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Versions: (draft-nikander-hip-dns) 00 01 02 03 04 05 06 07 08 09 RFC 5205

HIP Working Group                                            P. Nikander
Internet-Draft                             Ericsson Research Nomadic Lab
Expires: August 21, 2005                                     J. Laganier
                                                  LIP / Sun Microsystems
                                                       February 20, 2005

    Host Identity Protocol (HIP) Domain Name System (DNS) Extensions
                         draft-ietf-hip-dns-01

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each
   author represents that any applicable patent or other IPR claims of
   which he or she is aware have been or will be disclosed, and any of
   which he or she become aware will be disclosed, in accordance with
   RFC 3668.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 21, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document specifies two new resource records (RRs) for the Domain
   Name System (DNS), and how to use them with the Host Identity
   Protocol (HIP).  These RRs allow 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 Name or IP addresses of its Rendezvous Servers


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   (RVS).

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions used in this document  . . . . . . . . . . . . . .  5
   3.  Usage Scenarios  . . . . . . . . . . . . . . . . . . . . . . .  6
     3.1   Simple static singly homed end-host  . . . . . . . . . . .  7
     3.2   Mobile end-host  . . . . . . . . . . . . . . . . . . . . .  8
     3.3   Mixed Scenario . . . . . . . . . . . . . . . . . . . . . .  9
   4.  Overview of using the DNS with HIP . . . . . . . . . . . . . . 10
     4.1   Storing HI and HIT in DNS  . . . . . . . . . . . . . . . . 10
       4.1.1   Different types of HITs  . . . . . . . . . . . . . . . 10
     4.2   Storing Rendezvous Servers in the DNS  . . . . . . . . . . 11
     4.3   Initiating connections based on DNS names  . . . . . . . . 11
   5.  Storage Format . . . . . . . . . . . . . . . . . . . . . . . . 12
     5.1   HIPHI RDATA format . . . . . . . . . . . . . . . . . . . . 12
       5.1.1   HIT type format  . . . . . . . . . . . . . . . . . . . 12
       5.1.2   HIT algorithm format . . . . . . . . . . . . . . . . . 12
       5.1.3   PK algorithm format  . . . . . . . . . . . . . . . . . 12
       5.1.4   HIT format . . . . . . . . . . . . . . . . . . . . . . 13
       5.1.5   Public key format  . . . . . . . . . . . . . . . . . . 13
     5.2   HIPRVS RDATA format  . . . . . . . . . . . . . . . . . . . 13
       5.2.1   Preference format  . . . . . . . . . . . . . . . . . . 14
       5.2.2   Rendezvous server type format  . . . . . . . . . . . . 14
       5.2.3   Rendezvous server format . . . . . . . . . . . . . . . 14
   6.  Presentation Format  . . . . . . . . . . . . . . . . . . . . . 16
     6.1   HIPHI Representation . . . . . . . . . . . . . . . . . . . 16
     6.2   HIPRVS Representation  . . . . . . . . . . . . . . . . . . 16
     6.3   Examples . . . . . . . . . . . . . . . . . . . . . . . . . 17
   7.  Retrieving Multiple HITs and IPs from the DNS  . . . . . . . . 18
   8.  Transition mechanisms  . . . . . . . . . . . . . . . . . . . . 19
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 20
     9.1   Attacker tampering with an unsecure HIPHI RR . . . . . . . 20
     9.2   Attacker tampering with an unsecure HIPRVS RR  . . . . . . 20
     9.3   Opportunistic HIP  . . . . . . . . . . . . . . . . . . . . 21
     9.4   Unpublished Initiator HI . . . . . . . . . . . . . . . . . 21
     9.5   Hash and HITs Collisions . . . . . . . . . . . . . . . . . 21
   10.   IANA Considerations  . . . . . . . . . . . . . . . . . . . . 22
   11.   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . 23
   12.   References . . . . . . . . . . . . . . . . . . . . . . . . . 24
   12.1  Normative references . . . . . . . . . . . . . . . . . . . . 24
   12.2  Informative references . . . . . . . . . . . . . . . . . . . 25
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 25
   A.  Document Revision History  . . . . . . . . . . . . . . . . . . 26
       Intellectual Property and Copyright Statements . . . . . . . . 27



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1.  Introduction

   This document specifies two new resource records (RRs) for the Domain
   Name System (DNS) [1], and how to use them with the Host Identity
   Protocol (HIP) [10].  These RRs allow 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 Name or IP addresses of its Rendezvous
   Servers (RVS) [13].

