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Versions: 00 01 02 03 04 05 RFC 6537

HIP Research Group                                          J. Ahrenholz
Internet-Draft                                        The Boeing Company
Intended status: Informational                             July 26, 2010
Expires: January 27, 2011


        Host Identity Protocol Distributed Hash Table Interface
                        draft-irtf-hiprg-dht-01

Abstract

   This document specifies a common interface for using HIP with a
   Distributed Hash Table service to provide a name-to-Host-Identity-Tag
   lookup service and a Host-Identity-Tag-to-address lookup service.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on January 27, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.





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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  The OpenDHT interface  . . . . . . . . . . . . . . . . . . . .  4
   3.  HIP lookup services  . . . . . . . . . . . . . . . . . . . . .  7
     3.1.  HIP name to HIT lookup . . . . . . . . . . . . . . . . . .  8
     3.2.  HIP address lookup . . . . . . . . . . . . . . . . . . . . 10
   4.  HDRR - the HIP DHT Resource Record . . . . . . . . . . . . . . 14
   5.  Use cases  . . . . . . . . . . . . . . . . . . . . . . . . . . 16
   6.  Issues with DHT support  . . . . . . . . . . . . . . . . . . . 18
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 21
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . . 23
     A.1.  Changes from hiprg 00 to 01  . . . . . . . . . . . . . . . 23
     A.2.  Changes from Version ahrenholz 06 to hiprg 00  . . . . . . 23
     A.3.  Changes from Version 05 to 06  . . . . . . . . . . . . . . 23
     A.4.  Changes from Version 04 to 05  . . . . . . . . . . . . . . 23
     A.5.  Changes from Version 03 to 04  . . . . . . . . . . . . . . 23
     A.6.  Changes from Version 02 to 03  . . . . . . . . . . . . . . 23
     A.7.  Changes from Version 01 to 02  . . . . . . . . . . . . . . 23
     A.8.  Changes from Version 00 to 01  . . . . . . . . . . . . . . 24
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 25



























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1.  Introduction

   The Host Identity Protocol [RFC5201] 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.  As the current DNS system has been heavily optimized for
   address lookup, it may be worthwhile to experiment with other
   services such as those defined here.  DHTs manage such data well by
   applying a hash function that distributes data across a number of
   servers.  DHTs are also designed to support frequently updating
   stored values.  For an alternative method of using HITs to lookup IP
   addresses using DNS, see [I-D.ponomarev-hip-hit2ip].

   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 was available via the
   Internet for any program to store and retrieve arbitrary data.
   OpenDHT used a well defined XML-RPC interface, featuring put, get,
   and remove operations.  OpenLookup, while not implemented as a DHT,
   is another deployment of open source software compatible with this
   OpenDHT interface.  This document discusses a common way for HIP to
   use this OpenDHT interface, so that various HIP experimenters may
   employ lookup services in an interoperable fashion.

   This document represents the consensus of the HIP RG.  This document
   is not an IETF product and does not represent a standard.























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2.  The OpenDHT interface

   OpenDHT was a public deployment of Bamboo DHT servers that ran on
   about 150 PlanetLab nodes, retired in July 2009.  While the Bamboo
   project provided 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.  Another service compatible with this
   interface is OpenLookup.  One can run their own Bamboo nodes to set
   up a private ring of servers.

   OpenDHT was chosen because it was 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 the OpenDHT users guide at
   <http://opendht.org/users-guide.html>.


















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             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 return code 3
    indicates "failure" and is used for a modified OpenDHT server that
          performs signature and HIT verification, see Section 4.

             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.










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              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.  The key is a byte array used to index the
   record for storage and retrieval from the DHT.  The value is a byte
   array of the data being stored in the DHT.  The Application and
   client_library fields are meta-data used only for logging purposes.
   The ttl_sec field specifies the number of seconds that the DHT should
   store the value.  The secret_hash field allows values to be later
   removed from the DHT.  The maxvals and placemark fields are for
   retrieving a maximum number of values and for iterating get results.

   The return code of 0 "success" indicates a successful put or remove
   operation.  The return code of 1 "over capacity" means that a client
   is using too much storage space on the server.  The return value of 2
   "try again" indicates that the client should retry the put operation
   because a temporary problem prevented the server from accepting the
   put.

