Mobopts Working Group Y. Qiu Internet-Draft Institute for Infocomm Research Expires: May 7, 2009 F. Zhao Marvell R. Koodli Starent Networks November 3, 2008 Mobile IPv6 Location Privacy Solutions draft-irtf-mobopts-location-privacy-solutions-10 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." 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 May 7, 2009. Qiu, et al. Expires May 7, 2009 [Page 1] Internet-Draft MIP6 location privacy solutions November 2008 Abstract Mobile IPv6 (RFC 3775) enables a mobile node to remain reachable while it roams on the Internet. However, the location and movement of the mobile node can be revealed by IP addresses used in signaling or data packets. In this document, we consider the Mobile IPv6 location privacy problem described in RFC 4882, and propose efficient and secure techniques to protect location privacy of the mobile node. This document is a product of the IP Mobility Optimizations (MobOpts) Research Group. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Conventions and Terminology . . . . . . . . . . . . . . . . . 6 2.1. Conventions . . . . . . . . . . . . . . . . . . . . . . . 6 2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 9 4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 10 5. Reverse-Tunneled Correspondent Binding Update . . . . . . . . 13 5.1. The Procedure . . . . . . . . . . . . . . . . . . . . . . 13 5.2. Route Optimized Payload Packets . . . . . . . . . . . . . 15 5.3. Mobile Node Operation . . . . . . . . . . . . . . . . . . 16 5.3.1. Conceptual Data Structures . . . . . . . . . . . . . . 16 5.3.2. Reverse-tunneled Correspondent Binding Update to the Correspondent Node . . . . . . . . . . . . . . . . 16 5.3.3. Reverse-tunneled Correspondent Binding Acknowledgement from the Correspondent Node . . . . . 17 5.3.4. Route Optimized Payload Packets . . . . . . . . . . . 17 5.3.5. Receiving ICMP Error Message . . . . . . . . . . . . . 18 5.3.6. Binding Error from the Correspondent Node . . . . . . 18 5.3.7. Binding Refresh Request from the Correspondent Node . 18 5.4. Home Agent Operation . . . . . . . . . . . . . . . . . . . 18 5.5. Correspondent Node Operation . . . . . . . . . . . . . . . 19 5.5.1. Conceptual Data Structures . . . . . . . . . . . . . . 19 5.5.2. Reverse-tunneled Correspondent Binding Update from the Mobile Node . . . . . . . . . . . . . . . . . . . 19 5.5.3. Reverse-tunneled Correspondent Binding Acknowledgement to the Mobile Node . . . . . . . . . . 19 5.5.4. Route Optimized Payload Packets . . . . . . . . . . . 19 5.5.5. ICMP Error Message to the Mobile Node . . . . . . . . 20 5.5.6. Binding Error to the Mobile Node . . . . . . . . . . . 20 5.5.7. Binding Refresh Request to the Mobile Node . . . . . . 20 5.6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 21 6. IP Address Location Privacy Solution Using the Pseudo Home Address . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 6.1. Home Binding Update . . . . . . . . . . . . . . . . . . . 22 Qiu, et al. Expires May 7, 2009 [Page 2] Internet-Draft MIP6 location privacy solutions November 2008 6.1.1. Home Registration with IPsec Transport Mode . . . . . 22 6.1.2. Home Registration with IPsec Tunnel Mode . . . . . . . 25 6.1.3. Pseudo Home Address Registration . . . . . . . . . . . 25 6.1.4. Home De-registration . . . . . . . . . . . . . . . . . 26 6.2. Correspondent Binding Update Using the Pseudo Home Address . . . . . . . . . . . . . . . . . . . . . . . . . 27 6.2.1. Return Routability Procedure . . . . . . . . . . . . . 27 6.2.2. Route Optimized Correspondent Binding Update . . . . . 29 6.2.3. Reverse-tunneled Correspondent Binding Update . . . . 30 6.2.4. Using Different Pseudo Home Addresses with Different Correspondent Nodes . . . . . . . . . . . . 30 6.3. Payload Packets . . . . . . . . . . . . . . . . . . . . . 30 6.3.1. Reverse Tunneling Mode . . . . . . . . . . . . . . . . 30 6.3.2. Route Optimization Mode . . . . . . . . . . . . . . . 31 6.4. Prefix Discovery . . . . . . . . . . . . . . . . . . . . . 31 6.5. Mobile Node Operation . . . . . . . . . . . . . . . . . . 31 6.5.1. Conceptual Data Structures . . . . . . . . . . . . . . 31 6.5.2. Binding Update to the Home Agent . . . . . . . . . . . 32 6.5.3. Binding Acknowledgement from the Home Agent . . . . . 33 6.5.4. Home Test Init to the Home Agent . . . . . . . . . . . 34 6.5.5. Home Test from the Home Agent . . . . . . . . . . . . 35 6.5.6. Route Optimized Payload Packets . . . . . . . . . . . 35 6.5.7. Receiving ICMP Error Messages . . . . . . . . . . . . 36 6.5.8. Receiving Binding Refresh Request . . . . . . . . . . 36 6.6. Home Agent Operation . . . . . . . . . . . . . . . . . . . 37 6.6.1. Conceptual Data Structures . . . . . . . . . . . . . . 37 6.6.2. Binding Update from the Mobile Node . . . . . . . . . 37 6.6.3. Binding Acknowledgement to the Mobile Node . . . . . . 38 6.6.4. Home Test Init from the Mobile Node . . . . . . . . . 39 6.6.5. Home Test to the Mobile Node . . . . . . . . . . . . . 39 6.6.6. Binding Refresh Request to the Mobile Node . . . . . . 40 6.7. Correspondent Node Operation . . . . . . . . . . . . . . . 40 7. Extensions to Mobile IPv6 . . . . . . . . . . . . . . . . . . 41 7.1. Encrypted Home Address Destination Option . . . . . . . . 41 7.2. Extensions to the Type 2 Routing Header . . . . . . . . . 41 7.3. Pseudo Home Address Mobility Option . . . . . . . . . . . 42 7.4. Pseudo Home Address Acknowledgement Mobility Option . . . 44 8. Security Consideration . . . . . . . . . . . . . . . . . . . . 46 8.1. Home Binding Update . . . . . . . . . . . . . . . . . . . 46 8.2. Correspondent Binding Update . . . . . . . . . . . . . . . 47 8.3. Route-Optimized Payload Packets . . . . . . . . . . . . . 47 9. Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 48 10. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 49 11. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 49 12. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 49 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 50 13.1. Normative References . . . . . . . . . . . . . . . . . . . 50 13.2. Informative References . . . . . . . . . . . . . . . . . . 50 Qiu, et al. Expires May 7, 2009 [Page 3] Internet-Draft MIP6 location privacy solutions November 2008 Appendix A. Profiling Attack: Discussion . . . . . . . . . . . . 52 A.1. The Care-of Address . . . . . . . . . . . . . . . . . . . 52 A.2. Profiling on the Encrypted Home Address . . . . . . . . . 52 A.3. The IPsec SPI . . . . . . . . . . . . . . . . . . . . . . 53 A.4. The IPsec Sequence Number . . . . . . . . . . . . . . . . 53 A.5. The Regular Interval of Signaling Messages . . . . . . . . 54 A.6. The Sequence Number in the Binding Update Message . . . . 54 A.7. Multiple Concurrent Sessions . . . . . . . . . . . . . . . 54 A.8. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 55 Appendix B. Version History . . . . . . . . . . . . . . . . . . . 55 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 56 Intellectual Property and Copyright Statements . . . . . . . . . . 58 Qiu, et al. Expires May 7, 2009 [Page 4] Internet-Draft MIP6 location privacy solutions November 2008 1. Introduction IP address location privacy is concerned with unwittingly revealing the current location of a mobile node to eavesdroppers and to communicating parties. In the presence of mobility as defined in Mobile IPv6 [6], there are two related aspects: disclosing the care-of address to a correspondent node, and revealing the home address to an eavesdropper. A detailed description of the location privacy problem can be found in RFC 4882. In order to protect location privacy, a mobile node MUST not disclose the binding between its care-of address and its home address. In this document, we propose a set of extensions to the Mobile IPv6 specification to tackle the IP address location privacy problem. An issue related to IP address location privacy is "profiling", where the activities of a mobile node are linked and then analyzed. Profiled activities may contribute to compromising a mobile node's location privacy, especially when combined with additional information. Furthermore, once location privacy is compromised, it may lead to more targeted profiling. Therefore, in addition to protecting IP address location privacy, solutions to thwart profiling activities based on various IP fields, especially those related to Mobile IPv6 operation, should be considered. We propose two IP address location privacy solutions in this document. With the first solution (as described in Section 5), the mobile node can communicate with the correspondent node by using the real home address without causing location privacy breached by eavesdroppers. This is done by using parameters generated during the return routability procedure to mask the real home address, which provides an evolution towards location privacy protection based on return routability messages already specified in RFC 3775. With the second solution (as described in Section 6), the real home address, for example, when used during the home binding update procedure, is encrypted by using a cryptography algorithm; furthermore, during the return routability procedure and the correspondent binding update procedure, a "pseudo home address" (the definition of this new term and many other commonly used mobility related terms is provided in Section 2) is used instead of the real home address in various messages, which allows the mobile node to hide its real home address from both the correspondent node and eavesdroppers without additional extensions to the correspondent node needed. Moreover, the mobile node may mask the pseudo home address by using the mechanism specified in Section 5 to further enhance location privacy protection. Each of these two solutions addresses different needs arising from different scenarios and can be implemented on its own without relying on the other. In addition to the IP address location privacy solutions, we also discuss and propose solutions to address Qiu, et al. Expires May 7, 2009 [Page 5] Internet-Draft MIP6 location privacy solutions November 2008 the profiling attack in the appendix of this document. The solutions presented in this document are designed based on the following assumptions. First, we focus on location privacy issues arising when the mobile node attaches to a foreign link; location privacy issues when the mobile node attaches to its home link, if any, are not in the scope of this document. Second, we assume that IPsec is used to secure mobility signaling messages exchanged between the mobile node and the home agent; therefore, location privacy solutions when other security mechanisms are used are beyond the scope of this document. Third, we assume that eavesdroppers are passive attackers, e.g., an eavesdropper along the path traversed by traffic flows from or to the mobile node; that is, threats to location privacy posed by active attackers are also beyond the scope of this document. Fourth, in order to simplify analysis, we assume that both the correspondent node and the home agent are fixed nodes; if either is mobile, the same analysis and solutions for the mobile node may also apply. Last, we assume that an entity involved in the Mobile IPv6 operation, if supporting, MUST support the entirety of location privacy extensions applicable to itself; otherwise, it MUST not support any of such extensions. Note that such entity may choose to use one or a combination of some solutions described in this document to meet its needs of location privacy protection. This document represents the consensus of the MobOpts Research Group. It has been reviewed by the Research Group members active in the specific area of work. At the request of their chairs, this document has been comprehensively reviewed by multiple active contributors to the IETF Mobile IP related working groups. 2. Conventions and Terminology 2.1. Conventions The keywords "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 [1]. 2.2. Terminology In this document, we introduce two new terms, "pseudo home address" and "encrypted home address". The definition of these two terms is provided in the following. o Pseudo Home Address (pHoA): An unicast IPv6 address formed to replace the real home address used in certain Mobile IPv6 signaling or data packets. Without explicit indication, the Qiu, et al. Expires May 7, 2009 [Page 6] Internet-Draft MIP6 location privacy solutions November 2008 pseudo home address looks like a regular IPv6 address. o Encrypted Home Address (eHoA): The output when applying an encryption algorithm to the real home address with additional inputs, e.g., a key. The real home address can be recovered from the encrypted home address by using a decryption algorithm. In addition, we use commonly adopted mobility-related terms as defined in [6] and [11] throughout this document. Some of such terms are provided below for easier reference; nevertheless, we assume that readers are familiar with the basic operation of the Mobile IPv6 protocol as defined in RFC 3775, RFC 3776 and RFC 4877. o Mobile Node (MN): A Mobile IPv6 compliant mobile node that can roam on the Internet o Correspondent Node (CN): An IPv6 node that communicates with the mobile node o Home Network: The network where the mobile node is normally present when it is not roaming o Visited Network: The network that the mobile node uses to access the Internet when it is roaming o Home Agent (HA): A router on the mobile node's home network that provides forwarding support when the mobile node is roaming o Home Address (HoA): The mobile node's unicast IP address valid on its home network o Care-of Address (CoA): The mobile node's unicast IP address valid on the visited network o Return Routability (RR): A procedure which enables secure binding between the care-of address and the home address when no pre- existing security association exists between the mobile node and the correspondent node o Home Test Init (HoTI) / Home Test (HoT) / Care-of Test Init (CoTI) / Care-of Test (CoT): Messages used during the return routability procedure o Binding Update (BU): A message used by the mobile node to securely bind its care-of address to its home address at the correspondent node or the home agent Qiu, et al. Expires May 7, 2009 [Page 7] Internet-Draft MIP6 location privacy solutions November 2008 o Binding Acknowledgement (BA): A response to the binding update o Message Authentication Code (MAC): The value, which is computed using HMAC_SHA1 in this document, that protects both a message's integrity and its authenticity o Route Optimization: A mechanism that allows direct routing of packets between a roaming mobile node and its correspondent node, without having to traverse the home network o Reverse Tunneling or Bidirectional Tunneling: A mechanism used for packet forwarding between a roaming mobile node and its correspondent node via its home agent Qiu, et al. Expires May 7, 2009 [Page 8] Internet-Draft MIP6 location privacy solutions November 2008 3. Requirements In