Internet Engineering Task Force P. Dawes
Internet-Draft Vodafone Group
Intended status: Informational October 01, 2013
Expires: April 04, 2014
Security Mechanism Names for Media
draft-dawes-dispatch-mediasec-parameter-07.txt
Abstract
Negotiating the security mechanisms used between a Session Initiation
Protocol (SIP) user agent and its next-hop SIP entity is described in
RFC 3329 [4]. This document adds the capability to distinguish
security mechanisms that apply to the media plane by defining a new
Session Initiation Protocol (SIP) header field parameter to label
such security mechanisms.
Requirements Language
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 [3].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on April 04, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Access Network Protection . . . . . . . . . . . . . . . . . . 3
4. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Signalling security negotiation . . . . . . . . . . . . . 4
4.2. Header fields for signalling security negotiation . . . . 4
4.3. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.4. Protocol Operation . . . . . . . . . . . . . . . . . . . 5
4.4.1. The "mediasec" Header Field Parameter . . . . . . . . 5
4.4.2. Client Initiated . . . . . . . . . . . . . . . . . . 5
4.5. Security Mechanism Initiation . . . . . . . . . . . . . . 6
4.6. Duration of Security Assocations . . . . . . . . . . . . 6
4.7. Summary of Header Field Use . . . . . . . . . . . . . . . 7
5. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 7
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Initial Registration 3GPP . . . . . . . . . . . . . . . . 7
6.2. Re-Registration 3GPP . . . . . . . . . . . . . . . . . . 12
6.3. Client Initiated as per RFC 3329 . . . . . . . . . . . . 14
6.4. Server Initiated as per RFC 3329 . . . . . . . . . . . . 15
6.5. Using Media Plane Security . . . . . . . . . . . . . . . 16
7. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 17
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
9.1. Registry for Media Plane Security Mechanisms . . . . . . 18
9.2. Registration Template . . . . . . . . . . . . . . . . . . 19
9.3. Header Field Names . . . . . . . . . . . . . . . . . . . 19
9.4. Response Codes . . . . . . . . . . . . . . . . . . . . . 19
10. Security Considerations . . . . . . . . . . . . . . . . . . . 19
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . 19
11.2. Informative References . . . . . . . . . . . . . . . . . 20
Appendix A. Additional stuff . . . . . . . . . . . . . . . . . . 20
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 20
1. Problem Statement
In the 3GPP defined architecture and SIP profile for packet-domain
communication, SIP signalling is security protected at the network
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layer but media-plane traffic is not (it is protected by the cellular
wireless access). The SIP signalling security used by 3GPP runs from
the user device to the first hop proxy and negotiation of security
mechanism and the start of security protection is described in RFC
3329 [4]. Because the 3GPP architecture also allows access
technologies that do not protect media, e.g. WiFi, this document
extends the negotiation of security mechanism to the media plane.
During previous discussion of the topic of media plane security it
was suggested that DTLS-SRTP should be used, but 3GPP considered this
impractical to implement in the 3GPP-defined architecture and also
limited in terms of meeting all 3GPP requirements which include
protection of non-RTP media such as MSRP.
The purpose of this specification is to define a new header field
parameter for the Session Initiation Protocol (SIP) [1] that
distinguishes security mechanisms that apply to the media plane and
to create an IANA registry for these mechanisms. This header field
parameter may be used with the Security-Client, Security-Server, and
Security-Verify header fields defined by RFC 3329 [4].
2. Introduction
RFC 3329 [4] describes negotiation of a security mechanism for SIP
signalling between a UAC and its first hop proxy and allows a client
or network to ensure that protection of SIP signalling is is turned
on when the client registers with the network. SIP signalling is
then protected as it traverses the access network. To enable similar
protection for media, this document enables client and network to
exchange their security capabilities for the media plane combined
with the negotiation described in RFC 3329 [4]. Similar to the
signalling plane, the evolution of security mechanisms for media
often introduces new algorithms, or uncovers problems in existing
ones, making capability exchange of such mechanisms a necessity.
