draft-ietf-mmusic-4572-update-08.txt   draft-ietf-mmusic-4572-update-09.txt 
Network Working Group J. Lennox Network Working Group J. Lennox
Internet-Draft Vidyo Internet-Draft Vidyo
Obsoletes: 4572 (if approved) C. Holmberg Obsoletes: 4572 (if approved) C. Holmberg
Intended status: Standards Track Ericsson Intended status: Standards Track Ericsson
Expires: May 7, 2017 November 3, 2016 Expires: July 6, 2017 January 2, 2017
Connection-Oriented Media Transport over TLS in SDP Connection-Oriented Media Transport over TLS in SDP
draft-ietf-mmusic-4572-update-08 draft-ietf-mmusic-4572-update-09
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 that 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 document obsoletes RFC 4572, by clarifying the usage of multiple
fingerprints.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 7, 2017. This Internet-Draft will expire on July 6, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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7. Security Considerations . . . . . . . . . . . . . . . . . . . 11 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . 14 9.1. Normative References . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . 16 9.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 17 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
The Session Description Protocol (SDP) [14] provides a general- The Session Description Protocol (SDP) [8] provides a general-purpose
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 that 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) [10], specifies a general the Session Description Protocol (SDP) [7], 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 [13]. sessions that use the Transport Layer Security (TLS) protocol [10].
TLS protocol allows applications to communicate over a channel t TLS protocol allows applications to communicate over a channel t
provides confidentiality and data integrity. The TLS specification, provides confidentiality and data integrity. The TLS specification,
however, does not specify how specific protocols establish and use however, does not specify how specific protocols establish and use
this secure channel; particularly, TLS leaves the question of how to this secure channel; particularly, TLS leaves the question of how to
interpret and validate authentication certificates as an issue for interpret and validate authentication certificates as an issue for
the protocols that run over TLS. This document specifies such usage the protocols that run over TLS. This document specifies such usage
for the case of connection-oriented media transport. for the case of connection-oriented media transport.
Complicating this issue, endpoints exchanging media will often be Complicating this issue, endpoints exchanging media will often be
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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 that the integrity of SDP content is assured, allows the assuming that the integrity of SDP content is assured, allows the
secure use of self-signed certificates. Section 6 describes which secure use of self-signed certificates. Section 6 describes which
X.509 certificates are presented, and how they are used in TLS. X.509 certificates are presented, and how they are used in TLS.
Section 7 discusses additional security considerations. Section 7 discusses additional security considerations.
This document obsoletes [25] but remains backwards compatible with This document obsoletes [21] but remains backwards compatible with
older implementations. The changes from [25] are that it clarified older implementations. The changes from [21] are that it clarified
that multiple 'fingerprint' attributes can be used to carry that multiple 'fingerprint' attributes can be used to carry
fingerprints, calculated using different hash functions, associated fingerprints, calculated using different hash functions, associated
with a given certificate, and to carry fingerprints associated with with a given certificate, and to carry fingerprints associated with
multiple certificates. The fingerprint matching procedure, when multiple certificates. The fingerprint matching procedure, when
multiple fingerprints are provided, are also clarified. The document multiple fingerprints are provided, are also clarified. The document
also updates the preferred cipher suite with a stronger cipher suite, also updates the preferred cipher suite with a stronger cipher suite,
and removes the requirement to use the same hash function for and removes the requirement to use the same hash function for
calculating a certificate fingerprint and certificate signature. calculating a certificate fingerprint and certificate signature.
2. Terminology 2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
and "OPTIONAL" are to be interpreted as described in RFC 2119 [5] and document are to be interpreted as described in RFC 2119 [3].
indicate requirement levels for compliant implementations.
3. Overview 3. Overview
This section discusses the threat model that 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 of a multimedia session it is making available. session description of a multimedia session it is making available.
The classic example of this mode of operation is the Session The classic example of this mode of operation is the Session
Announcement Protocol (SAP) [17], in which SDP session descriptions Announcement Protocol (SAP) [15], in which SDP session descriptions
are periodically transmitted to a well-known multicast group. are periodically transmitted to a well-known multicast group.