this section, we detail the requirements that MUST be met by the Mobile IPv6 location privacy solutions, hereafter referred to as "the solution". R01: The solution MUST follow the framework and architecture of IPv6 and Mobile IPv6 (as specified in RFC 3775, RFC 3776 and RFC 4877). Existing standards, including the Mobile IPv6 protocol and other protocols that interact with Mobile IPv6, MUST be reused as much as possible and extended only if deemed necessary and to the extent needed for providing required location privacy protection. This means that the solution MUST be implemented in the IP layer level with most new functions introduced into the Mobile IP sublayer. R02: The solution MUST not interfere with the operation of IPsec. This means that the principles and the operation specified in RFC 3776 and RFC 4877 MUST be followed, for example, the IPsec security association and policy MUST be identified by the real home address. R03: The solution MUST provide back-compatibility in order for different Mobile IPv6 entities to work together even though they may have different capabilities. This requires the mobile node to be able to detect whether the home agent or the correspondent node supports the use of the location privacy solutions. R04: The solution MUST comply with the usual IETF security policies and recommendations, and particularly, it MUST not weaken security protection provided in RFC 3775. In addition, security issues specific to the solution MUST be fully addressed. R05: The overhead resulted from the solution, in terms of payloads or messages transmitted and memory, MUST be kept as minimal. Qiu, et al. Expires May 7, 2009 [Page 9] Internet-Draft MIP6 location privacy solutions November 2008 4. Solution Overview The IP address location privacy solutions proposed in this document intend to conceal the binding between the mobile node's real home address and its care-of address from eavesdroppers and the correspondent node, if needed. In this section, we present an overview of the proposed IP address location privacy solutions for Mobile IPv6. With the Mobile IPv6 specification, during the home binding update procedure, both the real home address and the care-of address are in the cleartext when either the IPsec tunnel mode or the IPsec transport mode is used, if no encryption. The solution to prevent the real home address being leaked to eavesdroppers on the MN-HA path during the home binding update procedure is described in Section 6.1. When the IPsec transport mode is used, the real home address carried in the home address destination option is encrypted by using a secret key shared between the mobile node and the home agent. The encrypted home address is carried in a new IPv6 destination option, called Encrypted Home Address option (see Section 7.1) in the home Binding Update message and in the Type 2 routing header with a new 'E' bit set as 1 (see Section 7.2) in the home Binding Acknowledgement message. Both the home agent and the mobile node can recover the real home address from the encrypted home address. Note that the IPsec related operation as specified in RFC 3776 and RFC 4877 is not changed with the use of the encrypted home address. When the IPsec tunnel mode is used, the solution is that when setting up an IPsec security association, the mobile node and the home agent MUST negotiate a non-null encryption algorithm to encrypt home binding signaling messages and the real home address therein. The methods described above are also used to enable location privacy protection during other mobility signaling message exchanges between the home agent and the mobile node, such as the prefix discovery procedure (see Section 6.4). When communicating with the correspondent node with the reverse tunneling mode, the mobile node can hide its current location from the correspondent node and eavesdroppers along the HA-CN path, since the care-of address is not included in payload packets transmitted on that path. Also, an IPsec security association with a non-null encryption algorithm established between the mobile node and the home agent can conceal the real home address carried in payload packets from eavesdroppers along the MN-HA path. To communicate with the correspondent node with the route optimization mode, the mobile node needs to perform the return routability procedure followed by the correspondent binding update procedure. With the current Mobile IPv6 specification, both the real Qiu, et al. Expires May 7, 2009 [Page 10] Internet-Draft MIP6 location privacy solutions November 2008 home address and the care-of address are visible to eavesdroppers in the correspondent Binding Update message and payload packets. Therefore, in order to send and receive packets through the optimized route and protect location privacy at the same time, the mobile node needs to disclose its care-of address and conceal its real home address. There are two different scenarios and we propose a different solution for each scenario. One scenario is that the correspondent node may be able to or already know the real home address, for example, when the correspondent node is the initiator of the communication. In this case, the mobile node needs to continue to use the real home address with the correspondent node in order to maintain session continuity and conceals the real home address from eavesdroppers. The solution for this scenario (hereinafter referred to as "reverse-tunneled correspondent binding update") is described in Section 5. With this solution, the mobile node exchanges the same return routability signaling messages as defined in RFC 3775 with the correspondent node; then, it derives a privacy management key from keygen tokens and uses this key to encrypt the real home address; finally, it reverse-tunnels an extended correspondent Binding Update message via the home agent to register the encrypted home address and the real home address at the correspondent node. After the correspondent registration, the mobile node and the correspondent node use the registered encrypted home address, instead of the real home address, in payload packets exchanged via the optimized route. The other scenario is that the mobile node prefers to conceal its real home address to both the correspondent node and eavesdroppers, for example, when the mobile node is the initiator of the communication and the correspondent node does not know the real home address. The solution for this scenario is described in Section 6.2. With this solution, firstly the mobile node obtains a home keygen token generated based on the pseudo home address during the home address test procedure; then the mobile node sends the correspondent Binding Update message to register the binding between the pseudo home address and the care-of address at the correspondent node via the optimized route. After the correspondent registration, the mobile node and the correspondent node use the registered pseudo home address, instead of the real home address, in payload packets exchanged via the optimized route. Note that the use of the pseudo home address is completely transparent to the correspondent node. Furthermore, we can throttle "profiling" on the pseudo home address by using a combination of these two solutions. That is, the mobile node uses the pseudo home address in the extended home address test procedure to obtain a home keygen token; then it uses the pseudo home address instead of the real home address in the reverse-tunneled Qiu, et al. Expires May 7, 2009 [Page 11] Internet-Draft MIP6 location privacy solutions November 2008 correspondent binding update procedure. With this solution, the encrypted pseudo home address used in route optimized payload packets looks different to eavesdroppers each time after a new round of the return routability procedure is completed. Such pseudo home address, before used with the correspondent node, MUST be registered with the home agent during the home registration procedure. The mobile node indicates the requested pseudo home address in a new mobility option, called Pseudo Home Address option (see Section 7.3), carried in the home Binding Update message and the home agent indicates the status of pseudo home address registration in another new mobility option, called Pseudo Home Address Acknowledgement option (see Section 7.4), carried in the home Binding Acknowledgement message. The pseudo home address MUST be routable in order for the home agent to intercept packets destined at this pseudo home address; furthermore, it is statistically difficult for other nodes to derive the real home address from the pseudo home address. A detailed description of pseudo home address generation can be found in Section 6.1.3.1. With extensions introduced in this document, the mobile node is able to discover whether the home agent and the correspondent node support the location privacy solutions or not. When present in the home Binding Update message, the Encrypted Home Address destination option and/or the Pseudo Home Address mobility option indicate that the mobile node requests the use of the location privacy solutions. If such Binding Update message is valid and the home agent supports the location privacy solutions for this particular mobile node, it responds with the Type 2 routing header with the 'E' bit set and/or the Pseudo Home Address Acknowledgement mobility option in the Binding Acknowledgement message. Similarly, the presence of the Encrypted Home Address destination option in the correspondent Binding Update message indicates to the correspondent node that the mobile node requests the use of the location privacy solutions. If such Binding Update message is valid and the correspondent node supports the location privacy solutions for this particular mobile node, it responds with the Type 2 routing header with the 'E' bit set in the correspondent Binding Acknowledgement message to the mobile node. If either the home agent or the correspondent node does not support the location privacy solutions, it rejects the mobile node's request by returning an ICMP Parameter Problem, Code 2, message. Furthermore, a home agent that recognizes such extensions but does not want to enable location privacy protection MAY redirect the mobile node to another home agent. If the request of using the location privacy solutions is rejected, the mobile node MAY either proceed without location privacy protection or choose to connect to a different home agent or stop communicating with such home agent or correspondent node. Qiu, et al. Expires May 7, 2009 [Page 12] Internet-Draft MIP6 location privacy solutions November 2008 5. Reverse-Tunneled Correspondent Binding Update In this section, we describe a solution that protects location privacy against eavesdroppers when the mobile node uses the real home address during communication with the correspondent node via the optimized route. Note that this solution does not require any change to return routability signaling messages. The detailed description is provided as follows. 5.1. The Procedure After the return routability procedure is completed, if the mobile node needs to protect location privacy and at the same time still use the real home address with the correspondent node, the mobile node derives a privacy management key, Kpm, from the Kbm, Kpm = HMAC_SHA1 (Kbm, 0). The mobile node uses Kpm to generate the encrypted home address as follows. encrypted home address = Enc(Kpm, the home address) Where Enc(.) is a symmetric key encryption algorithm. AES is the default encryption algorithm. The mobile node generates a correspondent Binding Update message and reverse-tunnels such message to the correspondent node via the home agent. The format of such message after encapsulation is shown as follows. Note that the encrypted home address is carried in the Encrypted Home Address option as defined in Section 7.1. IPv6 header (source = care-of address, destination = home agent) ESP header in tunnel mode IPv6 header (source = home address, destination = correspondent node) Destination option header Encrypted Home Address option (encrypted home address) Parameters: Alternative Care-of Address option (care-of address) sequence number (within the Binding Update message header) home nonce index (within the Nonce Indices option) care-of nonce index (within the Nonce Indices option) First (96, HMAC_SHA1 (Kbm, (care-of address | correspondent | BU))) This packet is protected by the IPsec security association with a non-null encryption algorithm, e.g., the same security association used for protecting other bi-directionally tunneled payload packets. If the home agent can process this packet successfully, it forwards Qiu, et al. Expires May 7, 2009 [Page 13] Internet-Draft MIP6 location privacy solutions November 2008 the following packet to the correspondent node. IPv6 header (source = home address, destination = correspondent node) Destination option header Encrypted Home Address option (encrypted home address) Parameters: Alternative Care-of Address option (care-of address) sequence number (within the Binding Update message header) home nonce index (within the Nonce Indices option) care-of nonce index (within the Nonce Indices option) First (96, HMAC_SHA1 (Kbm, (care-of address | correspondent | BU))) The operation performed by the correspondent node, after a reverse- tunneled correspondent Binding Update message is received, is described in Section 5.5. If such correspondent Binding Update message is processed successfully and an acknowledgement is requested, the correspondent node constructs a Binding Acknowledgement message shown as follows. IPv6 header (source = correspondent node, destination = home address) Type 2 Routing header with the 'E' bit set encrypted home address Parameters: Alternative Care-of Address option (care-of address) sequence number (within the Binding Update message header) First (96, HMAC_SHA1 (Kbm, (care-of address | correspondent | BA))) Once receiving this Binding Acknowledgement message, the home agent applies the IPsec security association with a non-null encryption algorithm to this message and forwards the following packet to the mobile node. IPv6 header (source = home agent, destination = care-of address) ESP header in tunnel mode IPv6 header (source = correspondent node, destination = home address) Type 2 Routing header with the 'E' bit set encrypted home address Parameters: Alternative Care-of Address option (care-of address) sequence number (within the Binding Update message header) First (96, HMAC_SHA1 (Kbm, (care-of address | correspondent | BA))) Qiu, et al. Expires May 7, 2009 [Page 14] Internet-Draft MIP6 location privacy solutions November 2008 The reverse-tunneled correspondent binding update procedure is completed after the mobile node processes the received Binding Acknowledgement message. To delete an established Binding Cache entry at the correspondent node, the mobile node reverse-tunnels the following Binding Update message via the home agent. Note that the Encrypted