3. Access Network Protection
Some access technologies, such as many cellular wireless accesses,
protect the data passed over them by default but some, such as WLAN,
do not. For accesses with no inherent protection, it is useful for
the media controlled by SIP signalling to be protected by default
because of vulnerability to eavesdropping. It is currently possible
for a UA to request protection of the media plane end-to-end by
including the crypto attribute in SDP at session setup. This does
not guarantee protection however, because it relies on support of
encryption by the called UA, or by another entity in the path taken
by the media. In some cases, the session will originate in an access
that protects the media and terminate in one that does not, meaning
that media is protected in all but some hops of its path. In cases
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where the same provider supplies the user equipment and provides the
IP access, the IP access technology that the UA will use is
predictable and the media is vulnerable only as far as the core
network. In such cases, the user equipment it is possible to protect
the media plane by encrypting at the UA and decrypting at the edge of
the core network, and for the user agent that originates or
terminates the session to expect the edge of the core network to be
capable of encrypting and decrypting media. The header field
parameter described in this document enables this case of first-hop
protection, which is typically provided by default to a user agent.
4. Solution
4.1. Signalling security negotiation
A specification already exists for setting up security for SIP
signaling between a client and its first-hop proxy, as defined in RFC
3329 [4] which gives an overview of the mechanism as follows:
1. Client ----------client list---------> Server
2. Client <---------server list---------- Server
3. Client ------(turn on security)------- Server
4. Client ----------server list---------> Server
5. Client <---------ok or error---------- Server
Figure 1: Security agreement message flow from RFC 3329
The security mechanism above ensures that SIP signalling is protected
between a client and its first hop entity but the media plane is
still unprotected. This document proposes that client and server
additionally exchange their media plane security capabilities at step
1 and 2. Media plane security needs to be applied on a per-media
basis at the time that media is initiated. Therefore the client and
server need not turn on media plane security immediately.
This document defines the "mediasec" header field parameter that
labels any of the Security-Client:, Security-Server:, or Security-
Verify: header fields as applicable to the media plane and not the
signalling plane.
4.2. Header fields for signalling security negotiation
The "mediasec" header field parameter defined in this document is
used with procedures defined in RFC 3329 [4] to distinguish media
plane security, with the difference that media plane security need
not be started immediately and can be applied and removed on-the-fly
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as media are added and removed within a session. The SIP responses
that can contain the Security-Client, Security-Server, and Security-
Verfiy header fields are SIP responses 421 (Extension Required) and
494 (Security Agreement Required) as defined in RFC 3329 [4].
4.3. Syntax
This document does not define any new SIP header fields, it defines a
header field parameter for header fields Security-Client, Security-
Server and Security-Verify defined in RFC 3329 [4].
4.4. Protocol Operation
4.4.1. The "mediasec" Header Field Parameter
The "mediasec" header field parameter may be used in the Security-
Client, Security-Server, or Security-Verfiy header fields defined in
RFC 3329 [4] to indicate that a header field applies to the media
plane. Any one of the media plane security mechanisms supported by
both client and server, if any, may be applied when a media stream is
started. Or a media stream may be set up without security.
Values in the Security-Client, Security-Server, or Security-Verfiy
header fields labelled with the "mediasec" header field parameter are
specfic to the media plane and specific to the secure media transport
protocol used on the media plane.
4.4.2. Client Initiated
A client wishing to use the security capability exchange of this
specification MUST add a Security-Client header field to a request
addressed to its first-hop proxy (i.e., the destination of the
request is the first-hop proxy). This header field contains a list
of all the media plane security mechanisms that the client supports.
The client SHOULD NOT add preference parameters to this list. The
client MUST add a "mediasec" header field parameter to the Security-
Client header field.
The contents of the Security-Client header field may be used by the
server to include any necessary information in its response.
As described in RFC 3329 [4], the response will be 494 if the client
includes "sec-agree" in the Require and Proxy-Require header fields,
or a 2xx response if the Require and Proxy-Require header fields do
not contain "sec-agree". The server MUST add its list to the
response even if there are no common security mechanisms in the
client's and server's lists. The server's list MUST NOT depend on
the contents of the client's list.
