[Docs] [txt|pdf] [Tracker] [Email] [Nits]

Versions: 00 01 draft-ietf-6man-stable-privacy-addresses

IPv6 maintenance Working Group (6man)                            F. Gont
Internet-Draft                                                   UK CPNI
Updates: 4862 (if approved)                            December 15, 2011
Intended status: Standards Track
Expires: June 17, 2012


  A method for Generating Stable Privacy-Enhanced Addresses with IPv6
              Stateless Address Autoconfiguration (SLAAC)
              draft-gont-6man-stable-privacy-addresses-00

Abstract

   This document specifies a method for generating IPv6 Interface
   Identifiers to be used with IPv6 Stateless Address Autoconfiguration
   (SLAAC), such that addresses configured using this method are stable
   within each subnet, but the Interface Identifier changes when hosts
   move from one network to another.  The aforementioned method is meant
   to be an alternative to generating Interface Identifiers based on
   IEEE identifiers, such that the same manageability benefits can be
   achieved without sacrificing the privacy of users.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.  This document may not be modified,
   and derivative works of it may not be created, and it may not be
   published except as an Internet-Draft.

   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/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 17, 2012.

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



Gont                      Expires June 17, 2012                 [Page 1]


Internet-Draft          Stable Privacy Addresses           December 2011


   (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.  Design goals . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Algorithm specification  . . . . . . . . . . . . . . . . . . .  6
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12






























Gont                      Expires June 17, 2012                 [Page 2]


Internet-Draft          Stable Privacy Addresses           December 2011


1.  Introduction

   [RFC4862] specifies the Stateless Address Autoconfiguration (SLAAC)
   for IPv6, which typically results in hosts configuring one or more
   "stable" addresses composed of a network prefix advertised by a local
   router, and an Interface Identifier (IID) that typically embeds a
   hardware address (using IEEE identifiers) [RFC4291].

   Static addresses are generally considered to simplify network
   management, since they simplify ACLs and logging.  However, since
   IEEE identifiers are typically globally unique, the resulting IPv6
   addresses can be leveraged to track and correlate the activity of a
   node, thus negatively affecting the privacy of users.

   The "Privacy Extensions for Stateless Address Autoconfiguration in
   IPv6" [RFC4941] were introduced to difficult the task of
   eavesdroppers and other information collectors to correlate the
   activities of a node, and basically result in temporary (and random)
   Interface Identifiers that are typically more difficult to leverage
   than those based on IEEE identifiers.  When privacy extensions are
   enabled, "privacy addresses" are employed for "outgoing
   communications", while the traditional IPv6 addresses based on IEEE
   identifiers are still used for "server" functions (i.e., receiving
   incoming connections).  Some flavor of these "Privacy Extensions"
   have been implemented in a variety of systems, some of which (notably
   Microsoft Windows Vista and Microsoft Windows 7) enable them by
   default.

   Privacy addresses can be challenging in a number of areas.  For
   example, from a network-management point of view, they tend to
   increase the complexity of enforcing access controls and event
   logging.  As a result, some organizations disable the use of privacy
   addresses even at the expense of reduced privacy [Broersma].  Also,
   they result in increased complexity, which might not be possible or
   desirable in some implementations (e.g., some embedded devices).

   In such scenarios in which "Privacy Extensions" are deliberately not
   used, addresses are generated using e.g.  IEEE identifiers, and are
   subject to the privacy issues discussed above.

   We note that even in those scenarios in which "Privacy Extensions"
   are not used, there is still no need or desire to negatively affect
   user privacy.  As a result, this document specifies a method to
   generate interface identifiers that are stable/constant within each
   subnet, but that change as hosts move from one network to another,
   thus keeping the "stability" properties of the interface identifiers
   specified in [RFC4291], while still preventing to correlate the
   activities of a node as it moves from one network to another.



