Network Working Group                                          A. Cooper
Internet-Draft                                                       CDT
Intended status: Informational                                   F. Gont
Expires: April 20, 2014                              Huawei Technologies
                                                               D. Thaler
                                                        October 17, 2013

     Privacy Considerations for IPv6 Address Generation Mechanisms


   This document discusses privacy and security considerations for
   several IPv6 address generation mechanisms, both standardized and
   non-standardized.  It evaluates how different mechanisms mitigate
   different threats and the trade-offs that implementors, developers,
   and users face in choosing different addresses or address generation

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 20, 2014.

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   document authors.  All rights reserved.

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   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect

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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Weaknesses in IEEE-identifier-based IIDs  . . . . . . . . . .   4
     3.1.  Correlation of activities over time . . . . . . . . . . .   5
     3.2.  Location tracking . . . . . . . . . . . . . . . . . . . .   6
     3.3.  Device-specific vulnerability exploitation  . . . . . . .   6
     3.4.  Address scanning  . . . . . . . . . . . . . . . . . . . .   6
   4.  Privacy and security properties of address generation
       mechanisms  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  IEEE-identifier-based IIDs  . . . . . . . . . . . . . . .   9
     4.2.  Static, manually configured IIDs  . . . . . . . . . . . .   9
     4.3.  Constant, semantically opaque IIDs  . . . . . . . . . . .  10
     4.4.  Cryptographically generated IIDs  . . . . . . . . . . . .  10
     4.5.  Stable, semantically opaque IIDs  . . . . . . . . . . . .  10
     4.6.  Temporary IIDs  . . . . . . . . . . . . . . . . . . . . .  10
     4.7.  DHCPv6 generation of IIDs . . . . . . . . . . . . . . . .  11
     4.8.  Transition/co-existence technologies  . . . . . . . . . .  11
   5.  Miscellaneous Issues with IPv6 addressing . . . . . . . . . .  12
     5.1.  Geographic Location . . . . . . . . . . . . . . . . . . .  12
     5.2.  Network Operation . . . . . . . . . . . . . . . . . . . .  12
     5.3.  Compliance  . . . . . . . . . . . . . . . . . . . . . . .  12
     5.4.  Intellectual Property Rights (IPRs) . . . . . . . . . . .  12
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   9.  Informative References  . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   IPv6 was designed to improve upon IPv4 in many respects, and
   mechanisms for address assignment were one such area for improvement.
   In addition to static address assignment and DHCP, stateless address
   autoconfiguration (SLAAC) was developed as a less intensive, fate-
   shared means of performing address configuration.  With stateless
   autoconfiguration, routers advertise on-link prefixes and hosts
   generate their own interface identifiers (IIDs) to complete their
   addresses.  Over the years, many interface identifier generation
   techniques have been defined, both standardized and non-standardized:

   o  Manual configuration

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      *  IPv4 address

      *  Service port

      *  Wordy

      *  Low-byte

   o  Stateless Address Auto-Cofiguration (SLAAC)

      *  IEEE 802 48-bit MAC or IEEE EUI-64 identifier

      *  Cryptographically generated [RFC3972]

      *  Temporary (also known as "privacy addresses") [RFC4941]

      *  Constant, semantically opaque (also known as random)

      *  Stable, semantically opaque

   o  DHCPv6-based [RFC3315]

   o  Specified by transition/co-existence technologies

      *  IPv4 address and port [RFC4380]

   Deriving the IID from a globally unique IEEE identifier [RFC2462] was
   one of the earliest mechanisms developed.  A number of privacy and
   security issues related to the interface IDs derived from IEEE
   identifiers were discovered after their standardization, and many of
   the mechanisms developed later aimed to mitigate some or all of these
   weaknesses.  This document identifies four types of threats against
   IEEE-identifier-based IIDs, and discusses how other existing
   techniques for generating IIDs do or do not mitigate those threats.
   For simplicity sake, most of the discussion in this document assumes
   that addresses have global scope.  However, the scope of an address
   just limits the number of potential nodes that might exploit such
   address for different malicious purposes (host-tracking, device-
   specific vulnerability exploitation, etc.).  Additionally, we note
   that even addresses with limited scopes (e.g. link-local) might leak
   out as a result of, for example, application-layer protocols (e.g.,
   consider email headers).

