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IPv6 maintenance Working Group (6man)                            F. Gont
Internet-Draft                                    SI6 Networks / UTN-FRH
Intended status: Standards Track                              C. Huitema
Expires: September 6, 2018                          Private Octopus Inc.
                                                             S. Krishnan
                                                       Ericsson Research
                                                                 G. Gont
                                                            SI6 Networks
                                                         M. Garcia Corbo
                                                           March 5, 2018

         Recommendation on Temporary IPv6 Interface Identifiers


   This document specifies a set of requirements for generating
   temporary addresses, and clarifies the stability requirements for
   IPv6 addresses, allowing for the use of only temporary addresses.

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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   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 September 6, 2018.

Copyright Notice

   Copyright (c) 2018 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
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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Problem statement . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Stability Requirements for IPv6 Addresses . . . . . . . . . .   4
   5.  Requirements for Temporary IPv6 Addresses . . . . . . . . . .   4
   6.  Future Work . . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   IPv6 StateLess Address AutoConfiguration (SLAAC) [RFC4862] has
   traditionally resulted in stable addresses, since the Interface
   Identifier (IID) has been generated by embedding a stable layer-2
   numeric identifier (e.g., a MAC address).  [RFC4941] originally
   implied, throughout the specification, that temporary addresses are
   generated and employed along with stable addresses.

   While the use of stable addresses (only) or mixed stable and
   temporary addresses can be desirable in a number of scenarios, there
   are other scenarios in which, for security and privacy reasons, a
   node may want to use only Temporary address (e.g., a temporary

   On the other hand, the lack of a formal set of requirements for
   temporary addresses led to a number of flaws in popular
   implementations and in the protocol specification itself, such as
   allowing for the correlation of network activity carried out with
   different addresses, reusing randomized identifiers across different
   networks, etc.

   This document clarifies the requirements for stability of IPv6
   addresses, such that nodes are not required to configure stable
   addresses, and may instead employ only temporary addresses.  It also
   specifies a set of requirements for the generation of temporary

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2.  Terminology

   This document employs the terms defined in [RFC7721].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  Problem statement

   When [RFC4941] was written, its authors wanted to prevent privacy and
   security attacks enabled by addresses that contain "an embedded
   interface identifier, which remains constant over time".  They
   observed that "Anytime a fixed identifier is used in multiple
   contexts, it becomes possible to correlate seemingly unrelated
   activity using this identifier."  They were concerned with both on-
   path attackers who would observe the IP addresses of packets observed
   in transit, and attackers that would have access to the logs of

   Since the publication of [RFC4941] in September 2007, our
   understanding of threats and mitigations has evolved.  The IETF is
   now officially concerned with Pervasive Monitoring [RFC7258], as well
   as the wide spread collection of information for advertising and
   other purposes, for example through the Real Time Bidding protocol
   used for advertising auctions [RTB25].

3.1.  Privacy requirements

   The widespread deployment of encryption advocated in [RFC7624] is a
   response to Pervasive Monitoring.  Encryption of communication
   reduces the amount of information that can be collected by monitoring
   data links, but does not prevent monitoring of IPv6 addresses
   embedded in clear text packet headers.  Stable IPv6 addresses enable
   the correlation of such data over time.

   MAC Address Randomization [IETFMACRandom] is another response to
   pervasive monitoring.  In conjunction with DHCP Anonymity [RFC7844],
   it ensures that devices cannot be tracked by their MAC Address or
   their DHCP identifiers when they connect to "hot spots".  However,
   the privacy effects of MAC Address Randomization would be nullified
   if a device kept using the same IPv6 address before and after a MAC-
   address randomization event.

   Many Web Browsers have options enabling browsing "in private".
   However, if the web connections during the private mode use the same
   IPv6 address as those in the public mode, web tracking systems
   similar to [RTB25] will quickly find the correlation between the

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   public personna of the user and the supposedly private connection.
   Similarly, many web browsers have options to "delete history",
   including deleting "cookies" and other persistent data.  Again, if
   the same IPv6 address is used before and after the deletion of
   cookies, web tracking systems will easily correlate the new activity
   with the prior data collection.

   Using temporary address alone may not be sufficient to prevent all
   forms of tracking.  It is however quite clear that some usage of
   temporary addresses is necessary to provide user privacy.  It is also
   clear that the usage of temporary addresses needs to be synchronized
   with other privacy defining event such as moving to a new network,
   performing MAC Address Randomization, or changing the privacy posture
   of a node.

