TOC 
Mobile Ad hoc Networking (MANET)U. Herberg
Internet-DraftT. Clausen
Intended status: Standards TrackLIX, Ecole Polytechnique
Expires: May 15, 2011November 11, 2010


MANET Cryptographical Signature TLV Definition
draft-ietf-manet-packetbb-sec-02

Abstract

This document describes general and flexible TLVs (type-length-value structure) for representing cryptographic signatures as well as timestamps, using the generalized MANET packet/message format [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.). It defines two Packet TLVs, two Message TLVs, and two Address Block TLVs, for affixing cryptographic signatures and timestamps to a packet, message and address, respectively.

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/.

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This Internet-Draft will expire on May 15, 2011.

Copyright Notice

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

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Table of Contents

1.  Introduction
2.  Terminology
3.  Applicability Statement
4.  Security Architecture
5.  Protocol Overview and Functioning
6.  Imported TLV Fields
7.  General Signature TLV Structure
    7.1.  Rationale
8.  General Timestamp TLV Structure
9.  Packet TLVs
    9.1.  Packet SIGNATURE TLV
    9.2.  Packet TIMESTAMP TLV
10.  Message TLVs
    10.1.  Message SIGNATURE TLV
    10.2.  Message TIMESTAMP TLV
11.  Address Block TLVs
    11.1.  Address Block SIGNATURE TLV
    11.2.  Address Block TIMESTAMP TLV
12.  IANA Considerations
    12.1.  TLV Registrations
        12.1.1.  Expert Review: Evaluation Guidelines
        12.1.2.  Packet TLV Type Registrations
        12.1.3.  Message TLV Type Registrations
        12.1.4.  Address Block TLV Type Registrations
    12.2.  New IANA Registries
        12.2.1.  Expert Review: Evaluation Guidelines
        12.2.2.  Hash Function
        12.2.3.  Cryptographic Algorithm
13.  Security Considerations
14.  Acknowledgements
15.  References
    15.1.  Normative References
    15.2.  Informative References
Appendix A.  Examples
    A.1.  Example of a Signed Message
§  Authors' Addresses




 TOC 

1.  Introduction

This document specifies:

This document requests from IANA:



 TOC 

2.  Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

This document uses the terminology and notation defined in [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.).



 TOC 

3.  Applicability Statement

MANET routing protocols using the format defined in [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.) are accorded the ability to carry additional information in control messages and packets, through inclusion of TLVs. Information so included MAY be used by a routing protocol, or by an extension of a routing protocol, according to its specification.

This document specifies how to include a cryptographic signature for a packet, message or address by way of such TLVs. This document also specifies how to treat "mutable" fields (<msg-hop-count> and <msg-hop-limit>), if present, in the message header when calculating signatures, such that the resulting signature can be correctly verified by any recipient, and how to include this signature.



 TOC 

4.  Security Architecture

Basic MANET routing protocol specifications are often "oblivious to security", however have a clause allowing a control message to be rejected as "badly formed" prior to it being processed or forwarded. Protocols such as [NHDP] (Clausen, T., Dean, J., and C. Dearlove, “MANET Neighborhood Discovery Protocol (NHDP),” July 2010.) and [OLSRv2] (Clausen, T., Dearlove, C., and P. Jacquet, “The Optimized Link State Routing Protocol version 2,” April 2010.) recognize external reasons (such as failure to verify a signature) for rejecting a message as "badly formed", and therefore "invalid for processing". This architecture is a result of the observation that with respect to security in MANETs, "one size rarely fits all" and that MANET routing protocol deployment domains have varying security requirements ranging from "unbreakable" to "virtually none". The virtue of this approach is that MANET routing protocol specifications (and implementations) can remain "generic", with extensions providing proper deployment-domain specific security mechanisms.

The MANET routing protocol "security architecture", in which this specification situates itself, can therefore be summarized as follows:

This document addresses the last of these issues, by specifying a common exchange format for cryptographic signatures, making reservations from within the Packet TLV, Message TLV and Address Block TLV registries of [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.), to be used (and shared) among MANET routing protocol security extensions, establishing two IANA registries for code-points for hash functions and cryptographic functions adhering to [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.).

With respect to [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.), this document:



 TOC 

5.  Protocol Overview and Functioning

This specification does not describe a protocol, nor does it mandate specific router or protocol behavior. It represents a purely syntactical representation of security related information for use with [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.) addresses, messages and packets, as well as establishes IANA registrations and registries.



 TOC 

6.  Imported TLV Fields

In this specification, the following TLV fields from [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.) are used:

<msg-hop-limit>
- hop limit of a message, as specified in Section 5.2 of [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.).
<msg-hop-count>
- hop count of a message, as specified in Section 5.2 of [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.).
<length>
- length of a TLV in octets, as specified in Section 5.4.1 of [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.).



