SIPPING K. Ono Internet-Draft S. Tachimoto Expires: December 22, 2003 NTT Corporation June 23, 2003 End-to-middle security in the Session Initiation Protocol(SIP) draft-ono-sipping-end2middle-security-00 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 December 22, 2003. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract End-to-end encryption for confidentiality services can conflict with some of the features provided by intermediaries. For example, if a SIP UA encrypts the message body by using S/MIME for end-to-end security, it cannot use features that the proxy employs to inspect the message body contained in the request. This situation requires 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 describes a method of achieving end-to-middle security, allowing a SIP UA to disclose message data to selected intermediaries and protect the data from being seen by other intermediaries. It describes how to apply S/MIME CMS EnvelopedData body for use in end-to-middle security. Ono & Tachimoto Expires December 22, 2003 [Page 1] Internet-Draft End-to-middle Security in SIP June 2003 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. Problems with the Existing Situations . . . . . . . . . . . . 4 3. Requirements for a Solution . . . . . . . . . . . . . . . . . 6 3.1 Requirements from UA's Perspective . . . . . . . . . . . . . . 6 3.2 Requirements from Proxy's Perspective . . . . . . . . . . . . 6 4. Overview of Proposed Mechanism . . . . . . . . . . . . . . . . 8 4.1 UAC Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.2 UAS Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.3 Proxy Behavior . . . . . . . . . . . . . . . . . . . . . . . . 11 4.4 Summary of Header Field Use . . . . . . . . . . . . . . . . . 11 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5.1 Request example . . . . . . . . . . . . . . . . . . . . . . . 13 5.2 Response example . . . . . . . . . . . . . . . . . . . . . . . 14 6. Security Considerations . . . . . . . . . . . . . . . . . . . 17 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19 References . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 21 Intellectual Property and Copyright Statements . . . . . . . . 22 Ono & Tachimoto Expires December 22, 2003 [Page 2] Internet-Draft End-to-middle Security in SIP June 2003 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]. This assumes a SIP UA trusts all proxy servers in a request path to decide whether or not to inspect the message bodies contained in a message. However, there is a model where trusted and partially-trusted proxy servers are mixed through a message path. The partially-trusted proxy servers are only trusted in terms of the SIP routing. Hop-by-hop confidentiality services using TLS are not suitable for this model. End-to-end confidentiality services using S/MIME are also not suitable when the intermediaries provide features based on reading the message bodies and/or headers. This problem is described in Section 23 of [2]. One example of such a feature is NAT/firewall control, where a midcom [5] agent co-located with a proxy server controls a NAT/firewall based on certain SDP attributes in a SIP transaction. Another example of such a feature is the archiving of instant messaging traffic, where the archiving function co-located with a proxy server logs the message bodies in the MESSAGE [6] method. In these cases, a UA might want to protect the message bodies and/or headers from proxy servers excluding a selected proxy, which provides these features. Such a proxy is not always the first hop for the UA. These situations require security between the UA and the intermediary proxy for the message bodies and/or message headers. We call this "end-to-middle security". End-to-middle security consists of authentication, message integrity, and message confidentiality. As for authentication, HTTP digest authentication described in [2] is used for user-to-proxy and proxy-to-user 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. Digital signatures in a Public Key Infrastructure, that is S/MIME CMS [7] SignedData body with certificate, can also be used for authentication. As for message integrity, S/MIME CMS SignedData body can be used. S/MIME CMS SignedData body is created with the original data and the originator's private key, and anyone can verify the integrity using the originator's public key and the certificate. Thus, S/MIME CMS SignedData body can be used for end-to-middle security at the same time as end-to-end security. However, proxy servers usually transfer SIP messages without interpreting the S/MIME bodies. This