2.  Terminology

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   This section clarifies the terminology used throughout this document.

   Public address:
      An address that has been published in a directory or other public
      location, such as the DNS, a SIP proxy, an application-specific
      DHT, or a publicly available URI.  A host's public addresses are
      intended to be discoverable by third parties.

   Stable address:
      An address that does not vary over time within the same network.
      Note that [RFC4941] refers to these as "public" addresses, but
      "stable" is used here for reasons explained in Section 4.

   Temporary address:
      An address that varies over time within the same network.

   Constant IID:
      An IPv6 Interface Identifier that is globally stable.  That is,
      the Interface ID will remain constant even if the node moves from
      one network to another.

   Stable IID:
      An IPv6 Interface Identifier that is stable within some specified
      context.  For example, an Interface ID can be globally stable
      (constant), or could be stable per network (meaning that the
      Interface ID will remain unchanged as long as a the node stays on
      the same network, but may change when the node moves from one
      network to another).

   Temporary IID:
      An IPv6 Interface Identifier that varies over time.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].  These words take their normative meanings only when they
   are presented in ALL UPPERCASE.

3.  Weaknesses in IEEE-identifier-based IIDs

   There are a number of privacy and security implications that exist
   for hosts that use IEEE-identifier-based IIDs.  This section
   discusses four generic attack types: correlation of activities over
   time, location tracking, device-specific vulnerability exploitation,
   and address scanning.  The first three of these rely on the attacker
   first gaining knowledge of the target host's IID.  This can be
   achieved by different types of attackers: the operator of a server to
   which the host connects, such as a web server or a peer-to-peer

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   server; an entity that connects to the same network as the target
   (such as a conference network or any public network); or an entity
   that is on-path to the destinations with which the host communicates,
   such as a network operator.

3.1.  Correlation of activities over time

   As with other identifiers, an IPv6 address can be used to correlate
   the activities of a host for at least as long as the lifetime of the
   address.  The correlation made possible by IEEE-identifier-based IIDs
   is of particular concern because MAC addresses are much more
   permanent than, say, DHCP leases.  MAC addresses tend to last roughly
   the lifetime of a device's network interface, allowing correlation on
   the order of years, compared to days for DHCP.

   As [RFC4941] explains,

      "[t]he use of a non-changing interface identifier to form
      addresses is a specific instance of the more general case where a
      constant identifier is reused over an extended period of time and
      in multiple independent activities.  Anytime the same identifier
      is used in multiple contexts, it becomes possible for that
      identifier to be used to correlate seemingly unrelated activity.
      ... The use of a constant identifier within an address is of
      special concern because addresses are a fundamental requirement of
      communication and cannot easily be hidden from eavesdroppers and
      other parties.  Even when higher layers encrypt their payloads,
      addresses in packet headers appear in the clear."

   IP addresses are just one example of information that can be used to
   correlate activities over time.  DNS names, cookies [RFC6265],
   browser fingerprints [Panopticlick], and application-layer usernames
   can all be used to link a host's activities together.  Although IEEE-
   identifier-based IIDs are likely to last at least as long or longer
   than these other identifiers, IIDs generated in other ways may have
   shorter or longer lifetimes than these identifiers depending on how
   they are generated.  Therefore, the extent to which a host's
   activities can be correlated depends on whether the host uses
   multiple identifiers together and the lifetimes of all of those
   identifiers.  Frequently refreshing an IPv6 address may not mitigate
   correlation if an attacker has access to other longer lived
   identifiers for a particular host.  This is an important caveat to
   keep in mind throughout the discussion of correlation in this
   document.  For further discussion of correlation, see Section 5.2.1
   of [I-D.iab-privacy-considerations].