   In the sections that follow, specific uses for these DHT operations
   and their XML fields are suggested for use with HIP.










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3.  HIP lookup services

   This draft defines a HIT lookup and address lookup service for use
   with HIP.  The HIT lookup uses a text name to discover a peer's HIT.
   The address lookup uses a peer's HIT to discover its current
   addresses.

   The two lookups are defined below:

         HDRR([CERT]) = get(SHA-1("name"))
         HDRR(LOCATOR, SEQ, HOST_ID, [CERT], HIP_SIG) = get(HIT_KEY)

   Both services use a HIP DHT Resource Record (HDRR) described in
   Section 4.  This is a wrapper around data contained in TLVs, similar
   to a HIP control packet.  The data contained in each HDRR differs
   between the two services.

   The HIT lookup service returns the Host Identity Tag of a peer given
   a name.  The name could be the FQDN, hostname, or some other alias.
   This HIT is found in the Sender's HIT field of the HDRR.  The HIT is
   the hash of the public-key based Host Identity as described in
   [RFC5201].  There are no security properties of the name, unlike the
   HIT.  An optional certificate may be included in the record, for
   validating the name, providing some measure of security.  Which
   certificates to consider trusted is a policy issue.  This service is
   intended for use when legacy DNS servers do not support HIP resource
   records, or when hosts do not have administrative access to publish
   their own DNS records.  Such an unmanaged naming service may help
   facilitate experimentation.

   The address lookup returns a locator and other validation data in the
   HDRR for a given HIT.  Before a HIP association can be initiated (not
   in opportunistic mode), a HIP host needs to know the peer's HIT and
   the current address at which the peer is reachable.  Often the HIT
   will be pre-configured, available via DNS lookup using a hostname
   lookup [RFC5205], or retrieved using the HIT lookup service defined
   in this document.  With HIP mobility [RFC5206], IP addresses may be
   used as locators and may often 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.

   These two separate lookups are defined instead of one because the
   address record is expected to change more frequently, while the name-



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   to-HIT binding should remain relatively constant.  Also the client
   and server validation of the two records is different, with the HIT
   lookup using certificates verifying the name and the address lookup
   using a signature produced by the bearer of a particular Host
   Identity/HIT.

   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 require pre-configuration.  However, discovering
   an available DHT server for servicing these lookups will require some
   additional configuration.

3.1.  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.

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

                                HIT publish

   +----------------+----------------------------------------+---------+
   | field          | value                                  | data    |
   |                |                                        | type    |
   +----------------+----------------------------------------+---------+
   | application    | "hip-name-hit"                         | string  |
   |                |                                        |         |
   | client_library | (implementation dependent)             | string  |
   |                |                                        |         |
   | key            | SHA-1 hash of a name                   | base64  |
   |                |                                        | encoded |
   |                |                                        |         |
   | value          | HDRR([CERT]), with the HIT to be       | base64  |
   |                | published contained in the Sender's    | encoded |
   |                | HIT field of the HDRR, and an optional |         |
   |                | certificate for validating the name    |         |
   |                | used as the key                        |         |
   |                |                                        |         |
   | ttl_sec        | lifetime for this record, value from   | numeric |
   |                | 0-604800 seconds                       | string  |
   |                |                                        |         |




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

                                HIT lookup

   +----------------+---------------------------------+----------------+
   | field          | value                           | data type      |
   +----------------+---------------------------------+----------------+
   | application    | "hip-name-hit"                  | string         |
   |                |                                 |                |
   | client_library | (implementation dependent)      | string         |
   |                |                                 |                |
   | key            | SHA-1 hash of a 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 a name                   | base64  |
   |                |                                        | encoded |
   |                |                                        |         |
   | value_hash     | SHA-1 hash of HDRR (value used during  | base64  |
   |                | publish) to remove                     | encoded |
   |                |                                        |         |
   | ttl_sec        | lifetime for the remove should be      | numeric |
   |                | greater than or equal to the amount of | string  |
   |                | time remaining for the record          |         |
   |                |                                        |         |
   | secret         | secret value (SHA-1 of this was used   | base64  |
   |                | 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



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   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.

