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.

Abstract

   This 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).

Table of Contents

   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

1.  Introduction

   This document specifies a new resource record (RR) for the Domain
   Name System (DNS) [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.

2.  Conventions Used in This Document

   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 [RFC2119].

3.  Usage Scenarios

   In this section, we briefly introduce a number of usage scenarios
   where the DNS is useful with the Host Identity Protocol.

   With HIP, most applications and ULPs are unaware of the IP addresses
   used to carry packets on the wire.  Consequently, a HIP node could
   take advantage of having multiple IP addresses for fail-over,
   redundancy, mobility, or renumbering, in a manner that is transparent
   to most ULPs and applications (because they are bound to HIs; hence,
   they are agnostic to these IP address changes).

   In these situations, for a node to be reachable by reference to its
   Fully Qualified Domain Name (FQDN), the following information should
   be stored in the DNS:

   o  A set of IP address(es) via A [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.

3.1.  Simple Static Singly Homed End-Host

   A HIP node (R) with a single static network attachment, wishing to be
   reachable by reference to its FQDN (www.example.com), would store in
   the DNS, in addition to its IP address(es) (IP-R), its Host Identity
   (HI-R) and Host Identity Tag (HIT-R) in a HIP resource record.

   An Initiator willing to associate with a node would typically issue
   the following queries:

   o  QNAME=www.example.com, QTYPE=HIP

   o  (QCLASS=IN is assumed and omitted from the examples)

   Which returns a DNS packet with RCODE=0 and one or more HIP RRs with
   the HIT and HI (e.g., HIT-R and HI-R) of the Responder in the answer
   section, but no RVS.

   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).

3.2.  Mobile end-host

   A mobile HIP node (R) wishing to be reachable by reference to its
   FQDN (www.example.com) would store in the DNS, possibly in addition
   to its IP address(es) (IP-R), its HI (HI-R), HIT (HIT-R), and the
   domain name(s) of its rendezvous server(s) (e.g., rvs.example.com) in
   HIP resource record(s).  The mobile HIP node also needs to notify its
   rendezvous servers of any change in its set of IP address(es).

   An Initiator willing to associate with such a mobile node would
   typically issue the following queries:

   o  QNAME=www.example.com, QTYPE=HIP

   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.

4.  Overview of Using the DNS with HIP

4.1.  Storing HI, HIT, and RVS in the DNS

   For any HIP node, its Host Identity (HI), the associated Host
   Identity Tag (HIT), and the FQDN of its possible RVSs can be stored
   in a DNS HIP RR.  Any conforming implementation may store a Host
   Identity (HI) and its associated Host Identity Tag (HIT) in a DNS HIP
   RDATA format.  HI and HIT are defined in 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.

4.2.  Initiating Connections Based on DNS Names

   On a HIP node, a Host Identity Protocol exchange SHOULD be initiated
   whenever a ULP attempts to communicate with an entity and the DNS
   lookup returns HIP resource records.

5.  HIP RR Storage Format

   The RDATA for a HIP RR consists of a public key algorithm type, the
   HIT length, a HIT, a public key, and optionally one or more
   rendezvous server(s).

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  HIT length   | PK algorithm  |          PK length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                           HIT                                 ~
   |                                                               |
   +                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     |                                         |
   +-+-+-+-+-+-+-+-+-+-+-+                                         +
   |                           Public Key                          |
   ~                                                               ~
   |                                                               |
   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               |
   ~                       Rendezvous Servers                      ~
   |                                                               |
   +             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             |
   +-+-+-+-+-+-+-+

   The HIT length, PK algorithm, PK length, HIT, and Public Key fields
   are REQUIRED.  The Rendezvous Servers field is OPTIONAL.

5.1.  HIT Length Format

   The HIT length indicates the length in bytes of the HIT field.  This
   is an 8-bit unsigned integer.

5.2.  PK Algorithm Format

   The PK algorithm field indicates the public key cryptographic
   algorithm and the implied public key field format.  This is an 8-bit
   unsigned integer.  This document reuses the values defined for the
   'algorithm type' of the IPSECKEY RR [RFC4025].

   Presently defined values are listed in Section 9 for reference.

5.3.  PK Length Format

   The PK length indicates the length in bytes of the Public key field.
   This is a 16-bit unsigned integer in network byte order.

5.4.  HIT Format

   The HIT is stored as a binary value in network byte order.

