draft-ietf-mmusic-comedia-tls-06.txt   rfc4572.txt 
Multiparty Multimedia Session J. Lennox Network Working Group J. Lennox
Control Columbia U. Request for Comments: 4572 Columbia U.
Expires: September 4, 2006 Category: Standards Track
Connection-Oriented Media Transport over the Transport Layer Security Connection-Oriented Media Transport over the Transport Layer Security
(TLS) Protocol in the Session Description Protocol (SDP) (TLS) Protocol in the Session Description Protocol (SDP)
draft-ietf-mmusic-comedia-tls-06
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document specifies how to establish secure connection-oriented This document specifies how to establish secure connection-oriented
media transport sessions over the Transport Layer Security (TLS) media transport sessions over the Transport Layer Security (TLS)
protocol using the Session Description Protocol (SDP). It defines a protocol using the Session Description Protocol (SDP). It defines a
new SDP protocol identifier, 'TCP/TLS'. It also defines the syntax new SDP protocol identifier, 'TCP/TLS'. It also defines the syntax
and semantics for an SDP 'fingerprint' attribute that identifies the and semantics for an SDP 'fingerprint' attribute that identifies the
certificate which will be presented for the TLS session. This certificate that will be presented for the TLS session. This
mechanism allows media transport over TLS connections to be mechanism allows media transport over TLS connections to be
established securely, so long as the integrity of session established securely, so long as the integrity of session
descriptions is assured. descriptions is assured.
This revision of the document reflects comments made during IESG This document extends and updates RFC 4145.
review.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction ....................................................3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology .....................................................4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Overview ........................................................4
3.1. SDP Operational Modes . . . . . . . . . . . . . . . . . . 4 3.1. SDP Operational Modes ......................................4
3.2. Threat Model . . . . . . . . . . . . . . . . . . . . . . . 5 3.2. Threat Model ...............................................5
3.3. The Need For Self-Signed Certificates . . . . . . . . . . 5 3.3. The Need for Self-Signed Certificates ......................5
3.4. Example SDP Description For TLS Connection . . . . . . . . 6 3.4. Example SDP Description for TLS Connection .................6
4. Protocol Identifiers . . . . . . . . . . . . . . . . . . . . . 6 4. Protocol Identifiers ............................................6
5. Fingerprint Attribute . . . . . . . . . . . . . . . . . . . . 7 5. Fingerprint Attribute ...........................................7
6. Endpoint Identification . . . . . . . . . . . . . . . . . . . 8 6. Endpoint Identification .........................................9
6.1. Certificate Choice . . . . . . . . . . . . . . . . . . . . 8 6.1. Certificate Choice .........................................9
6.2. Certificate Presentation . . . . . . . . . . . . . . . . . 9 6.2. Certificate Presentation ..................................10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10 7. Security Considerations ........................................10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 8. IANA Considerations ............................................12
Appendix A. Changes From Earlier Versions . . . . . . . . . . . 13 9. References .....................................................14
Appendix A.1. Changes From Draft -05 . . . . . . . . . . . . . . . 13 9.1. Normative References ......................................14
Appendix A.2. Changes From Draft -04 . . . . . . . . . . . . . . . 14 9.2. Informative References ....................................15
Appendix A.3. Changes From Draft -03 . . . . . . . . . . . . . . . 14
Appendix A.4. Changes From Draft -02 . . . . . . . . . . . . . . . 15
Appendix A.5. Changes From Draft -01 . . . . . . . . . . . . . . . 15
Appendix A.6. Changes From Draft -00 . . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1. Normative References . . . . . . . . . . . . . . . . . . . 15
9.2. Informative References . . . . . . . . . . . . . . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 18
Intellectual Property and Copyright Statements . . . . . . . . . . 19
1. Introduction 1. Introduction
The Session Description Protocol (SDP) [1] provides a general purpose The Session Description Protocol (SDP) [1] provides a general-purpose
format for describing multimedia sessions in announcements or format for describing multimedia sessions in announcements or
invitations. For many applications, it is desirable to establish, as invitations. For many applications, it is desirable to establish, as
part of a multimedia session, a media stream which uses a connection- part of a multimedia session, a media stream that uses a connection-
oriented transport. RFC 4145, Connection-Oriented Media Transport in oriented transport. RFC 4145, Connection-Oriented Media Transport in
the Session Description Protocol (SDP) [2], specifies a general the Session Description Protocol (SDP) [2], specifies a general
mechanism for describing and establishing such connection-oriented mechanism for describing and establishing such connection-oriented
streams; however, the only transport protocol it directly supports is streams; however, the only transport protocol it directly supports is
TCP. In many cases, session participants wish to provide TCP. In many cases, session participants wish to provide
confidentiality, data integrity, and authentication for their media confidentiality, data integrity, and authentication for their media
sessions. This document therefore extends the Connection-Oriented sessions. This document therefore extends the Connection-Oriented
Media specification to allow session descriptions to describe media Media specification to allow session descriptions to describe media
sessions that use the Transport Layer Security (TLS) protocol [3]. sessions that use the Transport Layer Security (TLS) protocol [3].
The TLS protocol allows applications to communicate over a channel The TLS protocol allows applications to communicate over a channel
which provides confidentiality and data integrity. The TLS that provides confidentiality and data integrity. The TLS
specification, however, does not specify how specific protocols specification, however, does not specify how specific protocols
establish and use this secure channel; particularly, TLS leaves the establish and use this secure channel; particularly, TLS leaves the
question of how to interpret and validate authentication certificates question of how to interpret and validate authentication certificates
as an issue for the protocols which run over TLS. This document as an issue for the protocols that run over TLS. This document
specifies such usage for the case of connection-oriented media specifies such usage for the case of connection-oriented media
transport. transport.
