P2PSIP Working Group M. Matuszewski Internet-Draft J-E. Ekberg Intended status: Informational P. Laitinen Expires: January 10, 2008 Nokia July 9, 2007 Security requirements in P2PSIP draft-matuszewski-p2psip-security-requirements-01.txt 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 January 10, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Matuszewski, et al. Expires January 10, 2008 [Page 1] Internet-Draft Security requirements in P2PSIP July 2007 Abstract This document is an analysis of security threats in the Peer-to-Peer SIP reference model presented in the P2PSIP concepts and terminology for P2PSIP document [1]. Typical security ontology is used as classification for the threats. The main security requirements for the architecture and its components are also presented. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. A P2PSIP network entity . . . . . . . . . . . . . . . . . 4 2.3. A P2PSIP system . . . . . . . . . . . . . . . . . . . . . 4 3. Security threats . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Replay Attacks . . . . . . . . . . . . . . . . . . . . . . 6 3.2. Message Insertion, Modification, Deletion . . . . . . . . 6 3.3. Man-In-The-Middle . . . . . . . . . . . . . . . . . . . . 7 3.4. Offline Cryptographic Attacks . . . . . . . . . . . . . . 7 3.5. Unauthorized Usage . . . . . . . . . . . . . . . . . . . . 7 3.6. Inappropriate Usage . . . . . . . . . . . . . . . . . . . 8 3.7. Denial of Service . . . . . . . . . . . . . . . . . . . . 8 3.8. Communication security threats . . . . . . . . . . . . . . 9 4. Security requirements . . . . . . . . . . . . . . . . . . . . 10 4.1. User requirements . . . . . . . . . . . . . . . . . . . . 10 4.2. System requirements . . . . . . . . . . . . . . . . . . . 10 4.2.1. Dependence of reachability of a centralized server . . 10 4.2.2. Scalability . . . . . . . . . . . . . . . . . . . . . 10 4.2.3. Preference of existing security mechanisms . . . . . . 11 4.2.4. Requirements on a base P2P algorithm . . . . . . . . . 11 4.2.5. Node and user identification . . . . . . . . . . . . . 11 4.2.6. Enrollment . . . . . . . . . . . . . . . . . . . . . . 11 4.2.7. Replay attacks . . . . . . . . . . . . . . . . . . . . 12 4.2.8. Data access . . . . . . . . . . . . . . . . . . . . . 12 4.2.9. Data validation . . . . . . . . . . . . . . . . . . . 13 4.2.10. Denial of Service (DOS) attacks . . . . . . . . . . . 13 4.2.11. Privacy . . . . . . . . . . . . . . . . . . . . . . . 13 4.2.12. Detection and rejection of badly behaving nodes . . . 13 4.2.13. Summary of the system requirements . . . . . . . . . . 14 5. Security Considerations . . . . . . . . . . . . . . . . . . . 16 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 7. Normative References . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 Intellectual Property and Copyright Statements . . . . . . . . . . 20 Matuszewski, et al. Expires January 10, 2008 [Page 2] Internet-Draft Security requirements in P2PSIP July 2007 1. Introduction The scope of this document is to analyse security threats concerning a P2PSIP overlay architecture as described in the concepts and terminology for Peer-to-Peer SIP (P2PSIP) document [1] and list security requirements for the architecture and its components. This document does not intend to propose solutions to overcome security threats, but it is more intended to list the security requirements that must be addressed in forthcoming P2PSIP specifications. This document complements the P2PSIP protocol framework and requirements document [3]. Matuszewski, et al. Expires January 10, 2008 [Page 3] Internet-Draft Security requirements in P2PSIP July 2007 2. Definitions This section defines a number of concepts that are key to understand the rest of the document. 2.1. General The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [2]. 2.2. A P2PSIP network entity A P2PSIP network entity is a user, peer, client, or other operative function or node that may become a part of a P2PSIP overlay. 