document mainly discusses the message confidentiality and integrity of end-to-middle security. Ono & Tachimoto Expires December 22, 2003 [Page 3] Internet-Draft End-to-middle Security in SIP June 2003 2. Problems with the Existing Situations We describe here examples of models in which trusted and partially-trusted proxy servers are mixed along a message path. These situations demonstrate the reasons for requiring end-to-middle security. In the following example, Proxy#1 server 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 1 . UA#1 has already known the public key certificate of Proxy#1, and it allows Proxy#1 to inspect the message bodies in a request for some purpose. However, User#1 does not know whether Proxy#2 is trustworthy, and thus wants to protect the message bodies in the request. Thus, there is the problem of granting a trusted intermediary permission to inspect message bodies while preserving their confidentiality with respect to other intermediaries. Even if UA#1's request message authorizes a selected proxy (Proxy#1) to see the message body, UA#1 is unable to authorize the same proxy to see the message body in the response from UA#2. Thus, there is the problem of designating and sharing a key that can be reused as a CEK for bidirectional exchanges of S/MIME-secured messages within SIP. Note: This document describes the two different problems and solutions. It might be a good idea to break this document into two separate drafts. Home network +---------------------+ | +-----+ +-----+ | +-----+ +-----+ User#1------| | |-----| |-----| |-----| |-- User#2 | +-----+ +-----+ | +-----+ +-----+ | UA#1 Proxy#1 | Proxy#2 UA#2 +---------------------+ Figure 1: Deployment example#1 In the next example, User#1 connects UA#1 to a proxy server in a visited 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 has to connect Proxy#1 via the proxy server of the visited network (Proxy A), because User#1 has to follow the policy of that network. Proxy A may perform access control based on the destination addresses of calls. User#1 trusts Proxy A to route requests, but not to inspect the message bodies they contained. User#1 trusts Proxy#1 both to route Ono & Tachimoto Expires December 22, 2003 [Page 4] Internet-Draft End-to-middle Security in SIP June 2003 requests and to inspect the message bodies for some purpose. The same problems exist as those in the first example. Visited network +---------------------+ | +-----+ +-----+ | +-----+ +-----+ +-----+ User#1 -- | | |-----| |-----| |-----| |-----| | | +-----+ +-----+ | +-----+ +-----+ +-----+ | UA#1 Proxy A | Proxy#1 Proxy#2 UA#2 +---------------------+ Figure 2: Deployment example#2 Ono & Tachimoto Expires December 22, 2003 [Page 5] Internet-Draft End-to-middle Security in SIP June 2003 3. Requirements for a Solution These requirements are similar to the general requirements described in the Internet Draft of the Session Policy Requirements [8]. The differences are that in this document a UA explicitly authorizes the use of the features provided by intermediaries. In [8], the intermediaries imposes a session policy without user authorization. This document describes security issues related to authorizing an intermediary to see message contents. 3.1 Requirements from UA's Perspective 1. The solution SHOULD work even with SIP end-to-end encryption for confidentiality service enabled. 2. It SHOULD work even with SIP end-to-end integrity service enabled. 3. It SHOULD have a minimal impact on the way to handle messages with S/MIME bodies. 4. It SHOULD allow a UA to request selected proxy servers to view selected message body. In addition, the request itself SHOULD be secure. 5. It SHOULD allow a UA to request the UA on the opposite-side to impose the same proxy policy on the same proxy server. In addition, the request itself SHOULD be secure. It is not appropriate for the UA on the opposite-side to have knowledge of the public key certificate of the proxy server on the originating network. This last requirement can be modified into the following: + The solution SHOULD allow a UA to request the opposite-side UA to reuse a content-encryption-key in subsequent messages during a dialog. + It SHOULD allow a UA to request a selected proxy server to keep a content-encryption-key in a message during a dialog. + The above requests themselves SHOULD be secure. 3.2 Requirements from Proxy's Perspective 1. The solution SHOULD have no impact on proxy servers that do not provide features based on S/MIME bodies in terms of handling the Ono & Tachimoto Expires December 22, 2003 [Page 6] Internet-Draft End-to-middle Security in SIP June 2003 existing SIP headers. 