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RFC 6078 - Host Identity Protocol (HIP) Immediate Carriage and C


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Internet Engineering Task Force (IETF)                      G. Camarillo
Request for Comments: 6078                                      J. Melen
Category: Experimental                                          Ericsson
ISSN: 2070-1721                                             January 2011

     Host Identity Protocol (HIP) Immediate Carriage and Conveyance
              of Upper-Layer Protocol Signaling (HICCUPS)

Abstract

   This document defines a new Host Identity Protocol (HIP) packet type
   called DATA.  HIP DATA packets are used to reliably convey
   authenticated arbitrary protocol messages over various overlay
   networks.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Engineering
   Task Force (IETF).  It represents the consensus of the IETF
   community.  It has received public review and has been approved for
   publication by the Internet Engineering Steering Group (IESG).  Not
   all documents approved by the IESG are a candidate for any level of
   Internet Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6078.

Copyright Notice

   Copyright (c) 2011 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.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Background on HIP  . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Message Formats  . . . . . . . . . . . . . . . . . . . . .  4
       3.1.1.  HIP Fixed Header . . . . . . . . . . . . . . . . . . .  4
       3.1.2.  HIP Parameter Format . . . . . . . . . . . . . . . . .  5
     3.2.  HIP Base Exchange, Updates, and State Removal  . . . . . .  5
   4.  Definition of the HIP_DATA Packet  . . . . . . . . . . . . . .  6
     4.1.  Definition of the SEQ_DATA Parameter . . . . . . . . . . .  8
     4.2.  Definition of the ACK_DATA Parameter . . . . . . . . . . .  8
     4.3.  Definition of the PAYLOAD_MIC Parameter  . . . . . . . . .  9
     4.4.  Definition of the TRANSACTION_ID Parameter . . . . . . . . 10
   5.  Generation and Reception of HIP_DATA Packets . . . . . . . . . 10
     5.1.  Handling of SEQ_DATA and ACK_DATA  . . . . . . . . . . . . 10
     5.2.  Generation of a HIP_DATA Packet  . . . . . . . . . . . . . 11
     5.3.  Reception of a HIP_DATA Packet . . . . . . . . . . . . . . 12
       5.3.1.  Handling of SEQ_DATA in a Received HIP_DATA Packet . . 13
       5.3.2.  Handling of ACK_DATA in a Received HIP_DATA Packet . . 14
   6.  Use of the HIP_DATA Packet . . . . . . . . . . . . . . . . . . 14
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 16
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     10.2. Informative references . . . . . . . . . . . . . . . . . . 16

1.  Introduction

   Two hosts can use HIP [RFC5201] to establish a security association
   (SA) between them in order to exchange arbitrary protocol messages
   over that security association.  The establishment of such a security
   association involves a four-way handshake referred to as the HIP base
   exchange.  When handling communications between the hosts, HIP
   supports mobility, multihoming, security, and NAT traversal.  Some
   applications require these features for their communications but
   cannot accept the overhead involved in establishing a security
   association (i.e., the HIP base exchange) before those communications
   can start.

   In this document, we define the HIP DATA packet, which can be used to
   convey (in a authenticated and reliable way) protocol messages to a
   remote host without running the HIP base exchange.  The HIP_DATA
   packet has the following semantics: unordered, duplicate free,
   reliable, and authenticated message-based delivery service.  We also
   discuss the trade-offs involved in using this packet (i.e., less
   overhead but also less denial-of-service (DoS) protection) and the
   situations where it is appropriate to use this packet.  The HIP_DATA
   packet is not intended to be a replacement for the Encapsulating
   Security Payload (ESP) transport; instead, it SHOULD NOT be used to
   exchange more than a few packets between peers.  If a continuous
   communication is required or communication that requires
   confidentiality protection then hosts MUST run the HIP base exchange
   to set up an ESP security association.  Additionally, APIs to higher-
   level protocols that might use this service are outside of the scope
   of this document.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].
   In addition, this document uses the terms defined in [RFC5201].

   Message Integrity Code (MIC)  is a collision-resistant hash sum
      calculated over the message that is being integrity protected.
      The MIC does not use secret keys, and thus it needs additional
      means to ensure that it has not been tampered with during
      transmission.  Essentially, the MIC is same as the Message
      Authentication Code (MAC) with the distinction that the MIC does
      not use secret keys.  The MIC is also often referred as the
      Integrity Check Value (ICV), fingerprint, or unkeyed MAC.