   As noted in [RFC4941], in some cases correlation is just as feasible
   for a host using an IPv4 address as for a host using an IEEE

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   identifier to generate its IID in its IPv6 address.  Hosts that use
   static IPv4 addressing or who are consistently allocated the same
   address via DHCPv4 can be tracked as described above.  However, the
   widespread use of both NAT and DHCPv4 implementations that assign the
   same host a different address upon lease expiration mitigates this
   threat in the IPv4 case as compared to the IEEE identifier case in

3.2.  Location tracking

   Because the IPv6 address structure is divided between a topological
   portion and an interface identifier portion, an interface identifier
   that remains constant when a host connects to different networks (as
   an IEEE-identifier-based IID does) provides a way for observers to
   track the movements of that host.  In a passive attack on a mobile
   host, a server that receives connections from the same host over time
   would be able to determine the host's movements as its prefix

   Active attacks are also possible.  An attacker that first learns the
   host's interface identifier by being connected to the same network
   segment, running a server that the host connects to, or being on-path
   to the host's communications could subsequently probe other networks
   for the presence of the same interface identifier by sending a probe
   packet (ICMPv6 Echo Request, or any other probe packet).  Even if the
   host does not respond (e.g. as a result of a personal firewall), the
   first hop router will usually respond with an ICMP Address
   Unreachable when the host is not present, and be silent when the host
   is present.

   Location tracking based on IP address is generally not possible in
   IPv4 since hosts get assigned wholly new addresses when they change

3.3.  Device-specific vulnerability exploitation

   IPv6 addresses that embed IEEE identifiers leak information about the
   device (Network Interface Card vendor, or even Operating System and/
   or software type), which could be leveraged by an attacker with
   knowledge of device/software-specific vulnerabilities to quickly find
   possible targets.  Attackers can exploit vulnerabilities in hosts
   whose IIDs they have previously obtained, or scan an address space to
   find potential targets.

3.4.  Address scanning

   The structure of IEEE-based identifiers used for address generation
   can be leveraged by an attacker to reduce the target search space

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   [I-D.ietf-opsec-ipv6-host-scanning].  The 24-bit Organizationally
   Unique Identifier (OUI) of MAC addresses, together with the fixed
   value (0xff, 0xfe) used to form a Modified EUI-64 Interface
   Identifier, greatly help to reduce the search space, making it easier
   for an attacker to scan for individual addresses using widely-known
   popular OUIs.  This erases much of the protection against address
   scanning that the larger IPv6 address space was supposed to provide
   as compared to IPv4.

4.  Privacy and security properties of address generation mechanisms

   Analysis of the extent to which a particular host is protected
   against the threats described in Section 3 depends on how each of a
   host's addresses is generated and used.  In some scenarios, a host
   configures a single global address and uses it for all
   communications.  In other scenarios, a host configures multiple
   addresses using different mechanisms and may use any or all of them.

   [RFC3041] (later obsoleted by [RFC4941]) sought to address some of
   the problems described in Section 3 by defining "temporary addresses"
   for outbound connections.  Temporary addresses are meant to
   supplement the other addresses that a device might use, not to
   replace them.  They use IIDs that are randomly generated and change
   daily by default.  The idea was for temporary addresses to be used
   for outgoing connections (e.g., web browsing) while maintaining the
   ability to use a stable address when more address stability is
   desired (e.g., in DNS advertisements).

   [RFC3484] originally specified that stable addresses be used for
   outbound connections unless an application explicitly prefers
   temporary addresses.  The default preference for stable addresses was
   established to avoid applications potentially failing due to the
   short lifetime of temporary addresses or the possibility of a reverse
   look-up failure or error.  However, [RFC3484] allowed that
   "implementations for which privacy considerations outweigh these
   application compatibility concerns MAY reverse the sense of this
   rule" and instead prefer by default temporary addresses rather than
   stable addresses.  Indeed most implementations (notably including
   Windows) chose to default to temporary addresses for outbound
   connections since privacy was considered more important (and few
   applications supported IPv6 at the time, so application compatibility
   concerns were minimal).  [RFC6724] then obsoleted [RFC3484] and
   changed the default to match what implementations actually did.

   The envisioned relationship in [RFC3484] between stability of an
   address and its use in "public" can be misleading when conducting
   privacy analysis.  The stability of an address and the extent to
   which it is linkable to some other public identifier are independent

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   of one another.  For example, there is nothing that prevents a host
   from publishing a temporary address in a public place, such as the
   DNS.  Publishing both a stable address and a temporary address in the
   DNS or elsewhere where they can be linked together by a public
   identifier allows the host's activities when using either address to
   be correlated together.