 TOC 

7.  General Signature TLV Structure

The following data structure allows representation of a cryptographic signature, including specification of the appropriate hash function and cryptographic function used for calculating the signature. This <signature> data structure is specified, using the regular expression syntax of [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.), as:

          <signature> := <hash-function>
                         <cryptographic-function>
                         <key-index>
                         <signature-value>

where:

<hash-function>
is an 8-bit unsigned integer field specifying the hash function.
<cryptographic-function>
is an 8-bit unsigned integer field specifying the cryptographic function.
<key-index>
is an 8-bit unsigned integer field specifying the key index of the key which was used to sign the message, which allows unique identification of different keys with the same originator. It is the responsibility of each key originator to make sure that actively used keys that it issues have distinct key indices and that all key indices have a value unequal to 0x00. Value 0x00 is reserved for a pre-installed, shared key.
<signature-value>
is an unsigned integer field, whose length is <length> - 3, and which contains the cryptographic signature.

The basic version of this TLV assumes that calculating the signature can be decomposed into:

signature-value = cryptographic-function(hash-function(content))

The hash function and the cryptographic function correspond to the entries in two IANA registries, set up by this specification in Section 12 (IANA Considerations).



 TOC 

7.1.  Rationale

The rationale for separating the hash function and the cryptographic function into two octets instead of having all combinations in a single octet - possibly as TLV type extension - is twofold: First, if further hash functions or cryptographic functions are added in the future, the number space might not remain continuous. More importantly, the number space of possible combinations would be rapidly exhausted. As new or improved cryptographic mechanism are continuously being developed and introduced, this format should be able to accommodate such for the foreseeable future.

The rationale for not including a field that lists parameters of the cryptographic signature in the TLV is, that before being able to validate a cryptographic signature, routers have to exchange or acquire keys (e.g. public keys). Any additional parameters can be provided together with the keys in that bootstrap process. It is therefore not necessary, and would even entail an extra overhead, to transmit the parameters within every message. One inherently included parameter is the length of the signature, which is <length> - 3 and which depends on the choice of the cryptographic function.



 TOC 

8.  General Timestamp TLV Structure

The following data structure allows the representation of a timestamp. This <timestamp> data structure is specified as:

       <timestamp> := <time-value>

where:

<time-value>
is an unsigned integer field, whose length is <length>, and which contains the timestamp. The value of this variable is to be interpreted by the routing protocol as specified by the type extension of the Timestamp TLV, see Section 12 (IANA Considerations).

A timestamp is essentially "freshness information". As such, its setting and interpretation is to be determined by the routing protocol (or the extension to a routing protocol) that uses it, and may e.g. correspond to a UNIX-timestamp, GPS timestamp or a simple sequence number.



 TOC 

9.  Packet TLVs

Two Packet TLVs are defined, for including the cryptographic signature of a packet, and for including the timestamp indicating the time at which the cryptographic signature was calculated.



 TOC 

9.1.  Packet SIGNATURE TLV

A Packet SIGNATURE TLV is an example of a Signature TLV as described in Section 7 (General Signature TLV Structure). When calculating the <signature-value> for a Packet, the signature is calculated over the three fields <hash-function>, <cryptographic-function> and <key-index> (in that order), concatenated with the entire Packet, including the packet header, all Packet TLVs (other than Packet SIGNATURE TLVs) and all included Messages and their message headers.

The following considerations apply:

The rationale for removing any Packet SIGNATURE TLV already present prior to calculating the signature, is that several signatures may be added to the same packet, e.g., using different signature functions.



 TOC 

9.2.  Packet TIMESTAMP TLV

A Packet TIMESTAMP TLV is an example of a Timestamp TLV as described in Section 8 (General Timestamp TLV Structure). If a packet contains a TIMESTAMP TLV and a SIGNATURE TLV, the TIMESTAMP TLV SHOULD be added to the packet before any SIGNATURE TLV, in order that it be included in the calculation of the signature.



 TOC 

10.  Message TLVs

Two Message TLVs are defined, for including the cryptographic signature of a message, and for including the timestamp indicating the time at which the cryptographic signature was calculated.



 TOC 

10.1.  Message SIGNATURE TLV

A Message SIGNATURE TLV is an example of a Signature TLV as described in Section 7 (General Signature TLV Structure). When determining the <signature-value> for a message, the signature is calculated over the three fields <hash-function>, <cryptographic-function>, and <key-index> (in that order), concatenated with the entire message with the following considerations:

The rationale for removing any Message SIGNATURE TLV already present prior to calculating the signature, is that several signatures may be added to the same message, e.g., using different signature functions.