Home Address option is optional during the correspondent binding de-registration and only the home keygen token is used to generate Kbm and Kpm, if needed, in this case. IPv6 header (source = care-of address, destination = home agent) ESP header in tunnel mode IPv6 header (source = home address, destination = correspondent node) Destination option header (optional) Encrypted Home Address option (encrypted home address) Parameters: Alternative Care-of Address option (care-of address) sequence number (within the Binding Update message header) home nonce index (within the Nonce Indices option) care-of nonce index (within the Nonce Indices option) First (96, HMAC_SHA1 (Kbm, (care-of address | correspondent | BU))) If an acknowledgement is requested, the correspondent node returns the following Binding Acknowledgement message to the mobile node. Such message is received and forwarded by the home agent to the mobile node. IPv6 header (source = correspondent node, destination = home address) Type 2 Routing header with the 'E' bit set (optional) encrypted home address Parameters: Alternative Care-of Address option (care-of address) sequence number (within the Binding Update message header) First (96, HMAC_SHA1 (Kbm, (care-of address | correspondent | BA))) 5.2. Route Optimized Payload Packets After the correspondent registration is completed successfully, subsequent payload packets are exchanged via the optimized route between the mobile node and the correspondent node. In such packets, only the encrypted home address carried in the Encrypted Home Address destination option and the Type 2 routing header is visible to Qiu, et al. Expires May 7, 2009 [Page 15] Internet-Draft MIP6 location privacy solutions November 2008 eavesdroppers. The format of payload packets sent from the mobile node to the correspondent node is shown as follows. IPv6 header (source = care-of address, destination = correspondent node) Destination option header Encrypted Home Address option (encrypted home address) Payloads The format of payload packets sent from the correspondent node to the mobile node is shown as follows. IPv6 header (source = correspondent node, destination = care-of address) Type 2 Routing header with the 'E' bit set encrypted home address Payloads 5.3. Mobile Node Operation 5.3.1. Conceptual Data Structures The Binding Update List entry for the correspondent registration is extended with a new field to store the current encrypted home address used with a particular correspondent node. The encrypted home address is stored when the mobile node sends a reverse-tunneled correspondent Binding Update message and when successfully processing the correspondent Binding Acknowledgement message, the mobile node updates the state of the corresponding Binding Update List entry. Note that the encrypted home address field is not valid in the Binding Update List entry for the home registration. Given that the encrypted home address is 128 bit long, it is expected that each encrypted home address or the combination of the encrypted home address and the correspondent node's IP address stored in the Binding Update List is unique, therefore the mobile node can use the encrypted home address or together with the correspondent node's IP address as a primary key to look up the Binding Update List. 5.3.2. Reverse-tunneled Correspondent Binding Update to the Correspondent Node After the return routability procedure, if the mobile node chooses to use the location privacy solution with the correspondent node, for example, based on its configuration, it generates the encrypted home address and the reverse-tunneled correspondent Binding Update message Qiu, et al. Expires May 7, 2009 [Page 16] Internet-Draft MIP6 location privacy solutions November 2008 as shown before. Note that the MAC is generated in the same way as specified in RFC 3775 and it does not need to cover the encrypted home address. The mobile node then either updates an existing or creates a new correspondent Binding Update List entry to store the encrypted home address, and forwards such message to the correspondent node through the reverse tunnel established with the home agent. 5.3.3. Reverse-tunneled Correspondent Binding Acknowledgement from the Correspondent Node When the mobile node receives a Binding Acknowledgement message from the correspondent node in response to a previously sent reverse- tunneled correspondent Binding Update message, and if such message contains a Type 2 routing header with the 'E' bit set, the mobile node considers that the correspondent node supports the location privacy solution. The mobile node authenticates such message based on RFC 3775. If succeed, the mobile node decrypts the encrypted home address and compares the result with the real home address, or compares the encrypted home address with the one stored in the Binding Update List entry. If they match, the mobile node considers that the correspondent registration is successfully completed and updates the state of the corresponding Binding Update List entry. If they do not match, the mobile node MAY start the correspondent binding update procedure again. 5.3.4. Route Optimized Payload Packets Note that in order to maintain session continuity, upper layers of the IP stack in the mobile node still use the real home address, even after the reverse-tunneled correspondent registration. A possible way of implementation is that when the Mobile IP sublayer at the mobile node receives a packet from the upper layer, the normal processing as specified in RFC 3775 is performed. After that, the Home Address option is replaced with the Encrypted Home Address option carrying the encrypted home address stored in the corresponding Binding Update List entry, and then the mobile node forwards the packet to the correspondent node via the optimized route. On the other hand, when the mobile node receives a payload packet carrying the Type 2 routing header with the 'E' bit set, the mobile node uses the encrypted home address (optionally together with the IP address of the correspondent node) to look up the Binding Update List. If there is one matched entry found, the mobile node accepts such packet, replaces the Encrypted Home Address option with the Home Address option carrying the real home address and processes such Qiu, et al. Expires May 7, 2009 [Page 17] Internet-Draft MIP6 location privacy solutions November 2008 packet based on RFC 3775. If no entry is found, the mobile node silently drops such packet. 5.3.5. Receiving ICMP Error Message The mobile node may receive an ICMP Parameter Problem, Code 2, message forwarded by the home agent via the bi-directional tunnel, for example, when the correspondent node does not support the use of the Encrypted Home Address option. If such message is received, the mobile node MUST not attempt to use the location privacy solution with such correspondent node. The mobile node may choose either not to or to communicate with the correspondent node without location privacy protection. 5.3.6. Binding Error from the Correspondent Node When the mobile node communicates with a correspondent node by using the encrypted home address, while there is no valid Binding Cache entry established at the correspondent node, a Binding Error message with the Status field set as 1 (unknown binding for Home Address destination option) may be received by the mobile node. Note that we do not specify a new Status value to be used in this case. This is because the implementation of the Binding Update List entry can contain an indication of whether an encrypted home address is currently used with the correspondent node. Once receiving such message, the mobile node can find out which encrypted home address is invalid by looking at the Home Address field of the Binding Error message. The mobile node may either perform the correspondent binding update procedure to establish a valid binding or communicate with the correspondent node in the bi-directional tunneling mode. 5.3.7. Binding Refresh Request from the Correspondent Node When the mobile node receives a Binding Refresh Request message sent from the correspondent node and forwarded by the home agent via the bi-directional tunnel, the mobile node needs to perform the correspondent binding update procedure to refresh the binding at the correspondent node. 5.4. Home Agent Operation With the solution described in this section, there is no new home agent operation to be specified. That is, the home agent behaves based on RFC 3775 when processing signaling or data packets. Qiu, et al. Expires May 7, 2009 [Page 18] Internet-Draft MIP6 location privacy solutions November 2008 5.5. Correspondent Node Operation 5.5.1. Conceptual Data Structures The Binding Cache entry is extended with a new field to store the current encrypted home address used with a particular mobile node. The encrypted home address is stored when the correspondent node successfully processes a reverse-tunneled correspondent Binding Update message. Given that the encrypted home address is 128 bit long, it is expected that each encrypted home address or the combination of the care-of address and the encrypted home address stored in the Binding Cache entry is unique, therefore the correspondent node can use the encrypted home address or together with the care-of address as a primary key to look up the Binding Cache. 5.5.2. Reverse-tunneled Correspondent Binding Update from the Mobile Node When receiving a reverse-tunneled Binding Update message with the Encrypted Home Address option, if the correspondent node supports the location privacy solution, it verifies this message by using the same method as defined in RFC 3775: the home address is the source IP address in this packet and the care-of address is carried in the Alternative Care-of Address option. If such authentication succeeds, the correspondent node generates Kpm and uses it to decrypt the encrypted home address, and compares the result with the source IP address. If they match, the correspondent node stores the encrypted home address in the corresponding Binding Cache entry. 5.5.3. Reverse-tunneled Correspondent Binding Acknowledgement to the Mobile Node If an acknowledgement to the reverse-tunneled correspondent Binding Update message is requested by the mobile node, the correspondent node returns a Binding Acknowledgement message with the Type 2 routing header with the 'E' bit set, if it supports the location privacy solution. The MAC in such Binding Acknowledgement message is generated in the same way as specified in RFC 3775 and does not need to cover the encrypted home address carried in the Type 2 routing header. 5.5.4. Route Optimized Payload Packets Note that in order to maintain session continuity, upper layers of the IP stack in the correspondent node still use the real home address, even after the reverse-tunneled correspondent registration. Qiu, et al. Expires May 7, 2009 [Page 19] Internet-Draft MIP6 location privacy solutions November 2008 A possible way of implementation is that when the IP layer at the correspondent node finishes processing the packet received from the upper layer based on RFC 3775, the real home address in the Type 2 routing header is replaced with the encrypted home address found in the corresponding Binding Cache entry and the 'E' bit is set as 1. Then this packet is forwarded to the mobile node via the optimized route. On the other hand, when the correspondent node receives a payload packet with the Encrypted Home Address option, it uses the encrypted home address (optionally together with the care-of address of the mobile node) to look up the Binding Cache. If there is one matched entry found, the correspondent node replaces the Encrypted Home Address option with the Home Address option carrying the real home address before forwarding the packet to the upper layer. If no matched entry is found, the correspondent node sends a Binding Error message to the source IP address, i.e., the care-of address of the mobile node. 5.5.5. ICMP Error Message to the Mobile Node When receiving a reverse-tunneled correspondent Binding Update message with the Encrypted Home Address option, if the correspondent node does not support location privacy extensions, it sends an ICMP Parameter Problem, Code 2, message to the source IP address (i.e., the home address of the mobile node) and the home agent then forwards such ICMP error message to the mobile node via the bi-directional tunnel. 5.5.6. Binding Error to the Mobile Node When the correspondent node receives a payload packet with the Encrypted Home Address option; however, there is no valid Binding Cache entry for this encrypted home address, it returns a Binding Error message with the Status code set as 1 to the source IP address of such packet; furthermore, the Home Address field in the Binding Error message MUST be copied from the Encrypted Home Address field in the Encrypted Home Address destination option of the offending packet, or set to the unspecified address if no such option appeared in the packet. 5.5.7. Binding Refresh Request to the Mobile Node When the correspondent node realizes that a Binding Cache entry is about to expire, it sends a Binding Refresh Request message to the real home address of the mobile node stored in the Binding Cache entry. Qiu, et al. Expires May 7, 2009 [Page 20] Internet-Draft MIP6 location privacy solutions November 2008 5.6. Summary With this solution, the real home address is visible as the source IP address along the HA-CN path. However, eavesdroppers on the HA-CN path can launch an attack to compromise the return routability procedure anyway. Despite the limitations of the existing return routability mechanism, this solution meets all the requirements we set for the location privacy solutions and provides a simple way to provide location privacy protection while allowing the use of the real home address with the correspondent node. Qiu, et al. Expires May 7, 2009 [Page 21] Internet-Draft MIP6 location privacy solutions November 2008 6. IP Address Location Privacy Solution Using the Pseudo Home Address 6.1. Home Binding Update When the mobile node attaches to a foreign link, it performs the home binding update procedure with the home agent, as specified in RFC 3775. In this section, we describe extensions to such procedure for providing location privacy protection. 6.1.1. Home Registration with IPsec Transport Mode As specified in RFC 3776, the IPsec transport security association is used to protect home registration signaling messages and the real home address is included in the Home Address destination option and the Type 2 routing header. To prevent eavesdroppers on the MN-HA path from breaching location privacy, we encrypt the real home address and use the encrypted home address in mobility signaling messages. 