   Moreover, because temporary addresses were designed to supplement
   other addresses generated by a host, the host may still configure a
   more stable address even if it only ever intentionally uses temporary
   addresses (as source addresses) for communication to off-link
   destinations.  An attacker can probe for the stable address even if
   it is never used as such a source address or advertised (e.g., in DNS
   or SIP) outside the link.

   This section compares the privacy and security properties of a
   variety of IID generation mechanisms and their possible usage
   scenarios, including scenarios in which a single mechanism is used to
   generate all of a host's IIDs and those in which temporary addresses
   are used together with addresses generated using a different IID
   generation mechanism.  The analysis of the exposure of each IID type
   to correlation assumes that IPv6 prefixes are shared by a reasonably
   large number of nodes.  As [RFC4941] notes, if a very small number of
   nodes (say, only one) use a particular prefix for an extended period
   of time, the prefix itself can be used to correlate the host's
   activities regardless of how the IID is generated.

   The table below provides a summary of the whole analysis.

   | Mechanism(s) | Correlation | Location   | Address    | Device     |
   |              |             | tracking   | scanning   | exploits   |
   | IEEE         | Possible    | Possible   | Possible   | Possible   |
   | identifier   | (for device | (for       |            |            |
   |              | lifetime)   | device     |            |            |
   |              |             | lifetime)  |            |            |
   |              |             |            |            |            |
   | Static       | Possible    | Depends on | Depends on | Depends on |
   | manual       | (for        | generation | generation | generation |
   |              | address     | mechanism  | mechanism  | mechanism  |
   |              | lifetime)   |            |            |            |
   |              |             |            |            |            |
   | Constant,    | Possible    | Possible   | No         | No         |
   | semantically | (for OS     | (for OS    |            |            |
   | opaque       | lifetime)   | lifetime)  |            |            |
   |              |             |            |            |            |
   | CGA          | Typically   | Typically  | No         | No         |

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   |              | possible    | possible   |            |            |
   |              | (for public | (for       |            |            |
   |              | key         | public key |            |            |
   |              | lifetime)   | lifetime)  |            |            |
   |              |             |            |            |            |
   | Stable,      | Possible    | No         | No         | No         |
   | semantically | (for OS     |            |            |            |
   | opaque       | lifetime)   |            |            |            |
   |              |             |            |            |            |
   | Temporary    | Only        | No         | No         | No         |
   |              | possible    |            |            |            |
   |              | for temp    |            |            |            |
   |              | address     |            |            |            |
   |              | lifetime    |            |            |            |
   |              |             |            |            |            |
   | DHCPv6       | Possible    | No         | Depends on | No         |
   |              | for lease   |            | DHCPv6     |            |
   |              | lifetime    |            | server imp |            |
   |              | (typically  |            | lementatio |            |
   |              | hours)      |            | n          |            |

   Table 1: Privacy and security properties of IID generation mechanisms

4.1.  IEEE-identifier-based IIDs

   As discussed in Section 3, addresses that use IIDs based on IEEE
   identifiers are vulnerable to all four threats.  They allow
   correlation and location tracking for the lifetime of the device
   since IEEE identifiers last that long and their structure makes
   address scanning and device exploits possible.

4.2.  Static, manually configured IIDs

   Because static, manually configured IIDs are stable, both correlation
   and location tracking are possible for the life of the address.

   The extent to which location tracking can be successfully performed
   depends, to a some extent, on the uniqueness of the employed
   Interface ID.  For example, one would expect "low byte" Interface IDs
   to be more widely reused than, for example, Interface IDs where the
   whole 64-bits follow some pattern that is unique to a specific
   organization.  Widely reused Interface IDs will typically lead to
   false positives when performing location tracking.

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   Whether manually configured addresses are vulnerable to address
   scanning and device exploits depends on the specifics of how the IIDs
   are generated.  For example, low-byte and IPv4-embedded IIDs will
   greatly reduce the search space when performing address scans.

4.3.  Constant, semantically opaque IIDs

   Although a mechanism to generate a constant, semantically opaque IID
   has not been standardized, it has been in wide use for many years on
   at least one platform (Windows).  Windows uses the [RFC4941] random
   generation mechanism in lieu of generating an IEEE-identifier-based
   IID.  This mitigates the device-specific exploitation and address
   scanning attacks, but still allows correlation and location tracking
   because the IID is constant across networks and time.