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Any subsequent SIP requests sent by the client to that server MAY
make use of the media security capabilities exchanged in the previous
step by including media plane security parameters in SDP in the
session or the media description. These requests MUST contain a
Security-Verify header field that mirrors the server's list received
previously in the Security-Server header field.
The server MUST check that the security mechanisms listed in the
Security-Verify header field of incoming requests correspond to its
static list of supported security mechanisms.
Note that, following the standard SIP header field comparison rules
defined in RFC 3261 [7], both lists have to contain the same security
mechanisms in the same order to be considered equivalent. In
addition, for each particular security mechanism, its parameters in
both lists need to have the same values.
The server can proceed processing a particular request if, and only
if, the list was not modified. If modification of the list is
detected, the server MUST respond to the client with a 494 (Security
Agreement Required) response. This response MUST include the
server's unmodified list of supported security mechanisms.
Once security capabilities have been exchanged between two SIP
entities, the same SIP entities MAY use the same security when
communicating with each other in different SIP roles. For example,
if a UAC and its outbound proxy exchange some media-plane security
mechanisms, they may try to use the same security for incoming
requests (i.e., the UA will be acting as a UAS).
The user of a UA SHOULD be informed about the results of the security
mechanism agreement. The user MAY decline to accept a particular
security mechanism, and abort further SIP communications with the
peer.
4.5. Security Mechanism Initiation
Once the client chooses a security mechanism from the list received
in the Security-Server header field from the server, it MAY initiate
that mechanism on a session level, or on a media level when it
initiates new media in an existing session.
4.6. Duration of Security Assocations
Once media-plane security capabilities have been exchanged, both the
server and the client need to know until when they can be used. The
media plane security mechanism setup is valid for as long as the UA
has a SIP signalling relationship with its first-hop proxy or until
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new keys are exchanged in SDP. The SDP used to set up media plane
security will be protected by a security association used to protect
SIP signalling and the media plane security mechanism can be used
until the signalling plane security association expires.
4.7. Summary of Header Field Use
The header fields defined in this document may be used to exchange
supported media plane security mechanisms between a UAC and other SIP
entities including UAS, proxy, and registrar. Information about the
use of headers in relation to SIP methods and proxy processing is
given in RFC 3329 [4] Table 1.
5. Backwards Compatibility
Security mechanisms that apply to the media plane only MUST NOT have
the same name as any signalling plane mechanism. If a signalling
plane security mechanism name is re-used for the media plane and
distinguished only by the "mediasec" parameter, then implementations
that do not recognize the "mediasec" parameter may incorrectly use
that security mechanism for the signalling plane.
6. Examples
The following examples illustrate the use of the mediasec header
field parameter defined above.
6.1. Initial Registration 3GPP
At initial registration, the client includes its supported media
plane security mechanisms in the SIP REGISTER request. The first-hop
proxy returns its supported media plane security mechanisms in the
SIP 401 (Unauthorized) response.
As per RFC 3329 [4], a UA negotiates the security mechanism for the
media plane to be used with its outbound proxy without knowing
beforehand which mechanisms the proxy supports, as shown in Figure 2
below.
UAC Proxy Registrar
user1_public1@home1.net pcscf1.home1.net registrar.home1.net
| | |
|------(1) REGISTER---->| |
| Security-Client: sdes-srtp; mediasec
| | |
| |---(2) REGISTER--->|
| | |
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| |<----(3) 401-------|
| | |
|<-----(4) 401----------| |
| Security-Server: sdes-srtp; mediasec
| | |
|-----(5) REGISTER----->| |
| Security-Client: sdes-srtp; mediasec
| Security-Verify: sdes-srtp; mediasec
| | |
| |---(6) REGISTER--->|
| | |
| |<----(7) 200 OK----|
| | |
|<-----(8) 200 OK------ | |
| | |
|------(9) INVITE------>| |
| Security-Verify: sdes-srtp; mediasec
| | |
| Content-Type: application/sdp |
| a=3ge2ae | |
| a=crypto:1 AES_CM_128_HMAC_SHA1_80
| inline:WVNfX19zZW1jdGwgKCkgewkyMjA7fQp9CnVubGVz|2^20|1:4
| FEC_ORDER=FEC_SRTP |
| | |
Figure 2: Exchange of Media Security Mechanisms at Initial
Registration
The UAC sends a REGISTER request (1) to its outbound proxy indicating
the security mechanisms for the media plane and that it supports in a
Security-Client: header field. Indication of media security
mechanisms is identified by the "mediasec" header field parameter.