Traditionally, these descriptions involve multicast conferences, but Traditionally, these descriptions involve multicast conferences, but
unicast sessions are also possible. (Connection-oriented media, unicast sessions are also possible. (Connection-oriented media,
obviously, cannot use multicast.) Recipients of a session obviously, cannot use multicast.) Recipients of a 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 [6]. Alternatively, SDP conferences can operate in offer-answer mode [4].
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
the mode of operation used by the Session Initiation Protocol (SIP) the mode of operation used by the Session Initiation Protocol (SIP)
[19]. [17].
3.2. Threat Model 3.2. Threat Model
Participants in multimedia conferences often wish to guarantee Participants in multimedia conferences often wish to guarantee
confidentiality, data integrity, and authentication for their media confidentiality, data integrity, and authentication for their media
sessions. This section describes various types of attackers and the sessions. This section describes various types of attackers and the
ways they attempt to violate these guarantees. It then describes how ways they attempt to violate these guarantees. It then describes how
the TLS protocol can be used to thwart the attackers. the TLS protocol can be used to thwart the attackers.
The simplest type of attacker is one who listens passively to the The simplest type of attacker is one who listens passively to the
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(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
that 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 [22] can be used to mechanism; SIP, for example, defines how S/MIME [23] 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.
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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 that 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 [10], except for the proto parameter and the first one in RFC 4145 [7], except for the proto parameter and the
the fingerprint attribute.) See the subsequent sections for fingerprint attribute.) See the subsequent sections for explanations
explanations of the example's TLS-specific attributes. of the example's TLS-specific attributes.
(Note: due to RFC formatting conventions, this document 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 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
Figure 1: Example SDP Description Offering a TLS Media Stream Figure 1: Example SDP Description Offering a TLS Media Stream
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 [14] for a discussion on transport Descriptions" section of SDP [8] 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 [13] over TCP. (Using TLS over other transport Security protocol [10] over TCP. (Using TLS over other transport
protocols is not discussed in 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 being the protocol using a fmt identifier to indicate the application 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 [10]. They also use the SDP attributes defined defined in RFC 4145 [7]. They also use the SDP attributes defined in
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 [2] certificates, as profiled Authentication certificates are X.509 [2] certificates, as profiled
by RFC 3279 [7], RFC 3280 [8], and RFC 4055 [9]. by RFC 3279 [5], RFC 5280 [11], and RFC 4055 [6].
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
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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
uppercase 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 [15], which uses unseparated lowercase hexadecimal authentication [24], 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 [11] in Figure 2. This syntax extends the BNF Backus-Naur Form [9] in Figure 2. This syntax extends the BNF syntax
syntax of SDP [14]. of SDP [8].
attribute =/ fingerprint-attribute attribute =/ fingerprint-attribute
fingerprint-attribute = "fingerprint" ":" hash-func SP fingerprint fingerprint-attribute = "fingerprint" ":" hash-func SP fingerprint
hash-func = "sha-1" / "sha-224" / "sha-256" / hash-func = "sha-1" / "sha-224" / "sha-256" /
"sha-384" / "sha-512" / "sha-384" / "sha-512" /
"md5" / "md2" / token "md5" / token
; Additional hash functions can only come ; Additional hash functions can only come
; from updates to RFC 3279 ; from updates to RFC 3279
fingerprint = 2UHEX *(":" 2UHEX) fingerprint = 2UHEX *(":" 2UHEX)
; 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
Following RFC 3279 [7] as updated by RFC 4055 [9], therefore, the Following RFC 3279 [5] as updated by RFC 4055 [6], therefore, the
defined hash functions are 'SHA-1' [1] [18], 'SHA-224' [1], 'SHA-256' defined hash functions are 'SHA-1' [1] [16], 'SHA-224' [1], 'SHA-256'
[1], 'SHA-384'[1], 'SHA-512' [1], 'MD5' [4], and 'MD2' [3], with [1], 'SHA-384'[1], 'SHA-512' [1], 'MD5' [13], with 'SHA-256'
'SHA-256' preferred. A new IANA registry of Hash Function Textual preferred. A new IANA registry of Hash Function Textual Names,
Names, specified in Section 8, allows for addition of future tokens, specified in Section 8, allows for addition of future tokens, but
but they may only be added if they are included in RFCs that update they may only be added if they are included in RFCs that update or
or obsolete RFC 3279 [7]. obsolete RFC 3279 [5].