6.1.1.1. Encrypted Home Address Generation The mobile node generates the encrypted home address by encrypting the real home address with a secret key, denoted by Kph, shared between the home agent and the mobile node. The real home address can be restored by decrypting the encrypted home address with the shared secret key. Note that encrypted home address is not routable. As specified in RFC 3776 and RFC 4877, an IPsec security association is established between the home agent and the mobile node either manually or dynamically through IKEv2, for example, during bootstrapping [12]. Kph can be generated either from the shared manual key or the dynamic keying material for the child security association, for example, Kph = HMAC_SHA1(Ks, 0) where Ks is either the shared manual key or Ks = SHA1(KEYMAT) [4]. Note that with such Kph generation methods, extensions to the IKEv2 protocol, e.g., explicit Kph negotiation, are not needed; because the implementation of the Mobile IP function can simply fetch the locally stored manual key or keying materials to generate Kph, if Kph is deemed as needed. How Kph is stored and retrieved is implementation specific. As an example, Kph can be stored in the associated IPsec security association entry in the Security Association Database (SAD), which allows the mobile node and the home agent to retrieve Kph by using the Security Parameters Index (SPI) to look up the SAD. Qiu, et al. Expires May 7, 2009 [Page 22] Internet-Draft MIP6 location privacy solutions November 2008 With Kph, the encrypted home address is computed by the mobile node as follows: encrypted home address = Enc(Kph, home address) where Enc(.) is a symmetric key encryption algorithm With Kph, the real home address is recovered from the encrypted home address as follows: home address = Dec(Kph, encrypted home address) where Dec(.) is the same as Enc(.) The encryption and decryption algorithm recommended in this document is AES with 128 bit long input and output. There is no additional padding or trimming needed with such AES algorithm. Dynamic Update The lifetime of Kph is associated with that of the IPsec security association; therefore Kph is updated when such IPsec security association is renewed or re-established. Within the lifetime of Kph, the mobile node MAY want to generate and use different encrypted home addresses to prevent tracking and profiling. To do so, the mobile node can first generate a sequence of secret keys, denoted by {K0, K1, ..., Kn}, from Kph, and then use Ki to generate different encrypted home addresses. To avoid maintaining an additional counter, the mobile node reuses the sequence number in the IPsec header for generating Ki. Furthermore, given the mobile node's normal movement pattern [6] and the long extended IPsec sequence number (64 bit), it is expected that there is no duplicated encrypted home address generated during the lifetime of the IPsec security association. The procedure to generate the encrypted home address with Ki is shown as follows. Ki = HMAC_SHA1(Kph, IPsec sequence number) encrypted home address = Enc(Ki, home address) The procedure for the home agent to restore the real home address is similar to what is described above: the home agent firstly generates Ki based on Kph and the IPsec sequence number in the received home Binding Update message, and then uses Ki to decrypt the encrypted home address. Note that during the home binding update procedure, the encrypted home address is generated only by the mobile node; the home agent Qiu, et al. Expires May 7, 2009 [Page 23] Internet-Draft MIP6 location privacy solutions November 2008 does not need to generate the encrypted home address using the method described above, since it can simply copy and return the received encrypted home address to the mobile node in a response. In other procedures initiated by the home agent, such as Binding Revocation [22], the home agent MAY need to generate the encrypted home address and the mobile node derives the real home address by using the method described above. Summary The encrypted home address generated by using the mechanism presented above has the following characteristics. First, thanks to the strength of AES, eavesdroppers cannot recover the real home address from the encrypted home address without the knowledge of the secret key shared between the home agent and the mobile node; and multiple dynamically updated encrypted home addresses cannot be correlated and the knowledge of many encrypted home addresses does not increase the possibility for eavesdroppers to recover the real home address. Second, the encrypted home address can be dynamically updated to throttle the profiling attack. That is, a different encrypted home address is present in every Binding Update message sent to the home agent, since the IPsec sequence number is incremented in each Binding Update message. An old encrypted home address cannot be reused in conjunction with an either new or old IPsec sequence number because either the real home address cannot be decrypted correctly or the packet is detected as a replayed packet by the IPsec anti-replay service, if available. In case that the anti- replay service is not supported, for example when a manual key is used, the mobile node should still use a (sequentially) increasing sequence number in the IPsec header to prevent an eavesdropped encrypted home address being replayed. Nevertheless, this is not a new vulnerability and does not compromise the security of the Mobile IPv6 protocol. 6.1.1.2. The Procedure The format of the modified home Binding Update message when the IPsec ESP transport mode is used is shown as follows. Qiu, et al. Expires May 7, 2009 [Page 24] Internet-Draft MIP6 location privacy solutions November 2008 IPv6 header (source = care-of address, destination = home agent) Destination option header Encrypted Home Address option (encrypted home address) ESP header in transport mode Mobility header Home Binding Update Alternative Care-of Address option (care-of address) Pseudo Home Address option (pseudo home address) In order to receive the response, including the indication of location privacy support, from the home agent, the mobile node needs to set the Acknowledgement (A) bit in the Binding Update message. The format of the modified home Binding Acknowledgement message when the IPsec ESP transport mode is used is shown as follows. IPv6 header (source = home agent, destination = care-of address) Type 2 Routing header with the 'E' bit set encrypted home address ESP header in transport mode Mobility header Binding Acknowledgement Pseudo Home Address Acknowledgement option (pseudo home address) Note that in the home Binding Acknowledgement message, the encrypted home address carried in the Type 2 routing header is the same as the one received in the Encrypted Home Address option of the home Binding Update message. 6.1.2. Home Registration with IPsec Tunnel Mode As specified in RFC 4877, the IPsec ESP tunnel mode security association can be used to protect the home binding signaling messages. To provide location privacy, a non-null encryption transform MUST be negotiated during the establishment of the IPsec security association. Therefore, the real home address is encrypted and encapsulated, and made invisible to eavesdroppers on the MN-HA path. The packet formats and processing rules are the same as specified in RFC 3775 and RFC 4877. 6.1.3. Pseudo Home Address Registration 6.1.3.1. Generation To protect location privacy in the route optimization mode, the mobile node replaces the real home address used in certain signaling and payload packets with the pseudo home address. Different from the encrypted home address, the pseudo home address needs to be routable Qiu, et al. Expires May 7, 2009 [Page 25] Internet-Draft MIP6 location privacy solutions November 2008 so that the home agent can intercept packets with the pseudo home address used as the destination address. Therefore, the pseudo home address is generated by concatenating one of the home network prefixes with a random bit string. There are many ways to generate such random bit string, for example, by using a random number generator or a secure encryption or hash algorithm, which prevents eavesdroppers from revealing the real home address. The prefix used to form the pseudo home address MUST be managed by the same home agent; however, it does not have to be the same as that assigned to the mobile node for generating the home address. Therefore, such pseudo home address ensures that, when used in the home address test messages, the same route path between the home agent and the correspondent node as when the real home address is used is traversed. 6.1.3.2. Registration The mobile node MUST register the pseudo home address to be used with the home agent before actually using it. To do so, the mobile node indicates a pseudo home address in the Pseudo Home Address mobility option in the Binding Update message sent to the home agent. If the home agent supports the location privacy solution, it performs the Duplicate Address Detection to detect whether this pseudo home address conflicts with other pseudo home addresses submitted from different mobile nodes. Based on the result, the home agent indicates whether to accept the pseudo home address by setting up the appropriate status code in the Pseudo Home Address Acknowledgement option in the Binding Acknowledgement message. If the home agent prefers the use of a different home network prefix from that of the requested pseudo home address, the home agent returns the new pseudo home address in the Pseudo Home Address Acknowledgement Mobility option to the mobile node. The mobile node MAY register the pseudo home address when it is about to communicate with a correspondent node with location privacy protection. In order to save message overhead, the mobile node MAY register multiple pseudo home addresses in one Binding Update message. The lifetime of registered pseudo home addresses is the same as the Home Binding Cache entry. The mobile node can add or delete any pseudo home address by using the Pseudo Home Address mobility option in the home Binding Update message. The home agent do not have to recover the real home address from such pseudo home address. 6.1.4. Home De-registration When the mobile node returns to its home link, the home de- registration procedure is the same as specified in RFC 3775, i.e., Qiu, et al. Expires May 7, 2009 [Page 26] Internet-Draft MIP6 location privacy solutions November 2008 the real home address is used as the source IP address in the Binding Update message and the destination IP address in the Binding Acknowledgement message. When the mobile node decides to disconnect from the home agent while at its foreign link, the format of the Binding Update and Acknowledgement is the same as that defined for the home registration, except that the Lifetime field is set as zero. The home agent deletes the corresponding Binding Cache entry including the registered pseudo home address, if any. 6.2. Correspondent Binding Update Using the Pseudo Home Address In this section, we specify a location privacy solution that allows the mobile node to communicate with the correspondent node in the route optimization mode without disclosing the real home address to the correspondent node and eavesdroppers. This solution is needed when the mobile node wants to conceal its real home address from the correspondent node and the correspondent node cannot obtain the mobile node's home address through other means, for example, by DNS query. In this case, the pseudo home address is used to replace the real home address in certain messages exchanged during the return routability procedure and the correspondent binding update procedure. There are two ways to send the correspondent Binding Update message, either via the optimized route or the reverse tunnel. While the former does not require the correspondent node to have any additional support beyond what is specified in RFC 3775, RFC 3776 and RFC 4877, the latter provides better location privacy protection by masking the pseudo home address with parameters generated during the return routability procedure. 6.2.1. Return Routability Procedure The location privacy solution specified in this section does not introduce any change to the care-of address test procedure as specified in RFC 3775. In the following, we highlight the extensions to the home address test procedure, during which the mobile node obtains a home keygen token generated based on the pseudo home address. The mobile node generates and sends a Home Test Init message to the home agent. The format of such message is shown as follows. IPv6 header (source = care-of address, destination = home agent) ESP header in tunnel mode IPv6 header (source = home address, destination = correspondent) Mobility Header (HoTI) Home Init Cookie Pseudo Home Address Mobility Option (pseudo home address) Qiu, et al. Expires May 7, 2009 [Page 27] Internet-Draft MIP6 location privacy solutions November 2008 The difference from what is specified in RFC 3775 is that the mobile node includes a Pseudo Home Address mobility option (see Section 7.3) in the Home Test Init message. The pseudo home address contained in the Pseudo Home Address option is selected by the mobile node from a set of pseudo home addresses that have been registered with the home agent during the home registration procedure. Note that the Home Test Init message is protected by an IPsec security association in the ESP tunnel mode with a non-null encryption algorithm and a non- null authentication algorithm, as specified in RFC 3776. When receiving a Home Test Init message, the home agent performs operation as specified in Section 6.6.4. If such operation succeeds when the Pseudo Home Address mobility option is present in the Home Test Init message, the home agent generates a Home Test Init message and forwards to the correspondent node. As shown in the following, the pseudo home address carried in the Pseudo Home Address mobility option is used as the source IP address in the forwarded Home Test Init message. IPv6 header (source = pseudo home address, destination = correspondent) Mobility Header (HoTI) Home Init Cookie The forwarded Home Test Init message looks the same to the correspondent node as what is specified in RFC 3775 and the correspondent node does not realize that the pseudo home address is used, and just generates a home keygen token using the same algorithm as specified in RFC 3775. home keygen token = First (64, HMAC_SHA1 (Kcn, (pseudo home address | nonce | 0))) The correspondent node then replies with a Home Test message. As shown in the following, the format of such Home Test message is the same as that specified in RFC 3776 and the pseudo home address is used as the destination IP address. IPv6 header (source = correspondent, destination = pseudo home address) Mobility Header (HoT) Home Init Cookie Home Keygen Token Home Nonce Index When the home agent intercepts such Home Test message using proxy Neighbor Discovery, it performs operation as specified in Section 6.6.5. If such operation succeeds, the home agent generates the following Home Test message and forwards to the mobile node. Qiu, et al. Expires May 7, 2009 [Page 28] Internet-Draft MIP6 location privacy solutions November 2008 IPv6 header (source = home agent, destination = care-of address) ESP header in tunnel mode IPv6 header (source = correspondent, destination = home address) Mobility Header (HoT) Home Init Cookie Home Keygen Token Home Nonce Index Pseudo Home Address Acknowledgement Mobility Option (pseudo home address) When the mobile node receives the Home Test message, it performs operation as specified in Section 6.5.5. If such operation succeeds, the mobile node obtains a home keygen token computed using the pseudo home address. After the care-of address test is completed, the mobile node hashes the care-of keygen token and the home keygen token together to generate Kbm using the same method as specified in RFC 3775. 