 TOC 

10.2.  Message TIMESTAMP TLV

A Message TIMESTAMP TLV is an example of a Timestamp TLV as described in Section 8 (General Timestamp TLV Structure). If a message contains a TIMESTAMP TLV and a SIGNATURE TLV, the TIMESTAMP TLV SHOULD be added to the message before the SIGNATURE TLV, in order that it be included in the calculation of the signature.



 TOC 

11.  Address Block TLVs

Two Address Block TLVs are defined, for associating a cryptographic signature to an address, and for including the timestamp indicating the time at which the cryptographic signature was calculated.



 TOC 

11.1.  Address Block SIGNATURE TLV

An Address Block SIGNATURE TLV is an example of a Signature TLV as described in Section 7 (General Signature TLV Structure). The signature is calculated over the three fields <hash-function>, <cryptographic-function>, and <key-index> (in that order), concatenated with the address, concatenated with any other values, for example, any other TLV value that is associated with that address. A routing protocol or routing protocol extension using Address Block SIGNATURE TLVs MUST specify how to include any such concatenated attribute of the address in the verification process of the signature.



 TOC 

11.2.  Address Block TIMESTAMP TLV

An Address Block TIMESTAMP TLV is an example of a Timestamp TLV as described in Section 8 (General Timestamp TLV Structure). If both a TIMESTAMP TLV and a SIGNATURE TLV are associated with an address, the timestamp value should be considered when calculating the value of the signature.



 TOC 

12.  IANA Considerations

This section specifies requests to IANA.



 TOC 

12.1.  TLV Registrations

This specification defines:

This specification requests:

IANA is requested to assign the same numerical value to the Packet TLV, Message TLV and Address Block TLV types with the same name.



 TOC 

12.1.1.  Expert Review: Evaluation Guidelines

For the registries for TLV type extensions where an Expert Review is required, the designated expert SHOULD take the same general recommendations into consideration as are specified by [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.).

For the Timestamp TLV, the same type extensions for all Packet, Message and Address TLVs should be numbered identically.



 TOC 

12.1.2.  Packet TLV Type Registrations

The Packet TLVs as specified in Table 1 (Packet TLV types) must be allocated from the "Packet TLV Types" namespace of [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.).



NameTypeType ExtensionDescription
SIGNATURE TBD3 0 Signature of a packet
    1-223 Expert Review
    224-255 Experimental Use
TIMESTAMP TBD4 0 Unsigned timestamp of arbitrary length, given by the TLV length field. The MANET routing protocol has to define how to interpret this timestamp
    1-223 Expert Review
    224-255 Experimental Use

 Table 1: Packet TLV types 



 TOC 

12.1.3.  Message TLV Type Registrations

The Message TLVs as specified in Table 2 (Message TLV types) must be allocated from the "Message TLV Types" namespace of [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.).



NameTypeType ExtensionDescription
SIGNATURE TBD1 0 Signature of a message
    1-223 Expert Review
    224-255 Experimental Use
TIMESTAMP TBD2 0 Unsigned timestamp of arbitrary length, given by the TLV length field.
    1-223 Expert Review
    224-255 Experimental Use

 Table 2: Message TLV types 



 TOC 

12.1.4.  Address Block TLV Type Registrations

The Address Block TLVs as specified in Table 3 (Address Block TLV types) must be allocated from the "Address Block TLV Types" namespace of [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.).



NameTypeType ExtensionDescription
SIGNATURE TBD1 0 Signature of an object (e.g. an address)
    1-223 Expert Review
    224-255 Experimental Use
TIMESTAMP TBD2 0 Unsigned timestamp of arbitrary length, given by the TLV length field.
    1-223 Expert Review
    224-255 Experimental Use

 Table 3: Address Block TLV types 



 TOC 

12.2.  New IANA Registries

This document introduces three namespaces that have been registered: Packet TLV Types, Message TLV Types, and Address Block TLV Types. This section specifies IANA registries for these namespaces and provides guidance to the Internet Assigned Numbers Authority regarding registrations in these namespaces.

The following terms are used with the meanings defined in [BCP26] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.): "Namespace", "Assigned Value", "Registration", "Unassigned", "Reserved", "Hierarchical Allocation", and "Designated Expert".

The following policies are used with the meanings defined in [BCP26] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.): "Private Use", "Expert Review", and "Standards Action".



 TOC 

12.2.1.  Expert Review: Evaluation Guidelines

For the registries for the following tables where an Expert Review is required, the designated expert SHOULD take the same general recommendations into consideration as are specified by [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.).



 TOC 

12.2.2.  Hash Function

IANA is requested to create a new registry for the hash functions that can be used when creating a signature. The initial assignments and allocation policies are specified in Table 4 (Hash-Function registry).