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.
5.1. Multiple Fingerprints 5.1. Multiple Fingerprints
Multiple SDP fingerprint attributes can be associated with an m- Multiple SDP fingerprint attributes can be associated with an m-
line. This can occur if multiple fingerprints have been calculated line. This can occur if multiple fingerprints have been calculated
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will be used for media associated with an m- line (e.g. if separate will be used for media associated with an m- line (e.g. if separate
certificates are used for RTP and RTCP), or where it is not known certificates are used for RTP and RTCP), or where it is not known
which certificate will be used when the fingerprints are exchanged. which certificate will be used when the fingerprints are exchanged.
In such cases, one or more fingerprints MUST be calculated for each In such cases, one or more fingerprints MUST be calculated for each
possible certificate. possible certificate.
An endpoint MUST, as a minimum, calculate a fingerprint using both An endpoint MUST, as a minimum, calculate a fingerprint using both
the 'SHA-256' hash function algorithm and the hash function used to the 'SHA-256' hash function algorithm and the hash function used to
generate the signature on the certificate for each possible generate the signature on the certificate for each possible
certificate. Including the hash from the signature algorithm ensures certificate. Including the hash from the signature algorithm ensures
interoperability with strict implementations of RFC 4572 [25]. interoperability with strict implementations of RFC 4572 [21].
Either of these fingerprints MAY be omitted if the endpoint includes Either of these fingerprints MAY be omitted if the endpoint includes
a hash with a stronger hash algorithm that it knows that the peer a hash with a stronger hash algorithm that it knows that the peer
supports, if it is known that the peer does not support the hash supports, if it is known that the peer does not support the hash
algorithm, or if local policy mandates use of stronger algorithms. algorithm, or if local policy mandates use of stronger algorithms.
If fingerprints associated with multiple certificates are calculated, If fingerprints associated with multiple certificates are calculated,
the same set of hash functions MUST be used to calculate fingerprints the same set of hash functions MUST be used to calculate fingerprints
for each certificate associated with the m- line. for each certificate associated with the m- line.
For each used certificate, an endpoint MUST be able to match at least For each used certificate, an endpoint MUST be able to match at least
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a certificate hash in order to look for a match. a certificate hash in order to look for a match.
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 that 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 [16] or secured by S/MIME [22] MAY description sent over HTTP/TLS [14] or secured by S/MIME [23] MAY
assert any identity in the certificate securing the media connection. assert any identity in the certificate securing the media connection.
Security protocols that provide only hop-by-hop integrity protection Security protocols that provide only hop-by-hop integrity protection
(e.g., the sips protocol [19], SIP over TLS) are considered (e.g., the sips protocol [17], SIP over TLS) are considered
sufficiently secure to allow the mode in which any valid identity is sufficiently secure to allow the mode in which any valid identity is
accepted. However, see Section 7 for a discussion of some security accepted. However, see Section 7 for a discussion of 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:
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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 that 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 fully-qualified domain name, the endpoint MAY use a specified as a fully-qualified domain name, the endpoint MAY use 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 of the session was o Alternately, if the SDP session description of the session was
transmitted over a protocol (such as SIP [19]) for which the transmitted over a protocol (such as SIP [17]) 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 that 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 5280 [11]. 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 [6] is being used, the client (the If the SDP offer/answer model [4] 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 [10]) begin listening for an role, it MUST (as specified in RFC 4145 [7]) 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 that 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 [17]), 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 [14] for security presented in Section 3. See the SDP specification [8] for security
considerations applicable to SDP in general. considerations applicable to SDP in general.
Offering a 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 cipher 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 cipher 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.)
