SIPPING K. Ono Internet-Draft S. Tachimoto Expires: August 16, 2004 NTT Corporation Feb 16, 2004 End-to-middle Security in the Session Initiation Protocol(SIP) draft-ono-sipping-end2middle-security-01 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 August 16, 2004. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract A Session Initiation Protocol (SIP) User Agent (UA) does not always trust all proxy servers in a request path enough to allow them inspect the message bodies and/or headers contained in a message. The UA might want to protect the message bodies and/or headers from all proxy servers except the particular proxy that provides services that depend on the ability to inspect them. In this situation, SIP needs a mechanism for securing information passed between the UA and an intermediary proxy, also called "end-to-middle security", which can work with end-to-end security. This document proposes mechanisms to achieve end-to-middle security, mainly data confidentiality for end-to-middle communication. Ono & Tachimoto Expires August 16, 2004 [Page 1] Internet-Draft End-to-middle security in SIP Feb 2004 Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [1]. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Overview of Proposed Mechanisms . . . . . . . . . . . . . . . 4 2.1 Creation of S/MIME CMS Bodies for UAs and Proxy servers . . . 4 2.2 Indicating the Target Content . . . . . . . . . . . . . . . . 5 2.3 Discovery of Proxy Server's Policies . . . . . . . . . . . . . 5 3. Behavior of UAs and Proxy Servers . . . . . . . . . . . . . . 7 3.1 UAC Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2 UAS Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.3 Proxy Behavior . . . . . . . . . . . . . . . . . . . . . . . . 8 4. Summary of Content-Disposition Header Field Use . . . . . . . 10 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5.1 Request Example . . . . . . . . . . . . . . . . . . . . . . . 11 5.2 Response Example . . . . . . . . . . . . . . . . . . . . . . . 12 6. Security Considerations . . . . . . . . . . . . . . . . . . . 14 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 18 Intellectual Property and Copyright Statements . . . . . . . . 19 Ono & Tachimoto Expires August 16, 2004 [Page 2] Internet-Draft End-to-middle security in SIP Feb 2004 1. Introduction The Session Initiation Protocol (SIP) [2] supports hop-by-hop security using TLS [3] and end-to-end security using S/MIME [4]. However, a UA sometimes wants to protect the message bodies and/or headers from all proxy servers except a selected proxy server, which provides some sort of service based on their content. Such a proxy is not always adjacent to the UA. These situations require security between the UA and the intermediary proxy server for the message bodies and/or message headers. We call this "end-to-middle security", where by "end" we mean a UA and by "middle" we mean a specific proxy. End-to-middle security is useful in a network where trusted and partially trusted proxy servers both exist in a message path. The partially trusted proxy servers are trusted only to view headers related to routing. The trusted proxy servers are trusted to view the message bodies and/or headers to provide services based on their content. For a UA requiring such services from intermediaries, end-to-end confidentiality will currently have to be disabled to take advantage of them. This problem is pointed out in Section 23 of [2]. Some examples of services that a proxy provides using the content of message bodies and/or headers follow. One example is firewall traversal. A midcom agent co-located with a proxy server controls a firewall entity. The agent needs to view certain Session Description Protocol (SDP) attributes in a message body or the same kind of data in a SIP header. Another example is the archiving of instant messaging traffic, where the archiving function co-located with a proxy server logs the message bodies in the MESSAGE method. A similar example is the archiving of all SIP headers and bodies traffic after being checked by the proxy server. These services might be deployed for financial or health care applications, where archiving communications is required by policies, as well as other applications. This document describes proposed mechanisms to achieve data confidentiality and the integrity of end-to-middle security to meet the requirements discussed in [9]. The major requirement is to be compatible with the end-to-end encryption that the S/MIME mechanism provides. Therefore, the proposed mechanisms are based on S/MIME. The mechanisms consists of the creation of encrypted data that is not readable by other proxy servers and the indication by the UA of the data that the UA requests the proxy server to read. In addition, it also includes a mechanism for the discovery of intermediate proxy servers. Ono & Tachimoto Expires August 16, 2004 [Page 