Network Working Group J. Lennox
Request for Comments: 4572 Columbia U.
Updates: 4145 July 2006
Category: Standards Track
Network Working Group J. Lennox
Request for Comments: 4572 Columbia U.
Updates: 4145 July 2006
Category: Standards Track
Connection-Oriented Media Transport over the Transport Layer Security (TLS) Protocol in the Session Description Protocol (SDP)
会话描述协议（SDP）中传输层安全（TLS）协议上的面向连接的媒体传输
Status of This Memo
关于下段备忘
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
本文件规定了互联网社区的互联网标准跟踪协议，并要求进行讨论和提出改进建议。有关本协议的标准化状态和状态，请参考当前版本的“互联网官方协议标准”（STD 1）。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (2006).
版权所有（C）互联网协会（2006年）。
Abstract
摘要
This document specifies how to establish secure connection-oriented media transport sessions over the Transport Layer Security (TLS) protocol using the Session Description Protocol (SDP). It defines a new SDP protocol identifier, 'TCP/TLS'. It also defines the syntax and semantics for an SDP 'fingerprint' attribute that identifies the certificate that will be presented for the TLS session. This mechanism allows media transport over TLS connections to be established securely, so long as the integrity of session descriptions is assured.
本文档指定如何使用会话描述协议（SDP）通过传输层安全（TLS）协议建立安全的面向连接的媒体传输会话。它定义了一个新的SDP协议标识符“TCP/TLS”。它还定义了SDP“指纹”属性的语法和语义，该属性标识将为TLS会话提供的证书。这种机制允许通过TLS连接安全地建立媒体传输，只要会话描述的完整性得到保证。
This document extends and updates RFC 4145.
本文档扩展并更新了RFC 4145。
Table of Contents
目录
1. Introduction ....................................................3
2. Terminology .....................................................4
3. Overview ........................................................4
3.1. SDP Operational Modes ......................................4
3.2. Threat Model ...............................................5
3.3. The Need for Self-Signed Certificates ......................5
3.4. Example SDP Description for TLS Connection .................6
4. Protocol Identifiers ............................................6
5. Fingerprint Attribute ...........................................7
6. Endpoint Identification .........................................9
6.1. Certificate Choice .........................................9
6.2. Certificate Presentation ..................................10
7. Security Considerations ........................................10
8. IANA Considerations ............................................12
9. References .....................................................14
9.1. Normative References ......................................14
9.2. Informative References ....................................15
1. Introduction ....................................................3
2. Terminology .....................................................4
3. Overview ........................................................4
3.1. SDP Operational Modes ......................................4
3.2. Threat Model ...............................................5
3.3. The Need for Self-Signed Certificates ......................5
3.4. Example SDP Description for TLS Connection .................6
4. Protocol Identifiers ............................................6
5. Fingerprint Attribute ...........................................7
6. Endpoint Identification .........................................9
6.1. Certificate Choice .........................................9
6.2. Certificate Presentation ..................................10
7. Security Considerations ........................................10
8. IANA Considerations ............................................12
9. References .....................................................14
9.1. Normative References ......................................14
9.2. Informative References ....................................15
The Session Description Protocol (SDP) [1] provides a general-purpose format for describing multimedia sessions in announcements or invitations. For many applications, it is desirable to establish, as part of a multimedia session, a media stream that uses a connection-oriented transport. RFC 4145, Connection-Oriented Media Transport in the Session Description Protocol (SDP) [2], specifies a general mechanism for describing and establishing such connection-oriented streams; however, the only transport protocol it directly supports is TCP. In many cases, session participants wish to provide confidentiality, data integrity, and authentication for their media sessions. This document therefore extends the Connection-Oriented Media specification to allow session descriptions to describe media sessions that use the Transport Layer Security (TLS) protocol [3].
会话描述协议（SDP）[1]提供了一种通用格式，用于描述公告或邀请中的多媒体会话。对于许多应用，希望建立使用面向连接的传输的媒体流，作为多媒体会话的一部分。RFC 4145，《会话描述协议（SDP）[2]中的面向连接的媒体传输》规定了用于描述和建立这种面向连接的流的一般机制；但是，它直接支持的唯一传输协议是TCP。在许多情况下，会话参与者希望为其媒体会话提供机密性、数据完整性和身份验证。因此，本文档扩展了面向连接的媒体规范，允许会话描述描述使用传输层安全（TLS）协议的媒体会话[3]。
The TLS protocol allows applications to communicate over a channel that provides confidentiality and data integrity. The TLS specification, however, does not specify how specific protocols establish and use this secure channel; particularly, TLS leaves the question of how to interpret and validate authentication certificates as an issue for the protocols that run over TLS. This document specifies such usage for the case of connection-oriented media transport.
TLS协议允许应用程序通过提供机密性和数据完整性的通道进行通信。然而，TLS规范并未规定特定协议如何建立和使用该安全通道；特别是，TLS将如何解释和验证身份验证证书的问题留给了在TLS上运行的协议。本文档规定了面向连接的媒体传输的这种用法。
Complicating this issue, endpoints exchanging media will often be unable to obtain authentication certificates signed by a well-known root certification authority (CA). Most certificate authorities charge for signed certificates, particularly host-based certificates; additionally, there is a substantial administrative overhead to obtaining signed certificates, as certification authorities must be able to confirm that they are issuing the signed certificates to the correct party. Furthermore, in many cases endpoints' IP addresses and host names are dynamic: they may be obtained from DHCP, for example. It is impractical to obtain a CA-signed certificate valid for the duration of a DHCP lease. For such hosts, self-signed certificates are usually the only option. This specification defines a mechanism that allows self-signed certificates can be used securely, provided that the integrity of the SDP description is assured. It provides for endpoints to include a secure hash of their certificate, known as the "certificate fingerprint", within the session description. Provided that the fingerprint of the offered certificate matches the one in the session description, end hosts can trust even self-signed certificates.