skipping to change at page 12, line 5 skipping to change at page 12, line 5
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 that other cases, end systems SHOULD maintain a cache of certificates that other
parties have previously presented using this mechanism. If possible, parties have previously presented using this mechanism. If possible,
users SHOULD be notified when an unsecured certificate associated users SHOULD be notified when an unsecured certificate associated
with a previously unknown end system is presented and SHOULD be with a previously unknown end system is presented and SHOULD be
strongly warned if a different unsecured certificate is presented by strongly warned if a different unsecured certificate is presented by
a party with which they have communicated in the past. In this way, a party with which they have communicated in the past. In this way,
even in the absence of integrity protection for SDP, the security of even in the absence of integrity protection for SDP, the security of
this document's mechanism is equivalent to that of the Secure Shell this document's mechanism is equivalent to that of the Secure Shell
(ssh) protocol [23], which is vulnerable to man-in-the-middle attacks (ssh) protocol [19], which is vulnerable to man-in-the-middle attacks
when two parties first communicate, but can detect ones that occur when two parties first communicate, but can detect ones that occur
subsequently. (Note that a precise definition of the "other party" subsequently. (Note that a precise definition of the "other party"
depends on the application protocol carrying the SDP message.) Users depends on the application protocol carrying the SDP message.) Users
SHOULD NOT, however, in any circumstances be notified about SHOULD NOT, however, in any circumstances be notified about
certificates described in SDP descriptions sent over an integrity- certificates described in SDP descriptions sent over an integrity-
protected channel. protected channel.
To aid interoperability and deployment, security protocols that 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
[19], SIP over TLS) are considered sufficiently secure to allow the [17], SIP over TLS) are considered sufficiently secure to allow the
mode in which any syntactically 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 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 or not a subjectAltName presented in a possible to determine whether or not a subjectAltName presented in a
remote certificate is expected 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 [20], 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 certificate for "sip:bob@example.com" may be legitimately signed by
a certification authority, but may still not be acceptable for a call a 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 RTP Control Protocol (RTCP) packets over a connection- RTP and RTP Control Protocol (RTCP) packets over a connection-
oriented channel. There was no consensus in the working group as to oriented channel. There was no consensus in the working group as to
whether it would be better to send Secure RTP packets [21] over a whether it would be better to send Secure RTP packets [18] over a
connection-oriented transport [24], or whether it would be better to connection-oriented transport [20], or whether it would be better to
send standard unsecured RTP packets over TLS using the mechanisms send standard unsecured RTP packets over TLS using the mechanisms
described in this document. The group consensus was to wait until a described in this document. The group consensus was to wait until a
use-case requiring secure connection-oriented RTP was presented. 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.
This document improves security from the RFC 4572 [25]. It updates This document improves security from the RFC 4572 [21]. It updates
the preferred hash function cipher suite from SHA-1 to SHA-256. By the preferred hash function cipher suite from SHA-1 to SHA-256, and
clarifying the usage and handling of multiple fingerprints, the removes the reference to the MD2 cipher suite.
By clarifying the usage and handling of multiple fingerprints, the
document also enables hash agility, and incremental deployment of document also enables hash agility, and incremental deployment of
newer, and more secure, cipher suites. newer, and more secure, cipher suites.
8. IANA Considerations 8. IANA Considerations
Note to IANA. No IANA considerations are changed from RFC4572 [25] Note to IANA. No IANA considerations are changed from RFC4572 [21]
so the only actions required are to update the registreis to point at so the only actions required are to update the registries to point at
this specification. this specification.
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 has been registered by IANA defined in Section 4. This proto value has been registered by IANA
under "Session Description Protocol (SDP) Parameters" under "proto". under "Session Description Protocol (SDP) Parameters" under "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
has been registered by IANA under "Session Description Protocol (SDP) has been registered by IANA under "Session Description Protocol (SDP)
Parameters" under "att-field (both session and media level)". Parameters" under "att-field (both session and media level)".
The SDP specification [14] states that specifications defining new The SDP specification [8] 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 [12] by production of, or reference to, a standards-track RFC process [12] 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 that update or obsolete RFC 3279 [7]. track RFCs that update or obsolete RFC 3279 [5].
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 [5], defining the use of the hash function in X.509
certificates. certificates.
Table 1 contains the initial values of this registry. Table 1 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 |
| "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 |
+--------------------+------------------------+-----------+ +--------------------+------------------------+-----------+
Table 1: IANA Hash Function Textual Name Registry Table 1: IANA Hash Function Textual Name Registry
skipping to change at page 14, line 45 skipping to change at page 14, line 47
Hash Standard", FIPS PUB 180-2, August 2002, Hash Standard", FIPS PUB 180-2, August 2002,
<http://csrc.nist.gov/publications/fips/fips180-2/ <http://csrc.nist.gov/publications/fips/fips180-2/
fips180-2.pdf>. fips180-2.pdf>.
