TOC 
Mobile Ad hoc Networking (MANET)U. Herberg
Internet-DraftT. Clausen
Intended status: Standards TrackLIX, Ecole Polytechnique
Expires: September 9, 2010March 08, 2010


MANET Cryptographical Signature TLV Definition
draft-herberg-manet-packetbb-sec-03

Abstract

This document describes a general and flexible TLV (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 to IETF in full conformance with the provisions of BCP 78 and BCP 79.

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

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Table of Contents

1.  Introduction
2.  Terminology
3.  Applicability Statement
4.  Protocol Overview and Functioning
5.  General Signature TLV Structure
    5.1.  Rationale
6.  General Timestamp TLV Structure
7.  Packet TLVs
    7.1.  Packet SIGNATURE TLV
    7.2.  Packet TIMESTAMP TLV
8.  Message TLVs
    8.1.  Message SIGNATURE TLV
    8.2.  Message TIMESTAMP TLV
9.  Address Block TLVs
    9.1.  Address Block SIGNATURE TLV
    9.2.  Address Block TIMESTAMP TLV
10.  IANA Considerations
    10.1.  TLV Registrations
        10.1.1.  Expert Review: Evaluation Guidelines
        10.1.2.  Packet TLV Type Registrations
        10.1.3.  Message TLV Type Registrations
        10.1.4.  Address Block TLV Type Registrations
    10.2.  New IANA Registries
        10.2.1.  Expert Review: Evaluation Guidelines
        10.2.2.  Hash Function
        10.2.3.  Cryptographic Algorithm
11.  Security Considerations
12.  Acknowledgements
13.  References
    13.1.  Normative References
    13.2.  Informative References
Appendix A.  Examples
    A.1.  Example of a Signed Message
§  Authors' Addresses




 TOC 

1.  Introduction

This document:

This document does not stipulate how to sign or validate messages. A specification of a routing protocol or routing protocol extension, using the security representation of this document, MUST specify appropriate interpretation of the TLVs. This document does specifically not suggest specific cryptographic algorithms or hash functions, but rather establishes IANA registries for such.



 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.). Additionally, it defines the following terminology:



 TOC 

3.  Applicability Statement

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

This document specifies how to include a cryptographic signature for a packet, message or address block by way of such TLVs. This document also specifies how to treat "mutable" fields (<msg-hop- count> and <msg-hop-limit>) 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. A MANET routing protocol, or an extension of a MANET routing protocol, MAY use such included cryptographic signatures for, for example, rejecting messages where signature verification fails.

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),” October 2009.) and [OLSRv2] (Clausen, T., Dearlove, C., and P. Jacquet, “The Optimized Link State Routing Protocol version 2,” September 2009.) recognize external reasons (such as failure to verify a signature) as being reasons 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. This document also makes 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. Finally, this document establishes two IANA registries for code-points for hash functions and cryptographic algorithms for use by protocols 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 

4.  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.) messages and packets, as well as establishes IANA registrations and registries.



 TOC 

5.  General Signature TLV Structure

The following data structure allows representation of a cryptographic signature, including specification of the appropriate hash function and cryptographic algorithm 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-algorithm>
                         <signature-value>

where:

<hash-function>
is an 8-bit unsigned integer field specifying the hash function.
<cryptographic-algorithm>
is an 8-bit unsigned integer field specifying the cryptographic algorithm.
<signature-value>
is an unsigned integer field, whose length is <tlv-length>-2, 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(message))

The hash function and the cryptographic algorithm correspond to the IANA registry in the two registries set up by this specification, see Section 10 (IANA Considerations).



 TOC 

5.1.  Rationale

The rationale for separating the hash function and the cryptographic algorithm 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 algorithms are added in the future, the number space might not remain continuous. More importantly, the number space of 256 possible combinations would be rapidly exhausted: 16 different hash functions and 16 different cryptographic algorithms would lead to exhaustion. 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 the following: Before being able to to validate a cryptographic signature, routers have to exchange keys (e.g. public keys). Any additional parameters can be exchanged together with the keys in this 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 tlv-length - 2 and which depends on the choice of the cryptographic algorithm.



 TOC 

6.  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 <tlv-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 (refer to Table 1 (Packet TLV types)).

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. This is out of the scope of this specification.



 TOC 

7.  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 

7.1.  Packet SIGNATURE TLV

A Packet SIGNATURE TLV is an example of a Signature TLV as described in Section 5 (General Signature TLV Structure). When calculating the <signature-value> for a Packet, the signature is calculated over the entire Packet, including the packet header, all Packet TLVs (other than Packet SIGNATURE TLVs) and all included Messages and their message headers.



 TOC 

7.2.  Packet TIMESTAMP TLV

A Packet TIMESTAMP TLV is an example of a Timestamp TLV as described in Section 6 (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 the SIGNATURE TLV, in order that it be included in the calculation of the signature.



 TOC 

8.  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 

8.1.  Message SIGNATURE TLV

A Message SIGNATURE TLV is an example of a Signature TLV as described in Section 5 (General Signature TLV Structure). When determining the <signature-value> for a message, the signature is calculated over the entire message with the following considerations:



 TOC 

8.2.  Message TIMESTAMP TLV

A Message TIMESTAMP TLV is an example of a Timestamp TLV as described in Section 6 (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 

9.  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 

9.1.  Address Block SIGNATURE TLV

An Address Block SIGNATURE TLV is an example of a Signature TLV as described in Section 5 (General Signature TLV Structure). The signature can be calculated over any object, including, for example, the address to which this TLV is associated to.



 TOC 

9.2.  Address Block TIMESTAMP TLV

An Address Block TIMESTAMP TLV is an example of a Timestamp TLV as described in Section 6 (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 

10.  IANA Considerations



 TOC 

10.1.  TLV Registrations

This specification defines:

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 

10.1.1.  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.).



 TOC 

10.1.2.  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 timestamp is assumed to increase strictly monotonously by steps of 1. The MANET routing protocol has to define how to interpret this timestamp
    1 Unsigned 32-bit timestamp as specified in [POSIX] (IEEE Computer Society, “1003.1-2008 Standard for Information Technology - Portable Operating System Interface (POSIX),” December 2008.)
    2 NTP timestamp format as defined in [RFC4330] (Mills, D., “Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI,” January 2006.)
    3 Signed timestamp of arbitrary length with no constraints such as monotonicity. In particular, it may represent any random value
    4-223 Expert Review
    224-255 Experimental Use

 Table 1: Packet TLV types 



 TOC 

10.1.3.  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. The timestamp is assumed to increase strictly monotonously by steps of 1. The MANET routing protocol has to define how to interpret this timestamp
    1 Unsigned 32-bit timestamp as specified in [POSIX] (IEEE Computer Society, “1003.1-2008 Standard for Information Technology - Portable Operating System Interface (POSIX),” December 2008.)
    2 NTP timestamp format as defined in [RFC4330] (Mills, D., “Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI,” January 2006.)
    3 Signed timestamp of arbitrary length with no constraints such as monotonicity. In particular, it may represent any random value
    4-223 Expert Review
    224-255 Experimental Use

 Table 2: Message TLV types 



 TOC 

10.1.4.  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. The timestamp is assumed to increase strictly monotonously by steps of 1. The MANET routing protocol has to define how to interpret this timestamp
    1 Unsigned 32-bit timestamp as specified in [POSIX] (IEEE Computer Society, “1003.1-2008 Standard for Information Technology - Portable Operating System Interface (POSIX),” December 2008.)
    2 NTP timestamp format as defined in [RFC4330] (Mills, D., “Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI,” January 2006.)
    3 Signed timestamp of arbitrary length with no constraints such as monotonicity. In particular, it may represent any random value
    4-223 Expert Review
    224-255 Experimental Use