   The current Internet architecture defines two global namespaces: IP
   addresses and domain names.  The Domain Name System provides a two
   way lookup between these two namespaces.  The HIP architecture [11]
   defines a new third namespace, called the Host Identity Namespace.
   This namespace is composed of Host Identifiers (HI) of HIP nodes.
   The Host Identity Tag (HIT) is one representation of an HI.  This
   representation is obtained by taking the output of a secure hash
   function applied to the HI, truncated to the IPv6 address size.  HITs
   are supposed to be used in the place of IP addresses within most ULPs
   and applications.

        +-----+                +-----+
        |     |-------I1------>|     |
        |  I  |<------R1-------|  R  |
        |     |-------I2------>|     |
        |     |<------R2-------|     |
        +-----+                +-----+

   The Host Identity Protocol [10] allows two HIP nodes to establish
   together a HIP Association.  A HIP association is bound to the nodes
   HIs rather than to their IP address(es).

   Although a HIP node can initiate HIP communication
   "opportunistically", i.e., without a priori knowledge of its peer's
   HI, doing so exposes both endpoints to Man-in-the-Middle attacks on
   the HIP handshake and its cryptographic protocol.  Hence, there is a
   desire to gain knowledge of peers' HI before applications and ULPs
   initiate communication.  Because many applications use the Domain
   Name System [1] to name nodes, DNSSEC [3] is a straightforward way to
   provision nodes with the HIP informations (i.e.  HI and possibly RVS)
   of nodes named in the DNS tree, without introducing or relying on an
   additional piece of infrastructure.




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                    +-----+
           +--I1--->| RVS |---I1--+
           |        +-----+       |
           |                      v
        +-----+                +-----+
        |     |<------R1-------|     |
        |  I  |-------I2------>|  R  |
        |     |<------R2-------|     |
        +-----+                +-----+

   The proposed HIP multi-homing mechanisms [12] allow a node to
   dynamically change its set of underlying IP addresses while
   maintaining IPsec SA and transport layer session survivability.  The
   HIP rendezvous extensions [13] proposal allows a HIP node to maintain
   HIP reachability while it is changing its current location (the node
   IP address(es)).  This rendezvous service is provided by a third
   party, the node's Rendezvous Server (RVS).  An initiator (I) willing
   to establish a HIP association with a responder (R) would typically
   initiate a HIP exchange by sending an I1 towards the RVS IP address
   rather than towards the responder IP address.  Then, the RVS,
   noticing that the receiver HIT is not its own, but the HIT of a HIP
   node registered for the rendezvous Service, would relay the I1 to the
   responder.  Typically the responder would then complete the exchange
   without further assistance from the RVS by sending an R1 directly to
   the initiator IP address.

   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 expected to be used mostly for on-the-wire
   communication between end hosts, while most ULPs and applications
   uses 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 HIPHI (HIP HI) resource record.
   Upon query by an application or ULP for a FQDN -> IP lookup, the
   resolver would then additionally perform an FQDN -> HI lookup, and
   use it to construct the resulting HI -> IP mapping (which is internal
   to the HIP layer).  The HIP layer uses the HI -> IP mapping to
   translate HIs and their local representations (HITs, IPv4 and
   IPv6-compatible LSIs) into IP addresses and vice versa.

   This draft introduces the following new DNS Resource Records:
      - HIPHI, for storing Host Identifiers and Host Identity Tags
      - HIPRVS, for storing rendezvous server information


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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 RFC2119 [4].























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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 application 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 which 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, a node wishing to be reachable by reference to
   its FQDN should store the following informations in the DNS:

   o  A set of IP address(es).
   o  A Host Identity (HI) and/or Host Identity Tag (HIT).
   o  An IP address or DNS name of its Rendezvous Server(s) (RVS).