Complicating this issue, endpoints exchanging media will often be Complicating this issue, endpoints exchanging media will often be
unable to obtain authentication certificates signed by a well-known unable to obtain authentication certificates signed by a well-known
root certification authority (CA). Most certificate authorities root certification authority (CA). Most certificate authorities
charge for signed certificates, particularly host-based certificates; charge for signed certificates, particularly host-based certificates;
additionally, there is a substantial administrative overhead to additionally, there is a substantial administrative overhead to
obtaining signed certificates, as certification authorities must be obtaining signed certificates, as certification authorities must be
able to confirm that they are issuing the signed certificates to the able to confirm that they are issuing the signed certificates to the
correct party. Furthermore, in many cases endpoints' IP addresses correct party. Furthermore, in many cases endpoints' IP addresses
and host names are dynamic: they may be obtained from DHCP, for and host names are dynamic: they may be obtained from DHCP, for
example. It is impractical to obtain a CA-signed certificate valid example. It is impractical to obtain a CA-signed certificate valid
for the duration of a DHCP lease. For such hosts, self-signed for the duration of a DHCP lease. For such hosts, self-signed
certificates are usually the only option. This specification defines certificates are usually the only option. This specification defines
a mechanism which allows self-signed certificates can be used a mechanism that allows self-signed certificates can be used
securely, provided that the integrity of the SDP description is securely, provided that the integrity of the SDP description is
assured. It provides for endpoints to include a secure hash of their assured. It provides for endpoints to include a secure hash of their
certificate, known as the "certificate fingerprint", within the certificate, known as the "certificate fingerprint", within the
session description. Provided the fingerprint of the offered session description. Provided that the fingerprint of the offered
certificate matches the one in the session description, end hosts can certificate matches the one in the session description, end hosts can
trust even self-signed certificates. trust even self-signed certificates.
The rest of this document is laid out as follows. An overview of the The rest of this document is laid out as follows. An overview of the
problem and threat model is given in Section 3. Section 4 gives the problem and threat model is given in Section 3. Section 4 gives the
basic mechanism for establishing TLS-based connected-oriented media basic mechanism for establishing TLS-based connected-oriented media
in SDP. Section 5 describes the SDP fingerprint attribute, which, in SDP. Section 5 describes the SDP fingerprint attribute, which,
assuming the integrity of SDP content is assured, allows the secure assuming that the integrity of SDP content is assured, allows the
use of self-signed certificates. Section 6 describes which X.509 secure use of self-signed certificates. Section 6 describes which
certificates are presented, and how they are used in TLS. Section 7 X.509 certificates are presented, and how they are used in TLS.
discusses additional security considerations. Section 7 discusses additional security considerations.
2. Terminology 2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [4] and and "OPTIONAL" are to be interpreted as described in RFC 2119 [4] and
indicate requirement levels for compliant implementations. indicate requirement levels for compliant implementations.
3. Overview 3. Overview
This section discusses the threat model which motivates TLS transport This section discusses the threat model that motivates TLS transport
for connection-oriented media streams. It also discusses in more for connection-oriented media streams. It also discusses in more
detail the need for end systems to use self-signed certificates. detail the need for end systems to use self-signed certificates.
3.1. SDP Operational Modes 3.1. SDP Operational Modes
There are two principal operational modes for multimedia sessions: There are two principal operational modes for multimedia sessions:
advertised and offer-answer. Advertised sessions are the simpler advertised and offer-answer. Advertised sessions are the simpler
mode. In this mode, a server publishes, in some manner, an SDP mode. In this mode, a server publishes, in some manner, an SDP
session description describing a multimedia session it is making session description of a multimedia session it is making available.
available. The classic example of this mode of operation is the The classic example of this mode of operation is the Session
Session Announcement Protocol (SAP) [15], in which SDP session Announcement Protocol (SAP) [15], in which SDP session descriptions
descriptions are periodically transmitted to a well-known multicast are periodically transmitted to a well-known multicast group.
group. Traditionally, these descriptions involve multicast Traditionally, these descriptions involve multicast conferences, but
conferences, but unicast sessions are also possible. (Connection- unicast sessions are also possible. (Connection-oriented media,
oriented media, obviously, cannot use multicast.) Recipients of a obviously, cannot use multicast.) Recipients of a session
session description connect to the addresses published in the session description connect to the addresses published in the session
description. These recipients may not previously have been known to description. These recipients may not previously have been known to
the advertiser of the session description. the advertiser of the session description.
Alternatively, SDP conferences can operate in offer-answer mode [5]. Alternatively, SDP conferences can operate in offer-answer mode [5].
This mode allows two participants in a multimedia session to This mode allows two participants in a multimedia session to
negotiate the multimedia session between them. In this model, one negotiate the multimedia session between them. In this model, one
participant offers the other a description of the desired session participant offers the other a description of the desired session
from its perspective, and the other participant answers with the from its perspective, and the other participant answers with the
desired session from its own perspective. In this mode, each of the desired session from its own perspective. In this mode, each of the
participants in the session has knowledge of the other one. This is participants in the session has knowledge of the other one. This is
skipping to change at page 5, line 38 skipping to change at page 5, line 38
communications. To thwart these attacks, TLS uses endpoint communications. To thwart these attacks, TLS uses endpoint
certificates. So long as the certificates' private keys have not certificates. So long as the certificates' private keys have not
been compromised, the endpoints have an external trusted mechanism been compromised, the endpoints have an external trusted mechanism
(most commonly, a mutually-trusted certification authority) to (most commonly, a mutually-trusted certification authority) to
validate certificates, and the endpoints know what certificate validate certificates, and the endpoints know what certificate
identity to expect, endpoints can be certain that such an attack has identity to expect, endpoints can be certain that such an attack has
not taken place. not taken place.
Finally, the most serious type of attacker is one who can modify or Finally, the most serious type of attacker is one who can modify or
redirect session descriptions: for example, a compromised or redirect session descriptions: for example, a compromised or
malicious SIP proxy server. Neither TLS itself, nor any mechanisms malicious SIP proxy server. Neither TLS itself nor any mechanisms
which use it, can protect an SDP session against such an attacker. that use it can protect an SDP session against such an attacker.
Instead, the SDP description itself must be secured through some Instead, the SDP description itself must be secured through some
mechanism; SIP, for example, defines how S/MIME [17] can be used to mechanism; SIP, for example, defines how S/MIME [17] can be used to
secure session descriptions. secure session descriptions.
3.3. The Need For Self-Signed Certificates 3.3. The Need for Self-Signed Certificates
SDP session descriptions are created by any endpoint that needs to SDP session descriptions are created by any endpoint that needs to
participate in a multimedia session. In many cases, such as SIP participate in a multimedia session. In many cases, such as SIP
phones, such endpoints have dynamically-configured IP addresses and phones, such endpoints have dynamically-configured IP addresses and
host names, and must be deployed with nearly zero configuration. For host names and must be deployed with nearly zero configuration. For
such an endpoint, it is for practical purposes impossible to obtain a such an endpoint, it is for practical purposes impossible to obtain a
certificate signed by a well-known certification authority. certificate signed by a well-known certification authority.
