--- 1/draft-ietf-ipv6-privacy-addrs-v2-01.txt 2006-02-05 00:03:08.000000000 +0100 +++ 2/draft-ietf-ipv6-privacy-addrs-v2-02.txt 2006-02-05 00:03:08.000000000 +0100 @@ -1,21 +1,21 @@ IPv6 Working Group T. Narten Internet-Draft IBM Corporation -Expires: April 22, 2005 R. Draves +Expires: June 23, 2005 R. Draves Microsoft Research S. Krishnan Ericsson - October 22, 2004 + December 23, 2004 Privacy Extensions for Stateless Address Autoconfiguration in IPv6 - draft-ietf-ipv6-privacy-addrs-v2-01 + draft-ietf-ipv6-privacy-addrs-v2-02 Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that @@ -26,21 +26,21 @@ 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. - This Internet-Draft will expire on April 22, 2005. + This Internet-Draft will expire on June 23, 2005. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract Nodes use IPv6 stateless address autoconfiguration to generate addresses using a combination of locally available information and information advertised by routers. Addresses are formed by combining @@ -77,39 +77,42 @@ 3.2.3 Alternate approaches . . . . . . . . . . . . . . . . . 14 3.3 Generating Temporary Addresses . . . . . . . . . . . . . . 14 3.4 Expiration of Temporary Addresses . . . . . . . . . . . . 15 3.5 Regeneration of Randomized Interface Identifiers . . . . . 16 3.6 Deployment Considerations . . . . . . . . . . . . . . . . 17 4. Implications of Changing Interface Identifiers . . . . . . . . 19 5. Defined Constants . . . . . . . . . . . . . . . . . . . . . . 20 6. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 21 7. Significant Changes from RFC 3041 . . . . . . . . . . . . . . 22 8. Changes from version 00 . . . . . . . . . . . . . . . . . . . 23 - 9. Security Considerations . . . . . . . . . . . . . . . . . . . 24 - 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25 - 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 26 - 11.1 Normative References . . . . . . . . . . . . . . . . . . . . 26 - 11.2 Informative References . . . . . . . . . . . . . . . . . . . 26 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 27 - Intellectual Property and Copyright Statements . . . . . . . . 29 + 9. Changes from version 01 . . . . . . . . . . . . . . . . . . . 24 + 10. Security Considerations . . . . . . . . . . . . . . . . . . 25 + 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26 + 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 27 + 12.1 Normative References . . . . . . . . . . . . . . . . . . . . 27 + 12.2 Informative References . . . . . . . . . . . . . . . . . . . 27 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 28 + Intellectual Property and Copyright Statements . . . . . . . . 30 1. Introduction Stateless address autoconfiguration [ADDRCONF] defines how an IPv6 node generates addresses without the need for a DHCPv6 server. Some types of network interfaces come with an embedded IEEE Identifier (i.e., a link-layer MAC address), and in those cases stateless address autoconfiguration uses the IEEE identifier to generate a 64- bit interface identifier [ADDRARCH]. By design, the interface identifier is likely to be globally unique when generated in this fashion. The interface identifier is in turn appended to a prefix to - form a 128-bit IPv6 address. + form a 128-bit IPv6 address. Note that an IPv6 identifier does not + necessarily have to be 64 bits in length, but the algorithm specified + in this document is targeted towards 64-bit interface identifiers. All nodes combine interface identifiers (whether derived from an IEEE identifier or generated through some other technique) with the reserved link-local prefix to generate link-local addresses for their attached interfaces. Additional addresses can then be created by combining prefixes advertised in Router Advertisements via Neighbor Discovery [DISCOVERY] with the interface identifier. Not all nodes and interfaces contain IEEE identifiers. In such cases, an interface identifier is generated through some other means @@ -148,26 +151,26 @@ the peer(s) it is communicating to, and can view the IPv6 addresses present in the datagrams. o An attacker who can access the communication logs of the peers with which the node has communicated. Since the identifier is embedded within the IPv6 address, which is a fundamental requirement of communication, it cannot be easily hidden. This document proposes a solution to this issue by generating interface identifiers which vary over time. - Please note that an attacker, who is on path, may be able to perform + Note that an attacker, who is on path, may be able to perform significant correlation based on o The payload contents of the packets on the wire o The characteristics of the packets such as packet size and timing Use of temporary addresses will not prevent such payload based - correlation + correlation. 1.2 Conventions used in this document 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 [RFC2119]. 