2.3. A P2PSIP system A P2PSIP system consists of a P2PSIP overlay as defined in [1] and one or more enrolment servers that issues unique identities and credentials that are used to authenticate and admit a P2PSIP network entity to the overlay and may provide an initial set of bootstrap nodes. Matuszewski, et al. Expires January 10, 2008 [Page 4] Internet-Draft Security requirements in P2PSIP July 2007 --->PSTN +------+ N +------+ +---------+ / | | A | | | Gateway |-/ | UA |####T#####| UA |#####| Peer |####### | Peer | N | Peer | | G | # P2PSIP | E | A | F | +---------+ # Client | | T | | # Protocol +------+ N +------+ # | # A # | NATNATNATNAT # | # # | \__/ NATNATNATNAT +-------+ v / \ # N | |=====/ UA \ +------+ A P2PSIP Overlay | | /Client\ | | T | Peer | |___C__| | UA | N Route Data | Q | ^ | Peer | A +-------+ | | D | T P2PSIP Peer Protocol # | | | N # | +------+ A # | # T # Enrolment | # N +-------+ +-------+ # protocol->| # A | | | | # | | #########T####| Proxy |########| Redir |###### v | N | Peer | | Peer |<----------\ | A | P | | R | v v T +-------+ +-------+ +-----------+ # Enrolment # # Server # \__/ <------------------------------> # # /\ +-----------+ / \ / UA \ /______\ SIP UA A A P2PSIP system Matuszewski, et al. Expires January 10, 2008 [Page 5] Internet-Draft Security requirements in P2PSIP July 2007 3. Security threats This section analyses security threats in the Peer-to-Peer SIP reference model. 3.1. Replay Attacks Replay attacks are a form of network attacks where a valid data transmission is repeated or delayed. A badly behaving node may take an older message sent by another node, resend it to the overlay, and thus replace any newer data with the old information present in this message. During those procedures, an attacker may be able to enroll credentials for himself, or replace existing entry in the P2PSIP overlay by an older entry. Thus, the architecture must consider this issue in the process of both enrollment and modification of P2PSIP resource (user) records in a P2PSIP overlay. 3.2. Message Insertion, Modification, Deletion The message insertion, modification, and deletion attacks are where an attacker is able to alter the messages being exchanged between two end points. A badly behaving node may: o change the data record in the overlay by changing incoming message, o discard query messages by discarding incoming messages, o generate incorrect responses to requests received from a legimite node that are directed to some other nodes. For example, the attack described in the last bullet above may lead to a lookup process being redirected to a malicious node or a requestor receiving corrupted data pointing to some other node. This would cause the overlay to contain unauthorized or outdated information about a resource or corrupted data being returned to the requestor. With these types of attacks the integrity of the P2PSIP system becomes compromised. This includes both the enrollment procedure and data stored in the P2PSIP overlay. This means that an attacker not only can prevent access to P2PSIP resource (user) records, but can also degradate the performance of the P2PSIP system making it useless from the end-user perspective. The second problem is of high importance in P2PSIP overlays that store user's reachability data which is much more time-critical than content stored in file sharing networks. Matuszewski, et al. Expires January 10, 2008 [Page 6] Internet-Draft Security requirements in P2PSIP July 2007 3.3. Man-In-The-Middle Man-in-the middle (m-i-m) attacks are prevalent in pairing and authentication procedures. Thus, the architecture must consider this issue in the process of enrollment, as well as during modification of P2PSIP resource (user) records in a P2PSIP overlay. During communication m-i-m attacks may lead to data leakage and modification. A badly behaving node can hijack a connection established between two legimite nodes, or just listen and/or modify messages exchanged between two nodes (as described in sections 3.1 and 3.2). For example an attacker may place two malicious nodes in the overlay. One of the nodes would redirect/proxy queries to the second malicious node that would appear as a target node. The issue is prevailing in a deployment scenario where some peers act as SIP registrars or/and SIP proxies that allow a conventional SIP UA to access resources of the overlay. In a distributed environment such as the P2PSIP overlay it is very difficult to trust all of peers in the overlay. An unmodified SIP UA sends an SIP Invite request towards an unknown peer that acts as a SIP proxy. If the SIP messages are not cryptographically protected, this peer may act maliciously and proxy a request to other than intended node or modify SDP messages in order to stay on the media path. Similarly a peer that acts as SIP Registrar may modify registration information before it sends it to a peer that is responsible for storing the P2PSIP user record of a registering SIP UA. In a similar way if a bootstrap process is fully decentralised and a bootstrap node is not trusted or authentication of the bootstrap node is not possible, then the joining node can easily be attacked, e.g. it may be redirected to another overlay controlled by the attacker. However, by using well-established authentication protocols, the m-i-m threat can be mitigated. 