[2] International Telecommunications Union, "Information [2] International Telecommunications Union, "Information
technology - Open Systems Interconnection - The Directory: technology - Open Systems Interconnection - The Directory:
Public-key and attribute certificate frameworks", Public-key and attribute certificate frameworks",
ITU-T Recommendation X.509, ISO Standard 9594-8, March ITU-T Recommendation X.509, ISO Standard 9594-8, March
2000. 2000.
[3] Kaliski, B., "The MD2 Message-Digest Algorithm", RFC 1319, [3] Bradner, S., "Key words for use in RFCs to Indicate
DOI 10.17487/RFC1319, April 1992,
<http://www.rfc-editor.org/info/rfc1319>.
[4] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
DOI 10.17487/RFC1321, April 1992,
<http://www.rfc-editor.org/info/rfc1321>.
[5] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[6] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model [4] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002, DOI 10.17487/RFC3264, June 2002,
<http://www.rfc-editor.org/info/rfc3264>. <http://www.rfc-editor.org/info/rfc3264>.
[7] Bassham, L., Polk, W., and R. Housley, "Algorithms and [5] Bassham, L., Polk, W., and R. Housley, "Algorithms and
Identifiers for the Internet X.509 Public Key Identifiers for the Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 3279, DOI 10.17487/RFC3279, April (CRL) Profile", RFC 3279, DOI 10.17487/RFC3279, April
2002, <http://www.rfc-editor.org/info/rfc3279>. 2002, <http://www.rfc-editor.org/info/rfc3279>.
[8] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet [6] Schaad, J., Kaliski, B., and R. Housley, "Additional
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
DOI 10.17487/RFC3280, April 2002,
<http://www.rfc-editor.org/info/rfc3280>.
[9] Schaad, J., Kaliski, B., and R. Housley, "Additional
Algorithms and Identifiers for RSA Cryptography for use in Algorithms and Identifiers for RSA Cryptography for use in
the Internet X.509 Public Key Infrastructure Certificate the Internet X.509 Public Key Infrastructure Certificate
and Certificate Revocation List (CRL) Profile", RFC 4055, and Certificate Revocation List (CRL) Profile", RFC 4055,
DOI 10.17487/RFC4055, June 2005, DOI 10.17487/RFC4055, June 2005,
<http://www.rfc-editor.org/info/rfc4055>. <http://www.rfc-editor.org/info/rfc4055>.
[10] Yon, D. and G. Camarillo, "TCP-Based Media Transport in [7] Yon, D. and G. Camarillo, "TCP-Based Media Transport in
the Session Description Protocol (SDP)", RFC 4145, the Session Description Protocol (SDP)", RFC 4145,
DOI 10.17487/RFC4145, September 2005, DOI 10.17487/RFC4145, September 2005,
<http://www.rfc-editor.org/info/rfc4145>. <http://www.rfc-editor.org/info/rfc4145>.
[11] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [8] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Specifications: ABNF", RFC 4234, DOI 10.17487/RFC4234, Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
October 2005, <http://www.rfc-editor.org/info/rfc4234>. July 2006, <http://www.rfc-editor.org/info/rfc4566>.
[12] Freed, N. and J. Klensin, "Media Type Specifications and [9] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Registration Procedures", RFC 4288, DOI 10.17487/RFC4288, Specifications: ABNF", STD 68, RFC 5234,
December 2005, <http://www.rfc-editor.org/info/rfc4288>. DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
[13] Dierks, T. and E. Rescorla, "The Transport Layer Security [10] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, (TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC4346, April 2006, DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc4346>. <http://www.rfc-editor.org/info/rfc5246>.
[14] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [11] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Description Protocol", RFC 4566, DOI 10.17487/RFC4566, Housley, R., and W. Polk, "Internet X.509 Public Key
July 2006, <http://www.rfc-editor.org/info/rfc4566>. Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<http://www.rfc-editor.org/info/rfc5280>.
[12] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<http://www.rfc-editor.org/info/rfc6838>.
9.2. Informative References 9.2. Informative References
[15] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., [13] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
Leach, P., Luotonen, A., and L. Stewart, "HTTP DOI 10.17487/RFC1321, April 1992,
Authentication: Basic and Digest Access Authentication", <http://www.rfc-editor.org/info/rfc1321>.
