rfc2574.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Network Working Group                                      U. Blumenthal
Request for Comments: 2574                     IBM T. J. Watson Research
Obsoletes: 2274                                                B. Wijnen
Category: Standards Track                      IBM T. J. Watson Research
                                                              April 1999


          User-based Security Model (USM) for version 3 of the
              Simple Network Management Protocol (SNMPv3)

Status of this Memo

   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.

Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

Abstract

   This document describes the User-based Security Model (USM) for SNMP
   version 3 for use in the SNMP architecture [RFC2571].  It defines the
   Elements of Procedure for providing SNMP message level security.
   This document also includes a MIB for remotely monitoring/managing
   the configuration parameters for this Security Model.

Table of Contents

   1.  Introduction                                                   3
   1.1.  Threats                                                      4
   1.2.  Goals and Constraints                                        5
   1.3.  Security Services                                            6
   1.4.  Module Organization                                          7
   1.4.1.  Timeliness Module                                          7
   1.4.2.  Authentication Protocol                                    8
   1.4.3.  Privacy Protocol                                           8
   1.5.  Protection against Message Replay, Delay and Redirection     8
   1.5.1.  Authoritative SNMP engine                                  8
   1.5.2.  Mechanisms                                                 9
   1.6.  Abstract Service Interfaces                                 10
   1.6.1.  User-based Security Model Primitives for Authentication   11
   1.6.2.  User-based Security Model Primitives for Privacy          11
   2.  Elements of the Model                                         12
   2.1.  User-based Security Model Users                             12



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   2.2.  Replay Protection                                           13
   2.2.1.  msgAuthoritativeEngineID                                  13
   2.2.2.  msgAuthoritativeEngineBoots and msgAuthoritativeEngineTime14
   2.2.3.  Time Window                                               15
   2.3.  Time Synchronization                                        15
   2.4.  SNMP Messages Using this Security Model                     16
   2.5.  Services provided by the User-based Security Model          17
   2.5.1.  Services for Generating an Outgoing SNMP Message          17
   2.5.2.  Services for Processing an Incoming SNMP Message          19
   2.6.  Key Localization Algorithm.                                 21
   3.  Elements of Procedure                                         21
   3.1.  Generating an Outgoing SNMP Message                         22
   3.2.  Processing an Incoming SNMP Message                         25
   4.  Discovery                                                     30
   5.  Definitions                                                   31
   6.  HMAC-MD5-96 Authentication Protocol                           50
   6.1.  Mechanisms                                                  50
   6.1.1.  Digest Authentication Mechanism                           50
   6.2.  Elements of the Digest Authentication Protocol              51
   6.2.1.  Users                                                     51
   6.2.2.  msgAuthoritativeEngineID                                  51
   6.2.3.  SNMP Messages Using this Authentication Protocol          51
   6.2.4.  Services provided by the HMAC-MD5-96 Authentication Module52
   6.2.4.1.  Services for Generating an Outgoing SNMP Message        52
   6.2.4.2.  Services for Processing an Incoming SNMP Message        53
   6.3.  Elements of Procedure                                       53
   6.3.1.  Processing an Outgoing Message                            54
   6.3.2.  Processing an Incoming Message                            54
   7.  HMAC-SHA-96 Authentication Protocol                           55
   7.1.  Mechanisms                                                  55
   7.1.1.  Digest Authentication Mechanism                           56
   7.2.  Elements of the HMAC-SHA-96 Authentication Protocol         56
   7.2.1.  Users                                                     56
   7.2.2.  msgAuthoritativeEngineID                                  57
   7.2.3.  SNMP Messages Using this Authentication Protocol          57
   7.2.4.  Services provided by the HMAC-SHA-96 Authentication Module57
   7.2.4.1.  Services for Generating an Outgoing SNMP Message        57
   7.2.4.2.  Services for Processing an Incoming SNMP Message        58
   7.3.  Elements of Procedure                                       59
   7.3.1.  Processing an Outgoing Message                            59
   7.3.2.  Processing an Incoming Message                            60
   8.  CBC-DES Symmetric Encryption Protocol                         61
   8.1.  Mechanisms                                                  61
   8.1.1.  Symmetric Encryption Protocol                             61
   8.1.1.1.  DES key and Initialization Vector.                      62
   8.1.1.2.  Data Encryption.                                        63
   8.1.1.3.  Data Decryption                                         63
   8.2.  Elements of the DES Privacy Protocol                        63