If two endpoints have no prior relationship, self-signed certificates If two endpoints have no prior relationship, self-signed certificates
cannot generally be trusted, as there is no guarantee that an cannot generally be trusted, as there is no guarantee that an
attacker is not launching a man-in-the-middle attack. Fortunately, attacker is not launching a man-in-the-middle attack. Fortunately,
however, if the integrity of SDP session descriptions can be assured, however, if the integrity of SDP session descriptions can be assured,
it is possible to consider those SDP descriptions themselves as a it is possible to consider those SDP descriptions themselves as a
prior relationship: certificates can be securely described in the prior relationship: certificates can be securely described in the
session description itself. This is done by providing a secure hash session description itself. This is done by providing a secure hash
of a certificate, or "certificate fingerprint", as an SDP attribute; of a certificate, or "certificate fingerprint", as an SDP attribute;
this mechanism is described in Section 5. this mechanism is described in Section 5.
3.4. Example SDP Description For TLS Connection 3.4. Example SDP Description for TLS Connection
Figure 1 illustrates an SDP offer which signals the availability of a Figure 1 illustrates an SDP offer that signals the availability of a
T.38 fax session over TLS. For the purpose of brevity, the main T.38 fax session over TLS. For the purpose of brevity, the main
portion of the session description is omitted in the example, showing portion of the session description is omitted in the example, showing
only the 'm' line and its attributes. (This example is the same as only the 'm' line and its attributes. (This example is the same as
the first one in RFC 4145 [2], except for the proto parameter and the the first one in RFC 4145 [2], except for the proto parameter and the
fingerprint attribute.) See the subsequent sections for explanations fingerprint attribute.) See the subsequent sections for explanations
of the example's TLS-specific attributes. of the example's TLS-specific attributes.
(Note: due to RFC formatting conventions, this draft splits SDP (Note: due to RFC formatting conventions, this document splits SDP
across lines whose content would exceed 72 characters. A backslash across lines whose content would exceed 72 characters. A backslash
character marks where this line folding has taken place. This character marks where this line folding has taken place. This
backslash and its trailing CRLF and whitespace would not appear in backslash and its trailing CRLF and whitespace would not appear in
actual SDP content.) actual SDP content.)
m=image 54111 TCP/TLS t38 m=image 54111 TCP/TLS t38
c=IN IP4 192.0.2.2 c=IN IP4 192.0.2.2
a=setup:passive a=setup:passive
a=connection:new a=connection:new
a=fingerprint:SHA-1 \ a=fingerprint:SHA-1 \
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4. Protocol Identifiers 4. Protocol Identifiers
The 'm' line in SDP specifies, among other items, the transport The 'm' line in SDP specifies, among other items, the transport
protocol to be used for the media in the session. See the "Media protocol to be used for the media in the session. See the "Media
Descriptions" section of SDP [1] for a discussion on transport Descriptions" section of SDP [1] for a discussion on transport
protocol identifiers. protocol identifiers.
This specification defines a new protocol identifier, 'TCP/TLS', This specification defines a new protocol identifier, 'TCP/TLS',
which indicates that the media described will use the Transport Layer which indicates that the media described will use the Transport Layer
Security protocol [3] over TCP. (Using TLS over other transport Security protocol [3] over TCP. (Using TLS over other transport
protocols is not discussed by this document.) The 'TCP/TLS' protocol protocols is not discussed in this document.) The 'TCP/TLS' protocol
identifier describes only the transport protocol, not the upper-layer identifier describes only the transport protocol, not the upper-layer
protocol. An 'm' line that specifies 'TCP/TLS' MUST further qualify protocol. An 'm' line that specifies 'TCP/TLS' MUST further qualify
the protocol using a fmt identifier, to indicate the application the protocol using a fmt identifier to indicate the application being
being run over TLS. run over TLS.
Media sessions described with this identifier follow the procedures Media sessions described with this identifier follow the procedures
defined in RFC 4145 [2]. They also use the SDP attributes defined in defined in RFC 4145 [2]. They also use the SDP attributes defined in
that specification, 'setup' and 'connection'. that specification, 'setup' and 'connection'.
5. Fingerprint Attribute 5. Fingerprint Attribute
Parties to a TLS session indicate their identities by presenting Parties to a TLS session indicate their identities by presenting
authentication certificates as part of the TLS handshake procedure. authentication certificates as part of the TLS handshake procedure.
Authentication certificates are X.509 [6] certificates, as profiled Authentication certificates are X.509 [6] certificates, as profiled
by RFC 3279 [7], RFC 3280 [8] and RFC 4055 [9]. by RFC 3279 [7], RFC 3280 [8], and RFC 4055 [9].
In order to associate media streams with connections, and to prevent In order to associate media streams with connections and to prevent
unauthorized barge-in attacks on the media streams, endpoints MUST unauthorized barge-in attacks on the media streams, endpoints MUST
provide a certificate fingerprint. If the X.509 certificate provide a certificate fingerprint. If the X.509 certificate
presented for the TLS connection matches the fingerprint presented in presented for the TLS connection matches the fingerprint presented in
the SDP, the endpoint can be confident that the author of the SDP is the SDP, the endpoint can be confident that the author of the SDP is
indeed the initiator of the connection. indeed the initiator of the connection.
A certificate fingerprint is a secure one-way hash of the DER A certificate fingerprint is a secure one-way hash of the DER
(distinguished encoding rules) form of the certificate. (Certificate (distinguished encoding rules) form of the certificate. (Certificate
fingerprints are widely supported by tools which manipulate X.509 fingerprints are widely supported by tools that manipulate X.509
certificates; for instance, the command "openssl x509 -fingerprint" certificates; for instance, the command "openssl x509 -fingerprint"
causes the command-line tool of the openssl package to print a causes the command-line tool of the openssl package to print a
certificate fingerprint, and the certificate managers for Mozilla and certificate fingerprint, and the certificate managers for Mozilla and
Internet Explorer display them when viewing the details of a Internet Explorer display them when viewing the details of a
certificate.) certificate.)
A fingerprint is represented in SDP as an attribute (an 'a' line). A fingerprint is represented in SDP as an attribute (an 'a' line).