2. Background This section discusses the problem in more detail, provides context @@ -240,43 +243,44 @@ address a client gets via DHCP can change over time, but in practice servers often return the same address to the same client (unless addresses are in such short supply that they are reused immediately by a different node when they become free). Thus, even within sites using DHCP, clients frequently end up using the same address for weeks to months at a time. For home users accessing the Internet over dialup lines, the situation is generally different. Such users do not have permanent connections and are often assigned temporary addresses each time they - connect to their ISP (e.g., AOL). Consequently, the addresses they - use change frequently over time and are shared among a number of - different users. Thus, an address does not reliably identify a - particular device over time spans of more than a few minutes. + connect to their ISP. Consequently, the addresses they use change + frequently over time and are shared among a number of different + users. Thus, an address does not reliably identify a particular + device over time spans of more than a few minutes. A more interesting case concerns always-on connections (e.g., cable modems, ISDN, DSL, etc.) that result in a home site using the same address for extended periods of time. This is a scenario that is just starting to become common in IPv4 and promises to become more of a concern as always-on internet connectivity becomes widely available. Finally, it should be noted that nodes that need a (non-changing) DNS name generally have static addresses assigned to them to simplify the configuration of DNS servers. Although Dynamic DNS [DDNS] can be - used to update the DNS dynamically, it is not yet widely deployed. - In addition, changing an address but keeping the same DNS name does - not really address the underlying concern, since the DNS name becomes - a non-changing identifier. Servers generally require a DNS name (so - clients can connect to them), and clients often do as well (e.g., - some servers refuse to speak to a client whose address cannot be - mapped into a DNS name that also maps back into the same address). - Section 4 describes one approach to this issue. + used to update the DNS dynamically, it may not always be available + depending on the administrative policy. In addition, changing an + address but keeping the same DNS name does not really address the + underlying concern, since the DNS name becomes a non-changing + identifier. Servers generally require a DNS name (so clients can + connect to them), and clients often do as well (e.g., some servers + refuse to speak to a client whose address cannot be mapped into a DNS + name that also maps back into the same address). Section 4 describes + one approach to this issue. 2.3 The Concern With IPv6 Addresses The division of IPv6 addresses into distinct topology and interface identifier portions raises an issue new to IPv6 in that a fixed portion of an IPv6 address (i.e., the interface identifier) can contain an identifier that remains constant even when the topology portion of an address changes (e.g., as the result of connecting to a different part of the Internet). In IPv4, when an address changes, the entire address (including the local part of the address) usually @@ -314,39 +318,39 @@ In summary, IPv6 addresses on a given interface generated via Stateless Autoconfiguration contain the same interface identifier, regardless of where within the Internet the device connects. This facilitates the tracking of individual devices (and thus potentially users). The purpose of this document is to define mechanisms that eliminate this issue, in those situations where it is a concern. 2.4 Possible Approaches - One way to avoid some of the problems discussed above is to use + One way to avoid having a static non-changing address is to use DHCPv6 [DHCPV6] for obtaining addresses. The DHCPv6 server could be configured to hand out addresses that change over time. But DHCPv6 will solve the privacy issue only if it frequently handed out constantly changing addresses to the nodes. Since this does not happen automatically, and is difficult to configure manually, DHCPv6 is not a self contained alternative for solving the privacy issues addressed by this document. However, in the absence of stateless address autoconfiguration, DHCPv6 can be used for distributing temporary addresses to clients. Another approach, compatible with the stateless address - autoconfiguration architecture, would be to change the interface id - portion of an address over time and generate new addresses from the - interface identifier for some address scopes. Changing the interface - identifier can make it more difficult to look at the IP addresses in - independent transactions and identify which ones actually correspond - to the same node, both in the case where the routing prefix