SIPPING K. Ono Internet-Draft S. Tachimoto Expires: November 9, 2004 NTT Corporation May 11, 2004 Requirements for End-to-Middle Security for the Session Initiation Protocol (SIP) draft-ietf-sipping-e2m-sec-reqs-02 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 November 9, 2004. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract A SIP User Agent (UA) does not always trust all intermediaries in its request path to inspect its message bodies and/or headers contained in its message. The UA might want to protect the message bodies and/ or headers from intermediaries except those that provide services based on its content. This situation requires a mechanism called "end-to-middle security" to secure information passed between the UA and intermediaries, which does not interfere with end-to-end security. This document defines a set of requirements for a mechanism to achieve end-to-middle security. Conventions used in this document Ono & Tachimoto Expires November 9, 2004 [Page 1] Internet-Draft End-to-Middle Security Requirements May 2004 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 [1]. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1 Examples of Models . . . . . . . . . . . . . . . . . . . . . 3 2.2 Service Examples . . . . . . . . . . . . . . . . . . . . . . 5 2.2.1 Logging Services for Instant Messages . . . . . . . . . . . 5 2.2.2 Non-emergency Call Routing Based on the Location Object . . 5 2.2.3 User Authentication . . . . . . . . . . . . . . . . . . . . 6 2.2.4 SDP-based Services . . . . . . . . . . . . . . . . . . . . . 6 3. Scope of End-to-Middle Security . . . . . . . . . . . . . . 7 4. Requirements for a Solution . . . . . . . . . . . . . . . . 9 4.1 General Requirements . . . . . . . . . . . . . . . . . . . . 9 4.2 Requirements for End-to-Middle Confidentiality . . . . . . . 10 4.3 Requirements for End-to-Middle Integrity . . . . . . . . . . 11 5. Security Considerations . . . . . . . . . . . . . . . . . . 12 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . 12 7. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . 12 7.1 Changes from 01.txt . . . . . . . . . . . . . . . . . . . . 12 7.2 Changes from 00.txt . . . . . . . . . . . . . . . . . . . . 13 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 13 References . . . . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . 16 Ono & Tachimoto Expires November 9, 2004 [Page 2] Internet-Draft End-to-Middle Security Requirements May 2004 1. Introduction The Session Initiation Protocol (SIP) [2] supports hop-by-hop security using Transport Layer Security (TLS) [3] and end-to-end security using Secure MIME (S/MIME) [4]. These security mechanisms assume that a SIP UA trusts all proxy servers along its request path to inspect the message bodies contained in the message, or a SIP UA does not trust any proxy servers to do so. However, there is a model where trusted and partially-trusted proxy servers are mixed along a message path. The partially-trusted proxy servers are only trusted to provide SIP routing, but these proxy servers are not trusted by users to inspect its data except routing headers. A hop-by-hop confidentiality service using TLS is not suitable for this model. An end-to-end confidentiality service using S/MIME is also not suitable when the intermediaries provide services based on reading the message bodies and/or headers. This problem is described in Section 23 of [2]. In some cases, a UA might want to protect its message bodies and/or headers from proxy servers along its request path except from those that provides services based on reading its message bodies and/or headers. Conversely, a proxy server might want to view the message bodies and/or headers to sufficiently provide these services. Such proxy servers are not always the first hop from the UA. This situation requires a security mechanism to secure message bodies and/ or headers between the UA and the proxy servers, yet disclosing information to those that need it. We call this "end-to-middle security". 