[Docs] [txt|pdf] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06

IRTF HIP Research Group                                     J. Ahrenholz
Internet-Draft                                        The Boeing Company
Expires: July 14, 2008                                  January 11, 2008


                           HIP DHT Interface
                      draft-ahrenholz-hiprg-dht-02

Status of this Memo

   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 becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on July 14, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2008).















Ahrenholz                 Expires July 14, 2008                 [Page 1]


Internet-Draft              HIP DHT Interface               January 2008


Abstract

   This document specifies a common interface for using HIP with a
   Distributed Hash Table service to provide a HIT-to-address lookup
   service and an unmanaged name-to-HIT lookup service.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  The OpenDHT interface  . . . . . . . . . . . . . . . . . . . .  4
   3.  HIP lookup services  . . . . . . . . . . . . . . . . . . . . .  7
     3.1.  HIP address lookup . . . . . . . . . . . . . . . . . . . .  7
     3.2.  HIP name to HIT lookup . . . . . . . . . . . . . . . . . . 10
   4.  HDRR - the HIP DHT Resource Record . . . . . . . . . . . . . . 13
   5.  When to use the HIP lookup services  . . . . . . . . . . . . . 15
   6.  Issues with DHT support  . . . . . . . . . . . . . . . . . . . 17
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 20
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . . 22
     A.1.  Changes from Version 01 to 02  . . . . . . . . . . . . . . 22
     A.2.  Changes from Version 00 to 01  . . . . . . . . . . . . . . 22
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 23
   Intellectual Property and Copyright Statements . . . . . . . . . . 24

























Ahrenholz                 Expires July 14, 2008                 [Page 2]


Internet-Draft              HIP DHT Interface               January 2008


1.  Introduction

   The Host Identity Protocol [I-D.ietf-hip-base] may benefit from a
   lookup service based on Distributed Hash Tables (DHTs).  The Host
   Identity namespace is flat, consisting of public keys, in contrast to
   the hierarchical Domain Name System.  These keys are hashed and
   prefixed to form Host Identity Tags (HITs) which appear as large
   random numbers.  The current DNS system does not provide a suitable
   lookup mechanism for these flat, random values, and has been heavily
   optimized for address lookup.  DHTs manage such data well by applying
   a hash function that distributes data across a number of servers.
   DHTs also feature good support for frequently updating stored values.

   One freely available implementation of a DHT is the Bamboo DHT, which
   is Java-based software that has been deployed on PlanetLab servers to
   form a free service named OpenDHT.  OpenDHT is available via the
   Internet for any program to store and retrieve arbitrary data.
   OpenDHT uses a well defined XML-RPC interface, featuring put, get,
   and remove operations.  This document discusses a common interface
   for HIP to be used with OpenDHT, so that various HIP implementations
   may leverage lookup services in an interoperable fashion.






























Ahrenholz                 Expires July 14, 2008                 [Page 3]


Internet-Draft              HIP DHT Interface               January 2008


2.  The OpenDHT interface

   OpenDHT is a public deployment of Bamboo DHT servers running on about
   150 PlanetLab nodes.  While the Bamboo project provides the actual
   software running on the servers, here we will refer only to OpenDHT,
   which uses a certain defined interface for the XML-RPC calls.  One
   can run their own Bamboo nodes to set up a private ring of servers,
   but here we are interested in providing a service for use with
   multiple, different HIP implementations.

   OpenDHT was chosen because it is a well-known, publicly available DHT
   used within the research community.  Its interface features a simple,
   standards-based protocol that can be easily implemented by HIP
   developers.  This document does not aim to dictate that only the
   services and servers described here should be used, but is rather
   meant to act as a starting point to gain experience with these
   services, choosing tools that are readily available.

   OpenDHT stores values using (hash) keys.  Keys are limited to 20
   bytes in length, and values can be up to 1024 bytes.  Values are
   stored for a certain number of seconds, up to a maximum of 604,800
   seconds (one week.)  See the OpenDHT website:
   <http://www.opendht.org/>

   Three RPC operations are supported: put, get, and rm (remove).  Put
   is called with key and value parameters, causing the value to be
   stored using the key as its hash index.  Get is called with the key
   parameter, when you have a key and want to retrieve the value.  Rm is
   called with a hash of the value to be removed along with a secret
   value, a hash of which was included in the put operation.