3] Internet-Draft End-to-middle security in SIP Feb 2004 2. Overview of Proposed Mechanisms First, UAs MUST support the creation of CMS EnvelopedData body for multiple recipients for end-to-middle confidentiality. For compatibility with end-to-end security, the data needs to be encrypted for UAs and selected proxy servers. Second, UAs SHOULD support an indication mechanism to specify content in S/MIME that needs to be disclosed to a selected proxy server. Proxy servers MUST support to inspect the indicated content in S/MIME CMS bodies. Third, UAs MAY support a discovery mechanism to find which proxy in a signaling path needs to inspect and/or validate what data. In some cases, UAs will be statically configured with the intermediary proxy's policies and so they would not need to use this discovery mechanism. Proxy servers SHOULD provide the discovery mechanism to notify their policies of UAs. 2.1 Creation of S/MIME CMS Bodies for UAs and Proxy servers Since end-to-middle security needs to be compatible with end-to-end security, a creation mechanism for S/MIME CMS body is required. For end-to-end data integrity, UAs use S/MIME CMS SignedData body that can be validated by any entity. Therefore no new CMS SignedData creation mechanism is required. For data confidentiality, UAs use S/MIME CMS EnvelopedData body, whose recipients are specified. There are two ways of creating this data. The first way is to create an S/MIME CMS EnvelopedData body that contains encrypted content that is addressed to multiple recipients, such as a UA and a selected proxy server. UA MUST create an CMS EnvelopedData body can contain multiple recipients for encrypted data as specified in [7]. The structure contains data encrypted with a content-encryption-key (CEK) and the CEK is then encrypted with different key-encryption-keys (KEKs), that are actually the public keys for each recipient. For example, one would be for the recipient UA and another would be for the selected proxy server in the end-to-middle case. The second way is to create multiple S/MIME CMS EnvelopedData bodies, one for each recipient. For example, one for UA and one for a selected proxy server, and make them part of a multipart MIME body. UAs SHOULD use this method when keying materials, such keys for use by Secure RTP (SRTP)[14], are included in the SDP. One CMS EnvelopedData body contains SDP that includes keying materials of an SRTP stream only for the UA, and the other EnvelopedData body contains an SDP that does not include the keying materials of an SRTP stream that are for the UA and a selected proxy server that needs to view SDP (i.e.: for a firewall control service). Ono & Tachimoto Expires August 16, 2004 [Page 4] Internet-Draft End-to-middle security in SIP Feb 2004 2.2 Indicating the Target Content When proxy servers receive a message, the proxy server MUST inspect the "Content-Disposition" MIME headers to determine whether to process the S/MIME bodies and if so, which one. UA MUST support a new parameter called "required-entity" in the "Content-Disposition" MIME header that indicates required proxy servers to view the content of the MIME body. There is less of an impact on proxy servers that do not support end-to-middle security because these proxy servers do not inspect the "Content-Disposition" MIME header anyway. Note: There is an altenative option that use a new SIP header. The proposed mechanism requires more cost on proxy servers to determine the necessity of MIME body handling than using a new SIP header. However, the proxy can view the indicated MIME body more effectively than using a new SIP header. In addition, using a new SIP header could be negative impact on intermediary proxy servers that do not support end-to-middle security, causing unnecessary processing load. We feel that this MIME header parameter mechanism is not as simple, but it is equally effective. 2.3 Discovery of Proxy Server's Policies A discovery mechanism for proxy server's policies is needed when UAs do not know the policies of the proxy server in a signaling path and the proxy server has its own policy for providing some services. When the proxy server receives a request in which it cannot view some data that must be read in order to proceed or the proxy server receives a request whose sending policy cannot be accepted, the proxy MUST send a response with an error code. If the request is in plain text, the error code SHOULD be 403 (Forbidden) accompanied with a required Content-Type, such as "application/sdp". If the request is in plain text and the digital signature of it is required for an integrity check, the error code SHOULD be 403 (Forbidden) accompanied with a required Content-Type that is "multipart/signed". If the request contains encrypted data, the error code SHOULD be 493 (Undecipherable), accompanied with a proxy's public key certificate and required Content-Type. Open Issues: Which header is