2. Use Cases 2.1 Examples of Models We describe here examples of models in which trusted and partially-trusted proxy servers both exist in a message path. These situations demonstrate the reasons why end-to-middle security is required. In the following example, User #1 does not know the security policies or services provided by Proxy server #1 (Proxy#1). User #1 sends a MESSAGE [5] request including S/MIME-encrypted message content for end-to-end security as shown in Figure 1. Proxy #1 erases the encrypted data in the request based on its strict security policy that prohibits the forwarding of unknown data. Or Proxy #1 rejects the request because it cannot offer a message logging service. For the MESSAGE request to correctly traverse Proxy #1, the UA will need to discover if end-to-end confidentiality will conflict with Ono & Tachimoto Expires November 9, 2004 [Page 3] Internet-Draft End-to-Middle Security Requirements May 2004 intermediary's services or security policies. Home network +---------------------+ | +-----+ +-----+ | +-----+ +-----+ User #1-----| | C |-----| * |-----| * |-----| C |-----User #2 | +-----+ +-----+ | +-----+ +-----+ | UA #1 Proxy #1 | Proxy #2 UA #2 +---------------------+ C: Content that UA #1 allows the entity to inspect *: Content that UA #1 prevents the entity from inspecting Figure 1: Deployment example #1 In the second example, Proxy server #1 is the home proxy server of User #1 using UA #1. User #1 communicates with User #2 through Proxy #1 and Proxy #2 as shown in Figure 2. Although User #1 already knows Proxy #1's security policy that requires the inspection of message contents in the MESSAGE request, User #1 does not know whether Proxy #2 is trustworthy, and thus wants to protect the message bodies in the request. UA #1 will need to be able to grant a trusted intermediary (Proxy #1) to inspect message bodies while preserving their confidentiality from other intermediaries (Proxy #2). Even if UA #1's request message authorizes a selected proxy server (Proxy #1) to inspect the message bodies, UA #1 is unable to authorize the same proxy server to inspect the message bodies in subsequent MESSAGE requests or the response from UA #2. Home network +---------------------+ | +-----+ +-----+ | +-----+ +-----+ User #1-----| | C |-----| C |-----| * |-----| C |----- User #2 | +-----+ +-----+ | +-----+ +-----+ | UA #1 Proxy #1 | Proxy #2 UA #2 +---------------------+ C: Content that UA #1 needs to disclose *: Content that UA #1 needs to protect Figure 2: Deployment example #2 In the third example, User #1 connects UA #1 to a proxy server in a visited (potentially insecure) network, e.g., a hotspot service or a roaming service. Since User #1 wants to utilize certain home network services, UA #1 connects to a home proxy server, Proxy #1. However, UA #1 must connect to Proxy #1 via the proxy server of the visited Ono & Tachimoto Expires November 9, 2004 [Page 4] Internet-Draft End-to-Middle Security Requirements May 2004 network (Proxy A), because User #1 must follow the policy of that network. Proxy A performs access control based on the destination addresses of calls. User #1 only trusts Proxy A to route requests, not to inspect the message bodies the requests contain as shown in Figure 3. User #1 trusts Proxy #1 both to route requests and to inspect the message bodies for some purpose. The same problems as in the second example also exist here. Visited network +---------------------+ | +-----+ +-----+ | +-----+ +-----+ +-----+ User #1 -- | | C |-----| * |-----| C |-----| * |-----| C | | +-----+ +-----+ | +-----+ +-----+ +-----+ | UA #1 Proxy A | Proxy #1 Proxy #2 UA #2 +---------------------+ C: Content that UA #1 needs to disclose *: Content that UA #1 needs to protect Figure 3: Deployment example #3 2.2 Service Examples We describe here several services that require end-to-middle security. 2.2.1 Logging Services for Instant Messages Logging Services is provided by the archiving function, which is located in the proxy server, that logs the message content exchanged between UAs. When instant message content contains private information, UACs (User Agent Clients) encrypt the message content for the UASs (User Agent Servers). Archiving function needs a way to log the content in a message body in bidirectional MESSAGE requests with decipherable conditions. The archiving function needs a way to verify the data integrity of the content before logging. The archiving function could be located at the originator network and/or the destination network. This service might be deployed for financial or health care applications, where archiving communication is required by policies, as well as other applications. 