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Internet Engineering Task Force                               D. Kuptsov
Internet-Draft                                                 A. Gurtov
Intended status: Informational        Helsinki Institute for Information
Expires: September 8, 2011                  Technology, Aalto University
                                                           March 7, 2011


                    Hierarchical Host Identity Tags
                         draft-kuptsov-hhit-02

Abstract

   This document describes the purpose, structure and possible use case
   of hierarchical host identity tags for HIP protocol.

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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Structure of HHIT . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Use case  . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   5.  Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6





































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1.  Introduction

   This document specifies the purpose, structure and possible use case
   of hierarchical host identity tags (HHIT) for Host Identity Protocol
   (HIP) RFC 5201 [RFC5201].

   The purpose of HHIT is to enable online verification of flat
   identifiers (in a scalable way), such as Host Identity Tags (HIT), by
   corresponding organizations that are responsible for clients holding
   such identifiers.  While one way of verifying whether HIT belongs to
   a client that is affiliated with some organization (or unit within
   organization) is to use certificates; such approach can be undesired
   because it (i) introduces high cost for certificate verification, and
   (ii) does not directly allow certificate status verification
   (consider the situation when private key of a particular host was
   stolen and firewall enforcing certificate verification does not check
   the revocation status of host's certificate).


2.  Structure of HHIT

   The following are the goals of HHIT: (i) allow any on the path
   security gateway to distinguish to which authority the identifier
   belongs, and later ask corresponding authority whether given HHIT is
   valid; (ii) prevent misuse of HHIT by attackers (specifically, the
   design allows to prevent replaying and constructing "fake" HHITs that
   will enable attackers to bypass the security gateways).

   The structure of hierarchical HHIT:






















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    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            OID                                |
   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |              HHIT             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         ENC_TIMESTAMP                         |
   +                                                               +
   |                                                               |
   +                                                               +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 1

   o  OID is organization identifier that depending of the application
      of HHIT can be globally unique (e.g., assigned by Internet
      Assigned Numbers Authority (IANA)), or unique within certain scope
      (e.g., within organization and assigned on per department or unit
      granularity).  Length of OID is 48 bits.

   o  HHIT is an output of a pseudo-random function (PRF) under one-time
      secret key and input taken as a concatenation of OID and flat
      identifier (HIT): HHIT=PRF(OID || HIT, secret) The length of HHIT
      field is 80 bits to guarantee sufficient level of security.

   o  ENC_TIMESTAMP field guarantees freshness of HHIT, it contains the
      timestamp when particular HHIT was generated.  This field is
      encrypted (using symmetric encryption function) under the same
      one-time secret as HHIT: ENC_TIMESTAMP = ENC(HHIT || #epoc,
      secret), where HHIT is as described above, #epoc is a timestamp
      indicating the time when HHIT was constructed, and secret is the
      next yet unused secret key from a key pull, assigned to a client
      by its authority.  Because the usage of block cipher is assumed
      for encryption, the length of ENC_TIMESTAMP field is a multiple of
      the block size of a particular encryption algorithm.  Since it is
      sufficient for #epoch to be on the scale of seconds, 48 bits
      reserved for this field.  As a result, the length of
      ENC_TIMESTAMP, when used together with AES-CBC algorithm, is 128
      bits.




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   Because total length of OID||HHIT||ENC_TIMESTAMP exceeds reserved 128
   bits for source address in HIP protocol, the source address may
   contain only OID||HHIT while ENC_TIMESTAMP can be carried as option
   in I1 packet.  Observe, that it is only rational to have
   ENC_TIMESTAMP filed in initial I1 packet.


3.  Use case

   Next we describe a possible use case: access control with HHIT:

                          Register HHIT (offline)
   +----------------------+------------------>+-------------+
   |                      |                   |  Domain 1   |
   |Client (from domain 1)|    Secret keys    |  authority  |
   +----------------------+<------------------+-------+-----+
                          |                  HHIT /\  | OK
                          |                       |   v
                          |   I1              +---+---------+
                          +------------------>|  Security   |-->...
                          +------------------>|  gateway    |
                          |   I1              +---+---+-----+
                          |                  HHIT |   /\
                          |   Register HHIT       v   |  Ok
   +----------------------+------------------>+-------------+
   |Client (from domain 2)|                   |  Domain 2   |
   |                      |    Secret keys    |  authority  |
   +----------------------+<------------------+-------+-----+

                                 Figure 2

   We outline the protocol interaction:

   o  Each end-host that belongs to some organization, or organizational
      unit, constructs its HIT (using the procedure described in RFC
      5201 [RFC5201]), and registers it in an offline (and out-of-band)
      manner in its organizational repository.  Depending on the
      application, the registration itself can involve authentication,
      e.g. using passwords, certificates, biometric information,
      passport, etc.  Upon verification, domain authority generates set
      of one-time-passwords (the number of such passwords again depends
      on the application needs), and for each secret s populates its
      database with the following records: HHIT = PRF(OID || HIT, s)
      Domain authority then returns list of secrets to client over
      secure channel (how this is achieved is out of scope).

   o  When a client wants to access the service that is behind security
      gateway, it chooses next unused one-time secret "unused secret"



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      and constructs the HHIT as PRF(OID || HIT, "unused secret"), it
      also takes the current #epoch "now" and constructs ENC_TIMESTAMP
      as ENC(HHIT || "now", "unused secret").  The I1 packet then
      contain the concatenation of OID, HHIT, and ENC_TIMESTAMP in the
      source address field.

   o  When security gateway receives such I1 packet, it will look-up the
      domain authority using OID found in the source address, and submit
      OID, HHIT, and ENC_TIMESTAMP.  Security gateway will buffer I1
      until it will receive (positive or negative) response from
      corresponding domain authority.

   o  Last, when domain authority receives OID, HHIT, and ENC_TIMESTAMP
      for verification it looks up for the proper secret using HHIT as
      index.  If the record was not found, the domain authority
      immediately responds to a gateway that information is not valid.
      Else, domain authority attempts to decrypt ENC_TIMESTAMP field to
      find #epoch.  It also registers the current time "now".  If "now"
      - #epoch > Delta, the HHIT will be considered as invalid, and
      negative response will be sent to security gateway, otherwise,
      domain authority will remove the record from the database, and
      reply to security gateway with positive response code.

   o  Security gateway will make a forwarding decision regarding
      particular buffered I1 packet based on the response it receives
      from domain authority: if the response is negative I1 packet is
      dropped, otherwise the state will be created and I1 will be
      forwarded.  Note, for consequent R1, I2, R2 packets the forwarding
      decisions by security gateway are done solely based on the stored
      internal state: if it exists the packets are forwarded, otherwise
      dropped.


4.  Security Considerations


5.  Normative References

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











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Authors' Addresses

   Dmitriy Kuptsov
   Helsinki Institute for Information Technology, Aalto University
   PO Box 19215
   TKK  00076 Aalto
   Finland

   Phone:
   Email: dmitriy.kuptsov@hiit.fi


   Andrei Gurtov
   Helsinki Institute for Information Technology, Aalto University
   PO Box 19215
   TKK  00076 Aalto
   Finland

   Phone:
   Email: gurtov@hiit.fi































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