2. It SHOULD have less impact on proxy servers that provide features based on S/MIME bodies. When a proxy server receives an S/MIME message, it should be able to quickly and easily determine the necessity to investigate the S/MIME body. This last requirement can be modified into the following: + It SHOULD allow proxy servers to quickly and easily determine whether to handle S/MIME bodies and, if so, how and which one. Ono & Tachimoto Expires December 22, 2003 [Page 7] Internet-Draft End-to-middle Security in SIP June 2003 4. Overview of Proposed Mechanism The proposed mechanism uses a new SIP header, "Proxy-Policy". The "Proxy-Policy" header indicates that a UA wants selected proxy servers to view selected S/MIME bodies. The proxy servers view the "Proxy-Policy" to determine whether to handle the S/MIME bodies and if so, which one. Note: An alternative mechanism would be to add a parameter in the "Content-Disposition" header. However, since proxy servers usually do not inspect the "Content-Disposition" header, it is not as good as using an additional SIP header. In addition, the proposed mechanism employs the "unprotectedAttrs" attribute in the S/MIME CMS EnvelopedData body to expresses a sender's preferences to reuse a content-encryption-key in subsequent messages during a dialog. Note: An alternative mechanism would be to add a parameter in the "Proxy-Policy" header. However, since the key reuse is executed after the investigation of CMS data, it is not necessary to be set at the SIP layer. In addition, since [9] has already defined the reuse method of content-encryption-key using the "unprotectedAttrs" attribute in the EnvelopedData, it is better to use the existing mechanism. We assume that UA#1 requires Proxy#1 to view the message body's SDP in order to control a firewall for the session in the situation shown in Figure 1. Since UA#1 requires end-to-end and end-to-middle confidentiality for the content of the SDP, it uses S/MIME CMS EnvelopedData for multiple recipients and sets the "Content-ID" header to identify the content. The "recipientInfos" data of the EnvelopedData contains the encrypted content-encryption-keys for each recipient of the same encrypted content. One of the "RecepientInfo" attributes is for Proxy#1, while another is for UA#2. UA#1 may use the "unprotectedAttrs" attribute to request UA#2 to reuse the content-encryption-key instead of a public key to encrypt a content-encryption-key of a response. +----------------+ +-------+ +-----+ +-----+ |E-CEK(C) with |--->|C, |---->| |----->|C, | |E-UA#2key(CEK)& | | | | | |CEK | |E-P#1key(CEK) | |CEK | | | | | +----------------+ +-------+ +-----+ +-----+ UA#1 Proxy#1(P#1) Proxy#2 UA#2 Ono & Tachimoto Expires December 22, 2003 [Page 8] Internet-Draft End-to-middle Security in SIP June 2003 C: Content of a request CEK: Content-encryption-key E-CEK(C): Content encrypted using CEK E-Xkey(CEK): CEK encrypted using X's public key. Figure 3: Overview of message with CMS EnvelopedData +----------------+ +-------+ +-----+ +----------------+ |C' |<---|C', |<----| |<-----|E-CEK'(C') with | |CEK' | |CEK' | | | |E-CEK(CEK')& | +----------------+ +-------+ +-----+ +----------------+ UA#1 Proxy#1(P#1) Proxy#2 UA#2 C': Content of a response CEK': Content-encryption-key. Figure 4: Overview of subsequent message with CMS EnvelopedData Issue:How does this mechanism apply for the case when Proxy#2 needs to inspect the message body contained in the request to UA#2? When UA#1 requires the message integrity for end-to-end and end-to-middle security, it uses the S/MIME CMS SignedData for the "message/sipfrag"[10] Content-type. When it requires confidentiality and integrity for the message, it uses the S/MIME SignedData of the S/MIME EnvelopedData for the message. 4.1 UAC Behavior When a UAC sends a request and it 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 uses S/ MIME EnvelopedData for UA#2 and Proxy#1. At the SIP layer, UA#1 requires Proxy#1 to decrypt selected content and to view the content by using the "Proxy-Policy" header. Proxy#1 then provides some feature 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 content-encryption-key as for the request. The UAC uses the "unprotectedAttrs" attribute to stipulate reuse of the content-encryption-key and indicate its identifier. Note: The "unprotectedAttrs" data is not protected, so it should Ono & Tachimoto Expires December 22, 2003 [Page 9] Internet-Draft End-to-middle Security in SIP June 2003 be protected using S/MIME SignedData. When the UAC sends a request and needs the 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 S/MIME CMS SignedData of the contents. At the SIP layer, UA#1 requires Proxy#1 to validate the integrity of the selected content by employing the "Proxy-Policy" header. 