4.  Stability Requirements for IPv6 Addresses

   Nodes are not required to generate addresses with any specific
   stability properties.  That is, the generation of stable addresses is
   OPTIONAL.  This means that a node may end up configuring only stable
   addresses, only Temporary, or both stable and temporary addresses.

5.  Requirements for Temporary IPv6 Addresses

   The requirements for temporary IPv6 addresses are as follows:

   1.  Temporary addresses MUST have a limited lifetime, which should be
       different for different addresses.  The lifetime of an address
       essentially limits the extent to which network activity
       correlation can be performed based on such address.

   2.  The lifetime of an address MUST be further reduced when privacy-
       meaningful events (such as a node attaching to a new network)
       takes place.

   3.  The resulting Interface Identifiers MUST be different 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.  This
       means that, given two addresses that employ different prefixes,
       it must be difficult for an outside entity to tell whether the
       addresses correspond to the same network interface or even
       whether they have been generated by the same host.

   4.  The resulting interface identifiers MUST NOT embed layer-2
       identifiers (e.g.  MAC addresses).

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   5.  It must be difficult for an outside entity to predict the
       Interface Identifiers that will be generated by the algorithm,
       even with knowledge of the Interface Identifiers generated for
       configuring other addresses.

   6.  The resulting Interface Identifiers MUST be semantically opaque
       [RFC7136] and MUST NOT follow any specific patterns.

   By definition, temporary addresses have a limited lifetime.  This is
   in contrast with e.g. stable addresses [RFC7217], that do not have
   have a limited lifetime.  Having a variable maximum lifetime prevents
   an observer from synchronizing with the temporary address
   regeneration; that is, from being able to expect when address will be
   regenerated, and thus infer that one newly observed addresses is the
   result of regenerating a previously observed one.

   The lifetime of an address should be further reduced by privacy-
   meaningful events.  For example, a host should not employ the same
   address across network attachment events.  That is, a host that de-
   attaches from a network and subsequently re-attaches to a (possibly
   different) network should regenerate all of its temporary addresses.
   Similarly, a host that implements MAC address randomization should
   regenerate all of its temporary addresses.  Other events, such as
   those discussed in Section 3.1 should also trigger the regeneration
   of all temporary addresses.

   The IIDs of addresses configured for different autoconfiguration
   prefixes must be different, such that traffic for those addresses
   cannot be correlated.

   The reuse of identifiers that have their own semantics or properties
   across different contexts or scopes can be detrimental for security
   and privacy [I-D.gont-predictable-numeric-ids] [RFC6973] [RFC4941].
   For example, if two different layer-3 protocols generate their
   addresses by embedding a layer-2 identifier (e.g., a MAC address),
   then the traffic for such protocols could be correlated (irrespective
   of whether the aforementioned layer-2 identifier has been randomized
   or not).  Besides, a node that generates an IPv6 address by embedding
   a link-layer address in the IPv6 address will, when configuring
   addresses for different prefixes, result in the same IID being used
   for such prefixes, thus allowing the corresponding traffic to be

   For security and privacy reasons, the IIDs generated for temporary
   addresses must not be predictable.  Otherwise, the node may be
   subject to many (if not all) of the security and privacy issues that
   are meant to be mitigated (please see [RFC7721].

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   Any semantics or patterns in an IID might be leveraged by an attacker
   to e.g.  reduce the search space when performing address-scanning
   attacks, infer the identity of the node, etc.

6.  Future Work

   This document clarifies the requirements for stability requirements
   for IPv6 addresses, and specifies requirements for temporary
   addresses.  A separate document
   ([I-D.gont-taps-address-usage-problem-statement]) discusses the
   tradeoffs involved when considering different stability properties of
   IPv6 addresses.

7.  IANA Considerations

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

8.  Security Considerations

   This document clarifies the stability requirements for IPv6
   addresses, and specifies requirements for the generation of temporary

   The security and privacy properties of IPv6 addresses have been
   discussed in detail in [RFC7721] and [RFC7707].

9.  Acknowledgements

   The authors would like to thank (in alphabetical order) Brian
   Carpenter and Lorenzo Colitti for providing valuable feedback on
   earlier versions of this document.

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 4086,
              DOI 10.17487/RFC4086, June 2005,

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   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,

   [RFC5453]  Krishnan, S., "Reserved IPv6 Interface Identifiers",
              RFC 5453, DOI 10.17487/RFC5453, February 2009,

   [RFC7136]  Carpenter, B. and S. Jiang, "Significance of IPv6
              Interface Identifiers", RFC 7136, DOI 10.17487/RFC7136,
              February 2014, <https://www.rfc-editor.org/info/rfc7136>.