The outbound proxy forwards the REGISTER request (2) to the registrar
with the Security-Client: header field removed as described in RFC
3329 [4].
The registrar responds with a 401 (Unauthorized) response (3) to the
REGISTER request.
The outbound proxy responds forwards the 401 (Unauthorized) response
(4) to the UAC with its own list of security mechanisms for the media
plane in the Security-Server: header field. Security mechanisms for
the media plane are distinguished by the "mediasec" header field
parameter.
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The UAC sends a second REGISTER request (5) using the security
credentials it received in the 401 (Unauthorized) response. The UAC
includes the security mechanisms for the media plane and that it
supports in a Security-Client: header field. The UAC also echos the
list of security mechanisms it received from the outbound proxy in
the Security-Server: header field. Media security mechanisms are
distinguished by the "mediasec" header field parameter.
The REGISTER request is forwarded to the registrar (6) and the
registrar responds with 200 OK (7), which is forwarded to the UAC
(8).
When the connection is successfully established, the UAC sends an
INVITE request(9) including an SDP description of the media plane
security to be used (a="e2ae" and a crypto attribute). This INVITE
contains a copy of the server's security list in a Security-Verify
header field. The server verifies it, and since it matches its
static list, it processes the INVITE and forwards it to the next hop.
If this example was run without the Security-Server header field in
Step (2), the UAC would not know what kind of security the other one
supports, and would be forced to make error-prone trials.
More seriously, if the Security-Verify header field was omitted in
Step (3), the whole process would be prone to MitM attacks. An
attacker could remove the media plane security description from the
header in Step (1), therefore preventing protection of the media
plane.
(1) REGISTER sip:registrar.home1.net SIP/2.0
Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd];comp=sigcomp;branch=z9hG4bKnashds7
Max-Forwards: 70
P-Access-Network-Info: 3GPP-UTRAN-TDD; utran-cell-id-3gpp=234151D0FCE11
From: <sip:user1_public1@home1.net>;tag=4fa3
To: <sip:user1_public1@home1.net>
Contact: <sip:[5555::aaa:bbb:ccc:ddd];comp=sigcomp>;expires=600000
Call-ID: apb03a0s09dkjdfglkj49111
Authorization: Digest username="user1_private@home1.net", realm="registrar.home1.net", nonce="", uri="sip:registrar.home1.net", response=""
Security-Client: ipsec-3gpp; alg=hmac-sha-1-96; spi-c=23456789; spi-s=12345678; port-c=2468; port-s=1357
Security-Client: sdes-srtp; mediasec ***new***
Require: sec-agree
Proxy-Require: sec-agree
CSeq: 1 REGISTER
Supported: path
Content-Length: 0
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(2) REGISTER sip:registrar.home1.net SIP/2.0
Via: SIP/2.0/UDP pcscf1.home1.net;branch=z9hG4bK351g45.1, SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd];comp=sigcomp;branch=z9hG4bKnashds7
Max-Forwards: 69
P-Access-Network-Info:
Path:
Require:
P-Visited-Network-ID:
P-Charging-Vector:
From:
To:
Contact:
Call-ID:
Authorization:
CSeq:
Supported:
Content-Length:
(3) SIP/2.0 401 Unauthorized