2.2.2 Non-emergency Call Routing Based on the Location Object The Location Object [6] includes private information as well as Ono & Tachimoto Expires November 9, 2004 [Page 5] Internet-Draft End-to-Middle Security Requirements May 2004 routing information for some proxy servers. Special proxy servers have the capability of location-based routing. When UAs want to employ location-based routing in non-emergency situations, the UAs need to connect with the proxy servers that have such a capability and disclose the content in the message body of the INVITE request that contains the Location Object. However, the Location Object needs to be protected from other proxy servers through the request path. The Location Object needs to be verified the integrity before location-based routing. Sometimes, if the UAC desires it, the Location Object needs to be transmitted to the UASs. 2.2.3 User Authentication 2.2.3.1 User Authentication using the AIBs The Authenticated Identity Bodies (AIBs) [7] is a digitally-signed data that is used as way to identify users. Proxy servers that need to authenticate a user verify the signature. When the originator needs anonymity, the user identity in the AIB is encrypted before being signed. Proxy servers that authenticate the user need to decrypt the body in order to view the user identity in the AIB. Such proxy servers can be located at adjacent and/or non-adjacent to the UA. The AIB could be included in all request/response messages. The proxy server needs to view it in request messages in order to authenticate users. Another proxy server sometimes needs to view it in response messages for user authentication. 2.2.3.2 User Authentication in HTTP Digest Authentication User authentication data for HTTP digest authentication includes two types of information. One is potentially private information, such as a user name, and another is information that can be used for "replay-attacks", such as the "response" parameter that is created by a calculation using a user's password. The user authentication data can be set in request messages, but not in response messages. This information needs to be transmitted securely to servers that authenticate users, located either at adjacent and/or non-adjacent to the UA. 2.2.4 SDP-based Services The following example are services based on the Session Description Protocol (SDP). After a session policy [8] mechanism establised, these services would employ other header field instead of the SDP. Note: The SIPPING WG is discussing these services as use cases of Ono & Tachimoto Expires November 9, 2004 [Page 6] Internet-Draft End-to-Middle Security Requirements May 2004 session policy. The session policy mechanism extracts information from the SDP that is to be viewed by proxy servers. With this mechanism, proxy servers need to view a new SIP header field instead of the SDP in a message body. However, the extracted information still includes the address and port information, that needs to be protected as well as the SDP. 2.2.4.1 Firewall Traversal A firewall entity that supports the SIP protocol, or a midcom [9] agent co-located with a proxy server, controls a firewall based on certain SDP attributes in the SDP offer/answer. The SDP includes the address and port information for media streams and/or key parameters of Secure RTP[10]. This requires UAs to encrypt the SDP for recipient UAs when needed. If the SDP is encrypted for end-to-end confidentiality, the proxy server operating as a midcom agent will have no way to provide firewall traversal as it can not inspect the SDP. Therefore, the proxy server needs to be able to decrypt the SDP. Also, the proxy server needs to verify the integrity of the SDP. The firewall entities could be located at the originator network and/or destination network. 2.2.4.2 SDP-based Call Admission Control (CAC) The SDP includes bandwidth information that is expected to be used for Call Admission Control (CAC). The SDP also includes the port information for media streams and/or key parameters of Secure RTP. This requires UAs to encrypt the SDP for recipient UAs when needed. On the other hand, a CAC function, which is located in a proxy server, needs to view the SDP offer/answer in INVITE/200 messages and/or UPDATE/200 messages. The 183 response could be used instead of INVITE-200 response. Note: Although the SDP offer/answer can be sent in the 200/ACK messages, it is too late to view the SDP for the first time in the 200 response for admission to create the call. If the CAC function found that the call is not acceptable and forced the disconnection of the call, it would cause a "ghost ring". 