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 S/MIME EnvelopedData with the "KEKRecipentInfo" type of "RecepientInfo" attribute, it should decrypt the "RecipentInfo" by using the same content-encryption-key as for the sending request. 4.2 UAS Behavior When a UAS sends a response for the request with this mechanism, using the same type of S/MIME CMS data is recommended. For example, if the UAS receives an INVITE request in which the SDP is encrypted by using S/MIME EnvelopedData, the recommended response would be a "200 OK" containing the encrypted SDP based on the the S/MIME EnvelopedData. In particular, when the S/MIME EnvelopedData of the request contains the "unprotectedAttrs" attribute specifying reuse of the content-encryption-key, the UAS SHOULD encrypt a content-encryption-key with the content-encryption-key that was used in the request, instead of a public key of the UAC. The UAS SHOULD use the S/MIME EnvelopedData to contain the encrypted SDP in the "200 OK" response. In addition, the UAS SHOULD set the same proxy server as in the request and the Content-id of the encrypted SDP in the "Proxy-Policy" header. If the UAS encrypted the SDP with a content-encryption-key that was itself encrypted with the content-encryption-key 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 S/MIME EnvelopedData, the UAS does not need to use the S/MIME EnvelopedData. 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 Ono & Tachimoto Expires December 22, 2003 [Page 10] Internet-Draft End-to-middle Security in SIP June 2003 and needs end-to-end and end-to-middle confidentiality of the message bodies and/or headers , it uses S/MIME 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 uses S/MIME to attach a digital signature. This is the same way the UAC normally performs with this mechanism. 4.3 Proxy Behavior When a proxy supporting this mechanism receives a message, the proxy server inspects the "Proxy-Policy" header. If the header includes the processing server's own name, the proxy server inspects the specified Content-ID. When the specified content is S/MIME EnvelopedData, the proxy server inspects it and tries to decrypt the "RecipientInfo" attribute. If the proxy 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 succeeds in this decryption, it inspects the "unprotectedAttrs" data of the S/MIME EnvelopedData. If the attribute gives the key's identifier, the proxy must keep the content-encryption-key with its identifier during the dialog. When it receives subsequent messages in the dialog, it tries to decrypt the "KEKRecipientInfo" type of "RecepientInfo" attribute by using this content-encryption-key. When the specified content is S/MIME SignedData, the proxy server inspects it and validates the digital signature. If the verification is unsuccessful, 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 transfers 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 "Proxy-Policy" header, the proxy ignores the header and perform as usual. 4.4 Summary of Header Field Use The following syntax specification uses the augmented Backus-Naur Form (BNF) as described in RFC-2234 [11]. Proxy-Policy = HCOLON proxy-uri *( SEMI (proxy-policy-param) ) proxy-uri = ( name-addr / addr-spec ) proxy-policy-param = content-id ( SEMI policy ) content-id = "cid" EQUAL cid Ono & Tachimoto Expires December 22, 2003 [Page 11] Internet-Draft End-to-middle Security in SIP June 2003 cid = LDQUOT dot-atom "@" (dot-atom / host) RDQUOT dot-atom = atom *( "." atom ) atom = 1*( alphanum / "-" / "!" / "%" / "*" / "_" / "+" / "'" / "`" / "~" ) policy = "policy" EQUAL ( token ) Information about the use of headers in relation to SIP methods and proxy processing is summarized in Table 1. Header field where proxy ACK BYE CAN INV OPT REG ----------------------------------------------------- Proxy-Policy R adr o o o o o o Proxy-Policy 200-699 adr - o - o o o Proxy-Policy 1xx adr - - - o - - Header field where proxy SUB NOT PRK IFO UPD MSG ----------------------------------------------------- Proxy-Policy R adr o o - o o o Proxy-Policy 200-699 adr o o - o o o Table 1: Summary of header field use The "where" column gives the request and response types in which the header field can be used. The values in the "where" column are as follows: * R: The header field may appear in requests * 200-699: A numeral range indicates response codes with