3.  Background on HIP

   The HIP specification [RFC5201] defines a number of messages and
   parameters.  The parameters are encoded as TLVs, as shown in
   Section 3.1.2.  Furthermore, the HIP header carries a Next Header
   field, allowing other arbitrary packets to be carried within HIP
   packets.

3.1.  Message Formats

3.1.1.  HIP Fixed Header

   The HIP packet format consists of a fixed header followed by a
   variable number of parameters.  The parameter format is described in
   Section 3.1.2.

   The fixed header is defined in Section 5.1 of [RFC5201] and copied
   below.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Next Header   | Header Length |0| Packet Type |  VER. | RES.|1|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Checksum             |           Controls            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Sender's Host Identity Tag (HIT)               |
      |                                                               |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               Receiver's Host Identity Tag (HIT)              |
      |                                                               |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      /                        HIP Parameters                         /
      /                                                               /
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The HIP header is logically an IPv6 extension header.  The HIP
   specification [RFC5201] defines handling only for Next Header value
   decimal 59, IPv6-NoNxt [PROTOCOL-NUMBERS], the IPv6 'no next header'
   value.  This document describes processing for Next Header values
   other than decimal 59, which indicates that there are either more
   extension headers and/or data following the HIP header.

3.1.2.  HIP Parameter Format

   The HIP parameter format is defined in Section 5.2.1 of [RFC5201],
   and copied below.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             Type            |C|             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      /                          Contents                             /
      /                                               +-+-+-+-+-+-+-+-+
      |                                               |    Padding    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type         Type code for the parameter.  16 bits long, C-bit
                   being part of the Type code.
      C            Critical.  One if this parameter is critical, and
                   MUST be recognized by the recipient; zero otherwise.
                   The C bit is considered to be a part of the Type
                   field.  Consequently, critical parameters are always
                   odd and non-critical ones have an even value.
      Length       Length of the Contents, in octets.
      Contents     Parameter specific, defined by Type.
      Padding      Padding, 0-7 octets, added if needed.

3.2.  HIP Base Exchange, Updates, and State Removal

   The HIP base exchange is a four-message authentication and key
   exchange protocol that creates shared, mutually authenticated keying
   material at the communicating parties.  These keying materials,
   together with associated public keys and IP addresses, form a HIP
   security association (SA).  The details of the protocol are defined
   in the HIP base exchange specification [RFC5201].

   In addition to creating the HIP SA, the base exchange messages may
   carry additional parameters that are used to create additional state.
   For example, the HIP ESP specification [RFC5202] defines how HIP can
   be used to create end-to-end, host-to-host IPsec ESP security
   associations, used to carry data packets.  However, it is important
   to understand that the HIP base exchange is by no means bound to
   IPsec; using IPsec ESP to carry data traffic forms just a baseline
   and ensures interoperability between initial HIP implementations.

   Once there is a HIP SA between two HIP-enabled hosts, they can
   exchange further HIP control messages.  Typically, UPDATE messages
   are used.  For example, the HIP mobility and multihoming
   specification [RFC5206] defines how to use UPDATE messages to change
   the set of IP addresses associated with a HIP SA.

   In addition to the base exchange and updates, the HIP base protocol
   specification also defines how one can remove a HIP SA once it is no
   longer needed.

4.  Definition of the HIP_DATA Packet

   The HIP DATA packet can be used to convey protocol messages to a
   remote host without running the HIP base exchange.  HIP DATA packets
   are transmitted reliably, as discussed in Section 5.  The payload of
   a HIP_DATA packet is placed after the HIP header and protected by a
   PAYLOAD_MIC parameter, which is defined in Section 4.3.  The
   following is the definition of the HIP_DATA packet (see the
   definition of notation in [RFC5201], Section 2.2):

      Header:
        Packet Type = 32
        SRC HIT = Sender's HIT
        DST HIT = Receiver's HIT

    IP ( HIP ( [HOST_ID, ] SEQ_DATA, PAYLOAD_MIC,  [ PAYLOAD_MIC, ..., ]
               HIP_SIGNATURE) PAYLOAD )

    IP ( HIP ( [HOST_ID, ] SEQ_DATA, ACK_DATA, PAYLOAD_MIC,
               [ PAYLOAD_MIC, ..., ] HIP_SIGNATURE) PAYLOAD )

    IP ( HIP ( [HOST_ID, ] ACK_DATA, HIP_SIGNATURE))

   The SEQ_DATA and ACK_DATA parameters are defined in Sections 4.1 and
   4.2, respectively.  They are used to provide a reliable delivery of
   HIP_DATA packets, as discussed in Section 5.