3. Scope of End-to-Middle Security End-to-middle security consists of user authentication, data integrity, and data confidentiality. The above examples mainly require data confidentiality of end-to-middle security. Proxy servers usually need to authenticate a user that sends a Ono & Tachimoto Expires November 9, 2004 [Page 7] Internet-Draft End-to-Middle Security Requirements May 2004 request message. HTTP digest authentication described in [2] can be used for user-to-proxy authentication of the request messages. With sending the "challenge" parameter, proxy servers can ask for UAs to send the "response" parameter for the authentication. The authenticating proxy is not limited to the first hop for the UA. Thus, HTTP digest authentication can be used for end-to-middle security. To avoid replay attacks, the HTTP digest authentication needs to be used with a security mechanism that contains confidentiality. Additionally, a digital signature obtained from a Public Key Infrastructure, S/MIME Cryptographic Message Syntax (CMS) SignedData body [11] and a digital signature within an AIB can be used for the authentication. Since these mechanisms achieve authentication for end-to-middle security, the requirements are not discussed in this document. Note: An encrypted identity in the AIB for anonymity cannot be directly used for user-to-proxy authentication, that is, end-to-middle authentication. With end-to-middle confidentiality, the AIB for anonymity can be used for end-to-middle authentication. Therefore, the AIB for anonymity is included in end-to-middle confidentiality. As for data integrity, proxy servers require validation of the content to be used for providing some services. The CMS SignedData body might be used as a mechanism for end-to-middle security. The CMS SignedData body can be created with the original data and the originator's private key, and anyone can verify the data integrity by using the originator's public key and the certificate. That is, proxy servers can verify the data integrity whenever they require. Thus, the CMS SignedData body could be used to implement end-to-middle security at the same time it is used for end-to-end security. Currently, there is no way for UAs to request a selected proxy server to verify a message with the CMS SignedData body. Some new mechanisms are needed to achieve data integrity for end-to-middle security. Note: If a malicious proxy server modifies the SignedData body, end-to-end integrity would collapse. If a malicious proxy server strips off the signature with the MIME headers of the multipart MIME, end-to-end integrity would also collapse. In this case, a recipient UA has no way to verify the data integrity. This document mainly discusses requirements for data confidentiality and the integrity of end-to-middle security. Proposed mechanisms are discussed in [12]. Ono & Tachimoto Expires November 9, 2004 [Page 8] Internet-Draft End-to-Middle Security Requirements May 2004 4. Requirements for a Solution We describe here requirements for a solution. The requirements are mainly applied during the phase of a dialog creation or sending a MESSAGE method. 4.1 General Requirements The following are general requirements for end-to-middle confidentiality and integrity. REQ-GEN-1: The solution SHOULD have little impact on the way a UA handles messages with S/MIME bodies. REQ-GEN-2: It SHOULD have no impact on proxy servers that do not provide services based on S/MIME bodies in terms of handling the existing SIP headers. REQ-GEN-3: It SHOULD have little impact on the standardized mechanism of proxy servers that provide services based on S/MIME bodies. A proxy server is prohibited to add/modify/delete a message body as described in [2]. A proxy server can view a message body following the standardized mechanism, although it is not desirable. When a proxy server receives an S/MIME message, it should be able to quickly and easily discover the necessity to investigate the S/MIME body. This can be restated as: + It SHOULD allow proxy servers to quickly and easily determine whether to handle S/MIME bodies and, if so, how and which ones. REQ-GEN-4: It SHOULD allow a proxy server to notify a UA about the proxy server's security policy for a request/response message, as well as what data is needed in order to provide a service. This requirement is necessary when the UA does not know in advance which proxy servers or domains need disclosing data and/or verification. Open Issue: Is it necessary for the proxy server to notify the UAS after receiving a response? Ono & Tachimoto Expires November 9, 2004 [Page 9] Internet-Draft End-to-Middle Security Requirements May 2004 4.2 Requirements for End-to-Middle Confidentiality REQ-CONF-1: The solution MUST be compatible with end-to-end encryption. The encrypted data can be shared with the