the appropriate one to use to set the required Content-Types in a response? When nested Content-Types are required such as "Content-Type: multipart/signed" for "Content-Type: application/pkcs7-mime;smime-type=enveloped-data", how will it be described? When the UA receives one of the above error codes, the UA needs to authenticate the proxy server. Therefore, the error code SHOULD Ono & Tachimoto Expires August 16, 2004 [Page 5] Internet-Draft End-to-middle security in SIP Feb 2004 contain the digital signature of the proxy server. In the worst case, this discovery mechanism requires two messages for each proxy server in the signaling path to establish a session between the UAs. In addition, it requires validation procedures using the digital signatures for all proxy servers. Since this causes a increase in the delay before session establishment, it is recommended that UAs learn in advance the policies of as many proxy servers as they can. Open Issue: How does this mechanism apply in the case when a proxy server needs to inspect the message body contained in the request in order to provide a service for a UAS? This might be happen where there a firewall in the network on the UAS's side. Ono & Tachimoto Expires August 16, 2004 [Page 6] Internet-Draft End-to-middle security in SIP Feb 2004 3. Behavior of UAs and Proxy Servers We describe here some examples of the behavior of UAs and proxy servers in a model in which trusted and partially trusted proxy servers are mixed along a message path. In the following example, User #1 does not know the services or security policies of Proxy #1. User#1 sends an INVITE request including encrypted SDP for end-to-end security as shown in Figure 1. Proxy #1 may reject the request because its inability to offer a firewall traversal service. Or Proxy #1 may delete the encrypted data from the body based on a security policy that prevents it from sending unknown data. 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 3.1 UAC Behavior When a UAC sends a request and requires end-to-end and end-to-middle confidentiality of the message bodies and/or headers, it uses S/MIME to encrypt them. In the above examples, UA #1 MUST use CMS EnvelopedData body for UA #2 and Proxy #1. At the SIP layer, UA #1 MUST require Proxy #1 to decrypt selected content and to view the content by using the "required-entity" parameter in the Content-Disposition header. Proxy #1 then provides some services based on the decrypted content. When the UAC needs Proxy #1 to inspect the message bodies and/or headers in the response, it SHOULD request the UAS to encrypt the response by using the same CEK as for the request. The UAC uses the "unprotectedAttrs" attribute to stipulate reuse of the CEK and indicate its identifier as described in [10] [11]. When the UAC sends a request and needs end-to-end and end-to-middle integrity for the message bodies and/or headers, it uses S/MIME to attach a digital signature. In the above examples, it uses the CMS SignedData body of the contents. At the SIP layer, UA #1 requires Proxy #1 to validate the integrity of the selected content by Ono & Tachimoto Expires August 16, 2004 [Page 7] Internet-Draft End-to-middle security in SIP Feb 2004 employing the "required-entity" parameter. When the UAC receives a response that uses S/MIME, it decrypts and/or validates the S/MIME bodies as usual. If it receives a response that uses CMS EnvelopedData body with the "KEKRecipientInfo" type of "RecepientInfo" attribute, it should decrypt the "RecipientInfo" by using the same CEK as for the sending request. 3.2 UAS Behavior When a UAS sends a response for the request with this mechanism, using the same type of S/MIME CMS body is recommended. For example, if the UAS receives an INVITE request in which the SDP is encrypted by using CMS EnvelopedData body, the recommended response would be a "200 OK" containing the encrypted SDP based on CMS EnvelopedData body. In particular, when the CMS EnvelopedData body of the request contains the "unprotectedAttrs" attribute specifying reuse of the CEK, the UAS SHOULD encrypt a CEK with the CEK that was used in the request, instead of the public key of the UAC. The UAS SHOULD use the CMS EnvelopedData body to contain the encrypted SDP in the "200 OK" response. In addition, the UAS SHOULD set the same proxy server in the "required-entity" parameter of the "Content-Dispositon" MIME header in the request. If the UAS encrypted the SDP with a CEK that was itself encrypted with the CEK in the request, the proxy server selected by the UAC can view the SDP in the "200 OK" response. Note: In the case when the response does not contain a message body, even if the request contains a message body and was encrypted by using CMS EnvelopedData body, the UAS does not need to use the CMS EnvelopedData body. When the UAS receives a request that uses S/MIME, it decrypts and/or validates the S/MIME bodies as usual. When the UAS sends a response for the request without this mechanism and needs end-to-end and end-to-middle confidentiality of the message bodies and/or headers , it MUST use CMS EnvelopedData to encrypt them. When the UAC sends a request and needs end-to-end and end-to-middle integrity of the message bodies and/or headers, it MUST use CMS SignedData to attach a digital signature. This is the same way the UAC normally performs with this mechanism. 