   The definitions below are taken from
   <http://opendht.org/users-guide.html>.


















Ahrenholz                 Expires July 14, 2008                 [Page 4]


Internet-Draft              HIP DHT Interface               January 2008


             The put operation takes the following arguments:

         +----------------+--------------------------------------+
         | field          | type                                 |
         +----------------+--------------------------------------+
         | application    | string                               |
         |                |                                      |
         | client_library | string                               |
         |                |                                      |
         | key            | byte array, 20 bytes max.            |
         |                |                                      |
         | value          | byte array, 1024 bytes max.          |
         |                |                                      |
         | ttl_sec        | four-byte integer, max. value 604800 |
         |                |                                      |
         | secret_hash    | optional SHA-1 hash of secret value  |
         +----------------+--------------------------------------+

     The server replies with an integer -- 0 for "success", 1 if it is
              "over capacity", and 2 indicating "try again".

             The get operation takes the following arguments:

     +----------------+---------------------------------------------+
     | field          | type                                        |
     +----------------+---------------------------------------------+
     | application    | string                                      |
     |                |                                             |
     | client_library | string                                      |
     |                |                                             |
     | key            | byte array, 20 bytes max.                   |
     |                |                                             |
     | maxvals        | four-byte singed integer, max. value 2^31-1 |
     |                |                                             |
     | placemark      | byte array, 100 bytes max.                  |
     +----------------+---------------------------------------------+

   The server replies with an array of values, and a placemark that can
                  be used for fetching additional values.












Ahrenholz                 Expires July 14, 2008                 [Page 5]


Internet-Draft              HIP DHT Interface               January 2008


              The rm operation takes the following arguments:

     +----------------+----------------------------------------------+
     | field          | type                                         |
     +----------------+----------------------------------------------+
     | application    | string                                       |
     |                |                                              |
     | client_library | string                                       |
     |                |                                              |
     | key            | byte array, 20 bytes max.                    |
     |                |                                              |
     | value_hash     | SHA-1 hash of value to remove                |
     |                |                                              |
     | ttl_sec        | four-byte integer, max. value 604800         |
     |                |                                              |
     | secret         | secret value (SHA-1 of this was used in put) |
     +----------------+----------------------------------------------+

     The server replies with an integer -- 0 for "success", 1 if it is
              "over capacity", and 2 indicating "try again".

   This is the basic XML-RPC interface provided by OpenDHT.  Each
   "field" from the above tables are XML tags that enclose their
   corresponding values.  Below, specific uses for HIP are suggested,
   along with values that can be used inside the fields shown above.


























Ahrenholz                 Expires July 14, 2008                 [Page 6]


Internet-Draft              HIP DHT Interface               January 2008


3.  HIP lookup services

   Here an address lookup and HIT lookup service are defined for use
   with HIP.  The address lookup uses a peer's HIT to discover its
   current addresses.  The HIT lookup uses a text name to discover a
   peer's HIT.

         HDRR = get(HIT_KEY)
         HIT = get(SHA1("name"))

   First is the address lookup, which uses a HIP DHT Resource Record
   (HDRR) described in Section 4.  Before a HIP association can be
   initiated (a non-opportunistic initiation), a HIP host needs the
   peer's HIT and the current address at which the peer is reachable.
   Often the HIT will be pre-configured or available via DNS lookup
   using a hostname lookup [I-D.ietf-hip-dns].  With HIP mobility
   [I-D.ietf-hip-mm], IP addresses may be used as locators that are
   often subject to change.  The Host Identity and the HIT remain
   relatively constant and can be used to securely identify a host, so
   the HIT serves as a suitable DHT key for storing and retrieving
   addresses.

   The address lookup service includes the peer's Host Identity and a
   signature over the locators.  This allows the DHT client or server to
   validate the address information stored in the DHT.

   Finally, the HIT lookup service can be used when legacy DNS servers
   do not support HIP resource records, or when hosts do not have
   administrative access to their DNS records.  This unmanaged naming
   service may help facilitate the HIP IRTF experiment.