Via: SIP/2.0/UDP pcscf1.home1.net;branch=z9hG4bK351g45.1, SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd];comp=sigcomp;branch=z9hG4bKnashds7
From: <sip:user1_public1@home1.net>;tag=4fa3
To: <sip:user1_public1@home1.net>; tag=5ef4
Call-ID: apb03a0s09dkjdfglkj49111
WWW-Authenticate: Digest realm="registrar.home1.net", nonce=base64(RAND + AUTN + server specific data), algorithm=AKAv1-MD5, ik="00112233445566778899aabbccddeeff", ck="ffeeddccbbaa11223344556677889900"
CSeq: 1 REGISTER
Content-Length: 0
(4) SIP/2.0 401 Unauthorized
Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd];comp=sigcomp;branch=z9hG4bKnashds7
From:
To:
Call-ID:
WWW-Authenticate: Digest realm="registrar.home1.net", nonce=base64(RAND + AUTN + server specific data), algorithm=AKAv1-MD5
Security-Server: ipsec-3gpp; q=0.1; alg=hmac-sha-1-96; spi-c=98765432; spi-s=87654321; port-c=8642; port-s=7531
Security-Server: sdes-srtp; mediasec ***new***
CSeq:
Content-Length:
(5) REGISTER sip:registrar.home1.net SIP/2.0
Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp;branch=z9hG4bKnashds7
Max-Forwards: 70
P-Access-Network-Info: 3GPP-UTRAN-TDD; utran-cell-id-3gpp=234151D0FCE11
From: <sip:user1_public1@home1.net>;tag=4fa3
To: <sip:user1_public1@home1.net>
Contact: <sip:[5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp>;expires=600000
Call-ID: apb03a0s09dkjdfglkj49111
Authorization: Digest username="user1_private@home1.net", realm="registrar.home1.net", nonce=base64(RAND + AUTN + server specific data), algorithm=AKAv1-MD5, uri="sip:registrar.home1.net", response="6629fae49393a05397450978507c4ef1"
Security-Client: ipsec-3gpp; alg=hmac-sha-1-96; spi-c=23456789; spi-s=12345678; port-c=2468; port-s=1357
Security-Verify: ipsec-3gpp; q=0.1; alg=hmac-sha-1-96; spi-c=98765432; spi-s=87654321; port-c=8642; port-s=7531
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Security-Client: sdes-srtp; mediasec ***new***
Security-Verify: sdes-srtp; mediasec ***new***
Require: sec-agree
Proxy-Require: sec-agree
CSeq: 2 REGISTER
Supported: path
Content-Length: 0
(6) REGISTER sip:registrar.home1.net SIP/2.0
Via: SIP/2.0/UDP pcscf1.home1.net;branch=z9hG4bK351g45.1, SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp;branch=z9hG4bKnashds7
Max-Forwards: 69
P-Access-Network-Info:
Path:
Require:
P-Visited-Network-ID:
P-Charging-Vector:
From:
To:
Contact:
Call-ID:
Authorization:
CSeq:
Supported:
Content-Length:
(7) SIP/2.0 200 OK
Via: SIP/2.0/UDP pcscf1.home1.net;branch=z9hG4bK351g45.1, SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp;branch=z9hG4bKnashds7
Path: <sip:term@pcscf1.visited1.net;lr>
From:
To:
Call-ID:
Contact: <sip:[5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp>;expires=600000
CSeq:
Date: Wed, 11 July 2001 08:49:37 GMT
P-Associated-URI: <sip:user1_public2@home1.net>, <sip:user1_public3@home1.net>, <sip:+1-212-555-1111 begin_of_the_skype_highlighting +1-212-555-1111 FREE end_of_the_skype_highlighting@home1.net;user=phone>
Content-Length:
(8) SIP/2.0 200 OK
Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp;branch=z9hG4bKnashds7
Path:
From:
To:
Call-ID:
Contact:
CSeq:
Date:
P-Associated-URI:
Content-Length:
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Figure 3: Use of mediasec parameter
6.2. Re-Registration 3GPP
Media plane security mechanisms are also exchanged when a
registration is refreshed or a new public identity is registered.