6.2.2. Route Optimized Correspondent Binding Update In this procedure, the mobile node MUST use the same pseudo home address used during the home address test procedure. As shown in the following, such pseudo home address is carried by the Home Address option in the correspondent Binding Update message. IPv6 header (source = care-of address, destination = correspondent) Destination option header Home Address destination option (pseudo home address) Parameters sequence number (within the Binding Update message header) home nonce index (within the Nonce Indices option) care-of nonce index (within the Nonce Indices option) First (96, HMAC_SHA1 (Kbm, (care-of address | correspondent | BU))) When the correspondent node receives the Binding Update message, it performs the same operation as specified in RFC 3775. If such operation succeeds and an acknowledgement is requested by the mobile node, the correspondent node replies with the following Binding Acknowledgement message. IPv6 header (source = correspondent, destination = care-of address) Parameters sequence number (within the Binding Update message header) First (96, HMAC_SHA1 (Kbm, (care-of address | correspondent | BA))) After the mobile node receives the Binding Acknowledgement message indicating that the correspondent registration succeeds, the mobile Qiu, et al. Expires May 7, 2009 [Page 29] Internet-Draft MIP6 location privacy solutions November 2008 node can now use the pseudo home address for communicating with the correspondent node. Such Binding Update message may also be used by the mobile node to delete a previously established binding at the correspondent node. In this case, similar to what is specified in RFC 3775, Kbm is generated exclusively from the home keygen token that is based on the pseudo home address. 6.2.3. Reverse-tunneled Correspondent Binding Update The mobile node may choose to use a masked pseudo home address during communication with the correspondent node. To do so, the mobile node performs the reverse-tunneled correspondent binding update procedure and uses the pseudo home address instead of the real home address during such procedure. The format of messages during such procedure is similar to what is described in Section 5 and Section 6.2.1. Note that only one Pseudo Home Address mobility option is included in the reversed tunneled correspondent Binding Update message. 6.2.4. Using Different Pseudo Home Addresses with Different Correspondent Nodes Based on its configuration and policy, the mobile node can choose to use the same or different pseudo home addresses when communicating with different correspondent nodes. Using a different pseudo home address with each correspondent node may help prevent the mobile node's activities from being linked and correlated. To do so, the mobile node selects a different but already registered pseudo home address and repeats the return routability procedure and the correspondent binding update procedure with each correspondent node. In addition, if the mobile node prefers, it MAY use different pseudo home addresses for different sessions with the same correspondent node. This typically requires additional configuration at the mobile node that associates a specific session (for example, identified by the port number and the protocol number among others) with a specific pseudo home address. This document does not intend to go into the details of such solution. 6.3. Payload Packets 6.3.1. Reverse Tunneling Mode The format of payload packets reverse-tunneled via the home agent is the same as specified in RFC 3775, except that an IPsec tunnel mode security association with a non-null encryption algorithm MUST be applied to such payload packets. Therefore, the binding between the Qiu, et al. Expires May 7, 2009 [Page 30] Internet-Draft MIP6 location privacy solutions November 2008 real home address and the care-of address is not leaked to eavesdroppers along the MN-HA path. 6.3.2. Route Optimization Mode When the route optimized correspondent binding update procedure is performed, the format of payload packets exchanged between the mobile node and the correspondent node is the same as specified in RFC 3775. Note that the pseudo home address is used in the Home Address destination and the Type 2 routing header. However, such difference is transparent to the correspondent node. The operation of the mobile node when communicating with the correspondent node via the route optimization mode is described in Section 6.5.6 in details. When the reverse tunneled correspondent binding update procedure is performed, the format of payload packets exchanged between the mobile node and the correspondent node is the same as specified in Section 5, except that the encrypted home address destination option and the Type 2 routing header actually contain an encrypted pseudo home address. The operation of the mobile node and the correspondent node is described in Section 5.3 and Section 5.5 in details. 6.4. Prefix Discovery Similar to the home Binding Update/Acknowledgement message, the ICMP Mobile Prefix Solicitation/Advertisement message can be protected by IPsec either in the transport mode or the tunnel mode. The solutions to protect location privacy during the prefix discovery procedure are similar to those used during the home binding update procedure. 6.5. Mobile Node Operation In this section, we describe the mobile node's operation when the location privacy solution is used. 6.5.1. Conceptual Data Structures 6.5.1.1. Pseudo Home Address Table We introduce a new data structure, called Pseudo Home Address table, to record the information of pseudo home addresses. The mobile node may maintain a Pseudo Home Address table for each home agent it registers with. Each entry in the table contains a pseudo home address and its associated state, i.e., "unconfirmed" or "confirmed". The mobile node usually creates new entries or updates existing ones with the "unconfirmed" state in the Pseudo Home Address table when sending the home Binding Update message to (re)register new or existing pseudo home address(es), and updates entries when receiving Qiu, et al. Expires May 7, 2009 [Page 31] Internet-Draft MIP6 location privacy solutions November 2008 the home Binding Acknowledgement message. The pseudo home address can be used as a key to search the table. There MUST be no duplicated pseudo home addresses stored in the Pseudo Home Address table. 6.5.1.2. Binding Update List The Binding Update List entry is extended with an additional field, called Encrypted Home Address. This field is valid in the Binding Update List entry for a home binding only and contains the encrypted home address used in the Binding Update message sent to a particular home agent. The Binding Update List can be searched by using the encrypted home address as a key. The Binding Update List entry is extended with another additional field, called Pseudo Home Address. This field MAY be implemented as a pointer that points to a corresponding entry in the Pseudo Home Address table and initialized as NULL when the Binding Update List entry is created (for example, when the mobile node sends a Binding Update message or a Home Test Init message to the home agent). For the binding sent to a specific home agent, the Pseudo Home Address field points to the first entry in the Pseudo Home Address table (or NULL if the table is empty), so that the mobile node can access all the pseudo home addresses registered at this home agent; on the other hand, for the binding sent to a specific correspondent node, the Pseudo Home Address field points to the Pseudo Home Address table entry that contains the actual pseudo home address used with this correspondent node (or NULL if no pseudo home address is used with this correspondent node). 6.5.2. Binding Update to the Home Agent The mobile node may decide to perform the home registration with location privacy protection, for example, when it attaches to a foreign link or when it needs to extend the lifetime of a registered home binding. If the IPsec transport mode is used, after performing the operation specified in RFC 3775 and RFC 3776, the mobile node generates the encrypted home address from the real home address using the method described in Section 6.1.1.1, replaces the Home Address option in the generated Binding Update message with the Encrypted Home Address option that carries the encrypted home address. If the mobile node needs to register some pseudo home addresses, for example, it wants to communicate with a correspondent node immediately after the home registration procedure, it includes one or more Pseudo Home Address mobility options in the Binding Update message. The mobile node may indicate the requested pseudo home address or zero in the Pseudo Home Qiu, et al. Expires May 7, 2009 [Page 32] Internet-Draft MIP6 location privacy solutions November 2008 Address field, if it requests the home agent to dynamically assign one. Finally, the mobile node sends the Binding Update message to the home agent, updates its Binding Update List entry and the Pseudo Home Address table to record the encrypted home address and the pseudo home address(es) used (with "unconfirmed" state). If the IPsec tunnel mode is used, the mobile node MUST negotiate a non-null encryption algorithm, for example, during the bootstrapping, and use it to protect the home Binding Update message as specified in RFC 3775 and RFC 4877. In addition, the mobile node can register the pseudo home address as described above. If the mobile node does not want to register the pseudo home address right now, but just wants to discover whether the home agent supports the location privacy solution, the mobile node includes a Pseudo Home Address mobility option without the Pseudo Home Address field in the Binding Update message sent to the home agent. In case that the mobile node needs to retransmit a Binding Update message, for example, due to failure to receive a Binding Acknowledgement message within a predefined time period, it generates and uses a new encrypted home address in the re-transmitted Binding Update message. After sending the home de-registration binding update message, in addition to the operation specified in RFC 3775, the mobile node MUST stop using any data structure specific to the location privacy solution and MAY delete them after the Binding Acknowledgement message is processed successfully. 6.5.3. Binding Acknowledgement from the Home Agent If the IPsec transport mode is used, when the mobile node receives a Binding Acknowledgement message with the 'E' bit set in the Type 2 routing header, the mobile node searches its Binding Update List using the encrypted home address as a key. If the mobile node finds a valid Binding Update List entry pending for an acknowledgement, the mobile node replaces the encrypted home address carried in the Binding Acknowledgement message with the real home address stored in the found Binding Update List entry. Then the mobile node follows the rules specified in RFC 3775 and RFC 3776 to process the Binding Acknowledgement message. If not found, the mobile node MAY follow the same method as described in Section 6.1.1.1 to decrypt the real home address from the encrypted home address before further processing. If the IPsec tunnel mode is used, the mobile node follows the rules specified in RFC 3775 and RFC 4877 to processing the Binding Acknowledgement message. Qiu, et al. Expires May 7, 2009 [Page 33] Internet-Draft MIP6 location privacy solutions November 2008 In addition, if one or more Pseudo Home Address Acknowledgement mobility options are present in the Binding Acknowledgement message, the mobile node checks the Status field in each option. If the Status field in one option is 0 (Success), such pseudo home address, if not existing, is added into the Pseudo Home Address table, and the state of the corresponding entry is set as "confirmed"; if the Status field in one option is '132', the mobile node SHOULD NOT request the home agent to dynamically assign the pseudo home address in the future; otherwise, the mobile node deletes any existing pseudo home address with the "unconfirmed" state (i.e., either an error code or no acknowledgement for such pseudo home address is received) from the Pseudo Home Address table. The mobile mode considers that the home agent supports the location privacy solution, if one or more of the following is received: o A valid Pseudo Home Address Acknowledgement mobility option with or without a Pseudo Home Address field o A valid Binding Acknowledgement message with the 'E' bit set in the Type 2 routing header Note that the mobile node MUST determine whether the home registration succeeds or not based on what is specified RFC 3775. 