使此问题复杂化的是，交换媒体的端点通常无法获得由知名的根证书颁发机构（CA）签署的身份验证证书。大多数证书颁发机构对签名证书，特别是基于主机的证书收取费用；此外，由于认证机构必须能够确认他们正在向正确的一方颁发已签署的证书，因此获取已签署的证书需要大量的管理开销。此外，在许多情况下，端点的IP地址和主机名是动态的：例如，它们可以从DHCP获得。获取在DHCP租约期间有效的CA签名证书是不切实际的。对于此类主机，自签名证书通常是唯一的选择。本规范定义了一种机制，允许安全地使用自签名证书，前提是确保SDP描述的完整性。它允许端点在会话描述中包含其证书的安全散列，称为“证书指纹”。如果提供的证书的指纹与会话描述中的指纹匹配，则终端主机甚至可以信任自签名证书。
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 basic mechanism for establishing TLS-based connected-oriented media
本文件的其余部分如下所示。第3节概述了问题和威胁模型。第4节给出了建立基于TLS的面向连接媒体的基本机制
in SDP. Section 5 describes the SDP fingerprint attribute, which, assuming that the integrity of SDP content is assured, allows the secure use of self-signed certificates. Section 6 describes which X.509 certificates are presented, and how they are used in TLS. Section 7 discusses additional security considerations.
在SDP中。第5节描述了SDP指纹属性，假设SDP内容的完整性得到保证，该属性允许安全使用自签名证书。第6节描述了提供的X.509证书，以及它们在TLS中的使用方式。第7节讨论了其他安全注意事项。
In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119 [4] and indicate requirement levels for compliant implementations.
在本文件中，关键词“必须”、“不得”、“要求”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照RFC 2119[4]中所述进行解释，并指明符合性实施的要求级别。
This section discusses the threat model that motivates TLS transport for connection-oriented media streams. It also discusses in more detail the need for end systems to use self-signed certificates.
本节讨论激励面向连接的媒体流TLS传输的威胁模型。它还更详细地讨论了终端系统使用自签名证书的必要性。
There are two principal operational modes for multimedia sessions: advertised and offer-answer. Advertised sessions are the simpler mode. In this mode, a server publishes, in some manner, an SDP session description of a multimedia session it is making available. The classic example of this mode of operation is the Session Announcement Protocol (SAP) [15], in which SDP session descriptions are periodically transmitted to a well-known multicast group. Traditionally, these descriptions involve multicast conferences, but unicast sessions are also possible. (Connection-oriented media, obviously, cannot use multicast.) Recipients of a session description connect to the addresses published in the session description. These recipients may not previously have been known to the advertiser of the session description.
多媒体会话有两种主要的操作模式：广告和提供答案。广告会话是更简单的模式。在这种模式下，服务器以某种方式发布其所提供的多媒体会话的SDP会话描述。这种操作模式的典型示例是会话公告协议（SAP）[15]，在该协议中，SDP会话描述定期传输到知名的多播组。传统上，这些描述涉及多播会议，但单播会话也是可能的。（显然，面向连接的媒体不能使用多播。）会话描述的收件人连接到会话描述中发布的地址。这些接收者之前可能不为会话描述的广告客户所知。
Alternatively, SDP conferences can operate in offer-answer mode [5]. This mode allows two participants in a multimedia session to negotiate the multimedia session between them. In this model, one participant offers the other a description of the desired session from its perspective, and the other participant answers with 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 the mode of operation used by the Session Initiation Protocol (SIP) [16].
或者，SDP会议可以在提供-应答模式下运行[5]。此模式允许多媒体会话中的两个参与者协商他们之间的多媒体会话。在这个模型中，一个参与者从自己的角度向另一个参与者提供所需会话的描述，另一个参与者从自己的角度回答所需会话。在这种模式下，会话中的每个参与者都知道另一个。这是会话启动协议（SIP）[16]使用的操作模式。
Participants in multimedia conferences often wish to guarantee confidentiality, data integrity, and authentication for their media sessions. This section describes various types of attackers and the ways they attempt to violate these guarantees. It then describes how the TLS protocol can be used to thwart the attackers.
多媒体会议的参与者通常希望保证其媒体会话的机密性、数据完整性和身份验证。本节介绍各种类型的攻击者以及他们试图违反这些保证的方式。然后描述了如何使用TLS协议阻止攻击者。
The simplest type of attacker is one who listens passively to the traffic associated with a multimedia session. This attacker might, for example, be on the same local-area or wireless network as one of the participants in a conference. This sort of attacker does not threaten a connection's data integrity or authentication, and almost any operational mode of TLS can provide media stream confidentiality.
最简单的攻击者类型是被动监听与多媒体会话相关的流量的攻击者。例如，该攻击者可能与会议参与者之一位于同一局域网或无线网络上。此类攻击者不会威胁连接的数据完整性或身份验证，并且几乎任何TLS操作模式都可以提供媒体流机密性。
More sophisticated is an attacker who can send his own data traffic over the network, but who cannot modify or redirect valid traffic. In SDP's 'advertised' operational mode, this can barely be considered an attack; media sessions are expected to be initiated from anywhere on the network. In SDP's offer-answer mode, however, this type of attack is more serious. An attacker could initiate a connection to one or both of the endpoints of a session, thus impersonating an endpoint, or acting as a man in the middle to listen in on their communications. To thwart these attacks, TLS uses endpoint certificates. So long as the certificates' private keys have not been compromised, the endpoints have an external trusted mechanism (most commonly, a mutually-trusted certification authority) to validate certificates, and the endpoints know what certificate identity to expect, endpoints can be certain that such an attack has not taken place.
更复杂的是，攻击者可以通过网络发送自己的数据流量，但不能修改或重定向有效流量。在SDP的“广告”作战模式下，这几乎不能被视为攻击；媒体会话预计将从网络上的任何位置启动。然而，在SDP的提供-应答模式下，这种类型的攻击更为严重。攻击者可以启动连接到会话的端点中的一个或两个端点，从而模拟端点，或者充当中间人来监听它们的通信。为了阻止这些攻击，TLS使用端点证书。只要证书的私钥没有被泄露，端点就有一个外部可信机制（最常见的是相互信任的证书颁发机构）来验证证书，并且端点知道预期的证书身份，端点就可以确定没有发生这种攻击。
Finally, the most serious type of attacker is one who can modify or redirect session descriptions: for example, a compromised or malicious SIP proxy server. Neither TLS itself nor any mechanisms that use it can protect an SDP session against such an attacker. Instead, the SDP description itself must be secured through some mechanism; SIP, for example, defines how S/MIME [17] can be used to secure session descriptions.
最后，最严重的攻击者类型是能够修改或重定向会话描述的攻击者：例如，受损或恶意的SIP代理服务器。TLS本身和使用它的任何机制都无法保护SDP会话免受此类攻击者的攻击。相反，SDP描述本身必须通过某种机制加以保护；例如，SIP定义了如何使用S/MIME[17]来保护会话描述。
SDP session descriptions are created by any endpoint that needs to participate in a multimedia session. In many cases, such as SIP phones, such endpoints have dynamically-configured IP addresses and host names and must be deployed with nearly zero configuration. For such an endpoint, it is for practical purposes impossible to obtain a certificate signed by a well-known certification authority.
SDP会话描述由需要参与多媒体会话的任何端点创建。在许多情况下，例如SIP电话，这样的端点具有动态配置的IP地址和主机名，并且必须以几乎为零的配置进行部署。对于这样一个端点，实际上不可能获得由知名的证书颁发机构签署的证书。
If two endpoints have no prior relationship, self-signed certificates cannot generally be trusted, as there is no guarantee that an attacker is not launching a man-in-the-middle attack. Fortunately, however, if the integrity of SDP session descriptions can be assured, it is possible to consider those SDP descriptions themselves as a prior relationship: certificates can be securely described in the session description itself. This is done by providing a secure hash of a certificate, or "certificate fingerprint", as an SDP attribute; this mechanism is described in Section 5.
如果两个端点没有优先关系，则自签名证书通常不可信，因为无法保证攻击者不会发起中间人攻击。然而，幸运的是，如果可以确保SDP会话描述的完整性，则可以将这些SDP描述本身看作先验关系：证书可以在会话描述本身中安全地描述。这是通过提供证书的安全散列或“证书指纹”作为SDP属性来实现的；第5节介绍了该机制。
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 portion of the session description is omitted in the example, showing 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 fingerprint attribute.) See the subsequent sections for explanations of the example's TLS-specific attributes.
图1显示了一个SDP产品，它通过TLS发出T.38传真会话可用性的信号。为简洁起见，本例中省略了会话描述的主要部分，仅显示“m”行及其属性。（该示例与RFC 4145[2]中的第一个示例相同，但proto参数和指纹属性除外。）有关示例TLS特定属性的解释，请参阅后续章节。
(Note: due to RFC formatting conventions, this document splits SDP across lines whose content would exceed 72 characters. A backslash character marks where this line folding has taken place. This backslash and its trailing CRLF and whitespace would not appear in actual SDP content.)
（注意：由于RFC格式约定，本文档在内容超过72个字符的行之间拆分SDP。反斜杠字符标记发生此行折叠的位置。此反斜杠及其尾部CRLF和空格不会出现在实际SDP内容中。）
m=image 54111 TCP/TLS t38
c=IN IP4 192.0.2.2
a=setup:passive
a=connection:new
a=fingerprint:SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
m=image 54111 TCP/TLS t38
c=IN IP4 192.0.2.2
a=setup:passive
a=connection:new
a=fingerprint:SHA-1 \
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
图1：提供TLS媒体流的示例SDP描述
The 'm' line in SDP specifies, among other items, the transport protocol to be used for the media in the session. See the "Media Descriptions" section of SDP [1] for a discussion on transport protocol identifiers.
SDP中的“m”行指定会话中媒体使用的传输协议，以及其他项。有关传输协议标识符的讨论，请参阅SDP[1]的“媒体描述”部分。
This specification defines a new protocol identifier, 'TCP/TLS', which indicates that the media described will use the Transport Layer Security protocol [3] over TCP. (Using TLS over other transport protocols is not discussed in this document.) The 'TCP/TLS' protocol identifier describes only the transport protocol, not the upper-layer protocol. An 'm' line that specifies 'TCP/TLS' MUST further qualify
本规范定义了一个新的协议标识符“TCP/TLS”，表示所述介质将通过TCP使用传输层安全协议[3]。（本文档不讨论在其他传输协议上使用TLS。）“TCP/TLS”协议标识符仅描述传输协议，而不描述上层协议。指定“TCP/TLS”的“m”行必须进一步限定
the protocol using a fmt identifier to indicate the application being run over TLS.
使用fmt标识符指示正在TLS上运行的应用程序的协议。
Media sessions described with this identifier follow the procedures defined in RFC 4145 [2]. They also use the SDP attributes defined in that specification, 'setup' and 'connection'.
使用此标识符描述的媒体会话遵循RFC 4145[2]中定义的过程。它们还使用该规范中定义的SDP属性“setup”和“connection”。
Parties to a TLS session indicate their identities by presenting authentication certificates as part of the TLS handshake procedure. Authentication certificates are X.509 [6] certificates, as profiled by RFC 3279 [7], RFC 3280 [8], and RFC 4055 [9].
作为TLS握手过程的一部分，TLS会话的各方通过出示身份验证证书来指示其身份。身份验证证书是X.509[6]证书，如RFC 3279[7]、RFC 3280[8]和RFC 4055[9]所述。
In order to associate media streams with connections and to prevent unauthorized barge-in attacks on the media streams, endpoints MUST provide a certificate fingerprint. If the X.509 certificate presented for the TLS connection matches the fingerprint presented in the SDP, the endpoint can be confident that the author of the SDP is indeed the initiator of the connection.