   When a HIP node wants to initiate a 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 a priori 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
   HIPHI RR is introduced.

   When a HIP node is frequently changing its IP address(es), the
   dynamic DNS update latency may prevent it from publishing its new IP
   address(es) in the DNS.  For solving this problem, the HIP
   architecture introduces Rendezvous Servers (RVS).  A HIP host uses a
   Rendezvous Server as a Rendezvous point, to maintain reachability
   with possible HIP initiators.  Such a HIP node would publish in the
   DNS its RVS IP address or DNS name in a HIPRVS RR, while keeping its
   RVS up-to-date with its current set of IP addresses.

   Then, when some other node wants to initiate a HIP exchange with such
   a responder, it retrieves the RVS IP address by looking up a HIPRVS
   RR at the FQDN of the responder, and sends an I1 to this IP address.
   The I1 will then be relayed by the RVS to the responder, which will
   then complete the HIP exchange, either directly or via the RVS [13].

   Note that storing HIP RR information in the DNS at a FQDN which is
   assigned to a non-HIP node might have ill effects on its reachability
   by HIP nodes.


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3.1  Simple static singly homed end-host

               [A? HIPRVS? HIPHI?]
               [www.example.com  ]          +-----+
          +-------------------------------->|     |
          |                                 | DNS |
          | +-------------------------------|     |
          | |  [A? HIPRVS? HIPHI?      ]    +-----+
          | |  [www.example.com        ]
          | |  [A IP-R                 ]
          | |  [HIPHI 10 3 2 HIT-R HI-R]
          | v
        +-----+                              +-----+
        |     |--------------I1------------->|     |
        |  I  |<-------------R1--------------|  R  |
        |     |--------------I2------------->|     |
        |     |<-------------R2--------------|     |
        +-----+                              +-----+

   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) in a HIPHI resource record.














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3.2  Mobile end-host

               [A? HIPRVS? HIPHI?]
               [www.example.com  ]          +-----+
         +--------------------------------->|     |
         |                                  | DNS |
         | +--------------------------------|     |
         | |   [A? HIPRVS? HIPHI?      ]    +-----+
         | |   [www.example.com        ]
         | |   [HIPRVS 1 2 IP-RVS      ]
         | |   [HIPHI 10 3 2 HIT-R HI-R]
         | |
         | |                +-----+
         | | +------I1----->| RVS |-----I1------+
         | | |              +-----+             |
         | | |                                  |
         | | |                                  |
         | v |                                  v
        +-----+                              +-----+
        |     |<---------------R1------------|     |
        |  I  |----------------I2----------->|  R  |
        |     |<---------------R2------------|     |
        +-----+                              +-----+

   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) in a HIPHI RR, and the IP
   address(es) of its Rendezvous Server(s) (IP-RVS) in HIPRVS resource
   record(s).  The mobile HIP node also need to notify its Rendezvous
   Servers of any change in its set of IP address(es).

   A host wanting to reach this mobile host would then send an I1 to one
   of its RVS.  Following, the RVS will relay the I1 up to the mobile
   node, which will complete the HIP exchange.








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3.3  Mixed Scenario

               [A? HIPRVS? HIPHI?]
               [www.example.com  ]          +-----+
         +--------------------------------->|     |
         |                                  | DNS |
         | +--------------------------------|     |
         | |   [A? HIPRVS? HIPHI?      ]    +-----+
         | |   [www.example.com        ]
         | |   [A IP-R1                ]
         | |   [A IP-R2                ]
         | |   [HIPRVS 1 2 IP-RVS1     ]
         | |   [HIPRVS 1 2 IP-RVS2     ]
         | |   [HIPHI 10 3 2 HIT-R HI-R]
         | |
         | |               +------+
         | | +-----I1----->| RVS1 |------I1------+
         | | |             +------+              |
         | v |                                   v
        +-----+                               +-----+
        |     |---------------I1------------->|     |
        |     |                               |     |
        |  I  |<--------------R1--------------|  R  |
        |     |---------------I2------------->|     |
        |     |<--------------R2--------------|     |
        +-----+                               +-----+
             |                                   ^
             |             +------+              |
             +-----I1----->| RVS2 |------I1------+
                           +------+

   A HIP node might be configured with more than one IP address
   (multi-homed), or Rendezvous Server (multi-reachable).  In these
   cases, it is possible that the DNS returns multiples A or AAAA RRs,
   as well as HIPRVS containing one or multiple Rendezvous Servers.  In
   addition to its set of IP address(es) (IP-R1, IP-R2), a multi-homed
   end-host would store in the DNS its HI (HI-R) in a HIPHI RR, and
   possibly the IP address(es) of its RVS(s) (IP-RVS1, IP-RVS2) in
   HIPRVS RRs.