Gont                      Expires June 17, 2012                 [Page 3]


Internet-Draft          Stable Privacy Addresses           December 2011


   On the other hand, even in scenarios in which "Privacy Extensions"
   are employed, IPv6 addresses based on IEEE identifiers are still
   typically used for performing "server" functions.  In such scenarios,
   implementation of the mechanism described in this document would
   still be desirable, such that the "stable" addresses used by hosts
   for "server" functions are not easily predictable (and hence
   difficult host-scanning).

   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].








































Gont                      Expires June 17, 2012                 [Page 4]


Internet-Draft          Stable Privacy Addresses           December 2011


2.  Design goals

   This document specifies a method for selecting interface identifiers
   to be used with IPv6 SLAAC, with the following goals:

   o  The resulting interface identifier remains constant/stable for
      each prefix used with SLAAC within each subnet.  That is, the
      algorithm generates the same interface identifier when configuring
      an address belonging to the same prefix within the same subnet.

   o  The resulting interface identifier does change when addresses are
      configured for different prefixes.  That is, if different
      autoconfiguration prefixes are used to configure addresses for the
      same network interface card, the resulting interface identifiers
      must be (statistically) different.

   o  It must be difficult for an outsider to predict the interface
      identifiers that will be generated by the algorithm, even with
      knowledge of the interface identifiers generated for configuring
      other addresses.

   o  The aforementioned interface identifiers are meant to be an
      alternative to those based on IEEE identifiers, as specified in
      [RFC4291].

   We note that of use of the algorithm specified in this document is
   (to a large extent) orthogonal to the use of "Privacy Extensions"
   [RFC4941].  Hosts that do not implment/use "Privacy Extensions" would
   have the benefit that they would not be subject to the host-tracking
   issues discussed in the previous section.  On the other hand, since
   hosts implementing "Privacy Extensions" still make use of IEEE-
   derived identifiers (mostly for performing "server" functions),
   implementation of this algorithm would still benefit such
   implementations, since it would prevent leakage of the Organizational
   Unique Identifier (OUI), which would be of help to attackers for
   host-scanning purposes [Gont-DEEPSEC2011] [CPNI-IPv6].















Gont                      Expires June 17, 2012                 [Page 5]


Internet-Draft          Stable Privacy Addresses           December 2011


3.  Algorithm specification

   IPv6 implementations conforming to this specification MUST generate
   interface identifiers with the algorithm specified in this section.
   The aforementioned algorithm MUST be employed for generating the
   interface identifiers for all the IPv6 addresses configured with
   SLAAC for a given interface, including IPv6 link-local addresses.

   1.  Compute a random (but stable) identifier with the expression:

       RID = F(Prefix, Modified_EUI64, Network_ID, secret_key)

       Where:

       RID:
          Random (but stable) identifier

       F():
          A pseudorandom function (PRF) that is not computable from the
          outside (without knowledge of the secret key).  The PRF could
          be implemented as a cryptographic hash of the concatenation of
          each of the function parameters .

       Prefix:
          The prefix to be used for SLAAC, as learned from an ICMPv6
          Router Advertisement message.

       Modified_EUI64:
          The Modified EUI-64 format identifier corresponding to this
          network interface.

       Network_ID:
          Some network specific data that identifies the subnet to which
          this interface is attached.  For example the IEEE 802.11 SSID
          corresponding to the network to which this interface is
          associated.  This parameter is OPTIONAL.

       secret_key:
          A secret key that is not known by the attacker.

   2.  The Interface Identifier is finally obtained by taking the
       leftmost 64 bits of the RID value computed in the previous step,
       and and setting bit 6 (the leftmost bit is numbered 0) to zero.
       This creates an interface identifier with the universal/local bit
       indicating local significance only.

   Note that the result of F() in the algorithm above is no more secure
   than the secret key.  If an attacker is aware of PRF is being used by



Gont                      Expires June 17, 2012                 [Page 6]


Internet-Draft          Stable Privacy Addresses           December 2011


   the victim (which we should expect), and the attacker can obtain
   enough material (i.e., addresses configured by the victim), the
   attacker may simply search the entire secret-key space to find
   matches.  To protect against this, the secret key should be of a
   reasonable length.  Key lengths of 128 bits should be adequate.  The
   secret key can either be a true random number [RFC4086], or some per-
   host secret.