为了将媒体流与连接相关联，并防止对媒体流进行未经授权的闯入攻击，端点必须提供证书指纹。如果为TLS连接提供的X.509证书与SDP中提供的指纹匹配，则端点可以确信SDP的作者确实是连接的发起人。
A certificate fingerprint is a secure one-way hash of the DER (distinguished encoding rules) form of the certificate. (Certificate fingerprints are widely supported by tools that manipulate X.509 certificates; for instance, the command "openssl x509 -fingerprint" causes the command-line tool of the openssl package to print a certificate fingerprint, and the certificate managers for Mozilla and Internet Explorer display them when viewing the details of a certificate.)
证书指纹是证书的DER（可分辨编码规则）形式的安全单向散列。（操作X.509证书的工具广泛支持证书指纹；例如，命令“openssl x509-fingerprint”使openssl包的命令行工具打印证书指纹，Mozilla和Internet Explorer的证书管理器在查看证书详细信息时显示指纹。）
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 hash value itself. The hash value is represented as a sequence of uppercase hexadecimal bytes, separated by colons. The number of bytes is defined by the hash function. (This is the syntax used by openssl and by the browsers' certificate managers. It is different from the syntax used to represent hash values in, e.g., HTTP digest authentication [18], which uses unseparated lowercase hexadecimal bytes. It was felt that consistency with other applications of fingerprints was more important.)
指纹在SDP中表示为属性（“A”行）。它由使用的哈希函数的名称，后跟哈希值本身组成。哈希值表示为大写十六进制字节序列，用冒号分隔。字节数由哈希函数定义。（这是openssl和浏览器的证书管理器使用的语法。它不同于HTTP摘要身份验证[18]中用于表示哈希值的语法，后者使用未分离的小写十六进制字节。人们认为与指纹的其他应用程序的一致性更为重要。）
The formal syntax of the fingerprint attribute is given in Augmented Backus-Naur Form [10] in Figure 2. This syntax extends the BNF syntax of SDP [1].
指纹属性的形式语法在图2中以增广的Backus-Naur形式[10]给出。此语法扩展了SDP[1]的BNF语法。
attribute =/ fingerprint-attribute
属性=/指纹属性
fingerprint-attribute = "fingerprint" ":" hash-func SP fingerprint
指纹属性=“指纹”“：”哈希函数SP指纹
hash-func = "sha-1" / "sha-224" / "sha-256" /
"sha-384" / "sha-512" /
"md5" / "md2" / token
; Additional hash functions can only come
; from updates to RFC 3279
hash-func = "sha-1" / "sha-224" / "sha-256" /
"sha-384" / "sha-512" /
"md5" / "md2" / token
; Additional hash functions can only come
; from updates to RFC 3279
fingerprint = 2UHEX *(":" 2UHEX) ; Each byte in upper-case hex, separated ; by colons.
指纹=2UHEX*（“：”2UHEX）；每个字节以大写十六进制表示，分开；科隆。
UHEX = DIGIT / %x41-46 ; A-F uppercase
UHEX = DIGIT / %x41-46 ; A-F uppercase
Figure 2: Augmented Backus-Naur Syntax for the Fingerprint Attribute
图2:Fingerprint属性的扩展Backus Naur语法
A certificate fingerprint MUST be computed using the same one-way hash function as is used in the certificate's signature algorithm. (This ensures that the security properties required for the certificate also apply for the fingerprint. It also guarantees that the fingerprint will be usable by the other endpoint, so long as the certificate itself is.) Following RFC 3279 [7] as updated by RFC 4055 [9], therefore, the defined hash functions are 'SHA-1' [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 registry of Hash Function Textual Names, specified in Section 8, allows for addition of future tokens, but they may only be added if they are included in RFCs that update or obsolete RFC 3279 [7]. Self-signed certificates (for which legacy certificates are not a consideration) MUST use one of the FIPS 180 algorithms (SHA-1, SHA-224, SHA-256, SHA-384, or SHA-512) as their signature algorithm, and thus also MUST use it to calculate certificate fingerprints.
必须使用与证书签名算法中使用的单向哈希函数计算证书指纹。（这确保证书所需的安全属性也适用于指纹。它还保证指纹将被另一个端点使用，只要证书本身是可用的。）根据RFC 4055[9]更新的RFC 3279[7]，因此，定义的哈希函数为'SHA-1'[11][19]，'SHA-224'[11]，“SHA-256”[11]、“SHA-384”[11]、“SHA-512”[11]、“MD5”[12]和“MD2”[13]，首选“SHA-1”。第8节中指定的新IANA哈希函数文本名称注册表允许添加将来的令牌，但只有当它们包含在更新或废弃RFC 3279[7]的RFC中时，才可以添加它们。自签名证书（不考虑遗留证书）必须使用FIPS 180算法之一（SHA-1、SHA-224、SHA-256、SHA-384或SHA-512）作为其签名算法，因此还必须使用它来计算证书指纹。
The fingerprint attribute may be either a session-level or a media-level SDP attribute. If it is a session-level attribute, it applies to all TLS sessions for which no media-level fingerprint attribute is defined.
指纹属性可以是会话级或媒体级SDP属性。如果它是会话级属性，则适用于未定义媒体级指纹属性的所有TLS会话。
An X.509 certificate binds an identity and a public key. If SDP describing a TLS session is transmitted over a mechanism that provides integrity protection, a certificate asserting any syntactically valid identity MAY be used. For example, an SDP description sent over HTTP/TLS [20] or secured by S/MIME [17] MAY assert any identity in the certificate securing the media connection.
X.509证书绑定身份和公钥。如果描述TLS会话的SDP通过提供完整性保护的机制传输，则可以使用断言任何语法有效标识的证书。例如，通过HTTP/TLS[20]发送或由S/MIME[17]保护的SDP描述可以在保护媒体连接的证书中声明任何标识。
Security protocols that provide only hop-by-hop integrity protection (e.g., the sips protocol [16], SIP over TLS) are considered sufficiently secure to allow the mode in which any valid identity is accepted. However, see Section 7 for a discussion of some security implications of this fact.
