Network Working Group L. Zhu
Request for Comments: 4537 P. Leach
Updates: 4120 K. Jaganathan
Category: Standards Track Microsoft Corporation
June 2006
Network Working Group L. Zhu
Request for Comments: 4537 P. Leach
Updates: 4120 K. Jaganathan
Category: Standards Track Microsoft Corporation
June 2006
Kerberos Cryptosystem Negotiation Extension
Kerberos密码系统协商扩展
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 an extension to the Kerberos protocol as defined in RFC 4120, in which the client can send a list of supported encryption types in decreasing preference order, and the server then selects an encryption type that is supported by both the client and the server.
本文档指定了RFC 4120中定义的Kerberos协议的扩展，在该扩展中，客户机可以按递减的优先顺序发送支持的加密类型列表，然后服务器选择客户机和服务器都支持的加密类型。
Table of Contents
目录
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . . 2
3. Negotiation Extension . . . . . . . . . . . . . . . . . . . . . 2
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . . 2
3. Negotiation Extension . . . . . . . . . . . . . . . . . . . . . 2
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . . 4
Under the current mechanism [RFC4120], the Kerberos Distribution Center (KDC) must limit the ticket session key encryption type (enctype) chosen for a given server to one it believes is supported by both the client and the server. If both the client and server understand a stronger enctype than the one selected by the KDC, they cannot negotiate it. As the result, the protection of application traffic is often weaker than necessary when the server can support different sets of enctypes depending on the server application software being used.
在当前机制[RFC4120]下，Kerberos分发中心（KDC）必须将为给定服务器选择的票证会话密钥加密类型（enctype）限制为它认为客户端和服务器都支持的类型。如果客户机和服务器都理解一个比KDC选择的更强大的enctype，则它们无法协商它。因此，当服务器可以根据所使用的服务器应用软件支持不同的EncType集时，应用程序通信量的保护往往比必要的弱。
This document specifies an extension to the Kerberos protocol to allow clients and servers to negotiate use of a different and possibly stronger cryptosystem in subsequent communication.
本文档指定了Kerberos协议的扩展，以允许客户端和服务器在后续通信中协商使用不同且可能更强的密码系统。
This extension utilizes an authorization data element in the authenticator of the AP-REQ message [RFC4120]. The client sends the list of enctypes that it supports to the server; the server then informs the client of its choice. The negotiated subkey is sent in the AP-REP message [RFC4120].
此扩展利用AP-REQ消息[RFC4120]的验证器中的授权数据元素。客户端向服务器发送其支持的加密类型列表；然后，服务器通知客户机其选择。协商的子密钥在AP-REP消息[RFC4120]中发送。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
本文件中的关键词“必须”、“不得”、“必需”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照[RFC2119]中所述进行解释。
If the client prefers an enctype over that of the service ticket session key, then it SHOULD send a list of enctypes in decreasing preference order to the server. Based on local policy, the client selects enctypes out of all the enctypes available locally to be included in this list, and it SHOULD NOT include enctypes that are less preferable than that of the ticket session key in the service ticket. In addition, the client SHOULD NOT include negative (local-use) enctype numbers unless it knows a priori that the server has been configured to use the same negative enctype numbers for the same enctypes.
如果客户机优先选择enctype而不是服务票证会话密钥的enctype，那么它应该以递减的优先顺序向服务器发送enctype列表。根据本地策略，客户端从本地可用的所有enctypes中选择要包括在此列表中的enctypes，并且它不应包括比服务票证中的票证会话密钥更可取的enctypes。此外，客户端不应包含负（本地使用）enctype编号，除非它事先知道服务器已配置为对相同enctype使用相同的负enctype编号。
The client sends the enctype list via the authorization-data of the authenticator in the AP-REQ [RFC4120]. A new authorization data element type AD-ETYPE-NEGOTIATION is defined.
客户端通过AP-REQ[RFC4120]中认证器的授权数据发送enctype列表。定义了一个新的授权数据元素类型AD-ETYPE-NEGOTIATION。
AD-ETYPE-NEGOTIATION 129
AD-ETYPE-129
This authorization data element itself is enclosed in the AD-IF-RELEVANT container; thus, a correctly implemented server that does not understand this element should ignore it [RFC4120]. The value of this authorization element contains the DER [X680] [X690] encoding of the following ASN.1 type:
此授权数据元素本身包含在AD-IF相关容器中；因此，不理解此元素的正确实现的服务器应该忽略它[RFC4120]。此授权元素的值包含以下ASN.1类型的DER[X680][X690]编码：
EtypeList ::= SEQUENCE OF Int32
-- Specifies the enctypes supported by the client.
-- This enctype list is in decreasing preference order
-- (favorite choice first).
-- Int32 is defined in [RFC4120].
EtypeList ::= SEQUENCE OF Int32
-- Specifies the enctypes supported by the client.
-- This enctype list is in decreasing preference order
-- (favorite choice first).
-- Int32 is defined in [RFC4120].
If the EtypeList is present and the server prefers an enctype from the client's enctype list over that of the AP-REQ authenticator subkey (if that is present) or the service ticket session key, the server MUST create a subkey using that enctype. This negotiated subkey is sent in the subkey field of AP-REP message, and it is then used as the protocol key or base key [RFC3961] for subsequent communication.