3.4. Offline Cryptographic Attacks The incentive to break a secure system dominates the effort to do so. It is likely that P2PSIP systems do not pose a likely target for attacks, and if state-of-the art security methods are used, the needed effort to break the system by breaking cryptography is very likely to be higher than by finding and exploiting software errors and vulnerabilities. 3.5. Unauthorized Usage The basic notions of authentication and authorization, when implemented correctly and consistently SHOULD protect against Matuszewski, et al. Expires January 10, 2008 [Page 7] Internet-Draft Security requirements in P2PSIP July 2007 unauthorized usage of the P2PSIP system. However, the trustworthiness of an identity may be weak i.e. the enrollment system might be fairly open and allow devices and persons that wish to attack the system. Thus, there is a significant threat of attacks from within the system. A peer may do a multitude of attacks towards the overlay including: o ignoring, changing, and deleting records in DHT that is it responsible for, o misbehaving during data lookups (ie, giving wrong node addresses, discarding queries) These attacks would cause DHT to contain unauthorized, outdated, and/or missing information about a resource as well as might cause lookups to fail. 3.6. Inappropriate Usage As the lookup and routing in the P2PSIP essentially provides a distributed storage for P2PSIP resource (user) records, this can be used in an inappropriate manner. If there is no access control to a resources stored in the overlay and any node can retrieve information stored in the overlay, an attacker may request data stored in the the P2PSIP resource (user) records and perform inappropriate usage attacks. Definitely the individual services provided by P2PSIP (messaging, real-time communication) have their respective threat models regarding inappropriate use (Spam, viruses, ...) but these can be considered out of scope for this document. 3.7. Denial of Service In the proposed P2PSIP architecture, the P2PSIP resource (user) records are not maintained in a central, trustworthy storage system, rather it is distributed among peers participating in the system. This implies that the presence of malicious peers can be considered to be probable rather than possible. In cases where authentication in the overlay is weak or where the system is fairly open to new participants the "infiltration" is trivial (e.g., Sybil attack). If nodes in the overlay can freely choose peer IDs and easily modify previously selected peer IDs the attacker may use join-leave attacks to place a malicious peer intentionally at any location in overlay and obtain control of the location in the overlay where the attacked user or resource (e.g. TURN@overlay.net) is registered. A malicious peer may discard, modify the data it is supposed to store and may discard lookup requests or reply with incorrect entries to the Matuszewski, et al. Expires January 10, 2008 [Page 8] Internet-Draft Security requirements in P2PSIP July 2007 incoming requests. However, DHTs typically distribute the the P2PSIP resource (user) records among its nodes in a fashion where the outcome (the storage node) is hard to predict and also copying of the P2PSIP resource (user) records to several nodes for increased robustness is the norm. Thus the infiltration, if done in a trivial manner, typically must be done with a fairly big number of nodes to achieve a probability of success in bringing down the system or at least denying service regarding selected peers and clients. The attacker may also try to register large number of resources to the P2PSIP overlay increasing processing load on the nodes that are responsible for storing the resources and limiting the overall capacity of the P2PSIP overlay network. It may also try to register all popular names preventing the name holders from registering their prefered URIs. Another critical point where a D-o-S attack can be mounted is the enrollment system. This is probably quite monolithic, and typical "network" D-o-S attacks (like SYN flooding) are probably possible in this domain. 