   The HOST_ID parameter is defined in Section 5.2.8 of [RFC5201].  This
   parameter is the sender's Host Identifier that is used to compute the
   HIP_DATA packet's signature and to verify it against the received
   signature.  The HOST_ID parameter is optional as it MAY have been
   delivered using out-of-band mechanism to the receiver.  If the host
   doesn't have reliable information that the corresponding node has its
   HOST_ID, it MUST always include the HOST_ID in the packet.  If the
   receiver is unable to verify the SIGNATURE, then the packet MUST be
   dropped and the appropriate NOTIFY packet SHOULD be sent to the
   sender indicating AUTHENTICATION_FAILED as described in [RFC5201],
   Section 5.2.16.

   The PAYLOAD_MIC parameter is defined in Section 4.3.  This parameter
   contains the MIC of the payload carried by the HIP_DATA packet.  The
   PAYLOAD_MIC contains the collision-resistant hash of the payload
   following the HIP DATA.  The PAYLOAD_MIC is included in the signed
   part of the HIP DATA packet and gives integrity protection for the
   packet as well as the payload carried after it.

   The HIP_SIGNATURE parameter is defined in Section 5.2.11 of
   [RFC5201].  It contains a signature over the contents of the HIP_DATA
   packet.  The calculation and verification of the signature is defined
   in Section 6.4.2. of [RFC5201].

   Section 5.3 of [RFC5201] states the following:

      In the future, an OPTIONAL upper-layer payload MAY follow the HIP
      header.  The Next Header field in the header indicates if there is
      additional data following the HIP header.

   We have chosen to place the payload after the HIP extension header
   and only to place a MIC of the payload into the HIP extension header
   in a PAYLOAD_MIC parameter because that way the data integrity is
   protected by a public key signature with the help of the MIC.  The
   payload that is protected by the PAYLOAD_MIC parameter has been
   linked to the appropriate upper-layer protocol by storing the upper-
   layer protocol number, 8 octets of payload data, and by calculating a
   hash sum (MIC) over the data.  The HIP_DATA packet MAY contain one or
   more PAYLOAD_MIC parameters, each bound to a different Next Header
   type.  The hash algorithm used to generate the MIC is the same as the
   algorithm used to generate the Host Identity Tag [RFC5201].

   Upper-layer protocol messages, such as overlay network control
   traffic, sent in HIP DATA messages may need to be matched to
   different transactions.  For this purpose, a DATA message MAY also
   contain a TRANSACTION_ID parameter.  The identifier value is a
   variable length bit string in network byte order that is unique for
   each transaction.  A response to a request uses the same identifier
   value, thereby allowing the receiver to match requests to responses.

4.1.  Definition of the SEQ_DATA Parameter

   The following is the definition of the SEQ_DATA parameter:

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             Type              |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sequence number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Type              4481
    Length            4
    Sequence number   32-bit unsigned integer in network byte order that
                      MUST NOT be reused before it has been acknowledged
                      by the receiver.

   This parameter has the critical bit set.  If it is not supported by
   the receiver, the packet MUST be dropped and the appropriate NOTIFY
   packet SHOULD be sent to the sender indicating
   UNSUPPORTED_CRITICAL_PARAMETER_TYPE as described in [RFC5201],
   Section 5.2.16.

4.2.  Definition of the ACK_DATA Parameter

   The following is the definition of the ACK_DATA parameter:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             Type              |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Acked Sequence number                     /
      /                                                               /
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type                    4545
      Length                  variable (multiple of 4)
      Acked Sequence number   A sequence of 32-bit unsigned integers in
                              network byte order corresponding to the
                              sequence numbers being acknowledged.

   This parameter has the critical bit set.  If it is not supported by
   the receiver, the packet MUST be dropped and the appropriate NOTIFY
   packet SHOULD be sent to the sender indicating
   UNSUPPORTED_CRITICAL_PARAMETER_TYPE as described in [RFC5201],
   Section 5.2.16.