end user and selected proxy servers, if needed. This requirement is necessary for logging service and the Location Object. REQ-CONF-2: It MUST NOT violate end-to-end encryption when the encrypted data does not need to be shared with any proxy servers. This requirement is necessary for SDP-based services. For example, keying materials for secure RTP (SRTP) in SDP [10] can be included only in the end-to-end encryption, if the UA's policy states as such. Open Issue: It sometimes occurs that a part of the SDP is for end-to-end encryption and another part is for end-to-middle encryption. Do we really need a new Content-Type such as "sdpfrag"? REQ-CONF-3: It SHOULD allow a UA to discover which proxy servers need to view data in a request/response message, as well as what data is needed. This requirement is necessary when the UA does not know which proxy servers or domains provide the data dependent services in advance. REQ-CONF-4: It SHOULD allow a UA to request selected proxy servers to view specific message bodies. The request itself SHOULD be secure. This requirement is necessary when the data-dependent service, such as logging service, the Location Object, or firewall traversal, is provided on demand of users. For example, the logging service could be provided on demand of users that needs to log some important messages. REQ-CONF-5: It SHOULD allow a UA to request that the recipient UA disclose information to the proxy server, that requesting UA is disclosing the information to. The request itself SHOULD be secure. This requirement is necessary for logging service for Ono & Tachimoto Expires November 9, 2004 [Page 10] Internet-Draft End-to-Middle Security Requirements May 2004 instant messages. Logging function sometimes requires to archive the bidirectional exchange of messages. It is not reasonable to expect that the recipient UA knows the public key certificate of the proxy server on the originating network. This can be restated as: + The solution SHOULD allow a UA to request the recipient UA to reuse a CEK in subsequent messages during a dialog. + It SHOULD allow a UA to request a selected proxy server to keep a CEK in a message during a dialog. The requests themselves SHOULD be secure. REQ-CONF-6: It MAY allow a UA to notify the recipient UA which proxy server needs to view data in a request/response in order to provide the services. REQ-CONF-7: It MAY allow a UA to notify the recipient UA what data the proxy server is permitted to view in a request/ response in order to provide the services. These last two requirements might be needed for firewall traversal when there is a firewall in the network connected to a UAS. A UAS needs to notify a UAC to disclose the SDP in an INVITE message to a proxy server that controls the firewall in the UAS network. Such notification might be applied in a registration phase. 4.3 Requirements for End-to-Middle Integrity REQ-INT-1: The solution SHOULD work even when the SIP end-to-end integrity service is enabled. This requirement is necessary for logging service, the Location Object, the AIB, and SDP-based services. REQ-INT-2: It SHOULD allow a UA to discover what data in a request/ response the proxy needs to verify in order to provide the service. This requirement is necessary when the UA does not know what data is used to provide the service in advance. Ono & Tachimoto Expires November 9, 2004 [Page 11] Internet-Draft End-to-Middle Security Requirements May 2004 REQ-INT-3: It SHOULD allow a UA to request selected proxy servers to verify specific message bodies. The request itself SHOULD be secure. This requirement is necessary when the data-dependent service, such as logging service, the Location Object, or firewall traversal, is provided on demand of users. For example, logging service could be provided on demand of users who needs to log some important messages. REQ-INT-4: It SHOULD allow a UA to request the recipient UA to send the verification data of the same information that the requesting UA is providing to the proxy server. The request itself SHOULD be secure. This requirement is necessary for logging service and the AIB. Logging service sometimes requires to archive the bidirectional exchange of messages. Mutual authentication of user-to-user requires to send a response with the AIB of the recipient UA. REQ-INT-5: It MAY allow a UA to notify the recipient UA what data the proxy server needs to verify in a request/response for the services. This requirements might be needed for firewall traversal when a firewall exists in the network connected to a UAS. A UAS needs to notify a UAC to disclose the SDP in an INVITE message to a proxy server that controls the firewall in the UAS network. Such notification might be applied in a registration phase. 