Hash function valueAlgorithmDescription
0 none The "identity function": the hash value of an object is the object itself
1-223   Expert Review
224-255   Experimental Use

 Table 4: Hash-Function registry 



 TOC 

12.2.3.  Cryptographic Algorithm

IANA is requested to create a new registry for the cryptographic function. Initial assignments and allocation policies are specified in Table 5 (Cryptographic function registry).



Cryptographic function valueAlgorithmDescription
0 none The "identity function": the value of an encrypted hash is the hash itself
1-223   Expert Review
224-255   Experimental Use

 Table 5: Cryptographic function registry 



 TOC 

13.  Security Considerations

This document does not specify a protocol itself. However, it provides a syntactical component for cryptographic signatures of messages and packets as defined in [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.). It can be used to address security issues of a protocol or extension that uses the component specified in this document. As such, it has the same security considerations as [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.).

In addition, a protocol that includes this component MUST specify the usage as well as the security that is attained by the cryptographic signatures of a message or a packet.

As an example, a routing protocol that uses this component to reject "badly formed" messages if a control message does not contain a valid signature, should indicate the security assumption that if the signature is valid, the message is considered valid. It also should indicate the security issues that are counteracted by this measure (e.g. link or identity spoofing) as well as the issues that are not counteracted (e.g. compromised keys).



 TOC 

14.  Acknowledgements

The authors would like to thank Jerome Milan (Ecole Polytechnique) for his advice as cryptographer. In addition, many thanks to Bo Berry (Cisco), Alan Cullen (BAE), Justin Dean (NRL), Christopher Dearlove (BAE), Paul Lambert (Marvell), and Henning Rogge (FGAN) for their constructive comments on the document.



 TOC 

15.  References



 TOC 

15.1. Normative References

[BCP26] Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” RFC 5226, BCP 26, May 2008.
[RFC2119] Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” RFC 2119, BCP 14, March 1997.
[RFC5444] Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” RFC 5444, February 2009.


 TOC 

15.2. Informative References

[NHDP] Clausen, T., Dean, J., and C. Dearlove, “MANET Neighborhood Discovery Protocol (NHDP),” work in progress draft-ietf-manet-nhdp-14.txt, July 2010.
[OLSRv2] Clausen, T., Dearlove, C., and P. Jacquet, “The Optimized Link State Routing Protocol version 2,” work in progress draft-ietf-manet-olsrv2-11.txt, April 2010.


 TOC 

Appendix A.  Examples



 TOC 

A.1.  Example of a Signed Message

The sample message depicted in Figure 1 (Example message with signature) is derived from the appendix of [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.). A SIGNATURE Message TLV has been added, with the value representing a 15 octet long signature of the whole message.



   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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |0 0 0 0 1 0 0 0|    Packet Sequence Number     | Message Type  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |1 1 1 1 0 0 1 1|0 0 0 0 0 0 0 0 0 1 0 0 1 1 0 0|   Orig Addr   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Originator Address (cont)           |   Hop Limit   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   Hop Count   |    Message Sequence Number    |0 0 0 0 0 0 0 0|
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |0 0 0 1 1 1 1 0|   SIGNATURE   |0 0 0 1 0 0 0 0|0 0 0 1 0 0 1 0|
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   Hash Func   |  Crypto Func  |    Key Index  |  Sign. Value  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    Signature Value (cont)                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    Signature Value (cont)                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    Signature Value (cont)                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |    Signature Value (cont)     |   TLV Type    |0 0 0 1 0 0 0 0|
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |0 0 0 0 0 1 1 0|                     Value                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Value (cont)                  |0 0 0 0 0 0 1 0|
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |0 0 1 1 0 0 0 0|0 0 0 0 0 0 1 0|              Mid              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |              Mid              | Prefix Length |0 0 0 0 0 0 0 0|
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |0 0 0 0 0 0 0 0|0 0 0 0 0 0 1 1|1 0 0 0 0 0 0 0|0 0 0 0 0 0 1 0|
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |             Head              |              Mid              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |              Mid              |              Mid              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1|   TLV Type    |0 0 0 1 0 0 0 0|
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |0 0 0 0 0 0 1 0|             Value             |   TLV Type    |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |0 0 1 0 0 0 0 0|  Index Start  |  Index Stop   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure 1: Example message with signature 



 TOC 

Authors' Addresses

  Ulrich Herberg
  LIX, Ecole Polytechnique
  91128 Palaiseau Cedex,
  France
Phone:  +33 1 6933 4126
Email:  ulrich@herberg.name
URI:  http://www.herberg.name/
  
  Thomas Heide Clausen
  LIX, Ecole Polytechnique
  91128 Palaiseau Cedex,
  France
Phone:  +33 6 6058 9349
Email:  T.Clausen@computer.org
URI:  http://www.thomasclausen.org/