6.5.4. Home Test Init to the Home Agent To enable location privacy protection during communication with the correspondent node in the route optimization mode, the mobile node generates a Home Test Init message based on what is specified in RFC 3775 and RFC 3776. In addition, if the Return Routability procedure is for a new session with the correspondent node, the mobile node selects any pseudo home address from those already registered with the home agent and stored in the Pseudo Home Address table; otherwise, the mobile node must use the same pseudo home address as used with the same correspondent node before. The selected pseudo home address is carried in the Pseudo Home Address mobility option of the generated Home Test Init message. Note that this Home Test Init message is protected by an IPsec security association with a non-null encryption algorithm. After sending the Home Test Init message to the home agent, if there is no Binding Update List entry existing for the correspondent node, the mobile node creates one entry that points to the pseudo home address used; otherwise, the mobile node updates the existing entry. Qiu, et al. Expires May 7, 2009 [Page 34] Internet-Draft MIP6 location privacy solutions November 2008 6.5.5. Home Test from the Home Agent When the mobile node receives a Home Test message from the home agent, it processes the packet based on processing rules specified in RFC 3775 and RFC 3776. If this is a valid packet and there is a Pseudo Home Address Acknowledgement option included, the mobile node examines the Status field inside this mobility option as follows: o If the Status field indicates that the home address test procedure using the pseudo home address succeeds (the Status field is 0), in addition to what is specified in RFC 3775, the mobile node prepares to use the pseudo home address carried in the Pseudo Home Address Acknowledgement option for the correspondent registration. o If the Status field indicates that the home address test procedure using the pseudo home address fails (the Status field is larger than 127), the mobile node can take steps to correct the cause of the error and retransmit the Home Test Init message, subject to the re-transmission limit specified in RFC 3775. If this is not done or it fails, then the mobile node SHOULD record in its Binding Update List that the future home address test procedure SHOULD NOT use the pseudo home address with this correspondent node. 6.5.6. Route Optimized Payload Packets After the mobile node completes the route optimized correspondent registration procedure using the pseudo home address, payload packets are sent to the correspondent node with the pseudo home address in the Home Address destination option. Note that payload packets when generated by upper layer applications still use the real home address. As an example of implementation, when such packets are passed to the Mobile IP layer, the operation specified in RFC 3775 is performed firstly. Then, the destination IP address (i.e., the correspondent node) is used to look up the Binding Update List to look for the pseudo home address to be used. If found, the pseudo home address is used to replace the real home address in the Home Address destination option; otherwise, the real home address is used. When the mobile node receives a payload packet with the Type 2 routing header, it needs to detect whether the location privacy solution is used. If so, it needs to replace the pseudo home address with the real home address before passing the received packet to the transport layer. As an example of implementation, the mobile node uses the source IP address (i.e., the correspondent node) to look up the Binding Update List. The mobile node performs one of the following operations: Qiu, et al. Expires May 7, 2009 [Page 35] Internet-Draft MIP6 location privacy solutions November 2008 o If the found Binding Update List entry contains a pseudo home address that matches with the IP address carried in the Type 2 routing header, the mobile node accepts the packet and replaces the pseudo home address with the real home address. The rest of operation is the same as specified in RFC 3775. o If the found Binding Update List entry does not contain a pseudo home address and the IP address carried in the Type 2 routing header matches with the real home address, the mobile node performs the operation specified in RFC 3775. o In all other cases, the mobile node silently drops the received payload packet. In case that the mobile node masks the pseudo home address and uses the reverse-tunneled correspondent binding update procedure, the mobile node performs the operation specified in Section 5.3.4, except that the pseudo home address rather than the real home address is expected. 6.5.7. Receiving ICMP Error Messages When the mobile node receives an ICMP Parameter Problem, Code 2, message as a response to the previously sent home Binding Update message, the mobile node MUST conclude that the home agent does not support the location privacy solution, and update the corresponding Binding Update List entry. The mobile node MAY discover and register with a different home agent, or continue with the same home agent without requesting the location privacy support. 6.5.8. Receiving Binding Refresh Request The Mobile Node may receive the Binding Refresh Request message from either the home agent or the correspondent node. If from the correspondent node, when the location privacy solution is used, the destination IP address is the pseudo home address. In this case, the mobile node needs to check the corresponding Binding Update List entry with such correspondent node, if such pseudo home address is invalid, the mobile node silently discards such message. Otherwise, the mobile node refreshes the binding with the correspondent node by using the same pseudo home address. If the Binding Refresh Request message with the encrypted home address is received from the home agent, the mobile node needs to derive the real home address firstly and then process such message. After that, the mobile node performs the home registration procedure with the home agent as described in Section 6.1. Qiu, et al. Expires May 7, 2009 [Page 36] Internet-Draft MIP6 location privacy solutions November 2008 6.6. Home Agent Operation In this section, we describe the home agent's operation when the location privacy solution is used. 6.6.1. Conceptual Data Structures The Binding Cache entry is extended with an additional field that points to a list of currently accepted pseudo home addresses. Note that each registered pseudo home address MUST be unique and all the registered pseudo home addresses SHOULD be organized in such a way that the associated Binding Cache entry can be quickly located when a pseudo home address is used as the key to look up the Binding Cache. 6.6.2. Binding Update from the Mobile Node When the home agent receives a Binding Update message with an Encrypted Home Address destination option, if the home agent does not recognize this destination option, it MUST send back an ICMP Parameter Problem, Code 2, message to the source IP address and drop the received Binding Update message. If the home agent recognizes this destination option, it looks up the SAD using the SPI, optionally together with the IPsec protocol type and the destination IP address. This returns the established security association used to process this received Binding Update message; otherwise, the home agent proceeds based on the IPsec related processing rules. The home agent SHOULD obtain Kph that may be stored with this security association. If Kph cannot be generated, the home agent MUST ignore the whole message and log the error. Otherwise, the home agent generates Ki based on Kph and the IPsec sequence number, recovers the real home address from the encrypted home address using the method specified in Section 6.1.1.1, and finally replaces the encrypted home address with the real home address. After transformation, the received Binding Update message looks like a RFC3775 compliant Binding Update message, thus the home agent continue to perform the operation specified in RFC 3775 and RFC 3776. The following operation will be performed if there is no any error during the Mobile IPv6 processing. If the received Binding Update message contains one or more Pseudo Home Address mobility options, the home agent MUST ignore such option if it does not recognize it. If the home agent recognizes such option, a Pseudo Home Address Acknowledgement mobility option is generated and some fields therein are set as follows: o If the Pseudo Home Address field received is empty, the Status field is set as 0 (Success) and the Pseudo Home Address field is empty. Qiu, et al. Expires May 7, 2009 [Page 37] Internet-Draft MIP6 location privacy solutions November 2008 o If the Pseudo Home Address field received is set as all zero, the Status field is set is 0 (Success) and a pseudo home address SHOULD be included in the Pseudo Home Address field, if the home agent supports the dynamic pseudo home address assignment; otherwise, the Status field is set as 132 (Dynamic pseudo home address assignment not available) and the Pseudo Home Address field is empty. o The Pseudo Home Address field received may contain an IPv6 address. If the format of such an IP address is incorrect, the Status field is set as 130 (Incorrect pseudo home address). Or if such IP address is invalid, for example, the prefix is not a valid home network prefix or this is detected as a duplicated IP address when the home agent performs the Duplicate Address Detection on such IP address, the Status field is set as 131 (Invalid pseudo home address). In both cases, the Pseudo Home Address field is empty. Or if the home agent suggests a different pseudo home address, the Status field is set as 0 (Success) and the new pseudo home address is included in the Pseudo Home Address field. Otherwise, if the home agent accepts the requested pseudo home address, the Status field is set as 0 (Success) and the same IP address is included in the Pseudo Home Address field. o If the home agent does not allow the mobile node to use the pseudo home address with the correspondent node, the Status field SHOULD be set as 129 (Administratively prohibited) and the Pseudo Home Address field is empty. o In case that the home agent does not accept the Pseudo Home Address mobility option for all other reasons, the Status field SHOULD be set as 128 (Failure, reason unspecified) and the Pseudo Home Address is empty. When receiving a Binding Update message protected with the IPsec tunnel mode, the home agent performs the operation specified in RFC 4877. When receiving and successfully processing a Binding Update message for de-registration from the mobile node, in addition to what is specified in RFC 3775, the home agent MUST delete data structures related to the location privacy extension. 6.6.3. Binding Acknowledgement to the Mobile Node If the mobile node sets the 'A' bit in the Binding Update message, the home agent generates a Binding Acknowledgement message using the real home address with the proper status code set. Then this Binding Acknowledgement message is processed by applying the IPsec security Qiu, et al. Expires May 7, 2009 [Page 38] Internet-Draft MIP6 location privacy solutions November 2008 association, as specified in RFC 3776. Finally, the home agent sets the 'E' bit in the Type 2 routing header and replaces the real home address therein with the encrypted home address received from the Encrypted Home Address destination option in the Binding Update message. The processing rules related to the Pseudo Home Address Acknowledgement mobility option are described in Section 6.6.2. When sending a Binding Acknowledgement message protected with the IPsec tunnel mode, the home agent performs the operation specified in RFC 4877. 6.6.4. Home Test Init from the Mobile Node When receiving a Home Test Init message from the mobile node, the home agent firstly verifies such message based on the IPsec processing rules as specified in RFC 3776. If fail, the home agent acts based on such IPsec processing rules. Otherwise, if the Pseudo Home Address option does not exist in the Home Test Init message, the home agent performs the operation as specified in RFC 3775. Otherwise, the following operation is performed. 1. The home agent looks up its Binding Cache by using the real home address as a key, if the pseudo home address carried in the Pseudo Home Address option does not match any pseudo home address associated with the corresponding Binding Cache entry (including when the Pseudo Home Address field is set as zero), it MUST reject such Home Test Init message by sending back a Home Test message including the Pseudo Home Address Acknowledgement option with the Status field set as 131 (Invalid pseudo home address). If there are multiple Pseudo Home Address options received, the home agent MAY use the first option and ignore others. 2. Otherwise, the home agent constructs a Home Test Init message with the pseudo home address as the source IP address, and forwards the Home Test Init message to the correspondent node. 6.6.5. Home Test to the Mobile Node When the home agent intercepts a Home Test message using proxy Neighbor Discovery, if the destination IP address matches with one of the real home addresses, the home agent performs the operation as specified in RFC 3775. Otherwise, the home agent uses the destination IP address to look up the Binding Cache to find if there is a matched pseudo home addresses. If not, the home agent discards such message silently; otherwise, the home agent generates a Home Test message with a Pseudo Home Address Acknowledgement option and Qiu, et al. Expires May 7, 2009 [Page 39] Internet-Draft MIP6 location privacy solutions November 2008 sends it to the mobile node. Inside the Pseudo Home Address Acknowledgement option, the Status field is set as zero (Success) and the Pseudo Home Address field is filled with the found pseudo home address. 6.6.6. Binding Refresh Request to the Mobile Node As specified in RFC 3775, the correspondent node may send a Binding Refresh Request message to the home address to request the Binding Cache entry to be refreshed. With the location privacy solution used, the correspondent node may send the Binding Refresh Request message to a pseudo home address registered in one Binding Cache entry. In this case, when the home agent receives a Binding Refresh Request message from the correspondent node, if the destination IP address is one of registered real home addresses, the home agent performs the operation specified in RFC 3775; otherwise, if such IP address is one of registered pseudo home addresses, the home agent finds the mobile node's real home address and sends the Binding Refresh Request message via the bi-directional tunnel to the mobile node. If the home agent wants to send a Binding Refresh Request message to the mobile node, it MAY apply the same IPsec security association for the home binding messages to the Binding Refresh Request message. 6.7. Correspondent Node Operation With the solution described in this section, when the correspondent node is involved in the route optimized correspondent binding update procedure, there is no new operation to be specified. That is, the correspondent node behaves based on RFC 3775 when processing signaling or data packets using the pseudo home address. On the other hand, when the correspondent node is involved in the reverse- tunnel correspondent binding update procedure with the pseudo home address used, the additional correspondent node operation is the same as specified in Section 5.5, except that the pseudo home address, instead of the real home address, is used. Qiu, et al. Expires May 7, 2009 [Page 40] Internet-Draft MIP6 location privacy solutions November 2008 7. Extensions to Mobile IPv6 7.1. Encrypted Home Address Destination Option This option is used in the Destination Option extension header (Next Header value = 60). Its format is shown as follows. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Option Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Encrypted Home Address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option Type A unique type for identifying the use of the encrypted home address (to be determined by IANA). Encrypted Home Address The encrypted home address generated from a either real or pseudo home address. The processing of other fields in the Encrypted Home Address option is the same as that of those fields in the Home Address option described in RFC 3775. Note that if the Encrypted Home Address option is present in a packet, the encrypted home address therein MUST not be treated as the real source IP address by the receiver. 