4.3.  Definition of the PAYLOAD_MIC Parameter

   The following is the definition of the PAYLOAD_MIC parameter:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Next Header  |                   Reserved                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Payload Data                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   /                         MIC Value                             /
   /                                               +-+-+-+-+-+-+-+-+
   |                                               |    Padding    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type              4577
   Length            Length in octets, excluding Type, Length, and
                     Padding.
   Next Header       Identifies the data that is protected by this MIC.
                     The values for this field are defined by IANA
                     "Protocol Numbers" [PROTOCOL-NUMBERS].
   Payload Data      Last 8 octets of the payload data over which the
                     MIC is calculated.  This field is used to
                     uniquely bind the PAYLOAD_MIC parameter to the Next
                     Header, in case there are multiple copies of the
                     same type.
   MIC Value         MIC computed over the data to which the Next
                     Header and Payload Data point.  The size of the MIC
                     is the natural size of the computation output
                     depending on the function used.

   This parameter has the critical bit set.  If it is not supported by
   the receiver, the packet MUST be dropped and the appropriate NOTIFY
   packet SHOULD be sent to the sender indicating
   UNSUPPORTED_CRITICAL_PARAMETER_TYPE as described in [RFC5201],
   Section 5.2.16.

   There is a theoretical possibility that when generating multiple
   PAYLOAD_MIC parameters that will be carried in a single packet, they
   would have identical Next Header and Payload Data fields; thus, it is
   required that PAYLOAD_MIC parameters MUST follow the natural order of
   extension headers in the packet so that it's possible to bind
   PAYLOAD_MICs to correct payload data.  In case the receiving host is
   still unable to identify the payloads, it MUST drop the packet and

   SHOULD send a NOTIFY packet to the sender indicating INVALID_SYNTAX
   as described in [RFC5201], Section 5.2.16.

4.4.  Definition of the TRANSACTION_ID Parameter

   The following is the definition of the TRANSACTION_ID parameter:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Type              |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Identifier                          /
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     /                                               |    Padding    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Type        4580
     Length      Length of the Identifier, in octets
     Identifier  The identifier value
     Padding     0-7 octets of padding if needed

                                 Figure 1

5.  Generation and Reception of HIP_DATA Packets

   HIP_DATA packets are transmitted reliably.  Reliable delivery is
   achieved through the use of retransmissions and of the SEQ_DATA and
   ACK_DATA parameters.

5.1.  Handling of SEQ_DATA and ACK_DATA

   A HIP_DATA packet MUST contain at least one of a SEQ_DATA or an
   ACK_DATA parameter; if both parameters are missing, then packet MUST
   be dropped as invalid.

   A HIP_DATA packet containing a SEQ_DATA parameter MUST contain one or
   more PAYLOAD_MIC parameters; otherwise, the packet MUST be dropped.
   The presence of a SEQ_DATA parameter indicates that the receiver MUST
   ACK the HIP_DATA packet.  A HIP_DATA packet that does not contain a
   SEQ_DATA parameter is simply an ACK of a previous HIP_DATA packet,
   and it MUST NOT be ACKed.

   A HIP_DATA packet containing an ACK_DATA parameter echoes the
   SEQ_DATA sequence numbers of the HIP_DATA packets being acknowledged.
   The ACK_DATA parameter MUST acknowledge at least one SEQ_DATA
   sequence number and MAY acknowledge multiple SEQ_DATA sequence
   numbers by adding all of them to the ACK_DATA parameter.

   A HIP_DATA packet MAY contain both a SEQ_DATA and an ACK_DATA
   parameter.  In this case, the ACK is being piggybacked on an outgoing
   HIP_DATA packet.  In general, HIP_DATA packets carrying SEQ_DATA
   SHOULD be ACKed upon completion of the processing of the HIP_DATA
   packet.  A host MAY choose to hold the HIP DATA packet carrying an
   ACK for a short period of time to allow for the possibility of
   piggybacking the ACK_DATA parameter, in a manner similar to TCP
   delayed acknowledgments.

5.2.  Generation of a HIP_DATA Packet

   When a host has upper-layer protocol data to send, it either runs the
   HIP base exchange and sends the data over a SA, or sends the data
   directly using a HIP_DATA packet.  Section 6 discusses when it is
   appropriate to use each method.  This section discusses the case when
   the host chooses to use a HIP_DATA packet to send the upper-layer
   protocol data.