3.8. Communication security threats This document assumes that the actual SIP service implementation provides its own communication security, and that P2PSIP adds to that only in providing a means for the communication endpoints to establish a shared key for further security needs. Otherwise, the communication security threats in that domain is out-of-scope for this discussion. As the intention is to modify the base P2P algorithm (e.g., DHT implementations) as little as possible, it can be assumed that the "storage facility and its communication" i.e. the DHT is unprotected. Instead, data stored there is protected independently of communication and where it is stored. The main places where communication security becomes an issue in the P2PSIP context is the enrollment process (where the actual communication mechanism may be out of scope) and the communication between a client and the corresponding peer or between peers. The last ones are subject to all typical threats in this domain, however they have been individually considered in the earlier sections of this chapter. Matuszewski, et al. Expires January 10, 2008 [Page 9] Internet-Draft Security requirements in P2PSIP July 2007 4. Security requirements This section describes requirements related to the security of a P2PSIP system. We divided the requirements into user requirements and system requirements. 4.1. User requirements The user wants available and reliable service that enables him to interact with other users and resources in a secure way. This means that the P2PSIP system MUST provide: o lookup and discovery of users and resources that is secure and reliable, o certainty of user and resource identity, o confidentiality and integrity of end-to-end multimedia communication, o easy and secure enrolment to the P2PSIP system, o privacy. 4.2. System requirements In order for a P2PSIP system to function properly and that the end user gets a proper service, there are several aspects that the P2PSIP system must take in to account. 4.2.1. Dependence of reachability of a centralized server Considering the nature of P2P in general, the dependence of reachability of a centralized server should be minimized. There may be unavoidable situations such as the enrollment process, where this is not possible. However, the normal functioning of connecting to as well as inserting, modifying, retrieving, and deleting of P2PSIP resource (user) records from the P2PSIP system should not depend on the reachability of a centralised server. 4.2.2. Scalability P2PSIP security should scale from a small ad-hoc network to a network with hundred millions of network nodes and users. Matuszewski, et al. Expires January 10, 2008 [Page 10] Internet-Draft Security requirements in P2PSIP July 2007 4.2.3. Preference of existing security mechanisms Although P2PSIP defines a new architecture, and thereby new interfaces and protocols, for security there are several standardized solutions for access control and communication security. Using established protocols minimizes potential security loopholes that need to be patched later, and implementation is eased if chosen security protocols already are widely implemented and used. 4.2.4. Requirements on a base P2P algorithm All of security operations should be specified in such a way that they do not impose new unnecessary requirements on a base P2P algorithm (e.g., DHT implementations) and limit its scalability. 4.2.5. Node and user identification The P2PSIP system must preserve user and resource identities. It must not be possible to steal a P2PSIP identity from another user. In order to prevent so-called Sybil attacks the attacker should not be able to easily register a unlimited number of IDs of his choice in the P2SIP overlay. The P2PSIP system should be able to control ID assignment. Once assigned, an ID or a set of IDs should be difficult to change. Because some attackers may try to use identities of another P2PSIP network entities it must be possible to verify the identity of another party. 4.2.6. Enrollment The ease for users to enroll to a P2PSIP system should be ensured as said in the section 4.1. The enrollment process defines the set of users and P2PSIP network entities that may participate in a P2PSIP system and issues them credentials. This process is defined by the P2PSIP system, and the policy who can participate to is done during this process. The enrolment process policy may define: o how many and what user IDs and peer IDs an user or a network node may register, o whether users are charged for the usage of the P2PSIP system, o and how often they must re-new their subscription to the P2PSIP system. As it was indicated in [3] the enrollment process may take several Matuszewski, et al. Expires January 10, 2008 [Page 11] Internet-Draft Security requirements in P2PSIP July 2007 measures in admitting a user or a