仅提供逐跳完整性保护的安全协议（例如sips协议[16]、TLS上的SIP）被认为是足够安全的，以允许接受任何有效身份的模式。但是，有关这一事实的一些安全影响的讨论，请参见第7节。
In situations where the SDP is not integrity-protected, however, the certificate provided for a TLS connection MUST certify an appropriate identity for the connection. In these scenarios, the certificate presented by an endpoint MUST certify either the SDP connection address, or the identity of the creator of the SDP message, as follows:
但是，在SDP不受完整性保护的情况下，为TLS连接提供的证书必须证明连接的适当身份。在这些场景中，端点提供的证书必须证明SDP连接地址或SDP消息创建者的身份，如下所示：
o If the connection address for the media description is specified as an IP address, the endpoint MAY use a certificate with an iPAddress subjectAltName that exactly matches the IP in the connection-address in the session description's 'c' line. Similarly, if the connection address for the media description is specified as a fully-qualified domain name, the endpoint MAY use a certificate with a dNSName subjectAltName matching the specified 'c' line connection-address exactly. (Wildcard patterns MUST NOT be used.)
o 如果将媒体描述的连接地址指定为IP地址，则终结点可以使用IP地址subjectAltName与会话描述的“c”行中连接地址中的IP完全匹配的证书。类似地，如果将媒体描述的连接地址指定为完全限定的域名，则端点可以使用dNSName subjectAltName与指定的“c”行连接地址完全匹配的证书。（不得使用通配符模式。）
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 identifiers (URIs), the endpoint MAY use a certificate with a uniformResourceIdentifier subjectAltName corresponding to the identity of the endpoint that generated the SDP. The details of what URIs are valid are dependent on the transmitting protocol. (For more details on the validity of URIs, see Section 7.)
o 或者，如果会话的SDP会话描述是通过协议（例如SIP[16]）传输的，对于该协议，会话参与者的身份由统一资源标识符（uri）定义，端点可以使用具有uniformResourceIdentifier subjectAltName的证书，该证书对应于生成SDP的端点的标识。哪些URI有效的详细信息取决于传输协议。（有关URI有效性的更多详细信息，请参见第7节。）
Identity matching is performed using the matching rules specified by 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 one of the set is considered acceptable. To support the use of certificate caches, as described in Section 7, endpoints SHOULD
使用RFC 3280[8]指定的匹配规则执行标识匹配。如果证书中存在给定类型的多个标识（例如，多个dNSName名称），则可以接受集合中任何一个的匹配。如第7节所述，为了支持证书缓存的使用，端点应该
consistently provide the same certificate for each identity they support.
始终为其支持的每个身份提供相同的证书。
In all cases, an endpoint acting as the TLS server (i.e., one taking the 'setup:passive' role, in the terminology of connection-oriented media) MUST present a certificate during TLS initiation, following the rules presented in Section 6.1. If the certificate does not match the original fingerprint, the client endpoint MUST terminate the media connection with a bad_certificate error.
在所有情况下，充当TLS服务器的端点（即，在面向连接的媒体术语中，扮演“设置：被动”角色的端点）必须按照第6.1节中的规则在TLS启动期间提供证书。如果证书与原始指纹不匹配，客户端终结点必须终止媒体连接，并出现错误的\u证书错误。
If the SDP offer/answer model [5] is being used, the client (the endpoint with the 'setup:active' role) MUST also present a certificate following the rules of Section 6.1. The server MUST request a certificate, and if the client does not provide one, or if the certificate does not match the provided fingerprint, the server endpoint MUST terminate the media connection with a bad_certificate error.
如果使用SDP提供/应答模型[5]，则客户端（具有“设置：活动”角色的端点）还必须按照第6.1节的规则提供证书。服务器必须请求证书，如果客户端未提供证书，或者证书与提供的指纹不匹配，则服务器端点必须终止媒体连接，并出现错误的\u证书。
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. 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 incoming connection as soon as it sends its offer. However, it MUST NOT assume that the data transmitted over the TLS connection is valid until it has received a matching fingerprint in an SDP answer. If the fingerprint, once it arrives, does not match the client's certificate, the server endpoint MUST terminate the media connection with a bad_certificate error, as stated in the previous paragraph.
请注意，在使用报价/应答模型时，媒体连接可能会超出报价人的应答。因此，如果报价人提供了“设置：被动”或“设置：actpass”角色，则其必须（如RFC 4145[2]中所述）在发送报价后立即开始侦听传入连接。但是，在收到SDP应答中的匹配指纹之前，不得假设通过TLS连接传输的数据有效。如果指纹到达后与客户端的证书不匹配，则服务器端点必须终止媒体连接，并出现bad_证书错误，如前一段所述。
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 available for clients to communicate certificate fingerprints to servers. In this case, servers MAY request client certificates, which SHOULD be signed by a well-known certification authority, or MAY allow clients to connect without a certificate.
如果未使用提供/应答（例如，如果SDP是通过会话公告协议[15]发送的），则没有安全通道可供客户端将证书指纹传送到服务器。在这种情况下，服务器可能会请求客户端证书，该证书应由知名的证书颁发机构签名，或者可能会允许客户端在没有证书的情况下进行连接。
This entire document concerns itself with security. The problem to be solved is addressed in Section 1, and a high-level overview is presented in Section 3. See the SDP specification [1] for security considerations applicable to SDP in general.
整个文件都涉及到安全问题。第1节讨论了要解决的问题，第3节介绍了高层次的概述。有关一般适用于SDP的安全注意事项，请参见SDP规范[1]。
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 accept any TLS connection with the given fingerprint. Instead, the
在SDP模式下提供TCP/TLS连接（或在SDP提供/应答模式下同意连接）不会使端点有义务接受具有给定指纹的任何TLS连接。相反
endpoint must engage in the standard TLS negotiation procedure to ensure that the TLS stream cipher and MAC algorithm chosen meet the security needs of the higher-level application. (For example, an offered stream cipher of TLS_NULL_WITH_NULL_NULL SHOULD be rejected in almost every application scenario.)