   1.  The host creates a HIP_DATA packet that contains a SEQ_DATA
       parameter.  The host is free to choose any value for the SEQ_DATA
       sequence number in the first HIP_DATA packet it sends to a
       destination.  After that first packet, the host MUST choose the
       value of the SEQ_DATA sequence number in subsequent HIP_DATA
       packets to the same destination so that no SEQ_DATA sequence
       number is reused before the receiver has closed the processing
       window for the previous packet using the same SEQ_DATA sequence
       number.  Practically, giving the values of the retransmission
       timers used with HIP_DATA packets, this means that hosts must
       wait the maximum likely lifetime of the packet before reusing a
       given SEQ_DATA sequence number towards a given destination.
       However, it is not required for the node to know the maximum
       packet lifetime.  Rather, it is assumed that the requirement can
       be met by maintaining the value as a simple, 32-bit, "wrap-
       around" counter, incremented each time a packet is sent.  It is
       an implementation choice whether to maintain a single counter for
       the node or multiple counters (one for each <source, destination>
       HIT pair).

   2.  The host creates the PAYLOAD_MIC parameter.  The MIC is a hash
       calculated over the whole PAYLOAD that the Next Header field of
       the PAYLOAD_MIC parameter indicates.  If there are multiple Next
       Header types that the host wants to protect, it SHOULD create
       separate PAYLOAD_MIC parameters for each of these.  The receiver
       MUST validate all these MICs as described in Section 5.3.1.  For
       calculating the MIC, the host MUST use the same hash algorithm as
       the one that has been used for generating the host's HIT as
       defined in Section 3.2. of [RFC5201].

   3.  The host creates the HIP_SIGNATURE parameter.  The signature is
       calculated over the whole HIP envelope, excluding any parameters
       after the HIP_SIGNATURE, as defined in Section 5.2.11. of
       [RFC5201].  The receiver MUST validate this signature.  It MAY
       use either the HI in the packet or the HI acquired by some other
       means.

   4.  The host sends the created HIP_DATA packet and starts a DATA
       timer.  The default value for the timer is 3 seconds.  If
       multiple HIP DATA packets are outstanding, multiple timers are in
       effect.

   5.  If the DATA timer expires, the HIP_DATA packet is resent.  The
       HIP DATA packet can be resent DATA_RETRY_MAX times.  The DATA
       timer MUST be exponentially backed off for subsequent
       retransmissions.  If no acknowledgment is received from the peer
       after DATA_RETRY_MAX times, the delivery of the HIP_DATA packet
       is considered unsuccessful and the application is notified about
       the error.  The DATA timer is canceled upon receiving an ACK from
       the peer that acknowledges receipt of the HIP_DATA packet.  The
       default value for DATA_RETRY_MAX SHOULD be 5 retries, but it MAY
       be changed through local policy.

5.3.  Reception of a HIP_DATA Packet

   A host receiving a HIP_DATA packet makes a decision whether or not to
   process the packet.  If the host, following its local policy,
   suspects that this packet could be part of a DoS attack.  The host
   MAY respond with an R1 packet to the HIP_DATA packet, if the packet
   contained SEQ_DATA and PAYLOAD_MIC parameters, in order to indicate
   that HIP base exchange MUST be completed before accepting payload
   packets from the originator of the HIP_DATA packet.

      From RFC 5201 (Section 4.1):

         The HIP base exchange serves to manage the establishment of
         state between an Initiator and a Responder.  The first packet,
         I1, initiates the exchange, and the last three packets, R1, I2,
         and R2, constitute an authenticated Diffie-Hellman [DIF76] key
         exchange for session key generation.

   If the host chooses to respond to the HIP DATA with an R1 packet, it
   creates a new R1 or selects a precomputed R1 according to the format
   described in [RFC5201], Section 5.3.2.  The host SHOULD drop the
   received data packet if it responded with an R1 packet to the
   HIP_DATA packet.  The sender of HIP_DATA packet is responsible for
   retransmission of the upper-layer protocol data after successful
   completion of the HIP base exchange.

   If the host, following its local policy, decides to process the
   incoming HIP_DATA packet, it processes the packet according to the
   following rules:

   1.  If the HIP_DATA packet contains a SEQ_DATA parameter and no
       ACK_DATA parameter, the HIP_DATA packet is processed and replied
       to as described in Section 5.3.1.