network node to the P2PSIP system, for example: o may require strong identity such as employment or provided by a trusted 3rd party or by the P2P operator, o may charge for the enrollment, o may apply reputation mechnisms. Although the user probably is the entity that enrolls to the P2PSIP system, the credentials that are the result of the enrollment are used to grant a device the right to function as a peer, client or any other operative function possible in the system. Thus the security of enrollment also translates to the security of the device itself where the credentials are stored, and threats related to device security in general. OPEN ISSUES: Who enrols to the P2PSIP system only a user or also peers? Do we need separate credentials for peers and users? What happens if a user is an owner of two or more nodes e.g. two peer nodes or two clients? Does each node requires a separate credential or only one credential is needed for all nodes that belong to a user? Can two devices be "logged on" at the same time? 4.2.7. Replay attacks An attacker should not be able to repeat or delay valid data transmission during enrollment and modification of P2PSIP resource (user) records in a P2PSIP overlay. 4.2.8. Data access An attacker should not be able to easily corrupt, delete, or overwrite data stored in P2PSIP resource (user) records as well as routing tables. Only authorized users should be able to modify, delete or overwrite their P2PSIP resource (user) records in the P2PSIP system. P2PSIP security should allow users and P2PSIP network entities to register the same resources (e.g. TURN@overlay.net), however each entity should have rights only to its own part of a resource record. In other words each entity should be able to perform the same operations on its own part of a resource record as in the case when a particular resurce belongs to only one user. The owner of the P2PSIP resource (user) records should be able to authorize other users and network entities to modify, delete their P2PSIP resource (user) records. Matuszewski, et al. Expires January 10, 2008 [Page 12] Internet-Draft Security requirements in P2PSIP July 2007 4.2.9. Data validation First and foremost it should be possible to verify that the data stored in or retrieved from the P2PSIP overlay is authentic, i.e. was not tampered by unauthorized P2PSIP network entities. The peer that stores a P2PSIP resource (user) records should be able to validate the data received in the process of P2PSIP resource (user) record insertion and modification. 4.2.10. Denial of Service (DOS) attacks It should not be possible to obtain control of the location in the overlay where the attacked user or resource is registered. The P2PSIP architecture should make sure that data stored in a P2PSIP overlay is persistent, meaning that even if a number of nodes (but not all of nodes in the overlay) fails the data stored by those nodes should not be lost. In addition the attacker should not be able to register unlimited number of resources in the overlay. 4.2.11. Privacy The security of P2PSIP systems must guarantee privacy of the P2PSIP network participants. The P2PSIP security should make an option for the users to indicate which other P2PSIP network entities can retrieve data stored in their P2PSIP resource (user) records. This means that the owner of a P2PSIP resource (user) record or an authorised P2PSIP network entity should be able to limit the access to his own records, and this feature should be enforced by the P2P network. It should also be difficult to monitor who is communicating with a particular user, or retreieve any contextual data about the user without the user's explicit consent. The P2PSIP network entities should be provided with option to encrypt data exchanged with other P2PSIP network entities. 4.2.12. Detection and rejection of badly behaving nodes It should be possible to limit potential damage caused by malfunctioning and badly behaving nodes in a P2PSIP system. As the policy taken by the P2PSIP system operator/community may be very liberal, any user can obtain the right to be a user of a P2PSIP system. It may be that some users behave badly intentionally in which case it should be possible limit the impact of the badly behaving nodes on the overall system security. It should be possible to identify badly behaving nodes, and exclude or reject them from the P2PSIP system. Matuszewski, et al. Expires January 10, 2008 [Page 13] Internet-Draft Security requirements in P2PSIP July 2007 4.2.13. Summary of the system requirements P2PSIP system requirements related