7.2. Extensions to the Type 2 Routing Header A new bit in the Reserved field of the Type 2 routing header is used to indicate that the encrypted home address is carried in this routing header. The format of the modified Type 2 routing header is shown as follows. Qiu, et al. Expires May 7, 2009 [Page 41] Internet-Draft MIP6 location privacy solutions November 2008 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len=2 |Routing Type=2 |Segments Left=1| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |E| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Encrypted Home Address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Encrypted Home Address (E) The Encrypted Home Address (E) bit is set to indicate that the encrypted home address is carried in the routing header. Encrypted Home Address The encrypted home address generated from a either real or pseudo home address. The processing of other fields in this type of the routing header is the same as described in RFC 3775. Note that if the Type 2 routing header with the 'E' set is present in a packet, the encrypted home address therein MUST not be treated as the real destination IP address by the receiver. 7.3. Pseudo Home Address Mobility Option This mobility option is included in the mobility header, including the Binding Update message and the Home Test Init message, and carries zero or one pseudo home address. The alignment requirement for this option is 4n. Its format is shown as follows. Qiu, et al. Expires May 7, 2009 [Page 42] Internet-Draft MIP6 location privacy solutions November 2008 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type (TBD) | Length | Prefix length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Pseudo Home Address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type A unique type for identifying the Pseudo Home Address mobility option (to be determined by IANA). Length The length of the Pseudo Home Address mobility option excluding the Type field and the Length field. It MUST be 2 when the Pseudo Home Address field is not present; otherwise, it MUST be 18. Prefix Length The length of the home network prefix of the included pseudo home address. When the Pseudo Home Address field is not present, the Prefix Length field MUST be set as zero. Reserved This field is reserved for future use. It MUST be set as zero by the sender and ignored by the receiver. Pseudo Home Address If present, the field contains a pseudo home address that the mobile node wants to use for location privacy protection or zero if the mobile node requests a pseudo home address from the home agent. This field is not present, if the mobile node only intends to discover whether the home agent supports the location privacy solutions. The Length field is used to detect whether the Pseudo Home Address field is present in the Pseudo Home Address mobility option. Qiu, et al. Expires May 7, 2009 [Page 43] Internet-Draft MIP6 location privacy solutions November 2008 7.4. Pseudo Home Address Acknowledgement Mobility Option This mobility option is included in the mobility header, including the Binding Acknowledgement message and the Home Test message sent to the mobile node, and carries zero or one pseudo home address. This mobility option is used to indicate the status of the pseudo home address registration and/or whether the home agent supports the location privacy solutions. The alignment requirement for this option is 2n. Its format is shown as follows. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type (TBD) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix length | Status | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Pseudo Home Address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type A unique type for identifying the Pseudo Home Address Acknowledgement mobility option (to be determined by IANA). Length The length of the Pseudo Home Address Acknowledgement mobility option excluding the Type field and the Length field. It MUST be 4 when the Pseudo Home Address field is not present; otherwise, it MUST be 20. Prefix Length The length of the home network prefix of the included pseudo home address. When the Pseudo Home Address field is not present, the Prefix Length MUST be set as zero. Status It indicates the status of the pseudo home address registration. Values from 0 to 127 indicate success. Higher Qiu, et al. Expires May 7, 2009 [Page 44] Internet-Draft MIP6 location privacy solutions November 2008 values indicate failure. The following values are reserved: 0 Success 128 Failure, reason unspecified 129 Administratively prohibited 130 Incorrect pseudo home address 131 Invalid pseudo home address 132 Dynamic pseudo home address assignment not available Reserved This field is reserved for future use. It MUST be set to zero by the sender and ignored by the receiver. Pseudo Home Address If present, the field contains a pseudo home address that the home agent registers for the mobile node to use for location privacy protection. This field is not present, when the home agent only needs to indicate that it supports the location privacy solutions as a response to the query from the mobile node. The Length field is used to detect whether the Pseudo Home Address field is present in the Pseudo Home Address Acknowledgement mobility option. Qiu, et al. Expires May 7, 2009 [Page 45] Internet-Draft MIP6 location privacy solutions November 2008 8. Security Consideration The solutions proposed in this document address one of security issues in the mobile environment, i.e., location privacy. Throughout the document, we provide a detailed analysis of how the proposed solutions address the location privacy problem when describing the solutions. We carefully design such solutions to make sure that they fit well into the Mobile IPv6 framework; therefore, the same threat analysis, security mechanisms (such as IPsec, the sequence number in binding signaling messages, the return routability procedure) and consideration as described in RFC 3775 still apply. Nevertheless, in the following we provide in-depth analysis on security threats involving the use of the location privacy solutions and demonstrate that the proposed solutions do not introduce any new vulnerability or weaken the strength of security protection of the original Mobile IPv6 protocol. 8.1. Home Binding Update Given the strong security strength of the cryptography algorithm used to generate the encrypted home address, eavesdroppers are unable to derive the real home address from the encrypted home address and thus to correlate the care-of address with the real home address. Moreover, the encrypted home address can be updated to prevent eavesdroppers from linking the mobile node's ongoing activities. The home agent can derive the real home address from the received encrypted home address efficiently due to the use of the symmetric cryptography algorithm on a small amount of data (in this case, 128 bits), thus the home agent can resist the Denial-of-Service attack when attackers flood the home agent with forged home Binding Update messages in order to exhaust CPU resource. During the pseudo home address registration, the home agent verifies that the requested pseudo home address is not in use by other mobile nodes; therefore the malicious mobile node cannot intercept ongoing sessions of a victim mobile node by registering the same pseudo home address. A malicious mobile node may attempt to register a larger number of pseudo home addresses in order to exhaust the pool of available pseudo home addresses and to prevent other mobile nodes using location privacy protection. The home agent MUST limit the number of pseudo home addresses that can be requested by a mobile node. Also with the IPsec security association between the home agent and the mobile node, if the misuse of the pseudo home address registration is detected, the home agent can identify the malicious mobile node and take further actions. Qiu, et al. Expires May 7, 2009 [Page 46] Internet-Draft MIP6 location privacy solutions November 2008 8.2. Correspondent Binding Update The return routability procedure using the pseudo home address follows the same principle of the original return routability procedure, i.e., the message exchange verifies that the mobile node is reachable at both the pseudo home address and the care-of address (this is because the pseudo home address is required to be routable). Furthermore, the extended return routability procedure also utilizes the same security mechanisms as defined in RFC 3775, such as the nonce, the node key, and the sequence number, to protect against attacks. Overall, it provides the same security strength as the original return routability procedure. The reverse-tunneled correspondent binding update procedure does not weaken security either. Although the real home address is transferred in the cleartext on the HA-CN path, eavesdroppers on such path can already perform more serious attacks against the mobile node with the Mobile IPv6 protocol. 8.3. Route-Optimized Payload Packets Using the Encrypted Home Address option in route optimized packets results in the same security implications when the Home Address option is used in such packets. For example, the Encrypted Home Address option may be used by attackers to launch reflection attacks, such as by indicating the IP address of a victim node in the Encrypted Home Address option. Similar to the processing rule for the Home Address option specified in RFC 3775, this document restricts the use of the Encrypted Home Address option: it can be used only if there is an established Binding Cache entry containing such encrypted (pseudo) home address. With the proposed location privacy solutions, the Type 2 routing header is extended to carry the encrypted (pseudo) home address, if the 'E' bit is set. The same threats specified in RFC 3775 for the Type 2 routing header are also possible when such routing header carries the encrypted (pseudo) home address. Similar processing rules are also used in this document to address such threat: if the encrypted (pseudo) home address in the Type 2 routing header does not match with that stored in the Binding Update List entry, the packet will be dropped. Qiu, et al. Expires May 7, 2009 [Page 47] Internet-Draft MIP6 location privacy solutions November 2008 9. Related Work Our work benefits from previous work and discussion on this topic. Similar to the concept of the pseudo home address, many drafts have proposed using a temporary identity to replace the mobile node's home address in the IPsec security association, Mobile IPv6 signaling messages and data packets. However, the details of how to generate and update this identity are absent. In the following, we provide a survey of related work. RFC 3041 [10] specifies a mechanism to generate randomized interface identifiers, which can be used to update the care-of address and the home address. However, with our solution, the prefix of a pseudo home address can be different from that of the real home address and other pseudo home addresses, which prevents eavesdroppers from correlating and analyzing IP traffic based on a common prefix. Furthermore, we also discuss about the interval of IP address update in the mobility scenario in order to resist the profiling attack both effectively and efficiently. In [16], the authors proposed using a temporary identity, called the Temporary Mobile Identifier (TMI), to replace the home address, and discussed the feasibility of utilizing the CBID/CGA/MAP to further protect location privacy. However, as a 128 bit random number, the TMI is not routable; therefore it is not suitable to be the source IP address in the Home Test Init message forwarded by the home agent to the correspondent node. Otherwise, the home agent cannot receive the Home Test message from the correspondent node. Furthermore, the draft does not specify how to update the TMI to address the profiling attack. In [14], the authors proposed a mechanism that uses an identity as the home address and periodically updates such identity by using a key and a previous identity as inputs to a cryptography algorithm. In [15], the authors proposed to update the mobile node's home address periodically to hide its movement. The new home address is generated from the current local network prefix, the Binding Update session key and the previous home address, and updated every time when the return routability procedure is performed. The generated home address is random, routable, recognizable and recoverable. In [18], the authors proposed a mechanism to achieve both route optimization and location privacy at the same time. This is done by discovering a tunneling agent near the correspondent node and bi- directionally tunneling data traffic between the mobile node and such tunneling agent. Qiu, et al. Expires May 7, 2009 [Page 48] Internet-Draft MIP6 location privacy solutions November 2008 10. IANA Consideration In this document, a new destination option, called the Encrypted Home Address destination option, is described in Section 7.1. This option needs a new type assignment from IANA from the IPv6 parameters registry. Furthermore, two new Mobility Header options, the Pseudo Home Address mobility option and the Pseudo Home Address Acknowledgement mobility option, are defined in Section 7.3 and Section 7.4 respectively. These two options need type assignment from the Mobility Header options registry. In addition, this document reserves a bit, called 'E' bit, from the Reserved field of the Type 2 routing header as described in Section 7.2. 11. Conclusion In this document, we proposed solutions to address location privacy issues in the context of mobility. The main idea is to hide the binding between the home address and the care-of address from eavesdroppers and the correspondent node, if possible. To do so, we apply cryptography algorithms to encrypt the real home address and generate the routable pseudo home address, design the new format of various mobility signaling messages and payload packets, and extend the functionality of mobility entities. Furthermore, we extensively discuss the profiling problem, and provide recommendations and solutions to mitigate the effects of the profiling attack. The solutions fulfill our requirements and achieve our design goals. The solutions we proposed are for the basic Mobile IPv6 protocol as specified in RFC 3775. Recently, many extensions to Mobile IPv6 have been proposed, such as the NEMO Basic Support protocol [19], Dual Stack Mobile IPv6 Support [20], Multiple Care-of Addresses Registration [21], Binding Revocation [22], Generic Signaling Message [23]. It is expected that the proposed location privacy solutions can be applied with no or minor modifications to address location privacy issues when these extensions are used. One of our future works is to clarify related issues, if any, when the location privacy solutions is used with new Mobile IPv6 extensions. 