   The value used in the publish and lookup response is the base64-
   encoded HDRR containing the HIT, and an optional certificate.  The
   HIT is stored in the Sender's HIT field in the HDRR header, and is a
   128-bit value than can be identified as a HIT both by its length and
   by the ORCHID prefix ([RFC4843]) that it starts with.

   If a certificate is included in this HIT record, the name used for
   the DHT key should be listed in the certificate.  The CERT parameter
   is defined in [I-D.ietf-hip-cert].  The Common Name (CN) field from
   the distinguished name (DN) of the X.509.v3 certificate should be
   used.  The server can hash this name to verify it matches the DHT
   key.

   The ttl_sec field specifies the number of seconds requested by the
   client that the entry should be stored by the DHT server, which is
   implementation or policy dependent.

   The secret_hash is an optional field used with HIT publish if the
   value will later be removed with an rm operation.  It is recommended
   that clients support these rm operations for the values they publish.
   The secret_hash contains the base64 encoded SHA-1 hash of some secret
   value known only to the publishing host.  A different secret value
   should be used for each put because rm requests are visible on the
   network.  The max_vals and placemark fields used with the HIT lookup
   are defined by the get XML-RPC interface.

3.2.  HIP address lookup

   Given a HIT, a lookup returns the IP address of the peer.  The
   address is contained in a LOCATOR TLV inside the HDRR, along with
   other validation data.  This interface has publish, lookup, and
   remove operations.  A summary of these three operations is listed
   below.  The abbreviated notation refers to the HIP parameter types;
   for example HIP_SIG is the HIP signature parameter defined by
   [RFC5201].  The details of these DHT operations is then described in
   greater detail.

         HDRR(LOCATOR, SEQ, HOST_ID, [CERT], HIP_SIG) = get(HIT_KEY)
         put(HIT_KEY, HDRR(LOCATOR, SEQ, HOST_ID, [CERT], HIP_SIG),
             [SHA-1(secret)])
         rm(HIT_KEY, SHA-1(HDRR), secret)

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



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   The HIT_KEY is the last 100 bits of the HIT appended with 60 zero
   bits.  This is the portion of the HIT used as a DHT key.  The last
   100 bits is used to avoid uneven distribution of the stored values
   across the DHT servers.  The first 28 bits is the HIT's ORCHID Prefix
   defined by [RFC4843], and this prefix is dropped because it is the
   same for all HITs, which would cause this uneven distribution.  Zero
   padding is appended to this 100-bit value to fill the length required
   by the DHT, 160 bits total.

                              Address publish

   +----------------+----------------------------------------+---------+
   | field          | value                                  | data    |
   |                |                                        | type    |
   +----------------+----------------------------------------+---------+
   | application    | "hip-addr"                             | string  |
   |                |                                        |         |
   | client_library | (implementation dependent)             | string  |
   |                |                                        |         |
   | key            | HIT_KEY                                | base64  |
   |                |                                        | encoded |
   |                |                                        |         |
   | value          | HDRR(LOCATOR, SEQ, HOST_ID, [CERT],    | base64  |
   |                | HIP_SIG), with the IP address to be    | encoded |
   |                | published contained in the LOCATOR TLV |         |
   |                | in the HDRR, along with other          |         |
   |                | validation data                        |         |
   |                |                                        |         |
   | ttl_sec        | amount of time HDRR should be valid,   | numeric |
   |                | or the lifetime of the preferred       | string  |
   |                | address, a value from 0-604800 seconds |         |
   |                |                                        |         |
   | secret_hash    | optional SHA-1 hash of secret value    | base64  |
   |                |                                        | encoded |
   +----------------+----------------------------------------+---------+
















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                              Address lookup

   +----------------+---------------------------------+----------------+
   | field          | value                           | data type      |
   +----------------+---------------------------------+----------------+
   | application    | "hip-addr"                      | string         |
   |                |                                 |                |
   | client_library | (implementation dependent)      | string         |
   |                |                                 |                |
   | key            | 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            | 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 HIT_KEY as defined
   above, 160 bits base64 encoded [RFC2045].  The value used in the
   publish and lookup response is the base64 encoded HDRR containing one
   or more LOCATORs.