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4.  Overview of using the DNS with HIP

4.1  Storing HI and HIT in DNS

   Any conforming implementation may store Host Identifiers in a DNS
   HIPHI RDATA format.  An implementation may also store a HIT along
   with its associated HI.  If a particular form of an HI or HIT does
   not already have a specified RDATA format, a new RDATA-like format
   SHOULD be defined for the HI or HIT.

4.1.1  Different types of HITs

   There are _currently_ two types of HITs.  HITs of the first type
   consists just of the least significant bits of the hash of the public
   key.  HITs of the second type consist of a binary prefix Host
   Assigning Authority (HAA) field, and only the last bits come from a
   hash of the Host Identity.  This latter format for HIT is recommended
   for 'well known' systems.  It is possible to support a resolution
   mechanism for these names in directories like DNS.

   Note that the format how HITs are stored in the DNS may be different
   form the format actually used in protocols, the HIP base exchange
   [10] included.  This is because the DNS RR explicitly contains the
   HIT type and algorithm, while some protocols may prefer to use a
   prefix to indicate the HIT type.  The implementations are expected to
   use the actual HI when comparing Host Identities.

4.1.1.1  Host Assigning Authority (HAA) field

   The 64 bits of HAA supports two levels of delegation.  The first is a
   registered assigning authority (RAA).  The second is a registered
   identity (RI, commonly a company).  The RAA is 24 bits with values
   assign sequentially by ICANN.  The RI is 40 bits, also assigned
   sequentially but by the RAA.

4.1.1.2  Storing HAA in DNS

   Any conforming implementation may store a domain name Host Assigning
   Authority (HAA) in a DNS HIPHI RDATA format.  A HAA MUST be stored
   like a Type 2 HIT, while the least significant bits of the HIT
   extracted from the HI hash output are set to zero, the Host Identity
   Length is set zero, and the Host Identity field is omitted.  If a
   particular form of a HAA does not already have an associated HIT
   specified RDATA format, a new RDATA-like format SHOULD be defined for
   the HIT/HAA.



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4.1.1.3  HI and HIT verification

   Upon return of a HIPHI RR, a host MUST always calculate the
   HI-derivative HIT to be used in the HIP exchange, as specified in the
   HIP architecture [11], while the HIT possibly embedded along SHOULD
   only be used as an optimization (e.g.  table lookup).

4.2  Storing Rendezvous Servers in the DNS

   The HIP Rendezvous server (HIPRVS) resource record indicates an
   address or a domain name of a RendezVous Server, towards which a HIP
   I1 packet might be sent to trigger the establishment of an
   association with the entity named by this resource record [13].

   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.

   Any conforming implementation may store Rendezvous Server's IP
   address(es) or DNS name in a DNS HIPRVS RDATA format.  If a
   particular form of a RVS reference does not already have a specified
   RDATA format, a new RDATA-like format SHOULD be defined for the RVS.

4.3  Initiating connections based on DNS names

   On a HIP node, a Host Identity Protocol exchange SHOULD be initiated
   whenever an Upper Layer Protocol attempt to communicate with an
   entity and the DNS lookup returns HIPHI and/or HIPRVS resource
   records.  If a DNS lookup returns one or more HIPRVS RRs and no A nor
   AAAA RRs, the afore mentioned HIP exchange SHOULD be initiated
   towards one of these RVS [10].  Since some hosts may choose not to
   have HIPHI information in DNS, hosts MAY implement support for
   opportunistic HIP.









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5.  Storage Format

5.1  HIPHI RDATA format

   The RDATA for a HIPHI RR consists of a HIT type, an algorithm type, a
   HIT, and a public key.

           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 type    | HIT algorithm |  PK algorithm |               |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    HIT        |
          ~                                                               ~
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                                                               /
          /                          Public Key                           /
          /                                                               /
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|


5.1.1  HIT type format

   The HIT type field indicates the Host Identity Tag (HIT) type and the
   implied HIT format.

   The following values are defined:

      0         No HIT is present
      1         A Type 1 HIT is present
      2         A Type 2 HIT is present
      3-6       Unassigned
      7         A HAA is present

5.1.2  HIT algorithm format

   The HIT algorithm indicates the hash algorithm used to generate the
   Host Identity Tag (HIT) from the HI.

   The following values are defined:

      0         Reserved
      1         SHA1
      2-255     Unassigned

5.1.3  PK algorithm format

   The PK algorithm field indicates the public key cryptographic


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   algorithm and the implied public key field format.  This document
   reuse the values defined for the 'algorithm type' of the IPSECKEY RR
   [14] 'gateway type' field.

   The presently defined values are given only informally:

      1 A DSA key is present, in the format defined in RFC2536 [5].
      2 A RSA key is present, in the format defined in RFC3110 [6].

5.1.4  HIT format

   There's currently two types of HITs, and a single type of HAA.  Both
   of them are stored in network byte order within a self-describing
   variable length wire-encoded <character-string> (as per Section 3.3
   of [2]):

   o  A *Type 1* HIT: least significant bits of the hash (e.g., SHA1) of
      the public key (Host Identity), which is possibly following in the
      HIPHI RR.
   o  A *Type 2* HIT: binary prefix (HAA) concatenated with a the least
      significant bits of the hash (e.g., SHA1) of the public key (Host
      Identity), which is possibly following in the HIPHI RR.
   o  A HAA: binary prefix (HAA) concatenated with 0, up to the
      associated HIT length.

5.1.5  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 [14] (which
   in turns contains the algorithm-specific portion of the KEY RR RDATA,
   all of the KEY RR DATA after the first four octets, corresponding to
   the same portion of the KEY RR that must be specified by documents
   that define a DNSSEC algorithm).

   In the future, if a new algorithm is to be used both by IPSECKEY RR
   and HIPHI RR, it would probably use the same public key encodings for
   both RRs.  Unless specified otherwise, the HIPHI public key field
   would use the same public key format as the IPSECKEY RR RDATA for the
   corresponding algorithm.

   The DSA key format is defined in RFC2536 [5].

   The RSA key format is defined in RFC3110 [6] and the RSA key size
   limit (4096 bits) is relaxed in the IPSECKEY RR [14] specification.

5.2  HIPRVS RDATA format

   The RDATA for a HIPRVS RR consists of a preference value, a


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   Rendezvous server type and either one or more Rendezvous server
   address, or one Rendezvous server domain name.

           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
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |  preference   |     type      |                               |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      Rendezvous server        |
          ~                                                               ~
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.2.1  Preference format

   This is an unsigned 8-bit value, used to specify the preference given
   to this RR amongst others at the same owner.  Lower values are
   preferred.  If there is a tie within some RR subset, the server
   should return a permutation (e.g.  round robin) of the set of RRs,
   such that the requester load is fairly balanced amongst all RRs of
   the set.

5.2.2  Rendezvous server type format

   The Rendezvous server type indicates the format of the information
   stored in the Rendezvous server field.

   This document reuses the type values for the 'gateway type' field of
   the IPSECKEY RR [14].  The presently defined values are given only
   informally:

   1.  One or more 4-byte IPv4 address(es) in network byte order are
       present.
   2.  One or more 16-byte IPv6 address(es) in network byte order are
       present.
   3.  One or more variable length wire-encoded domain names as
       described in section 3.3 of RFC1035 [2].  The wire-encoded format
       is self-describing, so the length is implicit.  The domain names
       MUST NOT be compressed.

5.2.3  Rendezvous server format

   The Rendezvous server field indicates one or more Rendezvous
   Server(s) IP address(es), or domain name(s).  A HIP I1 packet sent to
   any of these RVS would reach the entity named by this resource
   record.