It consists of the name of the hash function used, followed by the It consists of the name of the hash function used, followed by the
hash value itself. The hash value is represented as a sequence of hash value itself. The hash value is represented as a sequence of
upper-case hexadecimal bytes, separated by colons. The number of uppercase hexadecimal bytes, separated by colons. The number of
bytes is defined by the hash function. (This is the syntax used by bytes is defined by the hash function. (This is the syntax used by
openssl and by the browsers' certificate managers. It is different openssl and by the browsers' certificate managers. It is different
from the syntax used to represent hash values in, e.g., HTTP digest from the syntax used to represent hash values in, e.g., HTTP digest
authentication [18], which uses unseparated lower-case hexadecimal authentication [18], which uses unseparated lowercase hexadecimal
bytes. It was felt that consistency with other applications of bytes. It was felt that consistency with other applications of
fingerprints was more important.) fingerprints was more important.)
The formal syntax of the fingerprint attribute is given in Augmented The formal syntax of the fingerprint attribute is given in Augmented
Backus-Naur Form [10] in Figure 2. This syntax extends the BNF Backus-Naur Form [10] in Figure 2. This syntax extends the BNF
syntax of SDP [1]. syntax of SDP [1].
attribute =/ fingerprint-attribute attribute =/ fingerprint-attribute
fingerprint-attribute = "fingerprint" ":" hash-func SP fingerprint fingerprint-attribute = "fingerprint" ":" hash-func SP fingerprint
skipping to change at page 8, line 26 skipping to change at page 8, line 26
; Each byte in upper-case hex, separated ; Each byte in upper-case hex, separated
; by colons. ; by colons.
UHEX = DIGIT / %x41-46 ; A-F uppercase UHEX = DIGIT / %x41-46 ; A-F uppercase
Figure 2: Augmented Backus-Naur Syntax for the Fingerprint Attribute Figure 2: Augmented Backus-Naur Syntax for the Fingerprint Attribute
A certificate fingerprint MUST be computed using the same one-way A certificate fingerprint MUST be computed using the same one-way
hash function as is used in the certificate's signature algorithm. hash function as is used in the certificate's signature algorithm.
(This ensures that the security properties required for the (This ensures that the security properties required for the
certificate are also apply for the fingerprint. It also guarantees certificate also apply for the fingerprint. It also guarantees that
that the fingerprint will be usable by the other endpoint, so long as the fingerprint will be usable by the other endpoint, so long as the
the certificate itself is.) Following RFC 3279 [7] as updated by RFC certificate itself is.) Following RFC 3279 [7] as updated by RFC
4055 [9], therefore, the defined hash functions are 'SHA-1' [11] 4055 [9], therefore, the defined hash functions are 'SHA-1' [11]
[19], 'SHA-224' [11], 'SHA-256' [11], 'SHA-384' [11], 'SHA-512' [11], [19], 'SHA-224' [11], 'SHA-256' [11], 'SHA-384' [11], 'SHA-512' [11],
'MD5' [12], and 'MD2' [13], with 'SHA-1' preferred. A new IANA 'MD5' [12], and 'MD2' [13], with 'SHA-1' preferred. A new IANA
registry of Hash Function Textual Names, specified in Section 8, registry of Hash Function Textual Names, specified in Section 8,
allows for addition of future tokens, but they may only be added if allows for addition of future tokens, but they may only be added if
they are included in RFCs which update or obsolete RFC 3279 [7]. they are included in RFCs that update or obsolete RFC 3279 [7].
Self-signed certificates (for which legacy certificates are not a Self-signed certificates (for which legacy certificates are not a
consideration) MUST use one of the FIPS 180 algorithms (SHA-1, SHA- consideration) MUST use one of the FIPS 180 algorithms (SHA-1,
224, SHA-256, SHA-384, or SHA-512) as their signature algorithm, and SHA-224, SHA-256, SHA-384, or SHA-512) as their signature algorithm,
thus also MUST use it to calculate certificate fingerprints. and thus also MUST use it to calculate certificate fingerprints.
The fingerprint attribute may be either a session-level or a media- The fingerprint attribute may be either a session-level or a media-
level SDP attribute. If it is a session-level attribute, it applies level SDP attribute. If it is a session-level attribute, it applies
to all TLS sessions for which no media-level fingerprint attribute is to all TLS sessions for which no media-level fingerprint attribute is
defined. defined.
6. Endpoint Identification 6. Endpoint Identification
6.1. Certificate Choice 6.1. Certificate Choice
An X.509 certificate binds an identity and a public key. If SDP An X.509 certificate binds an identity and a public key. If SDP
describing a TLS session is transmitted over a mechanism which describing a TLS session is transmitted over a mechanism that
provides integrity protection, a certificate asserting any provides integrity protection, a certificate asserting any
syntactically valid identity MAY be used. For example, an SDP syntactically valid identity MAY be used. For example, an SDP
description sent over HTTP/TLS [20] or secured by S/MIME [17] MAY description sent over HTTP/TLS [20] or secured by S/MIME [17] MAY
assert any identity in the certificate securing the media connection. assert any identity in the certificate securing the media connection.
Security protocols which provide only hop-by-hop integrity Security protocols that provide only hop-by-hop integrity protection
protection, e.g., the sips protocol [16] (SIP over TLS), are (e.g., the sips protocol [16], SIP over TLS) are considered
considered sufficiently secure to allow the mode in which any valid sufficiently secure to allow the mode in which any valid identity is
identity is accepted. However, see Section 7 for a discussion of accepted. However, see Section 7 for a discussion of some security
some security implications of this fact. implications of this fact.
In situations where the SDP is not integrity-protected, however, the In situations where the SDP is not integrity-protected, however, the
certificate provided for a TLS connection MUST certify an appropriate certificate provided for a TLS connection MUST certify an appropriate
identity for the connection. In these scenarios, the certificate identity for the connection. In these scenarios, the certificate
presented by an endpoint MUST certify either the SDP connection presented by an endpoint MUST certify either the SDP connection
address, or the identity of the creator of the SDP message, as address, or the identity of the creator of the SDP message, as
follows: follows:
o If the connection address for the media description is specified o If the connection address for the media description is specified
as an IP address, the endpoint MAY use a certificate with an as an IP address, the endpoint MAY use a certificate with an
iPAddress subjectAltName which exactly matches the IP in the iPAddress subjectAltName that exactly matches the IP in the
connection-address in the session description's 'c' line. connection-address in the session description's 'c' line.
