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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: April 18, 2005                                      J. Laganier
                                                  LIP / Sun Microsystems
                                                        October 18, 2004


    Host Identity Protocol (HIP) Domain Name System (DNS) Extensions
                         draft-ietf-hip-dns-00

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 April 18, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   This document specifies two new resource records for the Domain Name
   System (DNS), and how to use them with the Host Identity Protocol
   (HIP).  These records allow a HIP node to store in the DNS its Host
   Identity (its public key), Host Identity Tag (a truncated hash of its
   public key), and Rendezvous Servers (RVS).




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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions used in this document  . . . . . . . . . . . . . .  5
   3.  Use cases  . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.1   Simple static singly homed end-host  . . . . . . . . . . .  7
     3.2   Mobile end-host  . . . . . . . . . . . . . . . . . . . . .  7
     3.3   Multi-homed Site or End-host . . . . . . . . . . . . . . .  7
   4.  Overview of using the DNS with HIP . . . . . . . . . . . . . .  8
     4.1   Different types of HITs  . . . . . . . . . . . . . . . . .  8
       4.1.1   Host Assigning Authority (HAA) field . . . . . . . . .  8
     4.2   Storing HI and HIT in DNS  . . . . . . . . . . . . . . . .  8
     4.3   Storing HAA in DNS . . . . . . . . . . . . . . . . . . . .  8
     4.4   Providing multiple IP addresses  . . . . . . . . . . . . .  9
       4.4.1   Storing Rendezvous Servers in the DNS  . . . . . . . .  9
     4.5   Initiating connections based on DNS names  . . . . . . . .  9
     4.6   HI and HIT verification  . . . . . . . . . . . . . . . . .  9
   5.  Storage Format . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.1   HIPHI RDATA format . . . . . . . . . . . . . . . . . . . . 10
       5.1.1   HIT type format  . . . . . . . . . . . . . . . . . . . 10
       5.1.2   HIT algorithm format . . . . . . . . . . . . . . . . . 10
       5.1.3   PK algorithm type format . . . . . . . . . . . . . . . 10
       5.1.4   HIT format . . . . . . . . . . . . . . . . . . . . . . 11
       5.1.5   Public key format  . . . . . . . . . . . . . . . . . . 11
     5.2   HIPRVS RDATA format  . . . . . . . . . . . . . . . . . . . 11
       5.2.1   Preference format  . . . . . . . . . . . . . . . . . . 12
       5.2.2   Rendezvous server type format  . . . . . . . . . . . . 12
       5.2.3   Rendezvous server format . . . . . . . . . . . . . . . 12
   6.  Transition mechanisms  . . . . . . . . . . . . . . . . . . . . 14
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
     7.1   Attacker tampering with an unsecure HIPHI RR . . . . . . . 15
     7.2   Attacker tampering with an unsecure HIPRVS RR  . . . . . . 15
     7.3   Opportunistic HIP  . . . . . . . . . . . . . . . . . . . . 16
     7.4   Anonymous Initiator  . . . . . . . . . . . . . . . . . . . 16
     7.5   Hash and HITs Collisions . . . . . . . . . . . . . . . . . 16
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 18
   10.   References . . . . . . . . . . . . . . . . . . . . . . . . . 19
   10.1  Normative references . . . . . . . . . . . . . . . . . . . . 19
   10.2  Informative references . . . . . . . . . . . . . . . . . . . 20
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 20
   A.  Using multiple HIs with multiple IPs . . . . . . . . . . . . . 21
   B.  Document Revision History  . . . . . . . . . . . . . . . . . . 23
       Intellectual Property and Copyright Statements . . . . . . . . 24







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1.  Introduction

   This document specifies two new resource records (RRs) for the Domain
   Name System (DNS) [7], and how to use them with the Host Identity
   Protocol (HIP) [9].  These records allow a HIP node to store in the
   DNS its Host Identity (its public key), Host Identity Tag (a
   truncated hash of its public key), and Rendezvous Servers (RVS) [12].

   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 [10]
   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 in some ULPs and
   applications.

   The Host Identity Protocol [9] allows two HIP nodes to establish a
   pair of unidirectional IPsec Security Association.  These SAs are
   bound to the HI instead of IP addresses.  The proposed HIP
   multi-homing mechanisms [11] 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
   [12] proposal allows a HIP node to maintain HIP reachability while
   not relying on dynamic DNS updates to make its peers aware of its
   current location (the set of IP address(es)).