如果EtypeList存在，并且服务器更喜欢客户端enctype列表中的enctype，而不是AP-REQ验证器子密钥（如果存在）或服务票证会话密钥的enctype，则服务器必须使用该enctype创建子密钥。该协商子密钥在AP-REP消息的子密钥字段中发送，然后用作协议密钥或基础密钥[RFC3961]，用于后续通信。
If the enctype of the ticket session key is included in the enctype list sent by the client, it SHOULD be the last on the list; otherwise, this enctype MUST NOT be negotiated if it was not included in the list.
如果客户机发送的enctype列表中包含票证会话密钥的enctype，则它应该是列表中的最后一个；否则，如果此enctype未包含在列表中，则不得协商此enctype。
This negotiation extension SHOULD NOT be used when the client does not expect the subkey in the AP-REP message from the server.
当客户端不希望从服务器获得AP-REP消息中的子密钥时，不应使用此协商扩展。
A note on key generation: The KDC has a strong Pseudo-Random Number Generator (PRNG); as such, the client can take advantage of the randomness provided by the KDC by reusing the KDC key data when generating keys. Implementations SHOULD use the service ticket session key value as a source of additional entropy when generating the negotiated subkey. If the AP-REQ authenticator subkey is present, it MAY also be used as a source of entropy.
关于密钥生成的注意事项：KDC有一个强伪随机数生成器（PRNG）；因此，客户端可以通过在生成密钥时重用KDC密钥数据来利用KDC提供的随机性。在生成协商的子密钥时，实现应该使用服务票证会话密钥值作为附加熵的来源。如果存在AP-REQ验证器子密钥，则它也可以用作熵源。
The server MAY ignore the preference order indicated by the client. The policy by which the client or the server chooses an enctype (i.e., how the preference order for the supported enctypes is selected) is a local matter.
服务器可以忽略客户端指示的首选项顺序。客户机或服务器选择enctype的策略（即，如何选择受支持enctype的首选顺序）是本地事务。
The client's enctype list and the server's reply enctype are part of encrypted data; thus, the security considerations are the same as those of the Kerberos encrypted data.
客户端的enctype列表和服务器的回复enctype是加密数据的一部分；因此，安全注意事项与Kerberos加密数据的安全注意事项相同。
Both the EtypeList and the server's sub-session key are protected by the session key or sub-session key used for the AP-REQ, and as a result, if a key for a stronger enctype is negotiated underneath a key for a weaker enctype, an attacker capable of breaking the weaker enctype can also discover the key for the stronger enctype. The advantage of this extension is to minimize the amount of cipher text encrypted under a weak enctype to which an attacker has access.
EtypeList和服务器的子会话密钥都受AP-REQ所用的会话密钥或子会话密钥的保护，因此，如果更强enctype的密钥在较弱enctype的密钥下协商，则能够破坏较弱enctype的攻击者也可以发现较强enctype的密钥。此扩展的优点是最大限度地减少攻击者可以访问的弱加密类型下加密的密文量。
The authors would like to thank the following individuals for their comments and suggestions: Ken Raeburn, Luke Howard, Tom Yu, Love Hornquist Astrand, Sam Hartman, and Martin Rex.
作者要感谢以下个人的评论和建议：肯·雷伯恩、卢克·霍华德、汤姆·余、洛夫·霍恩奎斯特·阿斯特兰、萨姆·哈特曼和马丁·雷克斯。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2119]Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[RFC3961] Raeburn, K., "Encryption and Checksum Specifications for Kerberos 5", RFC 3961, February 2005.
[RFC3961]Raeburn，K.，“Kerberos 5的加密和校验和规范”，RFC 3961，2005年2月。
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The Kerberos Network Authentication Service (V5)", RFC 4120, July 2005.
[RFC4120]Neuman，C.，Yu，T.，Hartman，S.，和K.Raeburn，“Kerberos网络身份验证服务（V5）”，RFC41202005年7月。
[X680] ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002, Information technology - Abstract Syntax Notation One (ASN.1): Specification of basic notation.
[X680]ITU-T建议X.680（2002）| ISO/IEC 8824-1:2002，信息技术-抽象语法符号1（ASN.1）：基本符号规范。
[X690] ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-1:2002, Information technology - ASN.1 encoding Rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER).
[X690]ITU-T建议X.690（2002）| ISO/IEC 8825-1:2002，信息技术-ASN.1编码规则：基本编码规则（BER）、规范编码规则（CER）和区分编码规则（DER）规范。
Authors' Addresses
作者地址
Larry Zhu Microsoft Corporation One Microsoft Way Redmond, WA 98052 US
Larry Zhu微软公司美国华盛顿州雷德蒙微软大道一号，邮编：98052
EMail: lzhu@microsoft.com
EMail: lzhu@microsoft.com
Paul Leach Microsoft Corporation One Microsoft Way Redmond, WA 98052 US
Paul Leach微软公司美国华盛顿州雷德蒙微软大道一号，邮编：98052
EMail: paulle@microsoft.com
EMail: paulle@microsoft.com
Karthik Jaganathan Microsoft Corporation One Microsoft Way Redmond, WA 98052 US
Karthik Jaganathan微软公司美国华盛顿州雷德蒙微软大道一号，邮编：98052
EMail: karthikj@microsoft.com
EMail: karthikj@microsoft.com
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Copyright (C) The Internet Society (2006).
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