which the header field can be used. * a: A proxy can add or concatenate the header field if it is not present. * r: A proxy must be able to read the header field, and thus it cannot be encrypted. * d: A proxy can delete a header field value. * o: The header field is optional. Ono & Tachimoto Expires December 22, 2003 [Page 12] Internet-Draft End-to-middle Security in SIP June 2003 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 the confidentiality of the SDP in INVITE message and the UA allows a proxy server to view the SDP in INVITE request. In addition, the UA needs to protect the policy for the proxy server. In the example encrypted message below, the text boxed in 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 Proxy-Policy: ss1.atlanta.example.com; cid="2UWQFN309shb3@atlanta.example.com" Content-Type: multipart/singed; protocol="application/pkcs7-signature"; micalg=sha1; boundary=boundary2 Content-Length: 878 --boundary1 Content-Type: multipart/mixed; boundary=boundary2 Content-Length: 568 --boundary2 Content-Type: message/sipfrag 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 Proxy-Policy: ss1.atlanta.example.com; cid="2UWQFN309shb3@atlanta.example.com" --boundary2 Content-Type: application/pkcs7-mime; smime-type=enveloped-data;name=smime.p7m Ono & Tachimoto Expires December 22, 2003 [Page 13] Internet-Draft End-to-middle Security in SIP June 2003 Content-Transfer-Encoding: base64 Content-Disposition: session; filename=smime.p7m;handling=required Content-ID: <2UWQFN309shb3@atlanta.example.com> Content-Length: 231 ****************************************************************** * (encryptedContentInfo) * * Content-Type: application/sdp * * Content-Length: 151 * * * * v=0 * * o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com* * s=- * * c=IN IP4 192.0.2.101 * * 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 * ****************************************************************** --boundary2-- --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: Ono & Tachimoto Expires December 22, 2003 [Page 14] Internet-Draft End-to-middle Security in SIP June 2003 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 Call-ID: 3848276298220188511@atlanta.example.com CSeq: 2 INVITE Contact: --boundary41 Content-Type: multipart/mixed; boundary=boundary2 Content-Length: 468 --boundary42 Content-Type: message/sipfrag From: Alice ;tag=9fxced76sl To: Bob ;tag=314159 Call-ID: 3848276298220188511@atlanta.example.com CSeq: 2 INVITE Contact: Date: Fri, 20 June 2003 13:02:03 GMT Proxy-Policy: ss1.atlanta.example.com; cid="2UWQFN309shb3@biloxi.example.com" --boundary2 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-ID: <2UWQFN309shb3@biloxi.example.com> Content-Length: 211 ****************************************************************** * (encryptedContentInfo) * * Content-Type: application/sdp * * Content-Length: 147 * * * * v=0 * Ono & Tachimoto Expires December 22, 2003 [Page 15] Internet-Draft End-to-middle Security in SIP June 2003 * 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 * ****************************************************************** --boundary42-- --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 December 22, 2003 [Page 16] Internet-Draft End-to-middle Security in SIP June 2003 6. Security Considerations This specification is about applying S/MIME-secured messages for use in end-to-middle security. It is also applying the CEK reuse method defined in [9]. This requires the same security consideration as those of [4] and [9]. Ono & Tachimoto Expires December 22, 2003 [Page 17] Internet-Draft End-to-middle Security in SIP June 2003 7. IANA Considerations This document requires a new header fields, namely "Proxy-Policy". Ono & Tachimoto Expires December 22, 2003 [Page 18] Internet-Draft End-to-middle Security in SIP June 2003 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 December 22, 2003 [Page 19] Internet-Draft End-to-middle Security in SIP June 2003 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] Farrell, S. and S. Turner, "Reuse of CMS Content Encryption Keys", RFC 3185, October 2001. [10] Sparks, R., "Internet Media Type message/sipfrag", RFC 3420, November 2002. [11] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. Ono & Tachimoto Expires December 22, 2003 [Page 20] Internet-Draft End-to-middle Security in SIP June 2003 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 December 22, 2003 [Page 21] Internet-Draft End-to-middle Security in SIP June 2003 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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