   These services reduce the amount of pre-configuration required at
   each HIP host.  The address of each peer no longer needs to be known
   ahead of time, if peers also participate by publishing their
   addresses.  If peers choose to publish their HITs with a name, peer
   HITs also no longer need pre-configuration.  However, discovering an
   available DHT server for servicing these lookups will require some
   additional configuration.

3.1.  HIP address lookup

   Given a HIT, a lookup returns the HIP DHT Resource Record (HDRR) for
   the peer.  This interface has publish, lookup, and remove operations.

         HDRR = get(HIT_KEY)
         put(HIT_KEY, HDRR, [secret])
         rm(HIT_KEY, HDRR, secret)




Ahrenholz                 Expires July 14, 2008                 [Page 7]


Internet-Draft              HIP DHT Interface               January 2008


   The HDRR is defined in Section 4.  It contains one or more locators
   that the peer wants to publish, and the peer's Host Identity and
   signature over the contents.

   The HIT_KEY is a portion of the HIT used as a DHT key.  [RFC4843]
   defines the HIT as a Prefix concatenated with 100 bits of hash:

            Input      :=  any bitstring
            Hash Input :=  Context ID | Input
            Hash       :=  Hash_function( Hash Input )
            ORCHID     :=  Prefix | Encode_100( Hash )

   The HIT_KEY is the Encode_100( Hash ) portion of the above
   definition.  This 100-bit value is zero padded to fill the length
   required by the DHT, 160 bits total.  The HIT's ORCHID Prefix is
   dropped because this would cause uneven distribution of the stored
   values across the DHT servers.

                              Address publish

   +----------------+----------------------------------------+---------+
   | field          | value                                  | data    |
   |                |                                        | type    |
   +----------------+----------------------------------------+---------+
   | application    | "hip-addr"                             | string  |
   |                |                                        |         |
   | client_library | (implementation dependent)             | string  |
   |                |                                        |         |
   | key            | 100-bit HIT_KEY                        | base64  |
   |                |                                        | encoded |
   |                |                                        |         |
   | value          | HDRR                                   | base64  |
   |                |                                        | encoded |
   |                |                                        |         |
   | ttl_sec        | amount of time HDRR should be valid,   | numeric |
   |                | or the lifetime of the preferred       | string  |
   |                | address                                |         |
   |                |                                        |         |
   | secret_hash    | optional SHA-1 hash of secret value    | base64  |
   |                |                                        | encoded |
   +----------------+----------------------------------------+---------+










Ahrenholz                 Expires July 14, 2008                 [Page 8]


Internet-Draft              HIP DHT Interface               January 2008


                              Address lookup

   +----------------+---------------------------------+----------------+
   | field          | value                           | data type      |
   +----------------+---------------------------------+----------------+
   | application    | "hip-addr"                      | string         |
   |                |                                 |                |
   | client_library | (implementation dependent)      | string         |
   |                |                                 |                |
   | key            | 100-bit HIT_KEY                 | base64 encoded |
   |                |                                 |                |
   | maxvals        | (implementation dependent)      | numeric string |
   |                |                                 |                |
   | placemark      | (NULL, or used from server      | base64 encoded |
   |                | reply)                          |                |
   +----------------+---------------------------------+----------------+

                         Address remove (optional)

   +----------------+-------------------------------------+------------+
   | field          | value                               | data type  |
   +----------------+-------------------------------------+------------+
   | application    | "hip-addr"                          | string     |
   |                |                                     |            |
   | client_library | (implementation dependent)          | string     |
   |                |                                     |            |
   | key            | 100-bit HIT_KEY                     | base64     |
   |                |                                     | encoded    |
   |                |                                     |            |
   | value_hash     | SHA-1 hash of HDRR (value used      | base64     |
   |                | during publish) to remove           | encoded    |
   |                |                                     |            |
   | ttl_sec        | old address lifetime                | numeric    |
   |                |                                     | string     |
   |                |                                     |            |
   | secret         | secret value (SHA-1 of this was     | base64     |
   |                | used in put)                        | encoded    |
   +----------------+-------------------------------------+------------+

   The application and client_library fields are used for logging in
   OpenDHT.  The client_library may vary between different
   implementations, specifying the name of the XML-RPC library used or
   the application that directly makes XML-RPC calls.