   2.  If the HIP_DATA packet contains an ACK_DATA parameter and no
       SEQ_DATA parameter, the HIP_DATA packet is processed as described
       in Section 5.3.2.

   3.  If the HIP_DATA packet contains both a SEQ_DATA parameter and an
       ACK_DATA parameter, the HIP_DATA packet is processed first as
       described in Section 5.3.2, and then the rest of the HIP_DATA
       packet is processed and replied to as described in Section 5.3.1.

5.3.1.  Handling of SEQ_DATA in a Received HIP_DATA Packet

   The following steps define the conceptual processing rules for
   handling a SEQ_DATA parameter in a received HIP_DATA packet.

   The system MUST verify the SIGNATURE in the HIP_DATA packet.  If the
   verification fails, the packet SHOULD be dropped and an error message
   logged.

   If the value in the received SEQ_DATA and the MIC value in the
   received PAYLOAD_MIC correspond to a HIP_DATA packet that has
   recently been processed, the packet is treated as a retransmission.
   It is recommended that a host cache HIP_DATA packets with ACKs to
   avoid the cost of generating a new ACK packet to respond to a
   retransmitted HIP_DATA packet.  The host MUST acknowledge, again,
   such (apparent) HIP_DATA packet retransmissions but SHOULD also
   consider rate-limiting such retransmission responses to guard against
   replay attacks.

   The system MUST verify the PAYLOAD_MIC by calculating the MIC over
   the PAYLOAD that the Next Header field indicates.  For calculating
   the MIC, the host will use the same hash algorithm that has been used
   to generate the sender's HIT as defined in Section 3.2. of [RFC5201].
   If the packet carried multiple PAYLOAD_MIC parameters, each of them
   are verified as described above.  If one or more of the verifications
   fail, the packet SHOULD be dropped and an error message logged.

   If a new SEQ parameter is being processed, the parameters in the HIP
   DATA packet are then processed.

   A HIP_DATA packet with an ACK_DATA parameter is prepared and sent to
   the peer.  This ACK_DATA parameter may be included in a separate HIP
   DATA packet or piggybacked in a HIP_DATA packet with a SEQ_DATA
   parameter.  The ACK_DATA parameter MAY acknowledge more than one of
   the peer's HIP_DATA packets.

5.3.2.  Handling of ACK_DATA in a Received HIP_DATA Packet

   The following steps define the conceptual processing rules for
   handling an ACK_DATA parameter in a received HIP_DATA packet.

   The system MUST verify the SIGNATURE in the HIP_DATA packet.  If the
   verification fails, the packet SHOULD be dropped and an error message
   logged.

   The sequence numbers reported in the ACK_DATA must match with a
   previously sent HIP_DATA packet containing SEQ_DATA that has not
   already been acknowledged.  If no match is found or if the ACK_DATA
   does not acknowledge a new HIP_DATA packet, the packet either MUST be
   dropped if no SEQ_DATA parameter is present or the processing steps
   in Section 5.3.1 are followed.

   The corresponding DATA timer is stopped so that the now acknowledged
   HIP_DATA packet is no longer retransmitted.  If multiple HIP_DATA
   packets are newly acknowledged, multiple timers are stopped.

6.  Use of the HIP_DATA Packet

   HIP currently requires that the four-message base exchange is
   executed at the first encounter of hosts that have not communicated
   before.  This may add additional RTTs (Round-Trip Times) to protocols
   based on a single message exchange.  However, the four-message
   exchange is essential to preserve the DoS protection nature of the
   base exchange.  The use of the HIP_DATA packet defined in this
   document reduces the initial overhead in the communications between
   two hosts.  However, the HIP_DATA packet itself does not provide any
   protection against DoS attacks.  Therefore, the HIP_DATA packet MUST
   only be used in environments whose policies provide protection
   against DoS attacks.  For example, a HIP-based overlay may have
   policies in place to control which nodes can join the overlay.
   However, authorization of who is allowed to join the overlay is
   beyond the scope of this specification.  Any particular node in the
   overlay may want to accept HIP_DATA packets from other nodes in the
   overlay, given that those other nodes were authorized to join the
   overlay.  However, the same node will not accept HIP_DATA packets
   from random nodes that are not part of the overlay.  Additionally,
   the HIP_DATA packet itself does not provide confidentiality for its
   payload.  Therefore, the HIP_DATA packet MUST NOT be used in

   environments that do not provide an appropriate level of
   confidentiality (e.g., a HIP-based overlay MUST NOT send HIP_DATA
   packets unless the connections between overlay nodes are encrypted).

