: It will replace the Responder's HI and RVS IP address by its own in a spoofed DNS packet sent to the Initiator HI, then redirect all exchanged packets to him and mount a MitM on HIP. In this case, HIP won't provide confidentiality nor Initiator HI protection from eavesdroppers. RFC3833]. RFC4025]. Presently defined values are shown here for reference only: 0 is reserved 1 is DSA 2 is RSA
In the future, if a new algorithm is to be used for the HIP RR, a new algorithm type and corresponding public key encoding should be defined for the IPSECKEY RR. The HIP RR should reuse both the same algorithm type and the same corresponding public key format as the IPSECKEY RR. RFC4025] specification, after which this document was framed. The authors would also like to thank the following people, who have provided thoughtful and helpful discussions and/or suggestions, that have helped improve this document: Jeff Ahrenholz, Rob Austein, Hannu Flinck, Olafur Gudmundsson, Tom Henderson, Peter Koch, Olaf Kolkman, Miika Komu, Andrew McGregor, Erik Nordmark, and Gabriel Montenegro. Some parts of this document stem from the HIP specification [RFC5201]. [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, November 1987. [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS Specification", RFC 2181, July 1997. [RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi, "DNS Extensions to Support IP Version 6", RFC 3596, October 2003. [RFC4025] Richardson, M., "A Method for Storing IPsec Keying Material in DNS", RFC 4025, March 2005. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, March 2005.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Resource Records for the DNS Security Extensions", RFC 4034, March 2005. [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Protocol Modifications for the DNS Security Extensions", RFC 4035, March 2005. [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, October 2006. [RFC5201] Moskowitz, R., Nikander, P., Jokela, P., Ed., and T. Henderson, "Host Identity Protocol", RFC 5201, April 2008. [RFC5204] Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) Rendezvous Extension", RFC 5204, April 2008. [RFC2536] Eastlake, D., "DSA KEYs and SIGs in the Domain Name System (DNS)", RFC 2536, March 1999. [RFC3110] Eastlake, D., "RSA/SHA-1 SIGs and RSA KEYs in the Domain Name System (DNS)", RFC 3110, May 2001. [RFC3833] Atkins, D. and R. Austein, "Threat Analysis of the Domain Name System (DNS)", RFC 3833, August 2004. [RFC4423] Moskowitz, R. and P. Nikander, "Host Identity Protocol (HIP) Architecture", RFC 4423, May 2006. [RFC5206] Henderson, T., Ed., "End-Host Mobility and Multihoming with the Host Identity Protocol", RFC 5206, April 2008.
Full Copyright Statement Copyright (C) The IETF Trust (2008). 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, THE IETF TRUST 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 procedures with respect to rights in RFC 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 firstname.lastname@example.org.