   Including the optional Network_ID parameter when computing the RID
   value above would cause the algorithm to produce a different
   Interface Identifier when connecting to different networks, even when
   configuring addresses belonging to the same prefix.  This means that
   a host would employ a different Interface ID as it moves from one
   network to another even for IPv6 link-local addresses.





































Gont                      Expires June 17, 2012                 [Page 7]


Internet-Draft          Stable Privacy Addresses           December 2011


4.  IANA Considerations

   There are no IANA registries within this document.  The RFC-Editor
   can remove this section before publication of this document as an
   RFC.














































Gont                      Expires June 17, 2012                 [Page 8]


Internet-Draft          Stable Privacy Addresses           December 2011


5.  Security Considerations

   This document specifies an algorithm for generating interface
   identifiers to be used with IPv6 Stateless Address Autoconfiguration
   (SLAAC), in replacement of e.g. the Modified EUI-64 format
   identifiers.  When compared to modified EUI-64 format identifiers,
   the identifiers specified in this document have a number of
   advantages:

   o  They prevent trivial host-tracking, since when a host moves from
      one network to another the prefix used for autoconfiguration will
      typically change, and hence the resulting interface identifier
      will also change.

   o  They mitigate host-scanning techniques which leverage predictable
      interface identifiers (e.g., known Organizational Unique
      Identifiers).

   Finally, we note that this algorithm is meant to be an alternative
   for e.g. the Modified EUI-64 format identifiers, but not for
   temporary-address methods such as that specified in [RFC4941].
   Clearly, temporary addresses can help reduce the attack exposure
   window, since the lifetime of each IPv6 address is reduced when
   compared to that of addresses generated with the method specified in
   this document.  Additionally, they may be of help to correlate
   different activities performed by the same host while attached to the
   same network.  However, we note that implementation of this algorithm
   would still benefit those hosts employing "Privacy Addresses", since
   it would prevent leakage of the IEEE Organizational Unique Identifier
   (OUI) when IEEE-identifier-derived addresses are used for serve-like
   functions, which can be of help to attackers for host-scanning
   purposes.



















Gont                      Expires June 17, 2012                 [Page 9]


Internet-Draft          Stable Privacy Addresses           December 2011


6.  Acknowledgements

   Fernando Gont would like to thank CPNI (http://www.cpni.gov.uk) for
   their continued support.















































Gont                      Expires June 17, 2012                [Page 10]


Internet-Draft          Stable Privacy Addresses           December 2011


7.  References

7.1.  Normative References

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

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

   [RFC4086]  Eastlake, D., Schiller, J., and S. Crocker, "Randomness
              Requirements for Security", BCP 106, RFC 4086, June 2005.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, September 2007.

7.2.  Informative References

   [Gont-DEEPSEC2011]
              Gont, "Results of a Security Assessment of the Internet
              Protocol version 6 (IPv6)",  DEEPSEC 2011 Conference,
              Vienna, Austria, November 2011, <http://
              www.si6networks.com/presentations/deepsec2011/
              fgont-deepsec2011-ipv6-security.pdf>.

   [Broersma]
              Broersma, R., "IPv6 Everywhere: Living with a Fully IPv6-
              enabled environment",  Australian IPv6 Summit 2010,
              Melbourne, VIC Australia, October 2010,
              <http://www.ipv6.org.au/summit/talks/Ron_Broersma.pdf>.

   [CPNI-IPv6]
              Gont, F., "Security Assessment of the Internet Protocol
              version 6 (IPv6)",  UK Centre for the Protection of
              National Infrastructure, (available on request).









Gont                      Expires June 17, 2012                [Page 11]


Internet-Draft          Stable Privacy Addresses           December 2011


Author's Address

   Fernando Gont
   UK CPNI

   Email: fgont@si6networks.com
   URI:   http://www.cpni.gov.uk












































Gont                      Expires June 17, 2012                [Page 12]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/