   The key for both address publish and lookup is the 100-bits of the
   HIT_KEY as defined above, plus 60-bits of zero padding, base64
   encoded [RFC2045].  The value used in the publish and lookup response
   is the base64 encoded HDRR containing one or more LOCATORs.



Ahrenholz                 Expires July 14, 2008                 [Page 9]


Internet-Draft              HIP DHT Interface               January 2008


   The ttl_sec field used with address publish includes the time-to-
   live, the number of seconds for which the entry will be stored by the
   DHT, which is set to the number of seconds remaining in the address
   lifetime.

   The secret_hash is an optional field used with address publish, used
   if the value will later be removed with an rm operation.  The
   secret_hash contains the base64 encoded SHA-1 hash of some secret
   value known only to the publishing host.  Clients SHOULD include the
   secret_hash and remove outdated values to reduce the amount of data
   the peer needs to handle.

   The max_vals and placemark fields used with address lookup are
   defined by the get XML-RPC interface.  The get operation needs to
   know the maximum number of values to retrieve.  The placemark is a
   value found in the server reply that causes the get to continue to
   retrieve values starting at where it left off.

3.2.  HIP name to HIT lookup

   Given the SHA-1 hash of a name, a lookup returns the HIT of the peer.
   The hash of a name is used because OpenDHT keys are limited to 20
   bytes, so this allows for longer names.  Publish, lookup, and remove
   operations are defined.

         HIT = get(SHA-1("name"))
         put(SHA-1("name", HIT, [secret])
         rm(SHA-1("name", HIT, secret)

                                HIT publish

   +----------------+----------------------------------+---------------+
   | field          | value                            | data type     |
   +----------------+----------------------------------+---------------+
   | application    | "hip-name-hit"                   | string        |
   |                |                                  |               |
   | client_library | (implementation dependent)       | string        |
   |                |                                  |               |
   | key            | SHA-1 hash of name               | base64        |
   |                |                                  | encoded       |
   |                |                                  |               |
   | value          | 128-bit HIT                      | base64        |
   |                |                                  | encoded       |
   |                |                                  |               |
   | ttl_sec        | name lifetime                    | numeric       |
   |                |                                  | string        |
   |                |                                  |               |




Ahrenholz                 Expires July 14, 2008                [Page 10]


Internet-Draft              HIP DHT Interface               January 2008


   | secret_hash    | optional SHA-1 hash of secret    | base64        |
   |                | value                            | encoded       |
   +----------------+----------------------------------+---------------+

                                HIT lookup

   +----------------+---------------------------------+----------------+
   | field          | value                           | data type      |
   +----------------+---------------------------------+----------------+
   | application    | "hip-name-hit"                  | string         |
   |                |                                 |                |
   | client_library | (implementation dependent)      | string         |
   |                |                                 |                |
   | key            | SHA-1 hash of name              | base64 encoded |
   |                |                                 |                |
   | maxvals        | (implementation dependent)      | numeric string |
   |                |                                 |                |
   | placemark      | (NULL, or used from server      | base64 encoded |
   |                | reply)                          |                |
   +----------------+---------------------------------+----------------+

                           HIT remove (optional)

   +----------------+------------------------------------+-------------+
   | field          | value                              | data type   |
   +----------------+------------------------------------+-------------+
   | application    | "hip-name-hit"                     | string      |
   |                |                                    |             |
   | client_library | (implementation dependent)         | string      |
   |                |                                    |             |
   | key            | SHA-1 hash of name                 | base64      |
   |                |                                    | encoded     |
   |                |                                    |             |
   | value_hash     | SHA-1 hash of address value to     | base64      |
   |                | remove                             | encoded     |
   |                |                                    |             |
   | ttl_sec        | name lifetime                      | numeric     |
   |                |                                    | string      |
   |                |                                    |             |
   | secret         | secret value (SHA-1 of this was    | base64      |
   |                | used in put)                       | encoded     |
   +----------------+------------------------------------+-------------+

   The key for both HIT publish and lookup is the SHA-1 hash of the
   name.  The name does not necessarily need to be associated with a
   valid DNS or host name.  It does not need to be related to the Domain
   Identifier found in HI TLV.  OpenDHT limits the keys to 20 bytes in
   length, so the SHA-1 hash is used to allow arbitrary name lengths.