Similarly, if the connection address for the media description is Similarly, if the connection address for the media description is
specified as a pfully-qualified domain name, the endpoint MAY use specified as a fully-qualified domain name, the endpoint MAY use a
a certificate with a dNSName subjectAltName matching the specified certificate with a dNSName subjectAltName matching the specified
'c' line connection-address exactly. (Wildcard patterns MUST NOT 'c' line connection-address exactly. (Wildcard patterns MUST NOT
be used.) be used.)
o Alternately, if the SDP session description describing the session
was transmitted over a protocol (such as SIP [16]) for which the o Alternately, if the SDP session description of the session was
transmitted over a protocol (such as SIP [16]) for which the
identities of session participants are defined by uniform resource identities of session participants are defined by uniform resource
identifiers (URIs), the endpoint MAY use a certificate with a identifiers (URIs), the endpoint MAY use a certificate with a
uniformResourceIdentifier subjectAltName corresponding to the uniformResourceIdentifier subjectAltName corresponding to the
identity of the endpoint which generated the SDP. The details of identity of the endpoint that generated the SDP. The details of
what URIs are valid are dependent on the transmitting protocol. what URIs are valid are dependent on the transmitting protocol.
(For more details on the validity of URIs, see Section 7.) (For more details on the validity of URIs, see Section 7.)
Identity matching is performed using the matching rules specified by Identity matching is performed using the matching rules specified by
RFC 3280 [8]. If more than one identity of a given type is present RFC 3280 [8]. If more than one identity of a given type is present
in the certificate (e.g., more than one dNSName name), a match in any in the certificate (e.g., more than one dNSName name), a match in any
one of the set is considered acceptable. To support the use of one of the set is considered acceptable. To support the use of
certificate caches, as described in Section 7, endpoints SHOULD certificate caches, as described in Section 7, endpoints SHOULD
consistently provide the same certificate for each identity they consistently provide the same certificate for each identity they
support. support.
6.2. Certificate Presentation 6.2. Certificate Presentation
In all cases, an endpoint acting as the TLS server, i.e., one taking In all cases, an endpoint acting as the TLS server (i.e., one taking
the 'setup:passive' role, in the terminology of connection-oriented the 'setup:passive' role, in the terminology of connection-oriented
media, MUST present a certificate during TLS initiation, following media) MUST present a certificate during TLS initiation, following
the rules presented in Section 6.1. If the certificate does not the rules presented in Section 6.1. If the certificate does not
match the original fingerprint, the client endpoint MUST terminate match the original fingerprint, the client endpoint MUST terminate
the media connection with a bad_certificate error. the media connection with a bad_certificate error.
If the SDP offer/answer model [5] is being used, the client (the If the SDP offer/answer model [5] is being used, the client (the
endpoint with the 'setup:active' role) MUST also present a endpoint with the 'setup:active' role) MUST also present a
certificate following the rules of Section 6.1. The server MUST certificate following the rules of Section 6.1. The server MUST
request a certificate, and if the client does not provide one, or if request a certificate, and if the client does not provide one, or if
the certificate does not match the provided fingerprint, the server the certificate does not match the provided fingerprint, the server
endpoint MUST terminate the media connection with a bad_certificate endpoint MUST terminate the media connection with a bad_certificate
error. error.
Note that when the offer/answer model is being used, it is possible Note that when the offer/answer model is being used, it is possible
for a media connection to outrace the answer back to the offerer. for a media connection to outrace the answer back to the offerer.
Thus, if the offerer has offered a 'setup:passive' or 'setup:actpass' Thus, if the offerer has offered a 'setup:passive' or 'setup:actpass'
role, it MUST (as specified in RFC 4145 [2]) begin listening for an role, it MUST (as specified in RFC 4145 [2]) begin listening for an
incoming connection as soon as it sends its offer. However, it MUST incoming connection as soon as it sends its offer. However, it MUST
NOT assume the data transmitted over the TLS connection is valid NOT assume that the data transmitted over the TLS connection is valid
until it has received a matching fingerprint in an SDP answer. If until it has received a matching fingerprint in an SDP answer. If
the fingerprint, once it arrives, does not match the client's the fingerprint, once it arrives, does not match the client's
certificate, the server endpoint MUST terminate the media connection certificate, the server endpoint MUST terminate the media connection
with a bad_certificate error, as stated in the previous paragraph. with a bad_certificate error, as stated in the previous paragraph.
If offer/answer is not being used (e.g., if the SDP was sent over the If offer/answer is not being used (e.g., if the SDP was sent over the
Session Announcement Protocol [15]), there is no secure channel Session Announcement Protocol [15]), there is no secure channel
available for clients to communicate certificate fingerprints to available for clients to communicate certificate fingerprints to
servers. In this case, servers MAY request client certificates, servers. In this case, servers MAY request client certificates,
which SHOULD be signed by a well-known certification authority, or which SHOULD be signed by a well-known certification authority, or
MAY allow clients to connect without a certificate. MAY allow clients to connect without a certificate.
7. Security Considerations 7. Security Considerations
This entire document concerns itself with security. The problem to This entire document concerns itself with security. The problem to
be solved is addressed in Section 1, and a high-level overview is be solved is addressed in Section 1, and a high-level overview is
presented in Section 3. See the SDP specification [1] for security presented in Section 3. See the SDP specification [1] for security
considerations applicable to SDP in general. considerations applicable to SDP in general.
Offering an TCP/TLS connection in SDP (or agreeing to one in SDP Offering a TCP/TLS connection in SDP (or agreeing to one in SDP
offer/answer mode) does not create an obligation for an endpoint to offer/answer mode) does not create an obligation for an endpoint to
accept any TLS connection with the given fingerprint. Instead, the accept any TLS connection with the given fingerprint. Instead, the
endpoint must engage in the standard TLS negotiation procedure to endpoint must engage in the standard TLS negotiation procedure to
ensure that the TLS stream cypher and MAC algorithm chosen meet the ensure that the TLS stream cipher and MAC algorithm chosen meet the
security needs of the higher-level application. (For example, an security needs of the higher-level application. (For example, an
offered stream cypher of TLS_NULL_WITH_NULL_NULL SHOULD be rejected offered stream cipher of TLS_NULL_WITH_NULL_NULL SHOULD be rejected
in almost every application scenario.) in almost every application scenario.)