端点必须参与标准TLS协商过程，以确保选择的TLS流密码和MAC算法满足更高级别应用程序的安全需求。（例如，在几乎所有应用场景中，都应拒绝提供TLS_NULL_与_NULL_NULL的流密码。）
Like all SDP messages, SDP messages describing TLS streams are conveyed in an encapsulating application protocol (e.g., SIP, Media Gateway Control Protocol (MGCP), etc.). It is the responsibility of the encapsulating protocol to ensure the integrity of the SDP security descriptions. Therefore, the application protocol SHOULD either invoke its own security mechanisms (e.g., secure multiparts) or, alternatively, utilize a lower-layer security service (e.g., TLS or IPsec). This security service SHOULD provide strong message authentication as well as effective replay protection.
与所有SDP消息一样，描述TLS流的SDP消息在封装的应用程序协议（例如SIP、媒体网关控制协议（MGCP））中传输。封装协议负责确保SDP安全描述的完整性。因此，应用程序协议应调用其自身的安全机制（例如，安全多部分），或者，利用较低层的安全服务（例如，TLS或IPsec）。此安全服务应提供强大的消息身份验证以及有效的重播保护。
However, such integrity protection is not always possible. For these cases, end systems SHOULD maintain a cache of certificates that other parties have previously presented using this mechanism. If possible, users SHOULD be notified when an unsecured certificate associated with a previously unknown end system is presented and SHOULD be strongly warned if a different unsecured certificate is presented by 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 this document's mechanism is equivalent to that of the Secure Shell (ssh) protocol [21], which is vulnerable to man-in-the-middle attacks when two parties first communicate, but can detect ones that occur subsequently. (Note that a precise definition of the "other party" depends on the application protocol carrying the SDP message.) Users SHOULD NOT, however, in any circumstances be notified about certificates described in SDP descriptions sent over an integrity-protected channel.
然而，这种完整性保护并不总是可能的。对于这些情况，终端系统应该维护其他方以前使用此机制提供的证书缓存。如果可能，当出现与以前未知的终端系统相关联的不安全证书时，应通知用户，并且如果过去与用户通信的一方出现了不同的不安全证书，则应强烈警告用户。这样，即使在SDP没有完整性保护的情况下，本文档机制的安全性也与Secure Shell（ssh）协议[21]的安全性相当，后者在双方首次通信时容易受到中间人攻击，但可以检测到随后发生的攻击。（请注意，“另一方”的精确定义取决于承载SDP消息的应用程序协议。）但是，在任何情况下，都不应通知用户通过完整性保护通道发送的SDP描述中描述的证书。
To aid interoperability and deployment, security protocols that provide only hop-by-hop integrity protection (e.g., the sips protocol [16], SIP over TLS) are considered sufficiently secure to allow the mode in which any syntactically valid identity is accepted in a certificate. This decision was made because sips is currently the integrity mechanism most likely to be used in deployed networks in the short to medium term. However, in this mode, SDP integrity is vulnerable to attacks by compromised or malicious middleboxes, e.g., SIP proxy servers. End systems MAY warn users about SDP sessions 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 integrity mechanisms be used.
为了帮助互操作性和部署，仅提供逐跳完整性保护的安全协议（例如sips协议[16]，SIP over TLS）被认为是足够安全的，以允许在证书中接受任何语法有效身份的模式。之所以作出这一决定，是因为sips是目前最有可能在中短期内用于已部署网络的完整性机制。但是，在此模式下，SDP完整性容易受到受损或恶意中间盒（例如SIP代理服务器）的攻击。终端系统可能会警告用户SDP会话仅以逐跳方式进行保护，并且TCP/TLS上运行的媒体格式定义可能会指定仅使用端到端完整性机制。
Depending on how SDP messages are transmitted, it is not always possible to determine whether or not a subjectAltName presented in a remote certificate is expected for the remote party. In particular, given call forwarding, third-party call control, or session descriptions generated by endpoints controlled by the Gateway Control Protocol [22], it is not always possible in SIP to determine what entity ought to have generated a remote SDP response. In general, when not using authenticity and integrity protection of SDP descriptions, a certificate transmitted over SIP SHOULD assert the endpoint's SIP Address of Record as a uniformResourceIndicator subjectAltName. When an endpoint receives a certificate over SIP asserting an identity (including an iPAddress or dNSName identity) other than the one to which it placed or received the call, it SHOULD alert the user and ask for confirmation. This applies whether certificates are self-signed, or signed by certification authorities; a certificate for sip:bob@example.com may be legitimately signed by 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 specification; the same consideration applies for S/MIME-signed SDP carried over SIP.)
根据SDP消息的传输方式，并不总是能够确定远程方是否需要远程证书中显示的subjectAltName。特别是，给定由网关控制协议控制的端点生成的呼叫转发、第三方呼叫控制或会话描述[22]，在SIP中并不总是能够确定应该生成远程SDP响应的实体。通常，当不使用SDP描述的真实性和完整性保护时，通过SIP传输的证书应将端点的SIP记录地址声明为uniformResourceIndicator subjectAltName。当端点通过SIP接收到一个证书，该证书断言一个身份（包括iPAddress或dNSName身份），而不是它拨打或接收呼叫的身份，它应该提醒用户并请求确认。无论证书是自行签署的，还是由认证机构签署的，这都适用；sip的证书：bob@example.com可以由证书颁发机构合法签署，但对于sip呼叫仍然不可接受：alice@example.com. （此问题并非本规范的特定问题；同样的考虑也适用于SIP中携带的S/MIME签名SDP。）
This document does not define any mechanism for securely transporting RTP and RTP Control Protocol (RTCP) packets over a connection-oriented channel. There was no consensus in the working group as to whether it would be better to send Secure RTP packets [23] over a connection-oriented transport [24], or whether it would be better to send standard unsecured RTP packets over TLS using the mechanisms described in this document. The group consensus was to wait until a use-case requiring secure connection-oriented RTP was presented.