3.3 Proxy Behavior Ono & Tachimoto Expires August 16, 2004 [Page 8] Internet-Draft End-to-middle security in SIP Feb 2004 When a proxy supporting this mechanism receives a message, the proxy server MUST inspect the "Content-Disposition" MIME header and the "required-entity" parameter of that. If the MIME header includes the processing server's own name, the proxy server MUST inspect the specified content. When the specified content is CMS EnvelopedData body, the proxy server MUST inspect it and try to decrypt the "recipientInfo" attribute. If the proxy server fails to decrypt that, it SHOULD cancel the subsequent procedure and respond with a 493 (Undecipherable) response if it is a request, or any existing dialog MAY be terminated. If the proxy server succeeds in this decryption, it MUST inspect the "unprotectedAttrs" data of the CMS EnvelopedData body. If the attribute gives the key's identifier, the proxy server MUST keep the CEK with its identifier during the dialog. When it receives subsequent messages in the dialog, it MUST try to decrypt the "KEKRecipientInfo" type of "recepientInfo" attribute by using this CEK. When the specified content is CMS SignedData body, the proxy server MUST inspect it and validate the digital signature. If the verification is failed, the proxy server SHOULD reject the subsequent procedure and respond with a 403 (Forbidden) response if the message is a request, or any existing dialog MAY be terminated. When the proxy server forwards the request, it modifies the routing headers normally. It does not need to modify the S/MIME body. If a proxy does not support this mechanism and receives a message with the "required-parameter" parameter in the "Content-Disposition" header, the proxy MUST ignore the header and perform as usual. Ono & Tachimoto Expires August 16, 2004 [Page 9] Internet-Draft End-to-middle security in SIP Feb 2004 4. Summary of Content-Disposition Header Field Use The following syntax specification uses the augmented Backus-Naur Form (BNF) as described in RFC-2234 [13]. The new parameter "required-entity" is defined in "required-param" as one of "disp-param". Content-Disposition = "Content-Disposition" HCOLON disp-type *( SEMI disp-param ) disp-type = "render" / "session" / "icon" / "alert" / disp-extension-token disp-param = handling-param / required-param / generic-param handling-param = "handling" EQUAL ( "optional" / "required" / other-handling ) other-handling = token disp-extension-token = token required-param = "required-entity" EQUAL proxy-uri *(COMMA proxy-uri) proxy-uri = ( name-addr / addr-spec ) Ono & Tachimoto Expires August 16, 2004 [Page 10] Internet-Draft End-to-middle security in SIP Feb 2004 5. Examples The following examples illustrate the use of the mechanism defined in the previous section. 5.1 Request Example In the following example, a UA needs SDP in an INVITE message to be confidential and the UA allows a proxy server to view the SDP in an INVITE request. In addition, the UA needs to protect the policy of the proxy server. In the example encrypted message below, the text with the box of asterisks ("*") is encrypted: INVITE alice@atlanta.example.com --> ss1.atlanta.example.com INVITE sip:bob@biloxi.example.com SIP/2.0 Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70 Route: From: Alice ;tag=9fxced76sl To: Bob Call-ID: 3848276298220188511@atlanta.example.com CSeq: 1 INVITE Contact: Date: Fri, 20 June 2003 13:02:03 GMT Content-Type: multipart/signed;protocol="application/pkcs7-signature"; micalg=sha1;boundary=boundary1 Content-Length: ... --boundary1 Content-Type: application/pkcs7-mime;smime-type=enveloped-data; name=smime.p7m Content-Transfer-Encoding: base64 Content-Disposition: session;filename=smime.p7m;handling=required; required-entity=ss1.atlanta.example.com Content-Length: ... ****************************************************************** * (encryptedContentInfo) * * Content-Type: application/sdp * * Content-Length: ... * * * * v=0 * * o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com* * s=- * * c=IN IP4 192.0.2.101 * Ono & Tachimoto Expires August 16, 2004 [Page 11] Internet-Draft End-to-middle security in SIP Feb 2004 * t=0 0 * * m=audio 49172 RTP/AVP 0 * * a=rtpmap:0 PCMU/8000 * * * * (recipientInfos) * * RecepientInfo[0] for ss1.atlanta.example.com public key * * RecepientInfo[1] for bob's public key * * * * (unprotectedAttr) * * CEKReference * ****************************************************************** --boundary1-- Content-Type: application/pkcs7-signature; name=smime.p7s Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename=smime.p7s;handling=required ghyHhHUujhJhjH77n8HHGTrfvbnj756tbB9HG4VQpfyF467GhIGfHfYT6 4VQpfyF467GhIGfHfYT6jH77n8HHGghyHhHUujhJh756tbB9HGTrfvbnj n8HHGTrfvhJhjH776tbB9HG4VQbnj7567GhIGfHfYT6ghyHhHUujpfyF4 7GhIGfHfYT64VQbnj756 --boundary1-- 5.2 Response Example In the following example, a UA sends a response with this mechanism. In the example encrypted message below, the text boxed in asterisks ("*") is encrypted: 200 OK bob@biloxi.example.com --> ss2.biloxi.example.com SIP/2.0 200 OK Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e418c4.1 ;received=192.0.2.222 Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1 ;received=192.0.2.111 Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9 ;received=192.0.2.101 Record-Route: , From: Alice ;tag=9fxced76sl To: Bob ;tag=314159 Ono & Tachimoto Expires August 16, 2004 [Page 12] Internet-Draft End-to-middle security in SIP Feb 2004 Call-ID: 3848276298220188511@atlanta.example.com CSeq: 2 INVITE Contact: Content-Type:multipart/signed;protocol="application/pkcs7-signature"; micalg=sha1;boundary=boundary41 Content-Length: ... --boundary41 Content-Type: application/pkcs7-mime; smime-type=enveloped-data;name=smime.p7m Content-Transfer-Encoding: base64 Content-Disposition: session; filename=smime.p7m;handling=required; Content-Length: ... ****************************************************************** * (encryptedContentInfo) * * Content-Type: application/sdp * * Content-Length: ... * * * * v=0 * * o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com * * s=- * * c=IN IP4 192.0.2.201 * * t=0 0 * * m=audio 3456 RTP/AVP 0 * * a=rtpmap:0 PCMU/8000 * * * * (recipientInfos) * * RecepientInfo[0] for KEKidentifier * ****************************************************************** --boundary41-- Content-Type: application/pkcs7-signature; name=smime.p7s Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename=smime.p7s;handling=required hhhHhHUujhJhjH77n8HHGTrfvbnj756tbB9HG4VQpfyF467GhIGfHfYT6 4VQpfyF467GhIGfHfYT6jH77n8HHGghyHhHUujhJh756tbB9HGTrfvbnj n8HHGTrfvhJhjH776tbB9HG4VQbnj7567GhIGfHfYT6ghyHhHUujpfyF4 7GhIGfHfYT64VQbnj756 --boundary41-- Ono & Tachimoto Expires August 16, 2004 [Page 13] Internet-Draft End-to-middle security in SIP Feb 2004 6. Security Considerations This specification is about applying S/MIME-secured messages for use in end-to-middle security. It is also about applying the CEK reuse method defined in [10]. This requires the same security consideration as those of [4] and [10]. Ono & Tachimoto Expires August 16, 2004 [Page 14] Internet-Draft End-to-middle security in SIP Feb 2004 7. IANA Considerations This document requires a new parameter in "Content-Disposition" header fields, namely "required-entity". Ono & Tachimoto Expires August 16, 2004 [Page 15] Internet-Draft End-to-middle security in SIP Feb 2004 8. Acknowledgments Thanks to Rohan Mahy and Cullen Jennings for their initial support of this concept, and to Jon Peterson for his helpful comments. Ono & Tachimoto Expires August 16, 2004 [Page 16] Internet-Draft End-to-middle security in SIP Feb 2004 References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 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] Srisuresh, P., Kuthan, J., Rosenberg, J., Brim, S., Molitor, A. and A. Rayhan, "Middlebox communication architecture and framework", RFC 3303, August 2002. [6] Campbell, Ed., B., Rosenberg, J., Schulzrinne, H., Huitema, C. and D. Gurle, "Session Initiation Protocol (SIP) Extension for Instant Messaging", RFC 3428, December 2002. [7] Housley, R., "Cryptographic Message Syntax", RFC 2630, June 1999. [8] Rosenberg, J., "Requirements for Session Policy for the Session Initiation Protocol (SIP)", draft-rosenberg-sipping-session-policy-req-00 (work in progress), December 2002. [9] Ono, K. and S. Tachimoto, "Requirements for end-to-middle security in the Session Initiation Protocol (SIP)", draft-ietf-sipping-e2m-sec-reqs-01 (work in progress), February 2004. [10] Farrell, S. and S. Turner, "Reuse of CMS Content Encryption Keys", RFC 3185, October 2001. [11] Ono, K. and S. Tachimoto, "Key reuse in S/MIME for SIP", draft-ono-sipping-keyreuse-smime-00 (work in progress), February 2004. [12] Sparks, R., "Internet Media Type message/sipfrag", RFC 3420, November 2002. [13] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. Ono & Tachimoto Expires August 16, 2004 [Page 17] Internet-Draft End-to-middle security in SIP Feb 2004 [14] 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. 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 August 16, 2004 [Page 18] Internet-Draft End-to-middle security in SIP Feb 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. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. 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