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rfc:rfc5205

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).

Nikander & Laganier Experimental [Page 1] RFC 5205 HIP DNS Extension April 2008

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

Nikander & Laganier Experimental [Page 2] RFC 5205 HIP DNS Extension April 2008

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].

Nikander & Laganier Experimental [Page 3] RFC 5205 HIP DNS Extension April 2008

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

Nikander & Laganier Experimental [Page 4] RFC 5205 HIP DNS Extension April 2008

 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.

Nikander & Laganier Experimental [Page 5] RFC 5205 HIP DNS Extension April 2008

 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

Nikander & Laganier Experimental [Page 6] RFC 5205 HIP DNS Extension April 2008

 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.

Nikander & Laganier Experimental [Page 7] RFC 5205 HIP DNS Extension April 2008

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.

Nikander & Laganier Experimental [Page 8] RFC 5205 HIP DNS Extension April 2008

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.

Nikander & Laganier Experimental [Page 9] RFC 5205 HIP DNS Extension April 2008

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.

Nikander & Laganier Experimental [Page 10] RFC 5205 HIP DNS Extension April 2008

 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. )

Nikander & Laganier Experimental [Page 11] RFC 5205 HIP DNS Extension April 2008

 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).

Nikander & Laganier Experimental [Page 12] RFC 5205 HIP DNS Extension April 2008

 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

Nikander & Laganier Experimental [Page 13] RFC 5205 HIP DNS Extension April 2008

 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.

Nikander & Laganier Experimental [Page 14] RFC 5205 HIP DNS Extension April 2008

 [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.

Nikander & Laganier Experimental [Page 15] RFC 5205 HIP DNS Extension 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/

Nikander & Laganier Experimental [Page 16] RFC 5205 HIP DNS Extension April 2008

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Nikander & Laganier Experimental [Page 17]

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