to security issues are summarized below: Req. 1: Dependence of reachability of a centralized server SHOULD be minimized. Req. 2: P2PSIP security SHOULD scale from a small ad-hoc network to a network with hundred millions of network nodes and users. Req. 3: Existing security mechanisms SHOULD be used as much as possible to protect P2PSIP functions, and avoid the need for standardizing new mechanisms. Req. 4: Security requirements on the base P2P algorithm (e.g., DHT implementations) used in P2PSIP SHOULD be minimized and SHOULD NOT limit its scalability. Req. 5: An enrollment process MUST be secured. Req. 6: The registered identities in a P2PSIP overlay MUST be preserved. The attacker should not be able to steal identity from another user. Req. 7: The enrollment process SHOULD make it difficult for an attacker to register many identites in a P2PSIP overlay and easily modify the registered identities. Req. 8: It should be difficult to select a particular peer ID e.g. peer ID assignment process SHOULD introduce some degree of randomness to peer identites. Req. 9: It MUST be possible to authenticate P2PSIP network entities. Req. 10: It MUST NOT be possible to repeat or delay valid data transmission during enrollment and modification of P2PSIP resource (user) records. Req. 11: The P2PSIP security MUST support integrity protection of the data being inserted or retrieved to/from an overlay. Req. 12: The P2PSIP network entities MUST be provided with an option to encrypt data exchanged with other P2PSIP network entities. Req. 13: Only authorized users and P2PSIP network entities MUST be able to join the P2PSIP system and insert, modify, delete or overwrite P2PSIP resource (user) records in the P2PSIP system. Matuszewski, et al. Expires January 10, 2008 [Page 14] Internet-Draft Security requirements in P2PSIP July 2007 Req. 14: If many users or P2PSIP network entities register the same resource in the P2PSIP overlay, each entity MUST have only rights to its own part of a resource record. Req. 15: An owner of P2PSIP resource (user) record MAY indicate which users or network entities can retrieve, modify, and delete data stored in their P2PSIP resource (user) records. P2PSIP peer SHOULD support access control set by the owner of P2PSIP resource (user) record. Req. 16: P2PSIP overlay protocols MUST be designed such a way so that the effect of DOS attacks on the P2PSIP overlay are being minimized. Req. 17: It SHOULD be possible to limit the impact of the badly behaving P2PSIP nodes on the overall system security. There SHOULD be an option to identify malfunctioning or badly behaving nodes, and exclude or reject them from the P2PSIP system. Matuszewski, et al. Expires January 10, 2008 [Page 15] Internet-Draft Security requirements in P2PSIP July 2007 5. Security Considerations This memo discusses security threats in P2PSIP overlay networks. Security aspects are discussed throughout the document. However, this document does not introduce any security risk by itself. Matuszewski, et al. Expires January 10, 2008 [Page 16] Internet-Draft Security requirements in P2PSIP July 2007 6. IANA Considerations There are no IANA considerations associated to this memo. Matuszewski, et al. Expires January 10, 2008 [Page 17] Internet-Draft Security requirements in P2PSIP July 2007 7. Normative References [1] Bryan, D., Matthews, P., Shim, P., and D. Willis, "Concepts and Terminology for Peer to Peer SIP", draft-willis-p2psip-concepts-04.txt (work in progress), April 2007. [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [3] Bryan, D., Baset, S., Matuszewski, M., and H. Sinnreich, "P2PSIP Protocol Framework and Requirements", draft-bryan-p2psip-requirements-00.txt (work in progress), July 2007. [4] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. Matuszewski, et al. Expires January 10, 2008 [Page 18] Internet-Draft Security requirements in P2PSIP July 2007 Authors' Addresses Marcin Matuszewski Nokia P.O.Box 407 NOKIA GROUP, FIN 00045 Finland Email: marcin.matuszewski@nokia.com Jan-Erik Ekberg Nokia P.O.Box 407 NOKIA GROUP, FIN 00045 Finland Email: jan-erik.ekberg@nokia.com Pekka Laitinen Nokia P.O.Box 407 NOKIA GROUP, FIN 00045 Finland Email: pekka.laitinen@nokia.com Matuszewski, et al. Expires January 10, 2008 [Page 19] Internet-Draft Security requirements in P2PSIP July 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). 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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. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Matuszewski, et al. Expires January 10, 2008 [Page 20]