Ahrenholz                 Expires July 14, 2008                [Page 11]


Internet-Draft              HIP DHT Interface               January 2008


   The value used in the publish and lookup response is the base64-
   encoded 128-bit HIT.

   The ttl_sec field specifies the number of seconds for which the entry
   will be stored by the DHT, which is implementation dependent.

   The secret_hash is an optional field used with HIT publish if the
   value will later be removed with an rm operation.  The secret_hash
   contains the base64 encoded SHA-1 hash of some secret value known
   only to the publishing host.  The max_vals and placemark fields used
   with the HIT lookup are defined by the get XML-RPC interface.








































Ahrenholz                 Expires July 14, 2008                [Page 12]


Internet-Draft              HIP DHT Interface               January 2008


4.  HDRR - the HIP DHT Resource Record

   The HIP DHT Resource Record uses the same binary format as HIP
   packets (defined in [I-D.ietf-hip-base].)  This packet encoding is
   used as a convenience, even though this data is actually a resource
   record stored and retrieved by the DHT servers, not a packet sent on
   the wire by a HIP protocol daemon.  Note that this HDRR format is
   different than the HIP RR used by the Domain Name System as defined
   in [I-D.ietf-hip-dns].

   HIP header values for the HDRR:

     HIP Header:
       Packet Type = 20 (this value is TBD)
       SRC HIT = Sender's HIT
       DST HIT = NULL

     HIP ( LOCATOR, HOST_ID, HIP_SIGNATURE )

   Valid control bits: A

   If the Responder HI is an anonymous one, the A control MUST be set.

   The Initiator HIT is set to the HIT that the host wishes to make
   available using the lookup service.  This HIT is the same one used to
   derive the HIT_KEY used as the DHT key.  The Responder HIT MUST be
   NULL (all zeroes) since the data is intended for any host.

   The LOCATOR parameter contains the addresses that the host wishes to
   make available using the lookup service.  A host may publish its
   current preferred IPv4 and IPv6 locators, for example.

   The HOST_ID parameter contains the Host Identity that corresponds
   with the Sender's HIT.  (The encoding of this parameter is defined in
   section 5.2.8 of [I-D.ietf-hip-base].)

   The HOST_ID parameter and HIP_SIGNATURE parameter MUST be used with
   the HDRR so that HIP clients receiving the record can validate the
   sender and the included LOCATOR parameter.  The HIT_KEY used for the
   DHT key will also be verified against the Host Identity.

   The client that receives the HDRR from the DHT response MUST perform
   the signature and HIT_KEY verification.  If the signature is invalid
   for the given Host Identity or the HIT_KEY used to retrieve the
   record does not match the Host Identity, the DHT record retrieved
   MUST be ignored.  Note that for client-only verification the DHT
   server does not need to be modified, so this would work on the
   existing OpenDHT PlanetLab deployment.



Ahrenholz                 Expires July 14, 2008                [Page 13]


Internet-Draft              HIP DHT Interface               January 2008


   The DHT server could also verify the SIGNATURE and HOST_ID.  This
   document primarily describes using the legacy OpenDHT service.  Such
   Host Identity and signature verification would require modifications
   to the DHT server software.  Users running their own server can run
   the Bamboo DHT software, on which OpenDHT is based, with some
   modifications.  The signature in the put needs to be verified using
   the given Host Identity, and the HIT_KEY provided as the key needs to
   match this Host Identity.  If either signature or HIT verification
   fails, the put is not recorded into the DHT.  Full specification of
   this HIP-aware server behavior is outside the scope of this draft.









































Ahrenholz                 Expires July 14, 2008                [Page 14]


Internet-Draft              HIP DHT Interface               January 2008


5.  When to use the HIP lookup services

   Below are some suggestions of when a HIP implementation may want to
   use the address and HIT lookup services.

   To learn of a peer's HIT, a host might first consult DNS using the
   peer's hostname if the DNS server supports the HIP Resource Record
   defined by [I-D.ietf-hip-dns].  Sometimes hosts do not have
   administrative authority over their DNS entries and/or the DNS server
   is not able to support HIP resource records.  Hosts may want to
   associate other non-DNS names with their HITs.  For these and other
   reasons, a host may use the HIT publish service defined in
   Section 3.2.  The peer HIT may be learned by performing a DHT lookup
   of such a name.