UAC Proxy Registrar
user1_public1@home1.net pcscf1.home1.net registrar.home1.net
| | |
| | |
|--------(1) REGISTER---->| |
| Security-Client: sdes-srtp; mediasec
| Security-Verify: sdes-srtp; mediasec
| | |
| |---(2) REGISTER--->|
| | |
| |<----(3) 200 OK----|
| | |
|<------(4) 200 OK------- | |
| | |
| | |
Figure 4: Exchange of Media Security Mechanisms at Re-Registration
The UAC sends a REGISTER request (1) and includes the security
mechanisms for the media plane and that it supports in a Security-
Client: header field. The UAC also echos the list of security
mechanisms it received from the outbound proxy in the Security-
Server: header field. Media security mechanisms are distinguished by
the "mediasec" header field parameter.
The REGISTER request is forwarded to the registrar (2) and the
registrar responds with 200 OK (3), which is forwarded to the UAC
(4).
(1) REGISTER sip:registrar.home1.net SIP/2.0
Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp;branch=z9hG4bKnashds7
Max-Forwards: 70
P-Access-Network-Info: 3GPP-UTRAN-TDD; utran-cell-id-3gpp=234151D0FCE11
From: <sip:user1_public1@home1.net>;tag=4fa3
To: <sip:user1_public1@home1.net>
Contact: <sip:[5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp>;expires=600000
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Call-ID: apb03a0s09dkjdfglkj49111
Authorization: Digest username="user1_private@home1.net", realm="registrar.home1.net", nonce=base64(RAND + AUTN + server specific data), algorithm=AKAv1-MD5, uri="sip:registrar.home1.net", response="6629fae49393a05397450978507c4ef1", integrity-protected="yes"
Security-Client: ipsec-3gpp; alg=hmac-sha-1-96; spi-c=23456789; spi-s=12345678; port-c=2468; port-s=1357
Security-Client: sdes-srtp; mediasec ***new***
Security-Verify: ipsec-3gpp; q=0.1; alg=hmac-sha-1-96; spi-c=98765432; spi-s=87654321; port-c=8642; port-s=7531
Security-Verify: sdes-srtp; mediasec ***new***
Require: sec-agree
Proxy-Require: sec-agree
CSeq: 3 REGISTER
Supported: path
Content-Length: 0
(2) REGISTER sip:registrar.home1.net SIP/2.0
Via: SIP/2.0/UDP pcscf1.home1.net;branch=z9hG4bK240f34.1, SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp;branch=z9hG4bKnashds7
P-Access-Network-Info:
Max-Forwards: 69
Path:
Require:
P-Visited-Network-ID:
P-Charging-Vector:
From:
To:
Contact:
Call-ID:
Authorization:
CSeq:
Supported:
Content-Length:
(3) SIP/2.0 200 OK
Via: SIP/2.0/UDP pcscf1.home1.net;branch=z9hG4bK240f34.1, SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp;branch=z9hG4bKnashds7
Path:
From:
To:
Call-ID:
Contact: <sip:[5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp>;expires=600000
CSeq:
Date: Wed, 11 July 2001 08:49:37 GMT
P-Associated-URI: <sip:user1_public2@home1.net>, <sip:user1_public3@home1.net>, <sip:+1-212-555-1111 begin_of_the_skype_highlighting +1-212-555-1111 FREE end_of_the_skype_highlighting@home1.net;user=phone>
Content-Length:
(4) SIP/2.0 200 OK
Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp;branch=z9hG4bKnashds7
Path:
From:
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To:
Call-ID:
Contact:
CSeq:
Date:
P-Associated-URI:
Content-Length:
Figure 5: Use of mediasec parameter
6.3. Client Initiated as per RFC 3329
Media plane security mechanisms are also exchanged at client
initiated security negotiation described in RFC 3329 [4].