   This document reuses the format used for the 'gateway' field of the
   IPSECKEY RR [14], but allows to concatenate several IP (v4 or v6)


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   addresses.  The presently defined formats for the data portion of the
   Rendezvous server field are given only informally:

   o  One or more 32-bit IPv4 address(es) in network byte order.
   o  One or more 128-bit IPv6 address(es) in network byte order.
   o  One or more variable length wire-encoded domain names as described
      in section 3.3 of RFC1035 [2].  The wire-encoded format is
      self-describing, so the length is implicit.  The domain names MUST
      NOT be compressed.





















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6.  Presentation Format

   This section specifies the representation of the HIPHI and HIPRVS RR
   in a zone data master file.

6.1  HIPHI Representation

   The HIT Type, HIT algorithm, PK algorithm, and Public Key are
   REQUIRED.  The HIT field is OPTIONAL.

   The HIT Type, HIT algorithm, and PK algorithm are represented as
   unsigned integers.

   The HIT field is represented as the Base16 encoding [8] (a.k.a.  hex
   or hexadecimal) of the public key.  If no HIT is to be indicated,
   then the HIT algorithm MUST be zero and the HIT field must be ".".

   The Public Key field is represented as the Base64 encoding [8] of the
   public key.

   The complete representation of the HPIHI record is:

   IN           HIPHI ( hit-type hit-algorithm pk-algorithm
                        base16-encoded-hit
                        base64-encoded-public-key )

6.2  HIPRVS Representation

   The Preference and RVS Type fields are REQUIRED.  At least one RVS
   field MUST be present.

   The HIT Type, HIT algorithm, and PK algorithm are represented as
   unsigned integers.

   The RVS field is represented by one or more:
   o  IPv4 dotted decimal address(es)
   o  IPv6 colon hex address(es)
   o  uncompressed domain name(s)

   The complete representation of the HPIRVS record is:

   IN           HIPRVS  ( preference rendezvous-server-type
                          rendezvous-server[1]
                                ...
                          rendezvous-server[n] )


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6.3  Examples

   Example of a node with a HI but no HIT:

   www.example.com           IN    HIPHI ( 0 1 2
                              .
                              AB3NzaC1kc3MAAACBAOBhKnTCPOuFBzZQX/N3O9dm9P9ivUIMoId== )

   Example of a node with a HI and a HIT:

   www.example.com           IN    HIPHI ( 1 1 2
                              120cf10ea842e0ba53320f1fe0ba5d3a3
                              AB3NzaC1kc3MAAACBAOBhKnTCPOuFBzZQX/N3O9dm9P9ivUIMoId== )

   Example of a node with an IPv6 RVS:

   www.example.com           IN    HIPRVS ( 10 2 2001:0db8:0200:1:20c:f1ff:fe0b:a533 )

   Example of a node with three IPv4 RVS:

   www.example.com           IN    HIPRVS ( 10 1 192.0.2.2 192.0.99.2 192.0.199.2)

   Example of a node with two named RVS:

   www.example.com           IN    HIPRVS ( 10 3 rvs.uk.example.com rvs.us.example.com )













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7.  Retrieving Multiple HITs and IPs from the DNS

   If a host receives multiple HITs in a response to a DNS query, those
   HITs MUST be considered to denote a single service, and be
   semantically equivalent from that point of view.  When initiating a
   base exchange with the denoted service, the host SHOULD be prepared
   to accept any of HITs as the peer's identity.  A host MAY implement
   this by using the opportunistic mode (destination HIT null in I1), or
   by sending multiple I1s, if needed.

   In particular, if a host receives multiple HITs and multiple IP
   addresses in response to a DNS query, the host cannot know how the
   HITs are reachable at the listed IP addresses.  The mapping may be
   any, i.e., all HITs may be reachable at all of the listed IP
   addresses, some of the HITs may be reachable at some of the IP
   addresses, or there may even be one-to-one mapping between the HITs
   and IP addresses.  In general, the host cannot know the mapping and
   MUST NOT expect any particular mapping.