portion - of an address changes and when it does not. + autoconfiguration architecture, would be to change the interface + identifier portion of an address over time and generate new addresses + from the interface identifier for some address scopes. Changing the + interface identifier can make it more difficult to look at the IP + addresses in independent transactions and identify which ones + actually correspond to the same node, both in the case where the + routing prefix portion of an address changes and when it does not. Many machines function as both clients and servers. In such cases, the machine would need a DNS name for its use as a server. Whether the address stays fixed or changes has little privacy implication since the DNS name remains constant and serves as a constant identifier. When acting as a client (e.g., initiating communication), however, such a machine may want to vary the addresses it uses. In such environments, one may need multiple addresses: a "public" (i.e., non-secret) server address, registered in the DNS, that is used to accept incoming connection requests from @@ -476,31 +480,28 @@ 1. Take the history value from the previous iteration of this algorithm (or a random value if there is no previous value) and append to it the interface identifier generated as described in [ADDRARCH]. 2. Compute the MD5 message digest [MD5] over the quantity created in the previous step. 3. Take the left-most 64-bits of the MD5 digest and set bit 6 (the left-most bit is numbered 0) to zero. This creates an interface identifier with the universal/local bit indicating local significance only. - 4. Compare the generated identifier against a list of known values - that should not be used. Inappropriate values include those used - in reserved anycast addresses [RFC2526], those used by ISATAP - [ISATAP], the value 0, and those already assigned to an address + 4. Compare the generated identifier against a list of reserved + interface identifiers and to those already assigned to an address on the local device. In the event that an unacceptable identifier has been generated, the node MUST restart the process at step 1 above, using the right-most 64 bits of the MD5 digest obtained in step 2 in place of the history value in step 1. 5. Save the generated identifier as the associated randomized interface identifier. - 6. Take the rightmost 64-bits of the MD5 digest computed in step 2) and save them in stable storage as the history value to be used in the next iteration of the algorithm. MD5 was chosen for convenience, and because its particular properties were adequate to produce the desired level of randomization. IPv6 nodes are already required to implement MD5 as part of IPsec [IPSEC], thus the code will already be present on IPv6 machines. In theory, generating successive randomized interface identifiers @@ -529,26 +530,26 @@ cases have configuration information that differs from one machine to another (e.g., user identity, security keys, serial numbers, etc.). One approach to generating a random initial history value in such cases is to use the configuration information to generate some data bits (which may remain constant for the life of the machine, but will vary from one machine to another), append some random data and compute the MD5 digest as before. 3.2.3 Alternate approaches - Please note that there are other approaches to generate random - interface identifiers, albeit with different goals and applicability. - One such approach is CGA [CGA], which generates a random interface - identifier based on the public key of the node. The goal of CGAs is - to prove ownership of an address and to prevent spoofing and stealing - of existing IPv6 addresses. They are used for securing neighbor + Note that there are other approaches to generate random interface + identifiers, albeit with different goals and applicability. One such + approach is CGA [CGA], which generates a random interface identifier + based on the public key of the node. The goal of CGAs is to prove + ownership of an address and to prevent spoofing and stealing of + existing IPv6 addresses. They are used for securing neighbor discovery using [SEND]. The CGA random interface identifier generation algorithm may not be suitable for privacy addresses because of the following properties o It requires the node to have a public key. This means that the node can still be identified by its public key o The random interface identifier process is computationally intensive and hence discourages frequent regeneration 3.3 Generating Temporary Addresses @@ -561,39 +562,35 @@ address autoconfiguration (i.e., the A bit is set), the node MUST perform the following steps: 1. Process the Prefix Information Option as defined in [ADDRCONF], either creating a new public address or adjusting the lifetimes of existing addresses, both public and temporary. If a received option will extend the lifetime of a public address, the lifetimes of temporary addresses should be extended, subject to the overall constraint that no temporary addresses should ever remain "valid" or "preferred" for a time longer than - (TEMP_VALID_LIFETIME-DESYNC_FACTOR) or - (TEMP_PREFERRED_LIFETIME-DESYNC_FACTOR) respectively. The - configuration variables TEMP_VALID_LIFETIME and - TEMP_PREFERRED_LIFETIME correspond to approximate target - lifetimes for temporary addresses. + (TEMP_VALID_LIFETIME - DESYNC_FACTOR) or (TEMP_PREFERRED_LIFETIME + - DESYNC_FACTOR) respectively. The configuration variables + TEMP_VALID_LIFETIME and TEMP_PREFERRED_LIFETIME correspond to + approximate target lifetimes for temporary addresses. 