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   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.  A different secret value should be used
   for each put because rm requests are visible on the network.

   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.

































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4.  HDRR - the HIP DHT Resource Record

   The HIP DHT Resource Record uses the same binary format as HIP
   packets (defined in [RFC5201].)  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 [RFC5205].  The reason it is different is that it is a different
   record from a functional point of view: in DNS, the query key is a
   FQDN, and the return value is a HIT, while here, the query key is a
   HIT.

   HIP header values for the HDRR:

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

     HDRR used with HIT lookup:
     HIP ( [CERT] )

     HDRR used with address lookup:
     HIP ( LOCATOR, SEQ, HOST_ID, [CERT], HIP_SIGNATURE )

   The Initiator HIT (Sender's HIT, SRC HIT) is set to the HIT that the
   host wishes to make available using the lookup service.  With the HIT
   lookup service, this is the main piece of information returned by a
   get operation.  For the address lookup service, this HIT is the same
   one used to derive the HIT_KEY used as the DHT key.  The Responder
   HIT (Receiver's HIT, DST HIT) must be NULL (all zeroes) since the
   data is intended for any host.

   The only other TLV used with the HIT lookup service is an optional
   CERT parameter containing a certificate for validating the name that
   is used as the DHT key.  The CERT parameter is defined in
   [I-D.ietf-hip-cert].  The DHT server can use the certificate to
   verify that the client is authorized to use the name used for the DHT
   key, using the hash of the name found in the certificate.  The Common
   Name (CN) field from the distinguished name (DN) of the X.509.v3
   certificate should be used.  Which certificates the server considers
   trusted is a policy issue.

   The remaining parameters described here are used with the address
   lookup service.

   The LOCATOR parameter contains the addresses that the host wishes to



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   make available using the lookup service.  A host may publish its
   current preferred IPv4 and IPv6 locators, for example.

   The SEQ parameter contains an unsigned 32-bit sequence number, the
   Update ID.  This is typically initialized to zero and incremented by
   one for each new HDRR that is published by the host.  The host should
   retain the last Update ID value it used for each HIT across reboots,
   or perform a self lookup in the DHT, since that number may be
   retained in the DHT records and will determine the preferred address
   used by peers.

   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 [RFC5201].)

   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

   The Sender's HIT in the HDRR should correspond with the key used for
   the lookup and Host Identity verification.  The Receiver's HIT should
   be NULL (all zeroes) in the HDRR header.

   When several HDRR records are returned by the server, the client
   should pick the most recent record as indicated by the Update ID in
   the SEQ TLV of the HDRR, and perform verification on that record.
   The order in which records are returned should not be considered.

   The DHT server can also verify the SIGNATURE and HOST_ID, with some
   modifications to the Bamboo DHT software and a new return code with
   the OpenDHT interface.  The signature in the put needs to be verified
   using the given Host Identity (public key), and the HIT_KEY provided
   as the lookup key needs to match this Host Identity according to the
   ORCHID generation method defined by [RFC4843].  If either signature
   or HIT verification fails, the put is not recorded into the DHT, and
   the server returns a failure code.  The failure code is an additional
   return code not defined by OpenDHT, with a value of 3.






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5.  Use cases

   Below are some suggestions of when a HIP implementation may want to
   use the HIT and address 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 [RFC5205].  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 3.1.  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 Rendezvous Server (RVS, from
   [RFC5204]) 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-
   HIT mapping.  The name-to-HIT binding needs to be refreshed



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   periodically before the TTL expires.

   When publishing data to the DHT server, care should be taken to check
   the response from the server.  The server may respond with an "over
   capacity" code, indicating that its resources are too burdened to
   honor the given size and TTL.  The host should then select another
   server for publishing, or reduce the TTL and retry the put operation.












































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6.  Issues with DHT support

   The DHT put operation does not replace existing values.  If a host
   does not remove its old HDRR before adding another, several entries
   may be present.  A client performing a lookup should determine the
   most recent address based on the Update ID from the SEQ TLV of the
   HDRR.  The order of values returned in the server's response may not
   be guaranteed.  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.
   The server may enforce a policy that requires clients to include a
   certificate when publishing a HIT, and only store HITs with a name
   that has been authorized by some trusted certificate.  Otherwise this
   is an unmanaged free-for-all service, and 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 formerly provided a
   DNS-based anycast service, when you performed a lookup of
   "opendht.nyuld.net", it returned 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 and certificates that may be used
   within the HDRR.


