   Although a HIP node can initiate HIP communication
   "opportunistically" (without a priori knowledge of its peer's HI),
   doing so exposes both endpoints to Man-in-the-Middle attacks on the
   HIP handshake.  Hence, there is a desire to gain knowledge of peers'
   HI before applications and ULPs initiate communication.

   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



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   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 [2].














































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3.  Use cases

   In this section, we briefly introduce a number of use cases 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 [12].

   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 HIP node having a single static network attachment, wishing to be
   reachable by reference to its FQDN, would store in the DNS, in
   addition to its IP address(es), its Host Identity (HI) in a HIPHI
   resource record.

3.2  Mobile end-host

   A mobile HIP node wishing to be reachable by reference to its FQDN
   would store in the DNS, instead of its IP address(es), its HI in a
   HIPHI RR, and the IP address(es) of its Rendezvous Server(s) 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.

3.3  Multi-homed Site or End-host

   A HIP node with several distinct network attachments is multi-homed.
   A HIP node attached to a network with multiple ISPs is in a
   multi-homed site will possibly have multiple prefixes and addresses.
   Such HIP node might also be reachable via several distinct Rendezvous
   Servers.  In addition to its set of IP address(es), a multi-homed
   end-host would store in the DNS its HI in a HIPHI RR, and possibly
   the IP address(es) of its RVS(s) in HIPRVS RRs.























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4.  Overview of using the DNS with HIP

4.1  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 [9]
   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  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.

   As IPv6 "global site-local" addresses were proposed in the IPv6 WG to
   replace IPv6 site-local address, it is questionable if HIP needs a
   kind of "global site-local" HAA, which would be generated by a given
   site by setting the RAA field to 0 while the RI field is filled by
   either random or EUI-48 bits.

4.2  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.

4.3  Storing HAA in DNS

   Any conforming implementation may store a site's Host Assigning
   Authority in a DNS HIPHI RDATA format.  A HAA MUST be stored
   similarly to a Type 2 HIT, while the least significant bits are set
   to 0.  If a particular form of a HAA does not already have an
   associated HIT specified RDATA format, a new RDATA-like format SHOULD



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   be defined for the HIT/HAA.

4.4  Providing multiple IP addresses

   With HIP, ULPs doesn't see which IP address is indeed used to carry
   packets on the wire.  Consequently, a HIP node could take advantage
   of having multiple IP addresses for ULPs and applications fail over,
   redundancy, etc.  This can be achieved either by storing multiple
   addresses in the DNS, while these addresses might be those of
   different IP interfaces or Rendezvous servers.

4.4.1  Storing Rendezvous Servers in the DNS

   The HIP Rendezvous server (HIPRVS) resource record indicates an
   address (or a FQDN resolvable into an address) towards which a HIP I1
   packet might be sent to trigger the establishment of an association
   with the entity named by this resource record.

   An RVS receiving such an I1 would then forward it to the appropriate
   responder (the owner of the destination HIT in this I1).  The
   responder will then complete the exchange with the initiator,
   possibly 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.

4.5  Initiating connections based on DNS names

   A Host Identity Protocol exchange SHOULD be initiated whenever the
   DNS lookup returns HIPHI resource records.  Furthermore, if the DNS
   lookups also returns HIPRVS resource records, the addresses of these
   RVS SHOULD be put in the destination IP addresses list while
   initiating the afore mentioned HIP exchange.  Since some hosts may
   choose not to have HIPHI information in DNS, hosts MAY implement
   support opportunistic HIP.

4.6  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 [10], while the HIT possibly embedded along SHOULD
   only be used as an optimization (e.g., table lookup).







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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 type format

   The algorithm type indicates the public key cryptographic algorithm



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   and the implied public key field format.  This document reuse the
   values defined for the 'algorithm type' of the IPSECKEY RR [13]
   'gateway type' field.

   The presently defined values are given only informally:

      0 No key is present.
      1 A DSA key is present, in the format defined in RFC2536 [3].
      2 A RSA key is present, in the format defined in RFC3110 [5].

5.1.4  HIT format

   There's currently two types of HITs, and a single type of HAA.  Both
   of them have a variable length and are stored within a single
   <character-string> holding the bits of the HITs or HAA:

   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 [13] (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 [3].

