rfc3414.txt

开发snmp的开发包有两个开放的SNMP开发库

Network Working Group                                      U. Blumenthal
Request for Comments: 3414                                     B. Wijnen
STD: 62                                              Lucent Technologies
Obsoletes: 2574                                            December 2002
Category: Standards Track


          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 (2002).  All Rights Reserved.

Abstract

   This document describes the User-based Security Model (USM) for
   Simple Network Management Protocol (SNMP) version 3 for use in the
   SNMP architecture.  It defines the Elements of Procedure for
   providing SNMP message level security.  This document also includes a
   Management Information Base (MIB) for remotely monitoring/managing
   the configuration parameters for this Security Model.  This document
   obsoletes RFC 2574.

Table of Contents

   1.        Introduction..........................................  4
   1.1.      Threats...............................................  4
   1.2.      Goals and Constraints.................................  6
   1.3.      Security Services.....................................  6
   1.4.      Module Organization...................................  7
   1.4.1.    Timeliness Module.....................................  8
   1.4.2.    Authentication Protocol...............................  8
   1.4.3.    Privacy Protocol......................................  8
   1.5.      Protection against Message Replay, Delay
             and Redirection.......................................  9
   1.5.1.    Authoritative SNMP engine.............................  9
   1.5.2.    Mechanisms............................................  9
   1.6.      Abstract Service Interfaces........................... 11




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   1.6.1.    User-based Security Model Primitives
             for Authentication.................................... 11
   1.6.2.    User-based Security Model Primitives
             for Privacy........................................... 12
   2.        Elements of the Model................................. 12
   2.1.      User-based Security Model Users....................... 12
   2.2.      Replay Protection..................................... 13
   2.2.1.    msgAuthoritativeEngineID.............................. 14
   2.2.2.    msgAuthoritativeEngineBoots and
             msgAuthoritativeEngineTime............................ 14
   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...... 20
   2.6.      Key Localization Algorithm............................ 22
   3.        Elements of Procedure................................. 22
   3.1.      Generating an Outgoing SNMP Message................... 22
   3.2.      Processing an Incoming SNMP Message................... 26
   4.        Discovery............................................. 31
   5.        Definitions........................................... 32
   6.        HMAC-MD5-96 Authentication Protocol................... 51
   6.1.      Mechanisms............................................ 51
   6.1.1.    Digest Authentication Mechanism....................... 51
   6.2.      Elements of the Digest Authentication Protocol........ 52
   6.2.1.    Users................................................. 52
   6.2.2.    msgAuthoritativeEngineID.............................. 53
   6.2.3.    SNMP Messages Using this Authentication Protocol...... 53
   6.2.4.    Services provided by the HMAC-MD5-96
             Authentication Module................................. 53
   6.2.4.1.  Services for Generating an Outgoing SNMP Message...... 53
   6.2.4.2.  Services for Processing an Incoming SNMP Message...... 54
   6.3.      Elements of Procedure................................. 55
   6.3.1.    Processing an Outgoing Message........................ 55
   6.3.2.    Processing an Incoming Message........................ 56
   7.        HMAC-SHA-96 Authentication Protocol................... 57
   7.1.      Mechanisms............................................ 57
   7.1.1.    Digest Authentication Mechanism....................... 57
   7.2.      Elements of the HMAC-SHA-96 Authentication Protocol... 58
   7.2.1.    Users................................................. 58
   7.2.2.    msgAuthoritativeEngineID.............................. 58
   7.2.3.    SNMP Messages Using this Authentication Protocol...... 59
   7.2.4.    Services provided by the HMAC-SHA-96
             Authentication Module................................. 59
   7.2.4.1.  Services for Generating an Outgoing SNMP Message...... 59
   7.2.4.2.  Services for Processing an Incoming SNMP Message...... 60
   7.3.      Elements of Procedure................................. 61



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   7.3.1.    Processing an Outgoing Message........................ 61
   7.3.2.    Processing an Incoming Message........................ 61
   8.        CBC-DES Symmetric Encryption Protocol................. 63
   8.1.      Mechanisms............................................ 63
   8.1.1.    Symmetric Encryption Protocol......................... 63
   8.1.1.1.  DES key and Initialization Vector..................... 64
   8.1.1.2.  Data Encryption....................................... 65
   8.1.1.3.  Data Decryption....................................... 65
   8.2.      Elements of the DES Privacy Protocol.................. 65
   8.2.1.    Users................................................. 65
   8.2.2.    msgAuthoritativeEngineID.............................. 66
   8.2.3.    SNMP Messages Using this Privacy Protocol............. 66
   8.2.4.    Services provided by the DES Privacy Module........... 66
   8.2.4.1.  Services for Encrypting Outgoing Data................. 66
   8.2.4.2.  Services for Decrypting Incoming Data................. 67
   8.3.      Elements of Procedure................................. 68
   8.3.1.    Processing an Outgoing Message........................ 68
   8.3.2.    Processing an Incoming Message........................ 69
   9.        Intellectual Property................................. 69
   10.       Acknowledgements...................................... 70
   11.       Security Considerations............................... 71
   11.1.     Recommended Practices................................. 71
   11.2.     Defining Users........................................ 73
   11.3.     Conformance........................................... 74
   11.4.     Use of Reports........................................ 75
   11.5.     Access to the SNMP-USER-BASED-SM-MIB.................. 75
   12.       References............................................ 75
   A.1.      SNMP engine Installation Parameters................... 78
   A.2.      Password to Key Algorithm............................. 80
   A.2.1.    Password to Key Sample Code for MD5................... 81
   A.2.2.    Password to Key Sample Code for SHA................... 82
   A.3.      Password to Key Sample Results........................ 83
   A.3.1.    Password to Key Sample Results using MD5.............. 83
   A.3.2.    Password to Key Sample Results using SHA.............. 83
   A.4.      Sample encoding of msgSecurityParameters.............. 83
   A.5.      Sample keyChange Results.............................. 84
   A.5.1.    Sample keyChange Results using MD5.................... 84
   A.5.2.    Sample keyChange Results using SHA.................... 85
   B.        Change Log............................................ 86
             Editors' Addresses.................................... 87
             Full Copyright Statement.............................. 88










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RFC 3414                     USM for SNMPv3                December 2002


1. Introduction

   The Architecture for describing Internet Management Frameworks
   [RFC3411] 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
   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 [RFC3411].

   This memo 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:



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   - 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:

   - 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.





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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.

   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