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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 the server performing some measure of
   verification, not much can be done to prevent these attacks.

   For the HIT lookup based on name (Section 3.1), 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.  A certificate may be included with the HIT which
   guarantees that the name used for the lookup has been authorized by
   some 3rd party authority.  Which certificates are considered trusted
   is a local policy issue.

   For the address lookup based on HIT (Section 3.2), 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, a legacy
   OpenDHT service without server modifications does 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 should perform
   signature and HIT verification of each put operation as described in
   Section 4.  Another option would be the server running HIP itself and
   requiring client authentication with a HIP association before
   accepting HDRR puts.  Further validation would be only accepting HIT
   and address records from the association bound to the same HIT.






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8.  IANA Considerations

   This document defines a new HIP Packet Type, the HIP Distributed Hash
   Table Resource Record (HDRR).  This packet type is defined in
   Section 4 with a value of 20.














































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9.  Acknowledgments

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













































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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.

   [RFC5201]  Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson,
              "Host Identity Protocol", RFC 5201, April 2008.

   [RFC5205]  Nikander, P. and J. Laganier, "Host Identity Protocol
              (HIP) Domain Name System (DNS) Extensions", RFC 5205,
              April 2008.

   [RFC5204]  Laganier, J. and L. Eggert, "Host Identity Protocol (HIP)
              Rendezvous Extension", RFC 5204, April 2008.

   [RFC5206]  Nikander, P., Henderson, T., Vogt, C., and J. Arkko, "End-
              Host Mobility and Multihoming with the Host Identity
              Protocol", RFC 5206, April 2008.

   [I-D.ponomarev-hip-hit2ip]
              Ponomarev, O. and A. Gurtov, "Embedding Host Identity Tags
              Data in DNS", draft-ponomarev-hip-hit2ip-04 (work in
              progress), July 2009.

   [I-D.ietf-hip-cert]
              Heer, T. and S. Varjonen, "HIP Certificates",
              draft-ietf-hip-cert-03 (work in progress), April 2010.



















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Appendix A.  Change Log

A.1.  Changes from hiprg 00 to 01

   Incorporated comments from Ari Keranen: added references to CERT
   draft and RFC 5204.  Added clarifications from OpenDHT user's guide.
   Simplified description of HIT_KEY.  Dropped RFC 2119 language.  Added
   IANA considerations.  Other minor corrections and clarifications.

A.2.  Changes from Version ahrenholz 06 to hiprg 00

   Document name changed to reflect acceptance as a HIPRG document.
   Text added to introduction about document acceptance.

A.3.  Changes from Version 05 to 06

   Use the HDRR format as return values for both services.  Added
   optional certificates for both services.  Added text about HIP-aware
   DHT server that validates HITs/signatures.  Added SEQ TLV to HDRR,
   removed text about ordering.  Relaxed statement about DNS and
   referenced draft-ponomarev-hip-hit2ip.  Added text describing why
   HDRR is different than DNS RR.  Added text about handling of source/
   destination HITs in HDRR.  Renamed Section 5 to "Use cases".  Added
   failure code for put.  Removed text about servers not honoring TTL.
   Added text clarifying what OpenLookup is.

A.4.  Changes from Version 04 to 05

   Reordered Sections 3.2 and 3.1, since the HIT lookup normally occurs
   before the address lookup.  Added text about why two separate lookups
   are defined.  Added text pertaining to the OpenDHT service retiring.

A.5.  Changes from Version 03 to 04

   Revised text about server treatment of TTL.

A.6.  Changes from Version 02 to 03

   Added text about TTL expiration, appending zero padding, HIT value
   usage.  Removed text on anonymous bit.  Use RFC references.

A.7.  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.



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A.8.  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.








































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Author's Address

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

   Email: jeffrey.m.ahrenholz@boeing.com










































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