   The RSA key format is defined in RFC3110 [5].

5.2  HIPRVS RDATA format

   The RDATA for a HIPRVS RR consists of a preference value, a
   Rendezvous server type and either one or more Rendezvous server



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   address, or one Rendezvous server FQDN.

           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 8-bit preference order for this record.  This used to
   specify the preference given to this RR amongst others at the same
   owner.  Lower values are preferred.  If there is a tie with some RRs,
   the server should return a set of RRs ordered in a load balancing
   manner (e.g., round robin).

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 [13].  The presently defined values are given only
   informally:

      0 Reserved.
      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 [1].  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 address(es) (or one
   or more FQDN(s) resolvable into one or more address(es)) towards
   which a HIP I1 packet might be send in order to reach the entity
   named by this resource record.

   This document reuses the format used for the 'gateway' field of the
   IPSECKEY RR [13], but allows to concatenate several IP (v4 or v6)
   addresses.  The presently defined formats for the data portion of the



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   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 [1].  The wire-encoded format is
      self-describing, so the length is implicit.  The domain names MUST
      NOT be compressed.











































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6.  Transition mechanisms

   During a transition period, instead of storing the HI or HIT in a
   HIPHI RR, the HIT MAY be stored in an AAAA RR.  If a HIT is stored in
   an AAAA RR, it MUST be returned as the last item in the set of AAAA
   RRs returned to avoid as most as possible conflicts with non-HIP IPv6
   nodes.

   During a transition period, similarly to what may happen with HITs,
   the RVS's IP address might be stored in an A or AAAA RR instead of a
   HIPRVS RR.  If a RVS IP address is stored in an A or AAAA RR, it MUST
   be returned as the last item in the set of returned RRs to avoid as
   most as possible conflicts with non-HIP IPv6 nodes.






































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7.  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 [13], 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 of using unpublished initiator and opportunistic mode
   in HIP.

   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.  This might be DNSSEC, or another secure channel to another
   directory lookup service.

   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.

7.1  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).

7.2  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 [12] ).
   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



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   spoofed DNS packet sent to the initiator HI, then redirect all
   exchanged packets through him and mount a MitM on HIP.  In this case
   HIP won't provide confidentiality nor initiator HI protection from
   eavesdroppers.

7.3  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.

7.4  Anonymous Initiator

   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.

7.5  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 rather use both the HI
   and HIT.

















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8.  IANA Considerations

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

   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 [13].  The presently defined numbers are
   given here only informally:

      0 is reserved
      1 is RSA
      2 is DSA

   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 [14].

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

      0         Reserved
      1         SHA1
      2-255     Unassigned

   Adding new reservations requires IETF consensus RFC2434 [14].

   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 [13].  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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9.  Acknowledgments

   Some parts of this draft stem from [9].  This work is heavily
   influenced by [13], which serves as a model for this document.

   The authors would like to thanks the following people, who have
   provided thoughtful and helpful discussions and/or suggestions, that
   have improved this document: Rob Austein, Hannu Flinck, Tom
   Henderson, Miika Komu, Andrew McGregor, Erik Nordmark, and Gabriel
   Montenegro.









































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10.  References

10.1  Normative references

   [1]   Mockapetris, P., "Domain names - implementation and
         specification", STD 13, RFC 1035, November 1987.

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

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

   [4]   Crawford, M., "Binary Labels in the Domain Name System", RFC
         2673, August 1999.

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

   [6]   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.

   [7]   Klensin, J., "Role of the Domain Name System (DNS)", RFC 3467,
         February 2003.

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

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

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

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

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

   [13]  Richardson, M., "A method for storing IPsec keying material in
         DNS", draft-ietf-ipseckey-rr-10 (work in progress), April 2004.




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10.2  Informative references

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

   [15]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on
         Security Considerations", BCP 72, RFC 3552, July 2003.


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.  Using multiple HIs with multiple IPs

   The RRs defined in this document are "flat", in the sense that the IP
   addresses and HIs are associated to an FQDN on an equality basis.  In
   the case where an FQDN is resolved into multiple HIs (HIPHI RRs) and
   IP addresses (A, AAAA or HIPRVS RRs), the requester cannot associate
   an IP address with a specific HI, nor the opposite.