12. Acknowledgement The authors would like to thank the co-authors of previous drafts from which this document is derived: Vijay Devarapalli, Hannu Flinck, Charlie Perkins, Feng Bao, Robert Deng, James Kempf, and Jianying Zhou. In addition, sincere appreciation is also extended to Claude Qiu, et al. Expires May 7, 2009 [Page 49] Internet-Draft MIP6 location privacy solutions November 2008 Castelluccia, Francis Dupont, Gabriel Montenegro, Greg Daley, Kilian Weniger, Takashi Aramaki, Wassim Haddad, Heejin Jang, and Michael Welzl for their valuable contributions, review and discussion. 13. References 13.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [2] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, December 2005. [3] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, December 2005. [4] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306, December 2005. [5] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [6] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. [7] Arkko, J., Devarapalli, V., and F. Dupont, "Using IPsec to Protect Mobile IPv6 Signaling Between Mobile Nodes and Home Agents", RFC 3776, June 2004. [8] Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with IKEv2 and the revised IPsec Architecture", RFC 4877, April 2007. [9] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. [10] Narten, T. and R. Draves, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001. [11] Koodli, R., "IP Address Location Privacy and Mobile IPv6: Problem Statement", RFC 4882, March 2007. 13.2. Informative References [12] Giaretta, G., Kempf, J., and V. Devarapalli, "Mobile IPv6 Bootstrapping in Split Scenario", RFC 5026, October 2007. Qiu, et al. Expires May 7, 2009 [Page 50] Internet-Draft MIP6 location privacy solutions November 2008 [13] Koodli, R., Devarapalli, V., Flinck, H., and C. Perkins, "Solutions for IP Address Location Privacy in the presence of IP Mobility", draft-koodli-mip6-location-privacy-solutions-00 (work in progress), February 2005. [14] Bao, F., Deng, R., Kempf, J., Qiu, Y., and J. Zhou, "Protocol for Protecting Movement of Mobile Nodes in Mobile IPv6", draft-qiu-mip6-mnprivacy-00 (work in progress), March 2005. [15] Bao, F., Deng, R., Kempf, J., Qiu, Y., and J. Zhou, "Protocol for Protecting Movement of Mobile Nodes in Mobile IPv6", draft-qiu-mip6-hiding-movement-00 (work in progress), March 2005. [16] Castelluccia, C., Dupont, F., and G. Montenegro, "Protocol for Protecting Movement of Mobile Nodes in Mobile IPv6", draft-dupont-mip6-privacyext-02 (work in progress), July 2005. [17] Daley, G., "Location Privacy and Mobile IPv6", draft-daley-mip6-locpriv-00 (work in progress), January 2004. [18] Weniger, K. and T. Aramaki, "Route Optimization and Location Privacy using Tunneling Agents (ROTA)", draft-weniger-rota-01 (work in progress), October 2005. [19] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert, "Network Mobility (NEMO) Basic Support Protocol", RFC 3963, January 2005. [20] Soliman, H., "Mobile IPv6 support for dual stack Hosts and Routers (DSMIPv6)", draft-ietf-mip6-nemo-v4traversal-06 (work in progress), November 2007. [21] Wakikawa, R., Devarapalli, V., Ernst, T., and K. Nagami, "Multiple Care-of Addresses Registration", draft-ietf-monami6-multiplecoa-09 (work in progress), August 2008. [22] Muhanna, A., Khalil, M., Gundavelli, S., Chowdhury, K., and P. Yegani, "Binding Revocation for IPv6 Mobility", draft-ietf-mext-binding-revocation-01 (work in progress), August 2008. [23] Haley, B. and S. Gundavelli, "Mobile IPv6 Generic Signaling Message", draft-ietf-mext-generic-signaling-message-00 (work in progress), August 2008. Qiu, et al. Expires May 7, 2009 [Page 51] Internet-Draft MIP6 location privacy solutions November 2008 Appendix A. Profiling Attack: Discussion Profiling attacks pose a significant threat to user privacy. By collecting and analyzing (either online or offline) IP traffic, attackers can obtain sensitive user information. In the context of mobility, although the profiling attack does not directly lead to compromise of location privacy in the way the disclosure of the binding between the home address and the care-of address does, attackers can infer the mobile node's roaming and track its movement (i.e., handover) by profiling the mobile node's communication based on certain fields in IP packets, such as a constant IPsec SPI used during the home registration. The more information collected, the higher probability location privacy is compromised, which in return results in more targeted profiling. We have taken the profiling problem into consideration When designing the solution to IP address location privacy; however, not all aspects of profiling attacks are addressed since the profiling problem spans multiple protocol layers. In the following, we provide a broad discussion on the profiling attack and protection mechanisms. Our discussion is organized based on how profiling attacks can be performed. Note that the following sections are not sorted based on any criteria or may not exhaustively list all the possible attack means (for example, profiling attacks based on upper layer payloads in data packets are not discussed). A.1. The Care-of Address Eavesdroppers on the MN-HA path and/or the MN-CN path can profile the mobile node's communication by collecting packets with the same care-of address. It is recommended that the mobile node periodically updates its care-of address by using DHCPv6 or IPv6 address privacy extension, even if it does not change its current attachment point. Furthermore, it is even better to change the network prefix of the care-of address periodically, since eavesdroppers may profile IP packets based on the common network prefix. Since the binding update procedure needs to be performed once the care-of address is changed, in order to reduce signaling overheads, the mobile node may choose to change its care-of address when the Binding Cache entry at the home agent or the correspondent node is about to expire. A.2. Profiling on the Encrypted Home Address Generated from either a real or pseudo home address, the encrypted home address can be dynamically updated, because a new key is generated when a new IPsec sequence number is used or a new round of Qiu, et al. Expires May 7, 2009 [Page 52] Internet-Draft MIP6 location privacy solutions November 2008 the return routability procedure is performed, which makes the encrypted home address look different in subsequent Binding Update and Acknowledgement messages. Nevertheless, the same encrypted home address is used in payload packets forwarded via the optimized route before the next round of the return routability procedure. Given the cost and overhead of updating the encrypted home address, the proposed location privacy solutions still provide a reasonable level of protection against such profiling attacks. A.3. The IPsec SPI Eavesdroppers on the MN-HA path can profile the mobile node's communication based on the SPI of an IPsec security association, e.g., that for protecting the home Binding Update and Acknowledgement message or for protecting bidirectional-tunneled payload packets. To resist this kind of the profiling attack, the IPsec SPI needs to be periodically updated. One way is that the mobile node and the home agent rekey the IPsec security association or perform re- authentication periodically. This may result in more signaling overhead. Another way is that the mobile node or the home agent generates a new SPI and then notifies each other by exchanging the Binding Update and Acknowledgement messages protected by an existing IPsec security association with a non-null encryption algorithm. In this way, the information of the new SPI is hidden from eavesdroppers. The new SPI MUST not conflict with other existing SPIs; and if the conflict is detected on one end point, another SPI MUST be generated and be synchronized with the other end point. The new SPI is applied to the next packet that needs to be protected by this IPsec security association. This solution requires close interaction between Mobile IP and IPsec, for example, when the home agent receives a new SPI suggested by the mobile node, it needs to change the corresponding SAD entry. A.4. The IPsec Sequence Number The IPsec sequence number is required to be larger than that in the previous valid IPsec packet if the anti-replay service is enabled. However, if the increment of such sequence number is fixed, for example, the IPsec sequence number is sequentially increased, it is possible for eavesdroppers to identify a sequence of IPsec packets that are from/to the same mobile node and to track activities of such mobile node. One possible solution is to randomize the increment of the IPsec sequence number on both end points (i.e., the mobile node and the home agent) of the IPsec security association. The algorithm to generate randomness is implementation specific, for example, it can be any random number generator, and independently chosen by each end point. Qiu, et al. Expires May 7, 2009 [Page 53] Internet-Draft MIP6 location privacy solutions November 2008 A.5. The Regular Interval of Signaling Messages As described in RFC 3775, certain signaling messages may be exchanged on the regular basis, for example, the correspondent registration needs to be performed every MAX_RR_BINDING_LIFETIME seconds and the home binding update procedure needs to be performed regularly, if the lifetime of the home Binding Cache entry is fixed. Such timing allows eavesdroppers to perform traffic analysis and correlate different messages. Due to background traffic and routing dynamics, the timing of messages observed by an eavesdropper at a certain vantage point may be irregular. Nevertheless, a better solution is to randomize the lifetime of the Binding Cache entry in the home agent and the correspondent node. A.6. The Sequence Number in the Binding Update Message RFC 3775 requires that the sequence number in the Binding Update message be larger than that in the previous valid Binding Update message for a particular mobile node. However, if the increment of the sequence number in the home or correspondent Binding Update message is fixed, for example, the sequence number is sequentially increased, it is possible for eavesdroppers on the MN-HA or MN-CN path to identify a sequence of Binding Update messages that are from the same mobile node and to track the movement of such mobile node. One possible solution is that the mobile node randomizes the increment of the sequence number used in subsequent Binding Update messages. The algorithm to generate randomness is implementation specific, for example, it can be any random number generator. Note that such algorithm is not needed when the sequence number is encrypted, for example, in the home Binding Update message protected by an IPsec tunnel mode security association. A.7. Multiple Concurrent Sessions It is possible for (colluded) eavesdroppers to correlate the mobile node's different sessions with the same or different correspondent nodes, for example, based on the same pseudo home address and/or the same care-of address. A possible solution is to use different pseudo home addresses and different care-of addresses in different sessions. Note that the mobile node may also use the same pseudo home address with different correspondent nodes, if such pseudo home address is masked by different privacy management keys generated during the return routability procedure with different correspondent nodes. Because in this way, the encrypted pseudo home addresses used with different correspondent nodes look different to eavesdroppers. Qiu, et al. Expires May 7, 2009 [Page 54] Internet-Draft MIP6 location privacy solutions November 2008 A.8. Summary As discussed above, there exist multiple means for eavesdroppers to correlate observed activities. For example, some IP fields, which contain certain constant values and remain unchanged for a long time, allow eavesdroppers to identify and link the mobile node's activities deterministicly; other means may be less reliable when used for traffic analysis and correlation, nevertheless, they provide additional hints to malicious attackers. The solution to the profiling attack is to update certain IP fields periodically. Generally, the more frequently, the higher probability that the profiling attack is resisted and also the higher the cost in terms of communication and processing overheads and complexity. As eavesdroppers can profile activities based on multiple fields, it may not be cost-effective to update some fields more frequently than others. Furthermore, it may reduce some overheads, if all the related IP fields are updated together with the same frequency. The profiling attack is a complicated issue. A complete solution would have to consider tradeoffs of many different factors, such as complexity, effectiveness and efficiency. Appendix B. Version History o v01 to v02 * Change the document structure. * Describe the process in detail how to derive a serials of secret keys. * New scheme to protect SPI profiling. * Use multi home link prefixes to generate pseudoHoA. * Propose two schemes of transferring the BU message to the HA in order to match the different protocols (RFC 3776 and IKEv2 in mobile IP). o v02 to v03 * Merger section 5.3.1.and 5.3.2 and a same BU process is employed to the correspondent node regardless initiator or responder. Qiu, et al. Expires May 7, 2009 [Page 55] Internet-Draft MIP6 location privacy solutions November 2008 * Introduce a term of identity address to ensure location privacy and communication session continuity o v03 to v04 * Describe and compare the modifications of processing bindings in more detail. * Reformat section 5.3. o v04 to v06 * Revise the algorithm proposed in section 4. * Update authors information. o v06 to v07 * Add traffic formats. * Update the section of IANA requirement. * Revise according to comments of reviewers Heejin and Vijay. o v07 to v08 * Re-edit section 1. * Update authors information. o v08 to v09 * Revise according to comments of reviewer Michael Welzl. o v09 to v10 * Re-organize and revise the document. Qiu, et al. Expires May 7, 2009 [Page 56] Internet-Draft MIP6 location privacy solutions November 2008 Authors' Addresses Ying Qiu Institute for Infocomm Research, Singapore 21 Heng Mui Keng Terrace Singapore 119613 Phone: +65-6874-6742 Email: qiuying@i2r.a-star.edu.sg Fan Zhao Marvell Semiconductor, Inc. 5488 Marvell Lane Santa Clara, CA 95054 US Email: fanzhao@marvell.com Rajeev Koodli Starent Networks, Corp. Email: rkoodli@starentnetworks.com Qiu, et al. Expires May 7, 2009 [Page 57] Internet-Draft MIP6 location privacy solutions November 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Qiu, et al. Expires May 7, 2009 [Page 58]