   It is RECOMMENDED that if a host receives multiple HITs, the host
   SHOULD first try to initiate the base exchange by using the
   opportunistic mode.  If the returned HIT does not match with any of
   the expected HITs, the host SHOULD retry by sending further I1s, one
   at time, trying out all of the listed HITs.  If the host receives an
   R1 for any of the I1s, the host SHOULD continue to use the successful
   IP address until an R1 with a listed HIT is received, or the host has
   tried all HITs, and try the other IP addresses only after that.  A
   host MAY also send multiple I1s in parallel, but sending such I1s
   MUST be rate limited to avoid flooding (as per Section 8.4.1 of
   [10]).











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8.  Transition mechanisms

   During a transition period, to allows to store the HIP informations
   of a node in a DNS server which does not support the HIPHI and HIPRVS
   RRs, A and AAAA RRs MAY be overloaded.  A HIT would typically be
   stored in a AAAA RR and a RVS in either a A or AAAA RR.  If such a
   situation occurs, the overloaded RRs MUST be returned as the last
   items of the returned RRs set (A or AAAA), to avoid as most as
   possible conflicts with non-HIP IPv6 nodes.





















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9.  Security Considerations

   Though the security considerations of the HIP DNS extensions still
   need to be more investigated and documented, this section contains a
   description of the known threats involved with the usage of the HIP
   DNS extensions.

   In a manner similar to the IPSECKEY RR [14], the HIP DNS Extensions
   allows to provision 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 Extensions introduce
   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 both the HIPHI and HIPRVS RRs from a trusted
   party trough a secure channel insuring proper data integrity of the
   RRs.  DNSSEC [3] provides such a secure channel.

   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.

9.1  Attacker tampering with an unsecure HIPHI RR

   The HIPHI 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 HIPHI 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 HIPHI
   and HIPRVS rewritten by the attacker).

9.2  Attacker tampering with an unsecure HIPRVS RR

   The HIPRVS RR contains a destination IP address where the named peer
   is reachable by an I1 (HIP Rendezvous Extensions IPSECKEY RR [13] ).
   Thus, an attacker able to tamper with this RRs 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 attacks are not specific to HIP
   and exist independently to whether or not HIP and the HIPRVS 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 owns in a
   spoofed DNS packet sent to the initiator HI, then redirect all


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   exchanged packets through him and mount a MitM on HIP.  In this case
   HIP won't provide confidentiality nor initiator HI protection from
   eavesdroppers.

9.3  Opportunistic HIP

   A HIP initiator may not be aware of its peer's HI, and/or its HIT
   (e.g., because the DNS does not contains HIP material, or the
   resolver isn't HIP-enabled), and attempt an opportunistic HIP
   exchange towards its known IP address, filling the responder HIT
   field with zeros in the I1 header.  Such an initiator is vulnerable
   to a MitM attack because it can't validate the HI and HIT contained
   in a replied R1.  Hence, an implementation MAY choose not to use
   opportunistic mode.

9.4  Unpublished Initiator HI

   A HIP initiator may choose to use an unpublished HI, which is not
   stored in the DNS by means of a HIPHI RR.  A responder associating
   with such an initiator knowingly risks a MitM attack because it
   cannot validate the initiator's HI.  Hence, an implementation MAY
   choose not to use unpublished mode.

9.5  Hash and HITs Collisions

   As many cryptographic algorithm, 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 a
   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 DNS, but SHOULD rather use
   HI-based authentication.









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10.  IANA Considerations

   IANA needs to allocate two new RR type code for HIPHI and HIPRVS from
   the standard RR type space.

   IANA needs to open a new registry for the HIPHI RR HIT type.  Defined
   types are:

      0         No HIT is present
      1         A Type 1 HIT is present
      2         A Type 2 HIT is present
      3-6       Unassigned
      7         A HAA is present

   Adding new reservations requires IETF consensus RFC2434 [16].

   IANA needs to open a new registry for the HIPHI RR HIT algorithm.
   Defined types are:

      0         Reserved
      1         SHA1
      2-255     Unassigned

   Adding new reservations requires IETF consensus RFC2434 [16].