Like all SDP messages, SDP messages describing TLS streams are Like all SDP messages, SDP messages describing TLS streams are
conveyed in an encapsulating application protocol (e.g., SIP, MGCP, conveyed in an encapsulating application protocol (e.g., SIP, Media
etc.). It is the responsibility of the encapsulating protocol to Gateway Control Protocol (MGCP), etc.). It is the responsibility of
ensure the integrity of the SDP security descriptions. Therefore, the encapsulating protocol to ensure the integrity of the SDP
the application protocol SHOULD either invoke its own security security descriptions. Therefore, the application protocol SHOULD
mechanisms (e.g., secure multiparts) or alternatively utilize a either invoke its own security mechanisms (e.g., secure multiparts)
lower-layer security service (e.g., TLS or IPsec). This security or, alternatively, utilize a lower-layer security service (e.g., TLS
service SHOULD provide strong message authentication as well as or IPsec). This security service SHOULD provide strong message
effective replay protection. authentication as well as effective replay protection.
However, such integrity protection is not always possible. For these However, such integrity protection is not always possible. For these
cases, end systems SHOULD maintain a cache of certificates which cases, end systems SHOULD maintain a cache of certificates that other
other parties have previously presented using this mechanism. If parties have previously presented using this mechanism. If possible,
possible, users SHOULD be notified when an unsecured certificate users SHOULD be notified when an unsecured certificate associated
associated with a previously unknown end system is presented, and with a previously unknown end system is presented and SHOULD be
SHOULD be strongly warned if a different unsecured certificate is strongly warned if a different unsecured certificate is presented by
presented by a party with which they have communicated in the past. a party with which they have communicated in the past. In this way,
In this way, even in the absence of integrity protection for SDP, the even in the absence of integrity protection for SDP, the security of
security of this document's mechanism is equivalent to that of the this document's mechanism is equivalent to that of the Secure Shell
Secure Shell (ssh) protocol [21], which is vulnerable to man-in-the- (ssh) protocol [21], which is vulnerable to man-in-the-middle attacks
middle attacks when two parties first communicate, but can detect when two parties first communicate, but can detect ones that occur
ones that occur subsequently. (Note that a precise definition of the subsequently. (Note that a precise definition of the "other party"
"other party" depends on the application protocol carrying the SDP depends on the application protocol carrying the SDP message.) Users
message.) Users SHOULD NOT, however, in any circumstances be SHOULD NOT, however, in any circumstances be notified about
notified about certificates described in SDP descriptions sent over certificates described in SDP descriptions sent over an integrity-
an integrity-protected channel. protected channel.
To aid interoperability and deployment, security protocols which To aid interoperability and deployment, security protocols that
provide only hop-by-hop integrity protection, e.g., the sips protocol provide only hop-by-hop integrity protection (e.g., the sips protocol
[16] (SIP over TLS), are considered sufficiently secure to allow the [16], SIP over TLS) are considered sufficiently secure to allow the
mode in which any syntactially valid identity is accepted in a mode in which any syntactically valid identity is accepted in a
certificate. This decision was made because sips is currently the certificate. This decision was made because sips is currently the
integrity mechanism most likely to be used in deployed networks in integrity mechanism most likely to be used in deployed networks in
the short to medium-term. However, in this mode, SDP integrity is the short to medium term. However, in this mode, SDP integrity is
vulnerable to attacks by compromised or malicious middleboxes, e.g. vulnerable to attacks by compromised or malicious middleboxes, e.g.,
SIP proxy servers. End systems MAY warn users about SDP sessions SIP proxy servers. End systems MAY warn users about SDP sessions
that are secured in only a hop-by-hop manner, and definitions of that are secured in only a hop-by-hop manner, and definitions of
media formats running over TCP/TLS MAY specify that only end-to-end media formats running over TCP/TLS MAY specify that only end-to-end
integrity mechanisms are to be used. integrity mechanisms be used.
Depending on how SDP messages are transmitted, it is not always Depending on how SDP messages are transmitted, it is not always
possible to determine whether a subjectAltName presented in a remote possible to determine whether or not a subjectAltName presented in a
certificate is expected or not for the remote party. In particular, remote certificate is expected for the remote party. In particular,
given call forwarding, third-party call control, or session given call forwarding, third-party call control, or session
descriptions generated by endpoints controlled by the Gateway Control descriptions generated by endpoints controlled by the Gateway Control
Protocol [22], it is not always possible in SIP to determine what Protocol [22], it is not always possible in SIP to determine what
entity ought to have generated a remote SDP response. In general, entity ought to have generated a remote SDP response. In general,
when not using authenticity and integrity protection of SDP when not using authenticity and integrity protection of SDP
descriptions, a certificate transmitted over SIP SHOULD assert the descriptions, a certificate transmitted over SIP SHOULD assert the
endpoint's SIP Address of Record as a uniformResourceIndicator endpoint's SIP Address of Record as a uniformResourceIndicator
subjectAltName. When an endpoint receives a certificate over SIP subjectAltName. When an endpoint receives a certificate over SIP
asserting an identity (including an iPAddress or dNSName identity) asserting an identity (including an iPAddress or dNSName identity)
other than the one to which it placed or received the call, it SHOULD other than the one to which it placed or received the call, it SHOULD
alert the user and ask for confirmation. This applies whether alert the user and ask for confirmation. This applies whether
certificates are self-signed, or signed by certification authorities; certificates are self-signed, or signed by certification authorities;
a certificate for sip:bob@example.com may be legitimately signed by a a certificate for sip:bob@example.com may be legitimately signed by a
certification authority, but may still not be acceptable for a call certification authority, but may still not be acceptable for a call
to sip:alice@example.com. (This issue is not one specific to this to sip:alice@example.com. (This issue is not one specific to this
specification; the same consideration applies for S/MIME-signed SDP specification; the same consideration applies for S/MIME-signed SDP
carried over SIP.) carried over SIP.)