2. One way an implementation can satisfy the above constraints is to associate with each temporary address a creation time (called CREATION_TIME) that indicates the time at which the address was created. When updating the preferred lifetime of an existing temporary address, it would be set to expire at whichever time is earlier: the time indicated by the received lifetime or (CREATION_TIME + TEMP_PREFERRED_LIFETIME - DESYNC_FACTOR). A similar approach can be used with the valid lifetime. + 3. When a new public address is created as described in [ADDRCONF], + the node SHOULD also create a new temporary address. - 3. When a new public address is created as described in [ADDRCONF] - (because the prefix advertised does not match the prefix of any - address already assigned to the interface, and the Valid Lifetime - in the option is not zero), the node SHOULD also create a new - temporary address. 4. When creating a temporary address, the lifetime values MUST be derived from the corresponding prefix as follows: * Its Valid Lifetime is the lower of the Valid Lifetime of the public address or TEMP_VALID_LIFETIME * Its Preferred Lifetime is the lower of the Preferred Lifetime of the prefix or TEMP_PREFERRED_LIFETIME-DESYNC_FACTOR. 5. A temporary address is created only if this calculated Preferred Lifetime is greater than REGEN_ADVANCE time units. In particular, an implementation MUST NOT create a temporary address with a zero Preferred Lifetime. @@ -626,21 +623,21 @@ temporary address SHOULD be regenerated slightly before its predecessor is deprecated. This is to allow sufficient time to avoid race conditions in the case where generating a new temporary address is not instantaneous, such as when duplicate address detection must be run. The node SHOULD start the address regeneration process REGEN_ADVANCE time units before a temporary address would actually be deprecated. As an optional optimization, an implementation MAY remove a deprecated temporary address that is not in use by applications or - upper-layers as detailed in Section 6 + upper-layers as detailed in Section 6. 3.5 Regeneration of Randomized Interface Identifiers The frequency at which temporary addresses changes depends on how a device is being used (e.g., how frequently it initiates new communication) and the concerns of the end user. The most egregious privacy concerns appear to involve addresses used for long periods of time (weeks to months to years). The more frequently an address changes, the less feasible collecting or coordinating information keyed on interface identifiers becomes. Moreover, the cost of @@ -684,21 +681,21 @@ Finally, when an interface connects to a new link, a new randomized interface identifier SHOULD be generated immediately together with a new set of temporary addresses. If a device moves from one ethernet to another, generating a new set of temporary addresses from a different randomized interface identifier ensures that the device uses different randomized interface identifiers for the temporary addresses associated with the two links, making it more difficult to correlate addresses from the two different links as being from the same node. The node MAY follow any process available to it, to determine that the link change has occurred. One such process is - described by Detecting Network Attachment [DNA] + described by Detecting Network Attachment [DNA]. 3.6 Deployment Considerations Devices implementing this specification MUST provide a way for the end user to explicitly enable or disable the use of temporary addresses. In addition, a site might wish to disable the use of temporary addresses in order to simplify network debugging and operations. Consequently, implementations SHOULD provide a way for trusted system administrators to enable or disable the use of temporary addresses. @@ -706,52 +703,54 @@ Additionally, sites might wish to selectively enable or disable the use of temporary addresses for some prefixes. For example, a site might wish to disable temporary address generation for "Unique local" [ULA] prefixes while still generating temporary addresses for all other global prefixes. Another site might wish to enable temporary address generation only for the prefixes 2001::/16 