   Once a peer HIT is learned or configured, an address lookup could be
   performed so that the LOCATORs can be cached and immediately
   available for when an association is requested.  Implementations
   might load a list of peer HITs on startup, resulting in several
   lookups that can take some time to complete.

   However, cached LOCATORs may quickly become obsolete, depending on
   how often the peer changes its preferred address.  Performing an
   address lookup before sending the I1 may be needed.  At this time the
   latency of a lookup may be intolerable, and a lookup could instead be
   performed after the I1 retransmission timer fires -- when no R1 reply
   has been received -- to detect any change in address.

   A HIP host should publish its preferred LOCATORs upon startup, so
   other hosts may determine where it is reachable.  The host needs to
   periodically refresh its HDRR entry because each entry carries a TTL
   and will eventually expire.  Also, when there is a change in
   preferred address, usually associated with sending UPDATE packets
   with included locator parameters, the host should update its HDRR
   with the DHT.  The old HDRR should be removed using the rm operation,
   if a secret value was used in the put.

   Addresses from the private address space should not be published to
   the DHT.  If the host is located behind a NAT, for example, the host
   could publish the address of its RVS to the DHT if that is how it is
   reachable.  In this case however, a peer could instead simply use the
   RVS field of the NATted host's HIP DNS record, which would eliminate
   a separate DHT lookup.

   A HIP host should also publish its HIT upon startup or whenever a new
   HIT is configured, for use with the HIT lookup service, if desired.
   The host should first check if the name already exists in the DHT by
   performing a lookup, to avoid interfering with an existing name-to-



Ahrenholz                 Expires July 14, 2008                [Page 15]


Internet-Draft              HIP DHT Interface               January 2008


   HIT mapping.  The name-to-HIT binding needs to be refreshed
   periodically before the TTL expires.

















































Ahrenholz                 Expires July 14, 2008                [Page 16]


Internet-Draft              HIP DHT Interface               January 2008


6.  Issues with DHT support

   Each put operation appends the new value to any existing values.  If
   a host does not remove its old HDRR before adding another, several
   entries may be present.  Therefore when performing an address lookup,
   the last HDRR in the DHT response list should be used and considered
   to contain the current preferred address.  Before performing each put
   a host should remove its old HDRR data using the rm operation.

   In the case of the HIT lookup service, there is nothing preventing
   different hosts from publishing the same name.  A lookup performed on
   this name will return multiple HITs that belong to different devices.
   This is an unmanaged free-for-all service, so this issue will not be
   solved here; it is recommended that a host simply pick another name.

   Selecting an appropriate DHT server to use is not covered here.  If a
   particular server becomes unavailable, the connect will timeout and
   some server selection algorithm should be performed, such as trying
   the next server in a configured list.  OpenDHT does provide a DNS-
   based anycast service, when you perform a lookup of
   "opendht.nyuld.net", it will return the two nearest OpenDHT servers.

   Because the put and get calls rely on outside servers located across
   the Internet, operations may have a latency involved that should be
   considered when using these services with HIP.

   The maximum size of 1024 bytes for the value field will limit the
   maximum size of the Host Identity that may be used within the HDRR.























Ahrenholz                 Expires July 14, 2008                [Page 17]


Internet-Draft              HIP DHT Interface               January 2008


7.  Security Considerations

   There are two classes of attacks on this information exchange between
   host and DHT server: attacks on the validity of the information
   provided by the DHT to the host (such as a spoofed DHT response) and
   attacks on the DHT records themselves (such as polluted records for a
   given key).  Without an authenticated and trusted service, not much
   can be done to prevent these attacks.

   For the address lookup based on HIT (Section 3.1), the validity of
   the DHT response can be checked with the HOST_ID and SIGNATURE
   parameters in the HDRR.  A HIP initiating host can also validate the
   DHT response after the R1 message is received during a HIP exchange.
   The Host Identity provided in the R1 can be hashed to obtain a HIT
   that can be checked against the original HIT.  However, the legacy
   OpenDHT service does not currently prevent an attacker from polluting
   the DHT records for a known HIT, thereby causing a denial-of-service
   attack, since server validation is not performed.