UAC Proxy UAS
| | |
|----(1) OPTIONS----->| |
| | |
|<-----(2) 494--------| |
| | |
|<=======TLS=========>| |
| | |
|----(3) INVITE------>| |
| |----(4) INVITE--->|
| | |
| |<---(5) 200 OK----|
|<----(6) 200 OK------| |
| | |
|------(7) ACK------->| |
| |-----(8) ACK----->|
| | |
| | |
| | |
| | |
|<-(Protected media)->|<---(Media)------>|
| | |
Figure 6: Negotiation Initiated by the Client.
After exchange of security capabilities, the UAC sends an INVITE
request(3) including an SDP description of the media plane security
to be used (a="e2ae" and a crypto attribute). This INVITE contains a
copy of the server's security list in a Security-Verify header field.
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The server verifies it, and since it matches its static list, it
processes the INVITE and forwards it to the next hop.
(1) OPTIONS sip:proxy.example.com SIP/2.0
Security-Client: tls
Security-Client: digest
Security-Client: sdes-srtp; mediasec
Require: sec-agree
Proxy-Require: sec-agree
(2) SIP/2.0 494 Security Agreement Required
Security-Server: ipsec-ike;q=0.1
Security-Server: tls;q=0.2
Security-Server: sdes-srtp; mediasec
(3) INVITE sip:proxy.example.com SIP/2.0
Security-Verify: ipsec-ike;q=0.1
Security-Verify: tls;q=0.2
Security-Verify: sdes-srtp; mediasec
Route: sip:callee@domain.com
Require: sec-agree
Proxy-Require: sec-agree
6.4. Server Initiated as per RFC 3329
Media plane security mechanisms are also exchanged at server
initiated security negotiation described in RFC 3329 [4].
UAC Proxy UAS
| | |
|-----(1) INVITE---->| |
| | |
|<-----(2) 421-------| |
| | |
|------(3) ACK------>| |
| | |
|<=======IKE========>| |
| | |
|-----(4) INVITE---->| |
| |----(5) INVITE--->|
| | |
| |<---(6) 200 OK----|
|<----(7) 200 OK-----| |
| | |
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|------(8) ACK------>| |
| |-----(9) ACK----->|
| | |
| | |
Figure 7: Negotiation Initiated by the Server.
Media security mechanisms are included in Security-Server: and
Security-Client: header fields in the same way as signalling security
mechanisms.
(1) INVITE sip:uas.example.com SIP/2.0
(2) SIP/2.0 421 Extension Required
Security-Server: ipsec-ike;q=0.1
Security-Server: tls;q=0.2
Security-Server: mechanism; mediasec
(4) INVITE sip:uas.example.com SIP/2.0
Security-Verify: ipsec-ike;q=0.1
Security-Verify: tls;q=0.2
Security-Verify: mechanism; mediasec
Figure 8: Negotiation Initiated by the Server.
6.5. Using Media Plane Security
To request end to access edge media security either on a session or
media level the UE sends, for example, an SDP Offer for an SRTP
stream containing one or more SDES crypto attributes, each with a key
and other security context parameters required according to RFC 4568
[8], together with the attribute "a=3ge2ae".
(3) INVITE sip:bob@ua2.example.com SIP/2.0
Security-Verify: ipsec-ike;q=0.1
Security-Verify: tls;q=0.2
Security-Verify: sdes-srtp;mediasec
Route: proxy.example.com
Require: sec-agree, mediasec
Proxy-Require: sec-agree, mediasec
Via: SIP/2.0/TCP proxy.example.com:5060;branch=z9hG4bK74bf9
Max-Forwards: 70
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From: Alice <sip:alice@ua1.example.com>;tag=9fxced76sl
To: Bob <sip:bob@ua2.example.com>
Call-ID: 3848276298220188511@ua1.example.com
CSeq: 1 INVITE
Contact: <sip:alice@ua1.example.com;transport=tcp>
Content-Type: application/sdp
Content-Length: 285
v=0
o=alice 2890844526 2890844526 IN IP4 ua1.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/SAVP 0
a=3ge2ae
a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:WVNfX19zZW1jdGwgKCkgewkyMjA7fQp9CnVubGVz|2^20|1:4
FEC_ORDER=FEC_SRTP
a=rtpmap:0 PCMU/8000
(4) INVITE sip:bob@ua2.example.com SIP/2.0
Route: sip:proxy.example.com
(5) SIP/2.0 200 OK
(6) SIP/2.0 200 OK
Security-Server: tls;q=0.2
Security-Server: sdes-srtp;mediasec
a=3ge2ae
a=crypto:1 AES_CM_128_HMAC_SHA1_80
a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:PS1uQCVeeCFCanVmcjkpPywjNWhcYD0mXXtxaVBR|2^20|1:4
Figure 9: Using media security
7. Formal Syntax
The following syntax specification uses the augmented Backus-Naur
Form (BNF) as described in RFC 5234 [RFC5234].