本文档未定义通过面向连接的通道安全传输RTP和RTP控制协议（RTCP）数据包的任何机制。对于是否最好通过面向连接的传输[24]发送安全RTP数据包[23]，或者是否最好使用本文件中描述的机制通过TLS发送标准的不安全RTP数据包，工作组中没有达成共识。小组的一致意见是等到提出了一个需要面向安全连接的RTP的用例。
TLS is not always the most appropriate choice for secure connection-oriented media; in some cases, a higher- or lower-level security protocol may be appropriate.
TLS并不总是面向安全连接的媒体的最合适选择；在某些情况下，更高或更低级别的安全协议可能是合适的。
This document defines an SDP proto value: 'TCP/TLS'. Its format is defined in Section 4. This proto value has been registered by IANA under "Session Description Protocol (SDP) Parameters" under "proto".
本文档定义了一个SDP协议值：“TCP/TLS”。其格式见第4节。IANA已在“proto”下的“会话描述协议（SDP）参数”下注册此proto值。
This document defines an SDP session and media-level attribute: 'fingerprint'. Its format is defined in Section 5. This attribute has been registered by IANA under "Session Description Protocol (SDP) Parameters" under "att-field (both session and media level)".
此文档定义SDP会话和媒体级别属性：“指纹”。其格式见第5节。IANA已在“att字段（会话和媒体级别）”下的“会话描述协议（SDP）参数”下注册此属性。
The SDP specification [1] states that specifications defining new proto values, like the 'TCP/TLS' proto value defined in this one,
SDP规范[1]指出定义新协议值的规范，如本规范中定义的“TCP/TLS”协议值，
must define the rules by which their media format (fmt) namespace is managed. For the TCP/TLS protocol, new formats SHOULD have an associated MIME registration. Use of an existing MIME subtype for the format is encouraged. If no MIME subtype exists, it is RECOMMENDED that a suitable one be registered through the IETF process [14] by production of, or reference to, a standards-track RFC that defines the transport protocol for the format.
必须定义管理其媒体格式（fmt）命名空间的规则。对于TCP/TLS协议，新格式应具有相关的MIME注册。鼓励对该格式使用现有的MIME子类型。如果不存在MIME子类型，建议通过IETF过程[14]通过生成或引用定义格式传输协议的标准跟踪RFC来注册合适的MIME子类型。
This specification creates a new IANA registry named "Hash Function Textual Names". It will not be part of the SDP Parameters.
该规范创建了一个名为“哈希函数文本名称”的新IANA注册表。它将不属于SDP参数的一部分。
The names of hash functions used for certificate fingerprints are registered by the IANA. Hash functions MUST be defined by standards-track RFCs that update or obsolete RFC 3279 [7].
用于证书指纹的哈希函数的名称由IANA注册。哈希函数必须由更新或废弃RFC 3279的标准跟踪RFC定义[7]。
When registering a new hash function textual name, the following information MUST be provided:
注册新的哈希函数文本名称时，必须提供以下信息：
o The textual name of the hash function.
o 哈希函数的文本名称。
o The Object Identifier (OID) of the hash function as used in X.509 certificates.
o 在X.509证书中使用的哈希函数的对象标识符（OID）。
o A reference to the standards-track RFC, updating or obsoleting RFC 3279 [7], defining the use of the hash function in X.509 certificates.
o 参考标准跟踪RFC，更新或淘汰RFC 3279[7]，定义X.509证书中哈希函数的使用。
Figure 3 contains the initial values of this registry.
图3包含此注册表的初始值。
Hash Function Name OID Reference
------------------ --- ---------
"md2" 1.2.840.113549.2.2 RFC 3279
"md5" 1.2.840.113549.2.5 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-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-512" 2.16.840.1.101.3.4.2.3 RFC 4055
Hash Function Name OID Reference
------------------ --- ---------
"md2" 1.2.840.113549.2.2 RFC 3279
"md5" 1.2.840.113549.2.5 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-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-512" 2.16.840.1.101.3.4.2.3 RFC 4055
Figure 3: IANA Hash Function Textual Name Registry
图3:IANA哈希函数文本名称注册表
[1] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006.
[1] Handley，M.，Jacobson，V.，和C.Perkins，“SDP：会话描述协议”，RFC4566，2006年7月。
[2] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the Session Description Protocol (SDP)", RFC 4145, September 2005.
[2] Yon，D.和G.Camarillo，“会话描述协议（SDP）中基于TCP的媒体传输”，RFC 41452005年9月。
[3] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.1", RFC 4346, April 2006.
[3] Dierks，T.和E.Rescorla，“传输层安全（TLS）协议版本1.1”，RFC 4346，2006年4月。
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[4] Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[5] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002.
[5] Rosenberg，J.和H.Schulzrinne，“具有会话描述协议（SDP）的提供/应答模型”，RFC 3264，2002年6月。
[6] International Telecommunications Union, "Information technology - Open Systems Interconnection - The Directory: Public-key and attribute certificate frameworks", ITU-T Recommendation X.509, ISO Standard 9594-8, March 2000.
[6] 国际电信联盟，“信息技术-开放系统互连-目录：公钥和属性证书框架”，ITU-T建议X.509，ISO标准9594-8，2000年3月。
[7] Bassham, L., Polk, W., and R. Housley, "Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3279, April 2002.
[7] Bassham，L.，Polk，W.，和R.Housley，“互联网X.509公钥基础设施证书和证书撤销列表（CRL）配置文件的算法和标识符”，RFC 3279，2002年4月。
[8] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3280, April 2002.