   Relying solely on client validation may be harmful.  An attacker can
   replay the put packets containing the signed HDRR, possibly causing
   stale or invalid information to exist in the DHT.  If an attacker
   replays the signed put message and changes some aspect each time, and
   if the server is not performing signature and HIT validation, there
   could be a multitude of invalid entries stored in the DHT.  When a
   client retrieves these records it would need to perform signature and
   HIT verification on each one, which could cause unacceptable amounts
   of delay or computation.

   To protect against this type of attack, the DHT server could be
   running HIP and requiring client authentication with a HIP
   association before accepting HDRR puts.  Also a HIP-aware DHT server
   could be developed to perform the HIT and signature verification of
   each put.  This is briefly described in Section 4.

   For the HIT lookup based on name (Section 3.2), there are no
   guarantees on the validity of the HIT.  Users concerned with the
   validity of HITs found in the DHT should simply exchange HITs out-of-
   band with peers.  Including a signature will not help here because
   the HIT that identifies the Host Identity for signing is not known
   ahead of time.










Ahrenholz                 Expires July 14, 2008                [Page 18]


Internet-Draft              HIP DHT Interface               January 2008


8.  IANA Considerations

   This document has no actions for IANA.
















































Ahrenholz                 Expires July 14, 2008                [Page 19]


Internet-Draft              HIP DHT Interface               January 2008


9.  Acknowledgments

   Thanks to Tom Henderson, Samu Varjonen, Andrei Gurtov, Miika Komu,
   and Kristian Slavov for providing comments.  Samu most notably
   contributed the resolver packet and its suggested parameters, which
   became the HDRR here.













































Ahrenholz                 Expires July 14, 2008                [Page 20]


Internet-Draft              HIP DHT Interface               January 2008


10.  References

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC4843]  Nikander, P., Laganier, J., and F. Dupont, "An IPv6 Prefix
              for Overlay Routable Cryptographic Hash Identifiers
              (ORCHID)", RFC 4843, April 2007.

   [I-D.ietf-hip-base]
              Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson,
              "Host Identity Protocol", draft-ietf-hip-base-10 (work in
              progress), October 2007.

   [I-D.ietf-hip-dns]
              Nikander, P. and J. Laganier, "Host Identity Protocol
              (HIP) Domain Name System (DNS) Extensions",
              draft-ietf-hip-dns-09 (work in progress), April 2007.

   [I-D.ietf-hip-mm]
              Henderson, T., "End-Host Mobility and Multihoming with the
              Host Identity Protocol", draft-ietf-hip-mm-05 (work in
              progress), March 2007.



























Ahrenholz                 Expires July 14, 2008                [Page 21]


Internet-Draft              HIP DHT Interface               January 2008


Appendix A.  Change Log

A.1.  Changes from Version 01 to 02

   sockaddr address format changed to use HIP DHT Resource Record
   containing the HIP LOCATOR format.  The HIT prefix is dropped before
   using it as a key.  Separate "secure" service was dropped, and
   signatures made mandatory.  Legacy versus hip-aware DHT servers are
   distinguished.  Text packet examples added.

A.2.  Changes from Version 00 to 01

   Removed the HIT lookup service -- using the LSI as a key to return a
   HIT as the value -- and added a HIT lookup service using names.

   Added support for OpenDHT remove.  Changed all occurrences of "Open
   DHT" to "OpenDHT".

   Added the Host Identity and a signature as a secure address lookup
   service, with text about running a modified OpenDHT server that can
   verify signed put messages based on Host Identity signatures.






























Ahrenholz                 Expires July 14, 2008                [Page 22]


Internet-Draft              HIP DHT Interface               January 2008


Author's Address

   Jeff Ahrenholz
   The Boeing Company
   P.O. Box 3707
   Seattle, WA
   USA

   Email: jeffrey.m.ahrenholz@boeing.com










































Ahrenholz                 Expires July 14, 2008                [Page 23]


Internet-Draft              HIP DHT Interface               January 2008


Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





Ahrenholz                 Expires July 14, 2008                [Page 24]


Html markup produced by rfcmarkup 1.123, available from https://tools.ietf.org/tools/rfcmarkup/