   IANA does not need to open a new registry for the HIPHI RR type for
   public key algorithms because the HIPHI RR reuse 'algorithms types'
   defined for the IPSECKEY RR [14].  The presently defined numbers are
   given here only informally:

      0 is reserved
      1 is RSA
      2 is DSA

   IANA does not need to open a new registry for the HIPRVS RR
   Rendezvous server type because the HIPHI RR reuse the 'gateway types'
   defined for the IPSECKEY RR [14].  The presently defined numbers are
   given here only informally:

      0 is reserved
      1 is IPv4
      2 is IPv6
      3 is a wire-encoded uncompressed domain name




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11.  Acknowledgments

   As usual in the IETF, this document is the result of a collaboration
   between many people.  The authors would like to thanks the author
   (Michael Richardson), contributors and reviewers of the IPSECKEY RR
   [14] specification, which this document was framed after.  The
   authors would also like to thanks the following people, who have
   provided thoughtful and helpful discussions and/or suggestions, that
   have helped improving this document: Rob Austein, Hannu Flinck, Tom
   Henderson, Miika Komu, Andrew McGregor, Erik Nordmark, and Gabriel
   Montenegro.  Some parts of this draft stem from [10].




















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12.  References

12.1  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]   Eastlake, D. and C. Kaufman, "Domain Name System Security
         Extensions", RFC 2065, January 1997.

   [4]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [5]   Eastlake, D., "DSA KEYs and SIGs in the Domain Name System
         (DNS)", RFC 2536, March 1999.

   [6]   Eastlake, D., "RSA/SHA-1 SIGs and RSA KEYs in the Domain Name
         System (DNS)", RFC 3110, May 2001.

   [7]   Bush, R., Durand, A., Fink, B., Gudmundsson, O. and T. Hain,
         "Representing Internet Protocol version 6 (IPv6) Addresses in
         the Domain Name System (DNS)", RFC 3363, August 2002.

   [8]   Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
         RFC 3548, July 2003.

   [9]   Thomson, S., Huitema, C., Ksinant, V. and M. Souissi, "DNS
         Extensions to Support IP Version 6", RFC 3596, October 2003.

   [10]  Moskowitz, R., Nikander, P. and P. Jokela, "Host Identity
         Protocol", draft-ietf-hip-base-01 (work in progress), October
         2004.

   [11]  Moskowitz, R. and P. Nikander, "Host Identity Protocol
         Architecture", draft-ietf-hip-arch-00 (work in progress),
         October 2004.

   [12]  Nikander, P., "End-Host Mobility and Multi-Homing with Host
         Identity Protocol", draft-ietf-hip-mm-00 (work in progress),
         October 2004.

   [13]  Laganier, J. and L. Eggert, "Host Identity Protocol (HIP)
         Rendezvous Extensions", draft-ietf-hip-rvs-00 (work in
         progress), October 2004.


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   [14]  Richardson, M., "A method for storing IPsec keying material in
         DNS", draft-ietf-ipseckey-rr-12 (work in progress), January
         2005.

12.2  Informative references

   [15]  Jokela, P., Moskowitz, R. and P. Nikander, "Using ESP transport
         format with HIP", draft-jokela-hip-esp-00 (work in progress),
         February 2005.

   [16]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
         Considerations Section in RFCs", BCP 26, RFC 2434, October
         1998.

Authors' Addresses

   Pekka Nikander
   Ericsson Research Nomadic Lab
   JORVAS  FIN-02420
   FINLAND

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

   Julien Laganier
   LIP (CNRS-INRIA-ENSL-UCBL) & Sun Labs (Sun Microsystems)
   180, Avenue de l'Europe
   Saint Ismier CEDEX  38334
   France

   Phone: +33 476 188 815
   EMail: ju@sun.com









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Appendix A.  Document Revision History

   +-----------+-------------------------------------------------------+
   | Revision  | Comments                                              |
   +-----------+-------------------------------------------------------+
   | 01        | Compared to draft-ietf-hip-dns-01: Removed HIP        |
   |           | rendezvous registration protocol. Removed references  |
   |           | to DNS. Added figures. Added text discussing multiple |
   |           | HITs and IP.                                          |
   |           |                                                       |
   | 00        | Initial version as a HIP WG item.                     |
   +-----------+-------------------------------------------------------+




















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