4.4.  Cryptographically generated IIDs

   Cryptographically generated addresses (CGAs) [RFC3972] bind a hash of
   the host's public key to an IPv6 address in the SEcure Neighbor
   Discovery (SEND) [RFC3971] protocol.  CGAs may be regenerated for
   each subnet prefix, but this is not required given that they are
   computationally expensive to generate.  A host using a CGA can be
   correlated for as long as the life of the public key.  If the host
   does not generate a new public key when it moves to a different
   network, its location can also be tracked.  CGAs do not allow device-
   specific exploitation or address scanning attacks.

4.5.  Stable, semantically opaque IIDs

   [I-D.ietf-6man-stable-privacy-addresses] specifies a mechanism that
   generates a unique random IID for each network.  A host that stays
   connected to the same network could therefore be tracked at length,
   whereas a mobile host's activities could only be correlated for the
   duration of each network connection.  Location tracking is not
   possible with these addresses.  They also do not allow device-
   specific exploitation or address scanning attacks.

4.6.  Temporary IIDs

   A host that uses only a temporary address mitigates all four threats.
   Its activities may only be correlated for the lifetime a single
   temporary address.

   A host that configures both an IEEE-identifier-based IID and
   temporary addresses makes the host vulnerable to the same attacks as
   if temporary addresses were not in use, although the viability of
   some of them depends on how the host uses each address.  An attacker
   can correlate all of the host's activities for which it uses its

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   IEEE-identifier-based IID.  Once an attacker has obtained the IEEE-
   identifier-based IID, location tracking becomes possible on other
   networks even if the host only makes use of temporary addresses on
   those other networks; the attacker can actively probe the other
   networks for the presence of the IEEE-identifier-based IID.  Device-
   specific vulnerabilities can still be exploited.  Address scanning is
   also still possible because the IEEE-identifier-based address will
   result in predictable patterns.

   If the host instead generates a constant semantically-opaque IID to
   use in a stable address for server-like connections together with
   temporary addresses for outbound connections (as is the default in
   Windows), it sees some improvements over the previous scenario.  The
   address scanning and device-specific exploitation attacks are no
   longer possible because the OUI is no longer embedded in any of the
   host's addresses.  However, correlation of some activities across
   time is still possible because the semantically opaque IID is
   constant.  And once an attacker has obtained the host's semantically
   opaque IID, location tracking is possible on any network by probing
   for that IID, even if the host only uses temporary addresses on those

   When used together with temporary addresses, the stable (per-
   network), semantically opaque IID generation mechanism
   [I-D.ietf-6man-stable-privacy-addresses] improves upon the previous
   scenario by eliminating the possibility for location tracking (since
   a different IID is generated for each subnet prefix).  Correlation of
   node activities within the same network will be typically possible
   for the lifetime of the stable address (which may still be lengthy
   for hosts that are not mobile).

4.7.  DHCPv6 generation of IIDs

   The security/privacy implications of DHCPv6-based addresses will
   typically depend on the specific DHCPv6 server software being
   employed.  For example, some DHCPv6-server implementations lease low-
   byte addresses, while others randomly select the IPv6 addresses they
   lease from the entire IPv6 address space they manage.  Thus, the
   security/privacy implications of DHCPv6-addresses will essentially be
   those of the policy with which the leased addresses are selected.

4.8.  Transition/co-existence technologies

   Addresses specified based on transition/co-existence technologies
   that embed an IPv4 address within an IPv6 address are not included in
   Table 1 because their privacy and security properties are inherited
   from the embedded address.  For example, Teredo [RFC4380] specifies a
   means to generate an IPv6 address from the underlying IPv4 address

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   and port, leaving many other bits set to zero.  This makes it
   relatively easy for an attacker to scan for IPv6 addresses by
   guessing the Teredo client's IPv4 address and port (which for many
   NATs is not randomized).  For this reason, popular implementations
   (e.g., Windows), began deviating from the standard by including 12
   random bits in place of zero bits.  This modification was later
   standardized in [RFC5991].