and 2002::/16 while disabling it for all other prefixes. To support this behavior, implementations SHOULD provide a way to enable and disable generation of temporary addresses for specific prefix subranges. This per-prefix setting SHOULD override the global settings on the node - with respect to the specified prefix subranges. + with respect to the specified prefix subranges. Note that the + pre-prefix setting can be applied at any granularity, and not + necessarily on a per subnet basis. The use of temporary addresses may cause unexpected difficulties with some applications. As described below, some servers refuse to accept communications from clients for which they cannot map the IP address - into an DNS name. In addition, some applications may not behave + into a DNS name. In addition, some applications may not behave robustly if temporary addresses are used and an address expires before the application has terminated, or if it opens multiple sessions, but expects them to all use the same addresses. Consequently, the use of temporary addresses SHOULD be disabled by default in order to minimize potential disruptions. Individual applications, which have specific knowledge about the normal duration of connections, MAY override this as appropriate. If a very small number of nodes(say only one) use a given prefix for - extended periods of time, just changing the interface identifier - part of the prefix may not be sufficient to ensure privacy, since - the prefix acts as a constant identifier. The procedures described - in this document are most effective when the prefix is reasonably non - static or is used by a fairly large number of nodes + extended periods of time, just changing the interface identifier part + of the address may not be sufficient to ensure privacy, since the + prefix acts as a constant identifier. The procedures described in + this document are most effective when the prefix is reasonably non + static or is used by a fairly large number of nodes. 4. Implications of Changing Interface Identifiers The IPv6 addressing architecture goes to some lengths to ensure that interface identifiers are likely to be globally unique where easy to do so. The widespread use of temporary addresses may result in a significant fraction of Internet traffic not using addresses in which - the interface id portion is globally unique. Consequently, usage of - the algorithms in this document may complicate providing such a - future flexibility, if global uniqueness is necessary. + the interface identifier portion is globally unique. Consequently, + usage of the algorithms in this document may complicate providing + such a future flexibility, if global uniqueness is necessary. - The desires of protecting individual privacy vs. the desire to + The desires of protecting individual privacy versus the desire to effectively maintain and debug a network can conflict with each other. Having clients use addresses that change over time will make it more difficult to track down and isolate operational problems. For example, when looking at packet traces, it could become more difficult to determine whether one is seeing behavior caused by a single errant machine, or by a number of them. Some servers refuse to grant access to clients for which no DNS name exists. That is, they perform a DNS PTR query to determine the DNS name, and may then also perform an AAAA query on the returned name to @@ -802,21 +801,21 @@ protocols are using it (but not before). This is in contrast to current approaches where addresses are removed from an interface when they become invalid [ADDRCONF], independent of whether or not upper layer protocols are still using them. For TCP connections, such information is available in control blocks. For UDP-based applications, it may be the case that only the applications have knowledge about what addresses are actually in use. Consequently, an implementation generally will need to use heuristics in deciding when an address is no longer in use. - The determination as to whether to use public vs. temporary + The determination as to whether to use public versus temporary addresses can in some cases only be made by an application. For example, some applications may always want to use temporary addresses, while others may want to use them only in some circumstances or not at all. Suitable API extensions will likely need to be developed to enable individual applications to indicate with sufficient granularity their needs with regards to the use of temporary addresses. Recommendations on DNS practices to avoid the problem described in Section 4 when reverse DNS lookups fail may be needed. [DNSOP] contains a more detailed discussion of the DNS related issues. @@ -861,64 +860,73 @@ be disabled. 