5.5.  Public Key Format

   Both of the public key types defined in this document (RSA and DSA)
   reuse the public key formats defined for the IPSECKEY RR [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.

5.6.  Rendezvous Servers Format

   The Rendezvous Servers field indicates one or more variable length
   wire-encoded domain names of rendezvous server(s), as described in
   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.

6.  HIP RR Presentation Format

   This section specifies the representation of the HIP RR in a zone
   master file.

   The HIT length field is not represented, as it is implicitly known
   thanks to the HIT field representation.

   The PK algorithm field is represented as unsigned integers.

   The HIT field is represented as the Base16 encoding [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[1]
                       ...
               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 )

7.  Examples

   In the examples below, the public key field containing no whitespace
   is wrapped since it does not fit in a single line of this document.

   Example of a node with HI and HIT but no RVS:

www.example.com.      IN  HIP ( 2 200100107B1A74DF365639CC39F1D578
                                AwEAAbdxyhNuSutc5EMzxTs9LBPCIkOFH8cIvM4p
9+LrV4e19WzK00+CI6zBCQTdtWsuxKbWIy87UOoJTwkUs7lBu+Upr1gsNrut79ryra+bSRGQ
b1slImA8YVJyuIDsj7kwzG7jnERNqnWxZ48AWkskmdHaVDP4BcelrTI3rMXdXF5D )

   Example of a node with a HI, HIT, and one RVS:

www.example.com.      IN  HIP ( 2 200100107B1A74DF365639CC39F1D578
                                AwEAAbdxyhNuSutc5EMzxTs9LBPCIkOFH8cIvM4p
9+LrV4e19WzK00+CI6zBCQTdtWsuxKbWIy87UOoJTwkUs7lBu+Upr1gsNrut79ryra+bSRGQ
b1slImA8YVJyuIDsj7kwzG7jnERNqnWxZ48AWkskmdHaVDP4BcelrTI3rMXdXF5D
                                rvs.example.com. )

   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. )

8.  Security Considerations

   This section contains a description of the known threats involved
   with the usage of the HIP DNS Extension.

   In a manner similar to the IPSECKEY RR [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.

8.1.  Attacker Tampering with an Insecure HIP RR

   The HIP RR contains public keying material in the form of the named
   peer's public key (the HI) and its secure hash (the HIT).  Both of
   these are not sensitive to attacks where an adversary gains knowledge
   of them.  However, an attacker that is able to mount an active attack
   on the DNS, i.e., tampers with this HIP RR (e.g., using DNS
   spoofing), is able to mount Man-in-the-Middle attacks on the
   cryptographic core of the eventual HIP exchange (Responder's HIP RR
   rewritten by the attacker).

   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.

8.2.  Hash and HITs Collisions

   As with many cryptographic algorithms, some secure hashes (e.g.,
   SHA1, used by HIP to generate a HIT from an HI) eventually become
   insecure, because an exploit has been found in which an attacker with
   reasonable computation power breaks one of the security features of
   the hash (e.g., its supposed collision resistance).  This is why a
   HIP end-node implementation SHOULD NOT authenticate its HIP peers
   based solely on a HIT retrieved from the DNS, but SHOULD rather use
   HI-based authentication.

8.3.  DNSSEC

   In the absence of DNSSEC, the HIP RR is subject to the threats
   described in RFC 3833 [RFC3833].

9.  IANA Considerations

   IANA has allocated one new RR type code (55) for the HIP RR from the
   standard RR type space.

   IANA does not need to open a new registry for public key algorithms
   of the HIP RR because the HIP RR reuses "algorithms types" defined
   for the IPSECKEY RR [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.

10.  Acknowledgments

   As usual in the IETF, this document is the result of a collaboration
   between many people.  The authors would like to thank the author
   (Michael Richardson), contributors, and reviewers of 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].

11.  References

11.1.  Normative references

   [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.

11.2.  Informative references

   [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.

Authors' Addresses

   Pekka Nikander
   Ericsson Research NomadicLab
   JORVAS  FIN-02420
   FINLAND

   Phone: +358 9 299 1
   EMail: pekka.nikander@nomadiclab.com


   Julien Laganier
   DoCoMo Communications Laboratories Europe GmbH
   Landsberger Strasse 312
   Munich  80687
   Germany

   Phone: +49 89 56824 231
   EMail: julien.ietf@laposte.net
   URI:   http://www.docomolab-euro.com/

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