   [RFC7217]  Gont, F., "A Method for Generating Semantically Opaque
              Interface Identifiers with IPv6 Stateless Address
              Autoconfiguration (SLAAC)", RFC 7217,
              DOI 10.17487/RFC7217, April 2014,

   [RFC8064]  Gont, F., Cooper, A., Thaler, D., and W. Liu,
              "Recommendation on Stable IPv6 Interface Identifiers",
              RFC 8064, DOI 10.17487/RFC8064, February 2017,

10.2.  Informative References

              NIST, "Secure Hash Standard (SHS)", FIPS
              Publication 180-4, March 2012,

              Gont, F. and I. Arce, "Security and Privacy Implications
              of Numeric Identifiers Employed in Network Protocols",
              draft-gont-predictable-numeric-ids-02 (work in progress),
              February 2018.

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              Gont, F., Gont, G., Corbo, M., and C. Huitema, "Problem
              Statement Regarding IPv6 Address Usage", draft-gont-taps-
              address-usage-problem-statement-00 (work in progress),
              February 2018.

              IANA, "Reserved IPv6 Interface Identifiers",

              Zuniga, JC., "MAC Privacy", November 2014,

              The Open Group, "The Open Group Base Specifications Issue
              7 / IEEE Std 1003.1-2008, 2016 Edition",
              Section 4.16 Seconds Since the Epoch, 2016,

              Ullrich, J. and E. Weippl, "Privacy is Not an Option:
              Attacking the IPv6 Privacy Extension",  International
              Symposium on Recent Advances in Intrusion Detection
              (RAID), 2015, <https://www.sba-research.org/wp-

   [RFC1321]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              DOI 10.17487/RFC1321, April 1992,

   [RFC3041]  Narten, T. and R. Draves, "Privacy Extensions for
              Stateless Address Autoconfiguration in IPv6", RFC 3041,
              DOI 10.17487/RFC3041, January 2001,

   [RFC6059]  Krishnan, S. and G. Daley, "Simple Procedures for
              Detecting Network Attachment in IPv6", RFC 6059,
              DOI 10.17487/RFC6059, November 2010,

   [RFC6151]  Turner, S. and L. Chen, "Updated Security Considerations
              for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
              RFC 6151, DOI 10.17487/RFC6151, March 2011,

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   [RFC6973]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
              Morris, J., Hansen, M., and R. Smith, "Privacy
              Considerations for Internet Protocols", RFC 6973,
              DOI 10.17487/RFC6973, July 2013,

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
              2014, <https://www.rfc-editor.org/info/rfc7258>.

   [RFC7624]  Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
              Trammell, B., Huitema, C., and D. Borkmann,
              "Confidentiality in the Face of Pervasive Surveillance: A
              Threat Model and Problem Statement", RFC 7624,
              DOI 10.17487/RFC7624, August 2015,

   [RFC7707]  Gont, F. and T. Chown, "Network Reconnaissance in IPv6
              Networks", RFC 7707, DOI 10.17487/RFC7707, March 2016,

   [RFC7721]  Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
              Considerations for IPv6 Address Generation Mechanisms",
              RFC 7721, DOI 10.17487/RFC7721, March 2016,

   [RFC7844]  Huitema, C., Mrugalski, T., and S. Krishnan, "Anonymity
              Profiles for DHCP Clients", RFC 7844,
              DOI 10.17487/RFC7844, May 2016,

   [RTB25]    Interactive Advertising Bureau (IAB), "Real Time Bidding
              (RTB) project, OpenRTB API Specification Version 2.5",
              December 2016, <http://www.iab.com/wp-

Authors' Addresses

   Fernando Gont
   SI6 Networks / UTN-FRH
   Evaristo Carriego 2644
   Haedo, Provincia de Buenos Aires  1706

   Phone: +54 11 4650 8472
   Email: fgont@si6networks.com
   URI:   http://www.si6networks.com

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   Christian Huitema
   Private Octopus Inc.
   Friday Harbor, WA  98250

   Email: huitema@huitema.net
   URI:   http://privateoctopus.com/

   Suresh Krishnan
   Ericsson Research
   8400 Decarie Blvd.
   Town of Mount Royal, QC

   Email: suresh.krishnan@ericsson.com

   Guillermo Gont
   SI6 Networks
   Evaristo Carriego 2644
   Haedo, Provincia de Buenos Aires  1706

   Phone: +54 11 4650 8472
   Email: ggont@si6networks.com
   URI:   https://www.si6networks.com

   Madeleine Garcia Corbo
   Servicios de Informacion del Transporte
   Neptuno 358
   Havana City  10400

   Email: madelen.garcia16@gmail.com

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