5. Security Considerations This document presents confidentiality and integrity requirements in Section 3. We need to consider how to prevent Denial-of-Service (DoS) attacks on proxy servers. The end-to-middle security requires additional processes such as data decryption and/or signature verification to proxy servers. Enabling end-to-middle security in proxy servers will increase the likelihood that receiving many messages will slow down the overall performance of those proxy servers. To avoid this consequence, proxy servers SHOULD authenticate the originator of the message before starting the process. [To be done: add some more requirements for preventing DoS attack.] Ono & Tachimoto Expires November 9, 2004 [Page 12] Internet-Draft End-to-Middle Security Requirements May 2004 6. IANA Considerations This document requires no additional considerations. 7. Changes 7.1 Changes from 01.txt o Extracted use cases from the Introduction section, and created a new section to describe the use cases in more detail. The use cases are also updated. o Deleted a few "may" words from the "Problem with Existing Situations" section to avoid confusion with "MAY" as a key word. o Added the relation between the requirements and the service examples. o Deleted the redundant requirements for discovery of the targeted-middle. The requirement is described only in the "Generic Requirements", not in the "Requirements for End-to-Middle Confidentiality/Integrity". o Changed the 4th requirement of end-to-middle confidentiality from "MUST" to "SHOULD". o Changed the 3rd requirement of end-to-middle integrity from "MUST" to "SHOULD". o Added some text about DoS attack prevention in the "Security Consideration" section. 7.2 Changes from 00.txt o Reworked the subsections in Section 4 to clarify the objectives, separating end-to-middle confidentiality and integrity. 8. Acknowledgments Thanks to Rohan Mahy and Cullen Jennings for their initial support of this concept, and to Jon Peterson, Gonzalo Camarillo, and Sean Olson for their helpful comments. References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Ono & Tachimoto Expires November 9, 2004 [Page 13] Internet-Draft End-to-Middle Security Requirements May 2004 Levels", RFC 2119, BCP 14, March 1997. [2] 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. [3] Allen, C. and T. Dierks, "The TLS Protocol Version 1.0", RFC 2246, January 1999. [4] Ramsdell, B., "S/MIME Version 3 Message Specification", RFC 2633, June 1992. [5] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C. and D. Gurle, "Session Initiation Protocol (SIP) Extension for Instant Messaging", RFC 3428, December 2002. [6] Cuellar, J., Morris, J., Mulligan, D., Peterson, J. and J. Polk, "Geopriv Requirements", RFC 3693, February 2004. [7] Peterson, J., "SIP Authenticated Identity Body (AIB) Format", draft-ietf-sip-authid-body-03.txt (work in progress), May 2004. [8] Rosenberg, J., "Requirements for Session Policy for the Session Initiation Protocol (SIP)", draft-ietf-sipping-session-policy-req-01 (work in progress), February 2004. [9] Srisuresh, P., Kuthan, J., Rosenberg, J., Brim, S., Molitor, A. and A. Rayhan, "Middlebox communication architecture and framework", RFC 3303, August 2002. [10] Andreasen, F., Baugher, M. and D. Wing, "Session Description Protocol Security Descriptions for Media Streams", draft-ietf-mmusic-sdescriptions-03.txt (work in progress), February 2004. [11] Housley, R., "Cryptographic Message Syntax", RFC 2630, June 1999. [12] Ono, K. and S. Tachimoto, "End-to-middle security in the Session Initiation Protocol(SIP)", draft-ono-sipping-end2middle-security-01 (work in progress), Feb. 2004. Ono & Tachimoto Expires November 9, 2004 [Page 14] Internet-Draft End-to-Middle Security Requirements May 2004 Authors' Addresses Kumiko Ono Network Service Systems Laboratories NTT Corporation 9-11, Midori-Cho 3-Chome Musashino-shi, Tokyo 180-8585 Japan EMail: ono.kumiko@lab.ntt.co.jp Shinya Tachimoto Network Service Systems Laboratories NTT Corporation 9-11, Midori-Cho 3-Chome Musashino-shi, Tokyo 180-8585 Japan EMail: tachimoto.shinya@lab.ntt.co.jp Ono & Tachimoto Expires November 9, 2004 [Page 15] Internet-Draft End-to-Middle Security Requirements May 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. 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