This document does not define any mechanism for securely transporting This document does not define any mechanism for securely transporting
RTP and RTCP packets over a connection-oriented channel. There was RTP and RTP Control Protocol (RTCP) packets over a
no consensus in the working group as to whether it would be better to connection-oriented channel. There was no consensus in the working
send Secure RTP packets [23] over a connection-oriented transport group as to whether it would be better to send Secure RTP packets
[24], or whether it would be better to send standard unsecured RTP [23] over a connection-oriented transport [24], or whether it would
packets over TLS using the mechanisms described in this document. be better to send standard unsecured RTP packets over TLS using the
The group consensus was to wait until a use-case requiring secure mechanisms described in this document. The group consensus was to
connection-oriented RTP was presented. wait until a use-case requiring secure connection-oriented RTP was
presented.
TLS is not always the most appropriate choice for secure connection- TLS is not always the most appropriate choice for secure connection-
oriented media; in some cases, a higher- or lower-level security oriented media; in some cases, a higher- or lower-level security
protocol may be appropriate. protocol may be appropriate.
8. IANA Considerations 8. IANA Considerations
This document defines an SDP proto value: 'TCP/TLS'. Its format is This document defines an SDP proto value: 'TCP/TLS'. Its format is
defined in Section 4. This proto value should be registered by IANA defined in Section 4. This proto value has been registered by IANA
on under "Session Description Protocol (SDP) Parameters" under under "Session Description Protocol (SDP) Parameters" under "proto".
"proto".
This document defines an SDP session and media level attribute: This document defines an SDP session and media-level attribute:
'fingerprint'. Its format is defined in Section 5. This attribute 'fingerprint'. Its format is defined in Section 5. This attribute
should be registered by IANA under "Session Description Protocol has been registered by IANA under "Session Description Protocol (SDP)
(SDP) Parameters" under "att-field (both session and media level)". Parameters" under "att-field (both session and media level)".
The SDP specification [1] states that specifications defining new The SDP specification [1] states that specifications defining new
proto values, like the 'TCP/TLS' proto value defined in this one, proto values, like the 'TCP/TLS' proto value defined in this one,
must define the rules by which their media format (fmt) namespace is must define the rules by which their media format (fmt) namespace is
managed. For the TCP/TLS protocol, new formats SHOULD have an managed. For the TCP/TLS protocol, new formats SHOULD have an
associated MIME registration. Use of an existing MIME subtype for associated MIME registration. Use of an existing MIME subtype for
the format is encouraged. If no MIME subtype exists, it is the format is encouraged. If no MIME subtype exists, it is
RECOMMENDED that a suitable one be registered through the IETF RECOMMENDED that a suitable one be registered through the IETF
process [14] by production of, or reference to, a standards-track RFC process [14] by production of, or reference to, a standards-track RFC
that defines the transport protocol for the format. that defines the transport protocol for the format.
This specification creates a new IANA registry named "Hash Function This specification creates a new IANA registry named "Hash Function
Textual Names". It will not be part of the SDP Parameters. Textual Names". It will not be part of the SDP Parameters.
The names of hash functions used for certificate fingerprints are The names of hash functions used for certificate fingerprints are
registered by the IANA. Hash functions MUST be defined by standards- registered by the IANA. Hash functions MUST be defined by standards-
track RFCs which update or obsolete RFC 3279 [7]. track RFCs that update or obsolete RFC 3279 [7].
When registering a new hash function textual name, the following When registering a new hash function textual name, the following
information MUST be provided. information MUST be provided:
o The textual name of the hash function. o The textual name of the hash function.
o The Object Identifier (OID) of the hash function as used in X.509 o The Object Identifier (OID) of the hash function as used in X.509
certificates. certificates.
o A reference to the standards-track RFC, updating or obsoleting RFC o A reference to the standards-track RFC, updating or obsoleting RFC
3279 [7], defining the use of the hash function in X.509 3279 [7], defining the use of the hash function in X.509
certificates. certificates.
Figure 3 contains the initial values of this registry. Figure 3 contains the initial values of this registry.
Hash Function Name OID Reference Hash Function Name OID Reference
------------------ --- --------- ------------------ --- ---------
"md2" 1.2.840.113549.2.2 RFC 3279 "md2" 1.2.840.113549.2.2 RFC 3279
"md5" 1.2.840.113549.2.5 RFC 3279 "md5" 1.2.840.113549.2.5 RFC 3279
skipping to change at page 13, line 35 skipping to change at page 14, line 5
"md2" 1.2.840.113549.2.2 RFC 3279 "md2" 1.2.840.113549.2.2 RFC 3279
"md5" 1.2.840.113549.2.5 RFC 3279 "md5" 1.2.840.113549.2.5 RFC 3279
"sha-1" 1.3.14.3.2.26 RFC 3279 "sha-1" 1.3.14.3.2.26 RFC 3279
"sha-224" 2.16.840.1.101.3.4.2.4 RFC 4055 "sha-224" 2.16.840.1.101.3.4.2.4 RFC 4055
"sha-256" 2.16.840.1.101.3.4.2.1 RFC 4055 "sha-256" 2.16.840.1.101.3.4.2.1 RFC 4055
"sha-384" 2.16.840.1.101.3.4.2.2 RFC 4055 "sha-384" 2.16.840.1.101.3.4.2.2 RFC 4055
"sha-512" 2.16.840.1.101.3.4.2.3 RFC 4055 "sha-512" 2.16.840.1.101.3.4.2.3 RFC 4055
Figure 3: IANA Hash Function Textual Name Registry Figure 3: IANA Hash Function Textual Name Registry
Appendix A. Changes From Earlier Versions
Note to the RFC-Editor: please remove this section prior to
publication as an RFC.
Appendix A.1. Changes From Draft -05
o Specified that hop-by-hop integrity protection counts as valid
integrity protection (though specific media formats can define
otherwise if they choose.)
o Allowed SDP descriptions which are integrity-protected to
advertise any subjectAltName in their certificates.
o Made session teardown a MUST following a bad certificate
fingerprint -- user notification is no longer an option in this
scenario.
o Established and populated a new IANA registry for Hash Function
Textual Names.
o Allowed announcement-mode (SAP-like) uses of TLS to request client
certificates, even though there is no way for clients to provide
certificate fingerprints in this case.
o Confidentiality is not required for secure transmission of SDP
descriptions, only integrity protection; removed this requirement.
o Established that user notification about bad certificate
identities only applies to certificates not sent over a protected
channel.
o Clarified the language on what identity must be asserted, for
certificates which must include specific identities.
o Clarified the scenarios in which users must be consulted on
whether certificates are acceptable.
o Clarified that TLS connections MUST NOT act upon data transmitted
over a TLS connection before they have verified the fingerprint.
o Clarified that the use of the same hash function for fingerprints
as for their corresponding certificates ensures that the
certificates' security properties are preserved for their
fingerprints.
o Standardized some terminology to properly reflect standard
security usage. Notably, "confidentiality" and "certification
authority" replaced "privacy" and "certificate authority"
respectively.
o Updated the references for Connection-Oriented Media in SDP (now
RFC 4145 [2]), ABNF (now RFC 4234 [10]), Media Type Registration
Procedures (now RFC 4288 [14]), and the SSH Protocol Architecture
(now RFC 4251 [21]).