"mediasec" is a "header field parameter", as defined by [RFC3968].
Header Field Name in which the parameter can appear.
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Security-Client
Security-Server
Security-Verify
Header Fields Parameter Name Values Reference
--------------- ---------------- -------- ---------
Security-Client mediasec No [this document]
Security-Server mediasec No [this document]
Security-Verify mediasec No [this document]
Name of the Header Field Parameter being registered.
"mediasec"
8. Acknowledgements
Remember, it's important to acknowledge people who have contributed
to the work.
This template was extended from an initial version written by Pekka
Savola and contributed by him to the xml2rfc project.
9. IANA Considerations
This specification creates a new registry for media plane security
mechanisms.
9.1. Registry for Media Plane Security Mechanisms
The IANA has created a subregistry for media plane security mechanism
token values to be used with the 'mediasec' header field parameter
under the Session Initiation Protocol (SIP) Parameters registry.
Security Mechanism Name for Media Reference
--------------------------------- ---------
As per the terminology in [RFC5226], the registration policy for new
media plane security mechanism token values shall be 'Specification
Required'.
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9.2. Registration Template
To: ietf-sip-sec-agree-mechanism-name@iana.org Subject: Registration
of a new SIP Security Agreement mechanism
Mechanism Name:
(Token value conforming to the syntax described in Section 4.3.)
Published Specification(s):
(Descriptions of new SIP media plane security agreement mechanisms
require a published specification.)
9.3. Header Field Names
This specification registers no new header fields.
9.4. Response Codes
This specification registers no new response codes.
10. Security Considerations
This specification is an extension of RFC 3329 [4] and as such shares
the same security considerations.
A further consideration of this specification is protection of the
cryptographic key to be used for SRTP and carried in SDP. In order
to protect this key, one of the security mechanisms defined in RFC
3329 [4] SHOULD be used in parallel with this specification.
11. References
11.1. Normative References
[1] authSurName, authInitials., "example1", year.
[2] authSurName, authInitials., "example2", year.
[3] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997,
<http://xml.resource.org/public/rfc/html/rfc2119.html>.
[4] Arkko, J., Torvinen, V., Camarillo, G., Niemi, A., and T.
Haukka, "Security Mechanism Agreement for the Session
Initiation Protocol (SIP)", RFC 3329, January 2003.
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[5] Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn,
G., and B. Palter, "Layer Two Tunneling Protocol "L2TP"",
RFC 2661, August 1999.
[6] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[7] 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.
[8] Andreasen, F., Baugher, M., and D. Wing, "Session
Description Protocol (SDP) Security Descriptions for Media
Streams", RFC 4568, July 2006.
[9] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, November 1998.
[10] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[11] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework
for Establishing a Secure Real-time Transport Protocol
(SRTP) Security Context Using Datagram Transport Layer
Security (DTLS)", RFC 5763, May 2010.
[12] Andreasen, F., "Session Description Protocol (SDP)
Capability Negotiation", RFC 5939, September 2010.
11.2. Informative References
[13] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
[14] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
Appendix A. Additional stuff
You can add appendices just as regular sections, the only difference
is that they go within the "back" element, and not within the
"middle" element. And they follow the "reference" elements.
Author's Address
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Peter Dawes
Vodafone Group Services Ltd.
Newbury
UK
Email: peter.dawes@vodafone.com
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