RFC 2617, DOI 10.17487/RFC2617, June 1999,
<http://www.rfc-editor.org/info/rfc2617>.
[16] Rescorla, E., "HTTP Over TLS", RFC 2818, [14] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000, DOI 10.17487/RFC2818, May 2000,
<http://www.rfc-editor.org/info/rfc2818>. <http://www.rfc-editor.org/info/rfc2818>.
[17] Handley, M., Perkins, C., and E. Whelan, "Session [15] Handley, M., Perkins, C., and E. Whelan, "Session
Announcement Protocol", RFC 2974, DOI 10.17487/RFC2974, Announcement Protocol", RFC 2974, DOI 10.17487/RFC2974,
October 2000, <http://www.rfc-editor.org/info/rfc2974>. October 2000, <http://www.rfc-editor.org/info/rfc2974>.
[18] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1 [16] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1
(SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001, (SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001,
<http://www.rfc-editor.org/info/rfc3174>. <http://www.rfc-editor.org/info/rfc3174>.
[19] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [17] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002, DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>. <http://www.rfc-editor.org/info/rfc3261>.
[20] Groves, C., Ed., Pantaleo, M., Ed., Anderson, T., Ed., and [18] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
T. Taylor, Ed., "Gateway Control Protocol Version 1",
RFC 3525, DOI 10.17487/RFC3525, June 2003,
<http://www.rfc-editor.org/info/rfc3525>.
[21] 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, DOI 10.17487/RFC3711, March 2004, RFC 3711, DOI 10.17487/RFC3711, March 2004,
<http://www.rfc-editor.org/info/rfc3711>. <http://www.rfc-editor.org/info/rfc3711>.
[22] Ramsdell, B., Ed., "Secure/Multipurpose Internet Mail [19] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Extensions (S/MIME) Version 3.1 Message Specification",
RFC 3851, DOI 10.17487/RFC3851, July 2004,
<http://www.rfc-editor.org/info/rfc3851>.
[23] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251,
January 2006, <http://www.rfc-editor.org/info/rfc4251>. January 2006, <http://www.rfc-editor.org/info/rfc4251>.
[24] Lazzaro, J., "Framing Real-time Transport Protocol (RTP) [20] Lazzaro, J., "Framing Real-time Transport Protocol (RTP)
and RTP Control Protocol (RTCP) Packets over Connection- and RTP Control Protocol (RTCP) Packets over Connection-
Oriented Transport", RFC 4571, DOI 10.17487/RFC4571, July Oriented Transport", RFC 4571, DOI 10.17487/RFC4571, July
2006, <http://www.rfc-editor.org/info/rfc4571>. 2006, <http://www.rfc-editor.org/info/rfc4571>.
[25] Lennox, J., "Connection-Oriented Media Transport over the [21] Lennox, J., "Connection-Oriented Media Transport over the
Transport Layer Security (TLS) Protocol in the Session Transport Layer Security (TLS) Protocol in the Session
Description Protocol (SDP)", RFC 4572, Description Protocol (SDP)", RFC 4572,
DOI 10.17487/RFC4572, July 2006, DOI 10.17487/RFC4572, July 2006,
<http://www.rfc-editor.org/info/rfc4572>. <http://www.rfc-editor.org/info/rfc4572>.
[22] Taylor, T., "Reclassification of RFC 3525 to Historic",
RFC 5125, DOI 10.17487/RFC5125, February 2008,
<http://www.rfc-editor.org/info/rfc5125>.
[23] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, DOI 10.17487/RFC5751, January
2010, <http://www.rfc-editor.org/info/rfc5751>.
[24] Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, "HTTP
Digest Access Authentication", RFC 7616,
DOI 10.17487/RFC7616, September 2015,
<http://www.rfc-editor.org/info/rfc7616>.
Appendix A. Acknowledgments Appendix A. Acknowledgments
This version of the document included significant contributions by This version of the document included significant contributions by
Cullen Jennings, Paul Kyzivat, Roman Shpount, and Martin Thomson. Cullen Jennings, Paul Kyzivat, Roman Shpount, and Martin Thomson.
Authors' Addresses Authors' Addresses
Jonathan Lennox Jonathan Lennox
Vidyo Vidyo
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