Appendix A.2. Changes From Draft -04
o The section discussing the difficulty of knowing what URI
identities are appropriate for SDP was expanded, adding a
reference to the Gateway Control Protocol.
o An un-cited informative reference was removed.
Appendix A.3. Changes From Draft -03
o The number of options in the protocol were significantly reduced:
a number of SHOULD requirements were elevated to MUST. Notably,
the use of the 'fingerprint' attribute, strict certificate
identity choices, and the use of the same digest algorithm for
fingerprints as for certificates were all made mandatory.
o Support for the digest algorithms from FIPS 180-2 [11] / RFC 4055
[9] ('SHA-224', 'SHA-256', 'SHA-384', and 'SHA-512') was added.
o Discussion was added about the difficulty of automatically
determining the URI a remote endpoint's certificate should assert,
especially in SIP in the presence of call forwarding or third-
party call control.
o The document was aligned with version -10 of
draft-ietf-mmusic-comedia [2]. This consisted mostly of wording
and formatting changes.
Appendix A.4. Changes From Draft -02
None, other than IPR boilerplate and reference updates. Draft -03
was a resubmission to refresh the draft's presence in the Internet-
Drafts repository.
Appendix A.5. Changes From Draft -01
o Made the use of SHA-1 fingerprints mandatory in self-signed
certificates.
o Aligned with version -09 of draft-ietf-mmusic-comedia [2], also
drawing some wording changes from that document.
o Forbid the use of wildcards for the dNS subjectAltName.
o Eliminated requirements on identities provided with self-signed
certificates.
o Recommended the use of a certificate cache when SDP integrity
protection cannot be assured.
o Explained that there is no currently supported mechanism for
securely sending RTP over connection-oriented media.
o Described the procedure for establishing media formats for TCP/
TLS.
Appendix A.6. Changes From Draft -00
o Significantly expanded introduction and motivation sections.
o Significant clarifications to other sections.
o Aligned with version -07 of draft-ietf-mmusic-comedia [2].
Protocol identifier changed from TLS to TCP/TLS at that document's
recommendation.
9. References 9. References
9.1. Normative References 9.1. Normative References
[1] Handley, M., "SDP: Session Description Protocol", [1] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
draft-ietf-mmusic-sdp-new-26 (work in progress), January 2006. Description Protocol", RFC 4566, July 2006.
[2] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the [2] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the
Session Description Protocol (SDP)", RFC 4145, September 2005. Session Description Protocol (SDP)", RFC 4145, September 2005.
[3] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", [3] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
RFC 2246, January 1999. Protocol Version 1.1", RFC 4346, April 2006.
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[5] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with [5] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002. Session Description Protocol (SDP)", RFC 3264, June 2002.
[6] International Telecommunications Union, "Information technology [6] International Telecommunications Union, "Information technology
- Open Systems Interconnection - The Directory: Public-key and - Open Systems Interconnection - The Directory: Public-key and
attribute certificate frameworks", ITU-T Recommendation X.509, attribute certificate frameworks", ITU-T Recommendation X.509,
skipping to change at page 17, line 4 skipping to change at page 15, line 18
[14] Freed, N. and J. Klensin, "Media Type Specifications and [14] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", BCP 13, RFC 4288, December 2005. Registration Procedures", BCP 13, RFC 4288, December 2005.
9.2. Informative References 9.2. Informative References
[15] Handley, M., Perkins, C., and E. Whelan, "Session Announcement [15] Handley, M., Perkins, C., and E. Whelan, "Session Announcement
Protocol", RFC 2974, October 2000. Protocol", RFC 2974, October 2000.
[16] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., [16] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002. Session Initiation Protocol", RFC 3261, June 2002.
[17] Ramsdell, B., "S/MIME Version 3 Message Specification", [17] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
RFC 2633, June 1999. (S/MIME) Version 3.1 Message Specification", RFC 3851, July
2004.
[18] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., [18] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication: Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication:
Basic and Digest Access Authentication", RFC 2617, June 1999. Basic and Digest Access Authentication", RFC 2617, June 1999.
[19] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1 (SHA1)", [19] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1 (SHA1)",
RFC 3174, September 2001. RFC 3174, September 2001.
[20] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [20] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[21] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Protocol [21] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Protocol
Architecture", RFC 4251, January 2006. Architecture", RFC 4251, January 2006.
[22] Groves, C., Pantaleo, M., Anderson, T., and T. Taylor, "Gateway [22] Groves, C., Pantaleo, M., Anderson, T., and T. Taylor, "Gateway
Control Protocol Version 1", RFC 3525, June 2003. Control Protocol Version 1", RFC 3525, June 2003.
[23] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. [23] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)", Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004. RFC 3711, March 2004.
[24] Lazzaro, J., "Framing RTP and RTCP Packets over Connection- [24] Lazzaro, J., "Framing Real-time Transport Protocol (RTP) and
Oriented Transport", draft-ietf-avt-rtp-framing-contrans-06 RTP Control Protocol (RTCP) Packets over Connection-Oriented
(work in progress), September 2005. Transport", RFC 4571, July 2006.
Author's Address Author's Address
Jonathan Lennox Jonathan Lennox
Columbia University Department of Computer Science Columbia University Department of Computer Science
450 Computer Science 450 Computer Science
1214 Amsterdam Ave., M.C. 0401 1214 Amsterdam Ave., M.C. 0401
New York, NY 10027 New York, NY 10027
US US
Email: lennox@cs.columbia.edu EMail: lennox@cs.columbia.edu
Intellectual Property Statement Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
skipping to change at page 19, line 29 skipping to change at page 17, line 45
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Disclaimer of Validity Acknowledgement
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is provided by the IETF
Internet Society. Administrative Support Activity (IASA).
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