6. Added a security considerations section to highlight the ingress filtering issues which can be caused by the use of temporary addresses as described in this document 7. Removed references to site-local addresses 8. Added a check for denial of service attacks using low valid lifetimes in router advertisements 9. Changed the document to use RFC2119 language 10. The node is now allowed to generate different interface identifiers for different prefixes, if it so desires. - 11. DAD is now performed on all unicast addresses created from the - same interface identifier instead of just the first one 8. Changes from version 00 This section summarizes the changes from version 00 of this draft 1. The algorithm used for generating random interface identifiers is no longer restricted to just MD5 2. Added a problem statement 3. Classified the references into normative and informative 4. Reduced default number of retries to 3 from 5 and added a configuration variable 5. Removed text about RA processing which is duplicated from [ADDRCONF] 6. Added text about the privacy implications of a non-changing prefix 7. Added a per-prefix enable/disable setting 8. Added text about the means of correlation 9. Clarified text about DHCPv6 10. Added reference to dnsop issues draft -9. Security Considerations +9. Changes from version 01 + + This section summarizes the changes from version 01 of this draft + 1. Clarifiying the length of interface identifier + 2. Added a per-prefix enable/disable knob as a SHOULD to retain + backward compatibility + 3. Removed normative reference to ISATAP to avoid downref problem + 4. Added text for per-prefix knobs to be applied at any granularity + 5. Moved RFC2526 to informative reference + +10. Security Considerations Ingress filtering has been and is being deployed as a means of preventing the use of spoofed source addresses in Distributed Denial of Service(DDoS) attacks. In a network with a large number of nodes, new temporary addresses are created at a fairly high rate. This might make it difficult for ingress filtering mechanisms to distinguish between legitimately changing temporary addresses and spoofed source addresses, which are "in-prefix"(They use a topologically correct prefix and non-existent interface ID). This can be addressed by using access control mechanisms on a per address basis on the network egress point. -10. Acknowledgements +11. Acknowledgements The authors would like to acknowledge the contributions of the ipv6 working group and, in particular, Ran Atkinson, Matt Crawford, Steve Deering, Allison Mankin, Peter Bieringer, Jari Arkko, Pekka Nikander, - Pekka Savola, and Francis Dupont for their detailed comments. + Pekka Savola, Francis Dupont, Brian Haberman, and Tatuya Jinmei for + their detailed comments. -11. References +12. References -11.1 Normative References +12.1 Normative References [ADDRARCH] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6) Addressing Architecture", RFC 3513, April 2003. [ADDRCONF] Thomson, S., Narten, T. and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", draft-ietf-ipv6-rfc2462bis-06 (work in progress), September 2004. @@ -933,24 +941,21 @@ [IPSEC] Kent, S. and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, November 1998. [MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April 1992. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. - [RFC2526] Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast - Addresses", RFC 2526, March 1999. - -11.2 Informative References +12.2 Informative References [CGA] Aura, T., "Cryptographically Generated Addresses (CGA)", draft-ietf-send-cga-06 (work in progress), April 2004. [COOKIES] Kristol, D. and L. Montulli, "HTTP State Management Mechanism", RFC 2965, October 2000. [DDNS] Vixie, P., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, April 1997. @@ -964,33 +969,31 @@ [DNA] Choi, J. and G. Daley, "Detecting Network Attachment in IPv6 Goals", draft-ietf-dna-goals-01 (work in progress), September 2004. [DNSOP] Durand, A., Ihren, J. and P. Savola, "Operational Considerations and Issues with IPv6 DNS", draft-ietf-dnsop-ipv6-dns-issues-09 (work in progress), August 2004. - [ISATAP] Templin, F., Gleeson, T., Talwar, M. and D. Thaler, - "Intra-Site Automatic Tunnel Addressing Protocol - (ISATAP)", draft-ietf-ngtrans-isatap-22 (work in - progress), May 2004. - [ONION] Reed, MGR., Syverson, PFS. and DMG. Goldschlag, "Proxies for Anonymous Routing", Proceedings of the 12th Annual Computer Security Applications Conference, San Diego, CA, December 1996. [RANDOM] Eastlake, D., Crocker, S. and J. Schiller, "Randomness Recommendations for Security", RFC 1750, December 1994. + [RFC2526] Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast + Addresses", RFC 2526, March 1999. + [SEND] Arkko, J., Kempf, J., Sommerfeld, B., Zill, B. and P. Nikander, "SEcure Neighbor Discovery (SEND)", draft-ietf-send-ndopt-06 (work in progress), July 2004. [ULA] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast Addresses", draft-ietf-ipv6-unique-local-addr-05 (work in progress), June 2004. Authors' Addresses