   The type of data to be sent is also relevant to whether the use of a
   HIP_DATA packet is appropriate.  HIP itself does not support
   fragmentation but relies on underlying IP-layer fragmentation.  This
   may lead to reliability problems in the case where a message cannot
   be easily split over multiple HIP messages.  Therefore, applications
   in environments where fragmentation could be an issue SHOULD NOT
   generate large HIP_DATA packets that may lead to fragmentation.  The
   implementation SHOULD check the MTU of the link before sending the
   packet, and if the packet size is larger than MTU, it SHOULD signal
   to the upper-layer protocol if the packet results in an ICMP error
   message.  Note that there are environments where fragmentation is not
   an issue.  For example, in some HIP-based overlays, nodes can
   exchange HIP_DATA packets on top of TCP connections that provide
   transport-level fragmentation and, thus, avoid IP-level
   fragmentation.

   HIP currently requires that all messages excluding I1s but including
   HIP_DATA packets are digitally signed.  This adds to the packet size
   and the processing capacity needed to send packets.  However, in
   applications where security is not paramount, it is possible to use
   very short keys, thereby reducing resource consumption.

7.  Security Considerations

   HIP is designed to provide secure authentication of hosts.  HIP also
   attempts to limit the exposure of the host to various denial-of-
   service and man-in-the-middle (MitM) attacks.  However, HIP_DATA
   packet, which can be sent without running the HIP base exchange
   between hosts has a trade-off that it does not provide the denial-of-
   service protection or confidentiality protection that HIP generally
   provides.  Thus, the host should consider always situations where it
   is appropriate to send or receive HIP_DATA packet.  If the
   communication consists more than few round trips of data or the data
   is highly sensitive in nature the host SHOULD run the base exchange
   with the peer host.

   HIP_DATA packet is designed to protect hosts from second preimage
   attacks allowing receiving host to be able to detect, if the message
   was tampered during the transport.  This property is also know as
   "weak collision-resistance".  If a host tries to generate a second
   preimage, it would need to generate it such that the last 8 octets
   match with the original message.

   When handling the PAYLOAD_MIC parameter in the receiving host, using
   the last 8 octets to identify the upper-layer protocol doesn't give
   any guarantee that the MIC would be correct; thus, an attacker could
   send packets where the next header and last 8 octets match the values
   carried by the PAYLOAD_MIC parameter.  Therefore, it is always
   mandatory to verify the MIC value by calculating the hash over the
   payload.

8.  IANA Considerations

   This document updates the IANA registry for HIP packet types by
   introducing a new packet type for the HIP_DATA (Section 4) packet.
   This document updates the IANA registry for HIP parameter types by
   introducing new parameter values for the SEQ_DATA (Section 4.1),
   ACK_DATA (Section 4.2), PAYLOAD_MIC (Section 4.3), and TRANSACTION_ID
   (Section 4.4) parameters.

9.  Acknowledgments

   Pekka Nikander was one of the original authors of the document.
   Also, in the usual IETF fashion, a large number of people have
   contributed to the actual text or ideas.  The list of these people
   include Miika Komu, Tobias Heer, Ari Keranen, Samu Varjonen, Thomas
   Henderson, and Jukka Ylitalo.  Our apologies to anyone whose name is
   missing.

10.  References

10.1.  Normative References

   [RFC2119]           Bradner, S., "Key words for use in RFCs to
                       Indicate Requirement Levels", BCP 14, RFC 2119,
                       March 1997.

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

   [PROTOCOL-NUMBERS]  IANA, "Protocol Numbers", <http://www.iana.org>.

10.2.  Informative references

   [RFC5202]           Jokela, P., Moskowitz, R., and P. Nikander,
                       "Using the Encapsulating Security Payload (ESP)
                       Transport Format with the Host Identity Protocol
                       (HIP)", RFC 5202, 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.

Authors' Addresses

   Gonzalo Camarillo
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   EMail: Gonzalo.Camarillo@ericsson.com

   Jan Melen
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   EMail: Jan.Melen@ericsson.com

 

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