[8] Housley，R.，Polk，W.，Ford，W.，和D.Solo，“Internet X.509公钥基础设施证书和证书撤销列表（CRL）配置文件”，RFC 32802002年4月。
[9] Schaad, J., Kaliski, B., and R. Housley, "Additional Algorithms and Identifiers for RSA Cryptography for use in the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 4055, June 2005.
[9] Schaad，J.，Kaliski，B.，和R.Housley，“互联网X.509公钥基础设施证书和证书撤销列表（CRL）配置文件中使用的RSA加密的其他算法和标识符”，RFC 4055，2005年6月。
[10] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 4234, October 2005.
[10] Crocker，D.和P.Overell，“语法规范的扩充BNF:ABNF”，RFC 42342005年10月。
[11] National Institute of Standards and Technology, "Secure Hash Standard", FIPS PUB 180-2, August 2002, <http://csrc.nist.gov/ publications/fips/fips180-2/fips180-2.pdf>.
[11] 国家标准与技术研究所，“安全哈希标准”，FIPS PUB 180-22002年8月<http://csrc.nist.gov/ 出版物/fips/fips180-2/fips180-2.pdf>。
[12] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April 1992.
[12] Rivest，R.，“MD5消息摘要算法”，RFC1321，1992年4月。
[13] Kaliski, B., "The MD2 Message-Digest Algorithm", RFC 1319, April 1992.
[13] Kaliski，B.，“MD2消息摘要算法”，RFC 1319，1992年4月。
[14] Freed, N. and J. Klensin, "Media Type Specifications and Registration Procedures", BCP 13, RFC 4288, December 2005.
[14] Freed，N.和J.Klensin，“介质类型规范和注册程序”，BCP 13，RFC 4288，2005年12月。
[15] Handley, M., Perkins, C., and E. Whelan, "Session Announcement Protocol", RFC 2974, October 2000.
[15] Handley，M.，Perkins，C.，和E.Whelan，“会话公告协议”，RFC 29742000年10月。
[16] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002.
[16] Rosenberg，J.，Schulzrinne，H.，Camarillo，G.，Johnston，A.，Peterson，J.，Sparks，R.，Handley，M.，和E.Schooler，“SIP：会话启动协议”，RFC 3261，2002年6月。
[17] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Message Specification", RFC 3851, July 2004.
[17] Ramsdell，B.，“安全/多用途Internet邮件扩展（S/MIME）版本3.1消息规范”，RFC 3851，2004年7月。
[18] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication: Basic and Digest Access Authentication", RFC 2617, June 1999.
[18] Franks，J.，Hallam Baker，P.，Hostetler，J.，Lawrence，S.，Leach，P.，Lootonen，A.，和L.Stewart，“HTTP认证：基本和摘要访问认证”，RFC 26171999年6月。
[19] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1 (SHA1)", RFC 3174, September 2001.
[19] Eastlake，D.和P.Jones，“美国安全哈希算法1（SHA1）”，RFC3174，2001年9月。
[20] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[20] Rescorla，E.，“TLS上的HTTP”，RFC 2818，2000年5月。
[21] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Protocol Architecture", RFC 4251, January 2006.
[21] Ilonen，T.和C.Lonvick，“安全外壳（SSH）协议架构”，RFC 42512006年1月。
[22] Groves, C., Pantaleo, M., Anderson, T., and T. Taylor, "Gateway Control Protocol Version 1", RFC 3525, June 2003.
[22] Groves，C.，Pantaleo，M.，Anderson，T.，和T.Taylor，“网关控制协议版本1”，RFC 35252003年6月。
[23] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004.
[23] Baugher，M.，McGrew，D.，Naslund，M.，Carrara，E.，和K.Norrman，“安全实时传输协议（SRTP）”，RFC 37112004年3月。
[24] Lazzaro, J., "Framing Real-time Transport Protocol (RTP) and RTP Control Protocol (RTCP) Packets over Connection-Oriented Transport", RFC 4571, July 2006.
[24] Lazzaro，J.，“面向连接传输上的帧实时传输协议（RTP）和RTP控制协议（RTCP）数据包”，RFC 4571，2006年7月。
Author's Address
作者地址
Jonathan Lennox Columbia University Department of Computer Science 450 Computer Science 1214 Amsterdam Ave., M.C. 0401 New York, NY 10027 US
乔纳森·伦诺克斯哥伦比亚大学计算机科学系450美国纽约州纽约市阿姆斯特丹大道1214号，邮编：0401，邮编：10027
EMail: lennox@cs.columbia.edu
EMail: lennox@cs.columbia.edu
Full Copyright Statement
完整版权声明
Copyright (C) The Internet Society (2006).
版权所有（C）互联网协会（2006年）。
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.
本文件受BCP 78中包含的权利、许可和限制的约束，除其中规定外，作者保留其所有权利。
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.
本文件及其包含的信息是按“原样”提供的，贡献者、他/她所代表或赞助的组织（如有）、互联网协会和互联网工程任务组不承担任何明示或暗示的担保，包括但不限于任何保证，即使用本文中的信息不会侵犯任何权利，或对适销性或特定用途适用性的任何默示保证。
Intellectual Property
知识产权
The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79.
IETF对可能声称与本文件所述技术的实施或使用有关的任何知识产权或其他权利的有效性或范围，或此类权利下的任何许可可能或可能不可用的程度，不采取任何立场；它也不表示它已作出任何独立努力来确定任何此类权利。有关RFC文件中权利的程序信息，请参见BCP 78和BCP 79。
Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr.
向IETF秘书处披露的知识产权副本和任何许可证保证，或本规范实施者或用户试图获得使用此类专有权利的一般许可证或许可的结果，可从IETF在线知识产权存储库获取，网址为http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org.
IETF邀请任何相关方提请其注意任何版权、专利或专利申请，或其他可能涵盖实施本标准所需技术的专有权利。请将信息发送至IETF的IETF-ipr@ietf.org.
Acknowledgement
确认
Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA).
RFC编辑器功能的资金由IETF行政支持活动（IASA）提供。