   Considering the following DNS-IP load balancing model: Multiple
   initiators are querying a DNS server with A or AAAA RRs at a given
   FQDN.  The DNS server replies with a round-robin ordered set of IP
   addresses, causing each initiator to connect to a different address
   (the first address of the set they received from the DNS).  This
   model can be extended to HIP by having the DNS returning a
   round-robin ordered set of HIs and IP addresses.  But then the
   problem is that the initiator would need to map each of these HIs to
   a subset of the returned set of IP addresses.  Hence, perhaps there
   is a need for having a "hierarchical" model for these RRs, which will
   allows to tie an HI to a specific subset of IP addresses, as
   illustrated in the figure below:

                                       FQDN
                                         |
                                     +---+---+
                                     |       |
                                     V       V
           FQDN                   HI1,HI2   HI3
            |                        |       |
    +---+---+---+---+---+          +-+-+     |
    |   |   |   |   |   |          |   |     |
    V   V   V   V   V   V          V   V     V
   IP1 IP2 IP3 HI1 HI2 HI3        IP1 IP2   IP3


   'Flat' DNS model Vs. 'Hierarchical' HI model

   However, as HIs and Type 1 HITs are not yet resolvable using the DNS,
   implementing such a model would certainly prove to be difficult.  The
   use of Distributed Hash Tables (DHTs) might help to resolve HIs, but
   at this point the whole story isn't known.  In the absence of HI
   resolvability, there is two solutions: index IP addresses and
   HIs/HITs used by HIP with a common key (e.g., the IP address, the
   HIT, a 8-bit int, etc.), or use a per-HI DNS name, pointed to by the
   FQDN global to the set of HIs, and pointing to the HIs, and IP
   addresses associated with this particular set of HIs.  to map to
   specific HIs, in a manner similar to what is done with NS RRs.

   In the first solution (indexing), each HIPHI, HIPRVS, and HIPLOC (a



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   new to-be-defined RR carrying the IP address of a HIP node, to be
   used by HIP instead of A and AAAA RRs, if present) would contain an
   additional HI index field allowing to link an HI with a subset of IP
   addresses and vice versa.  This solution is neither space-efficient,
   nor it is architecturally clean.

   In the second solution (parallel DNS names and bindings), the PTR RR
   is used to alias the name of a group of node into multiple FQDNs,
   which are then bound to set of HIs and IP addresses, as shown in the
   figure below.  These additional FQDNs are kind of HIP sub-FQDNs; an
   easy way to generate them is to suffix, or prefix the unqualified
   name with a sufficient number of bits of the HIT to prevent
   collisions local to a FQDN (e.g., foo.bar.com might haves multiple
   HIP sub-FQDNs: foo_2fa6.bar.com, foo_8cc4.bar.com, etc.).

                                       FQDN
                                         |
                                     +---+---+
                                     |       |
                                     V       V
      FQDN_1<--FQDN-->FQDN_2      HI1,HI2   HI3
        |               |            |       |
    +---+---+---+     +-+-+        +-+-+     |
    |   |   |   |     |   |        |   |     |
    V   V   V   V     V   V        V   V     V
   HI1 HI2 IP1 IP2   HI3 IP3      IP1 IP2   IP3


   The 'Hierarchical' HIP model fitting in a 'Flat' DNS model

   The current plan is to use the second solution unless HIP WG members
   express desire to have the first solution implemented.



















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Appendix B.  Document Revision History

   +-----------+-------------------------------------------------------+
   | Revision  | Comments                                              |
   +-----------+-------------------------------------------------------+
   | 00        | Compared to draft-nikander-hip-dns-00: Merge          |
   |           | multihomed site and end-host use cases. Remove HAA    |
   |           | related text not required for Type 2 HIT definition.  |
   |           | Remove IPv6 LSIs definitions. Replace fixed length    |
   |           | and algorithm Type 1 and Type 2 HITs by variable      |
   |           | length, type and algorithm HITs. Remove 'Policy       |
   |           | Considerations' section. Fill-in 'Security            |
   |           | Considerations' section. Allow for several IP         |
   |           | addresses in the same HIPRVS RR. Reuse the type       |
   |           | values and IANA registries of IPSECKEY RR. Add Annex  |
   |           | discussing alternatives for storing multiple          |
   |           | parallels FQDN-to-HI and HI-to-IP at a single FQDN.   |
   |           | Minor fixes to figures and their descriptive text.    |
   |           | Update references.                                    |
   +-----------+-------------------------------------------------------+































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