5.  Miscellaneous Issues with IPv6 addressing

5.1.  Geographic Location

   Since IPv6 subnets have unique prefixes, they reveal some information
   about the location of the subnet, just as IPv4 addresses do.  Hiding
   this information is one motivation for using NAT in IPv6 (see RFC
   5902 section 2.4).

5.2.  Network Operation

   It is generally agreed that IPv6 addresses that vary over time in a
   specific network tend to increase the complexity of event logging,
   trouble-shooting, enforcement of access controls and quality of
   service, etc.  As a result, some organizations disable the use of
   temporary addresses [RFC4941] even at the expense of reduced privacy

5.3.  Compliance

   Major IPv6 compliance testing suites required (and still require)
   implementations to support MAC-derived suffixes in order to be
   approved as compliant.  Implementations that fail to support MAC-
   derived suffixes are therefore largely not eligible to receive the
   benefits of compliance certification (e.g., use of the IPv6 logo,
   eligibility for government contracts, etc.).  This document
   recommends that these be relaxed to allow other forms of address
   generation that are more amenable to privacy.

5.4.  Intellectual Property Rights (IPRs)

   Some IPv6 addressing techniques might be covered by Intellectual
   Property rights, which might limit their implementation in different
   Operating Systems.  [CGA-IPR] and [KAME-CGA] discuss the IPRs on

6.  Security Considerations

   This whole document concerns the privacy and security properties of
   different IPv6 address generation mechanisms.

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7.  IANA Considerations

   This document does not require actions by IANA.

8.  Acknowledgements

   The authors would like to thank Bernard Aboba and Rich Draves.

9.  Informative References

              Broersma, R., "IPv6 Everywhere: Living with a Fully
              IPv6-enabled environment", Australian IPv6 Summit 2010,
              Melbourne, VIC Australia, October 2010, October 2010,

   [CGA-IPR]  IETF, "Intellectual Property Rights on RFC 3972", 2005.

              Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
              Morris, J., Hansen, M., and R. Smith, "Privacy
              Considerations for Internet Protocols", draft-iab-privacy-
              considerations-09 (work in progress), May 2013.

              Gont, F., "A Method for Generating Semantically Opaque
              Interface Identifiers with IPv6 Stateless Address
              Autoconfiguration (SLAAC)", draft-ietf-6man-stable-
              privacy-addresses-14 (work in progress), October 2013.

              Gont, F. and T. Chown, "Network Reconnaissance in IPv6
              Networks", draft-ietf-opsec-ipv6-host-scanning-02 (work in
              progress), July 2013.

              KAME, "The KAME IPR policy and concerns of some
              technologies which have IPR claims", 2005.

              Microsoft, "IPv6 interface identifiers", 2013.

              Electronic Frontier Foundation, "Panopticlick", 2011.

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

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Internet-Draft       IPv6 Address Generation Privacy        October 2013

   [RFC1972]  Crawford, M., "A Method for the Transmission of IPv6
              Packets over Ethernet Networks", RFC 1972, August 1996.

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

   [RFC2462]  Thomson, S. and T. Narten, "IPv6 Stateless Address
              Autoconfiguration", RFC 2462, December 1998.

   [RFC2464]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
              Networks", RFC 2464, December 1998.

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

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3484]  Draves, R., "Default Address Selection for Internet
              Protocol version 6 (IPv6)", RFC 3484, February 2003.

   [RFC3971]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
              Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, March 2005.

   [RFC4380]  Huitema, C., "Teredo: Tunneling IPv6 over UDP through
              Network Address Translations (NATs)", RFC 4380, February

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

   [RFC5991]  Thaler, D., Krishnan, S., and J. Hoagland, "Teredo
              Security Updates", RFC 5991, September 2010.

   [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
              April 2011.

   [RFC6724]  Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, September 2012.

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Authors' Addresses

   Alissa Cooper
   1634 Eye St. NW, Suite 1100
   Washington, DC  20006

   Phone: +1-202-637-9800

   Fernando Gont
   Huawei Technologies
   Evaristo Carriego 2644
   Haedo, Provincia de Buenos Aires  1706

   Phone: +54 11 4650 8472

   Dave Thaler
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052

   Phone: +1 425 703 8835

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