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   8.2.1.  Users                                                     63
   8.2.2.  msgAuthoritativeEngineID                                  64
   8.2.3.  SNMP Messages Using this Privacy Protocol                 64
   8.2.4.  Services provided by the DES Privacy Module               64
   8.2.4.1.  Services for Encrypting Outgoing Data                   64
   8.2.4.2.  Services for Decrypting Incoming Data                   65
   8.3.  Elements of Procedure.                                      66
   8.3.1.  Processing an Outgoing Message                            66
   8.3.2.  Processing an Incoming Message                            66
   9.  Intellectual Property                                         67
   10. Acknowledgements                                              67
   11. Security Considerations                                       69
   11.1. Recommended Practices                                       69
   11.2. Defining Users                                              71
   11.3. Conformance                                                 72
   11.4. Use of Reports                                              72
   11.5. Access to the SNMP-USER-BASED-SM-MIB                        72
   12. References                                                    73
   13. Editors' Addresses                                            75
   A.1.  SNMP engine Installation Parameters                         76
   A.2.  Password to Key Algorithm                                   78
   A.2.1.  Password to Key Sample Code for MD5                       79
   A.2.2.  Password to Key Sample Code for SHA                       80
   A.3.  Password to Key Sample Results                              81
   A.3.1.  Password to Key Sample Results using MD5                  81
   A.3.2.  Password to Key Sample Results using SHA                  81
   A.4.  Sample encoding of msgSecurityParameters                    82
   A.5.  Sample keyChange Results                                    83
   A.5.1.  Sample keyChange Results using MD5                        83
   A.5.2.  Sample keyChange Results using SHA                        84
   B.  Change Log                                                    85
   C.  Full Copyright Statement                                      86

1.  Introduction

   The Architecture for describing Internet Management Frameworks
   [RFC2571] describes that an SNMP engine is composed of:

     1) a Dispatcher
     2) a Message Processing Subsystem,
     3) a Security Subsystem, and
     4) an Access Control Subsystem.

   Applications make use of the services of these subsystems.

   It is important to understand the SNMP architecture and the
   terminology of the architecture to understand where the Security
   Model described in this document fits into the architecture and



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   interacts with other subsystems within the architecture.  The reader
   is expected to have read and understood the description of the SNMP
   architecture, as defined in [RFC2571].

   This memo [RFC2274] describes the User-based Security Model as it is
   used within the SNMP Architecture.  The main idea is that we use the
   traditional concept of a user (identified by a userName) with which
   to associate security information.

   This memo describes the use of HMAC-MD5-96 and HMAC-SHA-96 as the
   authentication protocols and the use of CBC-DES as the privacy
   protocol. The User-based Security Model however allows for other such
   protocols to be used instead of or concurrent with these protocols.
   Therefore, the description of HMAC-MD5-96, HMAC-SHA-96 and CBC-DES
   are in separate sections to reflect their self-contained nature and
   to indicate that they can be replaced or supplemented in the future.

   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].

1.1.  Threats

   Several of the classical threats to network protocols are applicable
   to the network management problem and therefore would be applicable
   to any SNMP Security Model.  Other threats are not applicable to the
   network management problem.  This section discusses principal
   threats, secondary threats, and threats which are of lesser
   importance.

   The principal threats against which this SNMP Security Model should
   provide protection are:

   - Modification of Information
     The modification threat is the danger that some unauthorized entity
     may alter in-transit SNMP messages generated on behalf of an
     authorized principal in such a way as to effect unauthorized
     management operations, including falsifying the value of an object.

   - Masquerade
     The masquerade threat is the danger that management operations not
     authorized for some user may be attempted by assuming the identity
     of another user that has the appropriate authorizations.

   Two secondary threats are also identified.  The Security Model
   defined in this memo provides limited protection against:





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   - Disclosure
     The disclosure threat is the danger of eavesdropping on the
     exchanges between managed agents and a management station.
     Protecting against this threat may be required as a matter of local
     policy.

   - Message Stream Modification
     The SNMP protocol is typically based upon a connection-less
     transport service which may operate over any sub-network service.
     The re-ordering, delay or replay of messages can and does occur
     through the natural operation of many such sub-network services.
     The message stream modification threat is the danger that messages
     may be maliciously re-ordered, delayed or replayed to an extent
     which is greater than can occur through the natural operation of a
     sub-network service, in order to effect unauthorized management
     operations.

   There are at least two threats that an SNMP Security Model need not
   protect against.  The security protocols defined in this memo do not
   provide protection against:

   - Denial of Service
     This SNMP Security Model does not attempt to address the broad
     range of attacks by which service on behalf of authorized users is
     denied.  Indeed, such denial-of-service attacks are in many cases
     indistinguishable from the type of network failures with which any
     viable network management protocol must cope as a matter of course.
   - Traffic Analysis
     This SNMP Security Model does not attempt to address traffic
     analysis attacks.  Indeed, many traffic patterns are predictable -
     devices may be managed on a regular basis by a relatively small
     number of management applications - and therefore there is no
     significant advantage afforded by protecting against traffic
     analysis.

1.2.  Goals and Constraints

   Based on the foregoing account of threats in the SNMP network
   management environment, the goals of this SNMP Security Model are as
   follows.

   1) Provide for verification that each received SNMP message has
      not been modified during its transmission through the network.

   2) Provide for verification of the identity of the user on whose
      behalf a received SNMP message claims to have been generated.





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   3) Provide for detection of received SNMP messages, which request
      or contain management information, whose time of generation was
      not recent.

   4) Provide, when necessary, that the contents of each received
      SNMP message are protected from disclosure.

   In addition to the principal goal of supporting secure network
   management, the design of this SNMP Security Model is also influenced
   by the following constraints: