Cryptographically Generated Addresses (CGA)
RFC 3972

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Network Working Group                                            T. Aura
Request for Comments: 3972                            Microsoft Research
Category: Standards Track                                     March 2005

              Cryptographically Generated Addresses (CGA)

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   This document describes a method for binding a public signature key
   to an IPv6 address in the Secure Neighbor Discovery (SEND) protocol.
   Cryptographically Generated Addresses (CGA) are IPv6 addresses for
   which the interface identifier is generated by computing a
   cryptographic one-way hash function from a public key and auxiliary
   parameters.  The binding between the public key and the address can
   be verified by re-computing the hash value and by comparing the hash
   with the interface identifier.  Messages sent from an IPv6 address
   can be protected by attaching the public key and auxiliary parameters
   and by signing the message with the corresponding private key.  The
   protection works without a certification authority or any security
   infrastructure.

Aura                        Standards Track                     [Page 1]
RFC 3972         Cryptographically Generated Addresses        March 2005

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  CGA Format . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  CGA Parameters and Hash Values . . . . . . . . . . . . . . . .  5
   4.  CGA Generation . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  CGA Verification . . . . . . . . . . . . . . . . . . . . . . .  9
   6.  CGA Signatures . . . . . . . . . . . . . . . . . . . . . . . . 10
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
       7.1.  Security Goals and Limitations . . . . . . . . . . . . . 12
       7.2.  Hash Extension . . . . . . . . . . . . . . . . . . . . . 13
       7.3.  Privacy Considerations . . . . . . . . . . . . . . . . . 15
       7.4.  Related Protocols  . . . . . . . . . . . . . . . . . . . 15
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
       9.1.  Normative References . . . . . . . . . . . . . . . . . . 17
       9.2.  Informative References . . . . . . . . . . . . . . . . . 18
   Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
       A.  Example of CGA Generation. . . . . . . . . . . . . . . . . 20
       B.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . 21
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 21
   Full Copyright Statements. . . . . . . . . . . . . . . . . . . . . 22

1.  Introduction

   This document specifies a method for securely associating a
   cryptographic public key with an IPv6 address in the Secure Neighbor
   Discovery (SEND) protocol [RFC3971].  The basic idea is to generate
   the interface identifier (i.e., the rightmost 64 bits) of the IPv6
   address by computing a cryptographic hash of the public key.  The
   resulting IPv6 address is called a cryptographically generated
   address (CGA).  The corresponding private key can then be used to
   sign messages sent from the address.  An introduction to CGAs and
   their application to SEND can be found in [Aura03] and [AAKMNR02].

   This document specifies:

   o  how to generate a CGA from the cryptographic hash of a public key
      and auxiliary parameters,

   o  how to verify the association between the public key and the CGA,
      and

   o  how to sign a message sent from the CGA, and how to verify the
      signature.

Aura                        Standards Track                     [Page 2]
RFC 3972         Cryptographically Generated Addresses        March 2005

   To verify the association between the address and the public key, the
   verifier needs to know the address itself, the public key, and the
   values of the auxiliary parameters.  The verifier can then go on to
   verify messages signed by the owner of the public key (i.e., the
   address owner).  No additional security infrastructure, such as a
   public key infrastructure (PKI), certification authorities, or other
   trusted servers, is needed.

   Note that because CGAs themselves are not certified, an attacker can
   create a new CGA from any subnet prefix and its own (or anyone
   else's) public key.  However, the attacker cannot take a CGA created
   by someone else and send signed messages that appear to come from the