 Table 3: Address Block TLV types 



 TOC 

10.2.  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 

10.2.1.  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 

10.2.2.  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 MD5 The hash function as specified in [RFC1321] (Rivest, R., “The MD5 Message-Digest Algorithm,” April 1992.)
2 SHA1 The hash function as specified in [RFC3174] (Eastlake, D. and P. Jones, “US Secure Hash Algorithm 1 (SHA1),” September 2001.)
3 SHA256 The hash function as specified in [SHA256] (National Institute of Standards and Technology, “Secure Hash Algorithm,” August 2002.)
4-223   Expert Review
224-255   Experimental Use

 Table 4: Hash-Function registry 



 TOC 

10.2.3.  Cryptographic Algorithm

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



Cryptographic algorithm valueAlgorithmDescription
0 none The "identity function": the value of an encrypted hash is the hash itself
1 RSA RSA as specified in [RFC2437] (Kaliski, B. and J. Staddon, “PKCS #1: RSA Cryptography Specifications Version 2.0,” October 1998.)
2 DSA DSA as specified in [DSA] (National Institute of Standards & Technology, “Digital Signature Standard,” May 1994.)
3 HMAC HMAC as specified in [RFC2104] (Krawczyk, H., Bellare, M., and R. Canetti, “HMAC: Keyed-Hashing for Message Authentication,” February 1997.)
4 3DES 3DES as specified in [3DES] (American National Standards Institute, “Triple Data Encryption Algorithm Modes of Operation,” 1998.)
5 AES AES as specified in [AES] (National Institute of Standards & Technology, “Advanced Encryption Standard (AES),” November 2001.)
6-223   Expert Review
224-255   Experimental Use

 Table 5: Cryptographic algorithm registry 



 TOC 

11.  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 

12.  Acknowledgements

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



 TOC 

13.  References



 TOC 

13.1. 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 

13.2. Informative References

[3DES] American National Standards Institute, “Triple Data Encryption Algorithm Modes of Operation,” ANSI X9.52-1998, 1998.
[AES] National Institute of Standards & Technology, “Advanced Encryption Standard (AES),” FIPS 197, November 2001.
[DSA] National Institute of Standards & Technology, “Digital Signature Standard,” NIST, FIPS PUB 186, May 1994.
[NHDP] Clausen, T., Dean, J., and C. Dearlove, “MANET Neighborhood Discovery Protocol (NHDP),” work in progress draft-ietf-manet-nhdp-11.txt, October 2009.
[OLSRv2] Clausen, T., Dearlove, C., and P. Jacquet, “The Optimized Link State Routing Protocol version 2,” work in progress draft-ietf-manet-olsrv2-10.txt, September 2009.
[POSIX] IEEE Computer Society, “1003.1-2008 Standard for Information Technology - Portable Operating System Interface (POSIX),” Base Specifications Issue 7, December 2008.
[RFC1321] Rivest, R., “The MD5 Message-Digest Algorithm,” RFC 1321, April 1992 (TXT).
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, “HMAC: Keyed-Hashing for Message Authentication,” RFC 2104, February 1997 (TXT).
[RFC2437] Kaliski, B. and J. Staddon, “PKCS #1: RSA Cryptography Specifications Version 2.0,” RFC 2437, October 1998 (TXT, HTML, XML).
[RFC3174] Eastlake, D. and P. Jones, “US Secure Hash Algorithm 1 (SHA1),” RFC 3174, September 2001 (TXT).
[RFC4330] Mills, D., “Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI,” RFC 4330, January 2006 (TXT).
[SHA256] National Institute of Standards and Technology, “Secure Hash Algorithm,” NIST FIPS 180-2, August 2002.


 TOC 

Appendix A.  Examples



 TOC 

A.1.  Example of a Signed Message

The sample message depicted in Figure 1 (Example message with signature) is taken from the appendix of [RFC5444] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” February 2009.). However, a SIGNATURE Message TLV has been added. It is assumed that the SIGNATURE TLV type is lesser than the TLV type of the second message TLV (i.e. it comes first in the order of Message TLVs). The TLV value represents a 16 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  |        Signature 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/