rfc1352.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                                         J. Galvin
Request for Comments: 1352            Trusted Information Systems, Inc.
                                                          K. McCloghrie
                                               Hughes LAN Systems, Inc.
                                                               J. Davin
                                    MIT Laboratory for Computer Science
                                                              July 1992


                        SNMP Security Protocols

Status of this Memo

   This document specifies an IAB standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements. Please refer to the current edition of the "IAB
   Official Protocol Standards" for the standardization state and status
   of this protocol. Distribution of this memo is unlimited.

Table of Contents

   1.    Abstract . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.    Introduction . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.1   Threats  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.2   Goals and Constraints  . . . . . . . . . . . . . . . . . . .   5
   2.3   Security Services  . . . . . . . . . . . . . . . . . . . . .   6
   2.4   Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . .   6
   2.4.1   Message Digest Algorithm . . . . . . . . . . . . . . . . .   7
   2.4.2   Symmetric Encryption Algorithm . . . . . . . . . . . . . .   8
   3.    SNMP Party   . . . . . . . . . . . . . . . . . . . . . . . .   9
   4.    Digest Authentication Protocol . . . . . . . . . . . . . . .  11
   4.1   Generating a Message   . . . . . . . . . . . . . . . . . . .  14
   4.2   Receiving a Message  . . . . . . . . . . . . . . . . . . . .  15
   5.    Symmetric Privacy Protocol . . . . . . . . . . . . . . . . .  16
   5.1   Generating a Message   . . . . . . . . . . . . . . . . . . .  17
   5.2   Receiving a Message  . . . . . . . . . . . . . . . . . . . .  18
   6.    Clock and Secret Distribution  . . . . . . . . . . . . . . .  19
   6.1   Initial Configuration    . . . . . . . . . . . . . . . . . .  20
   6.2   Clock Distribution   . . . . . . . . . . . . . . . . . . . .  22
   6.3   Clock Synchronization  . . . . . . . . . . . . . . . . . . .  24
   6.4   Secret Distribution  . . . . . . . . . . . . . . . . . . . .  26
   6.5   Crash Recovery   . . . . . . . . . . . . . . . . . . . . . .  28
   7.    Security Considerations  . . . . . . . . . . . . . . . . . .  30
   7.1   Recommended Practices  . . . . . . . . . . . . . . . . . . .  30
   7.2   Conformance    . . . . . . . . . . . . . . . . . . . . . . .  33
   7.3   Protocol Correctness . . . . . . . . . . . . . . . . . . . .  34
   7.3.1   Clock Monotonicity Mechanism . . . . . . . . . . . . . . .  35
   7.3.2   Data Integrity Mechanism . . . . . . . . . . . . . . . . .  36



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RFC 1352                SNMP Security Protocols                July 1992


   7.3.3   Data Origin Authentication Mechanism . . . . . . . . . . .  36
   7.3.4   Restricted Administration Mechanism  . . . . . . . . . . .  36
   7.3.5   Ordered Delivery Mechanism   . . . . . . . . . . . . . . .  37
   7.3.6   Message Timeliness Mechanism . . . . . . . . . . . . . . .  38
   7.3.7   Selective Clock Acceleration Mechanism . . . . . . . . . .  38
   7.3.8   Confidentiality Mechanism  . . . . . . . . . . . . . . . .  39
   8.    Acknowledgements . . . . . . . . . . . . . . . . . . . . . .  39
   9.    References . . . . . . . . . . . . . . . . . . . . . . . . .  40
   10.   Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  41

1.  Abstract

   The Simple Network Management Protocol (SNMP) specification [1]
   allows for the protection of network management operations by a
   variety of security protocols.  The SNMP administrative model
   described in [2] provides a framework for securing SNMP network
   management. In the context of that framework, this memo defines
   protocols to support the following three security services:

     o data integrity,

     o data origin authentication, and

     o data confidentiality.

   Please send comments to the SNMP Security Developers mailing list
   ([e-mail]).

2.  Introduction

   In the model described in [2], each SNMP party is, by definition,
   associated with a single authentication protocol.  The authentication
   protocol provides a mechanism by which SNMP management communications
   transmitted by the party may be reliably identified as having
   originated from that party. The authentication protocol defined in
   this memo also reliably determines that the message received is the
   message that was sent.

   Similarly, each SNMP party is, by definition, associated with a
   single privacy protocol. The privacy protocol provides a mechanism by
   which SNMP management communications transmitted to said party are
   protected from disclosure. The privacy protocol in this memo
   specifies that only authenticated messages may be protected from
   disclosure.

   These protocols are secure alternatives to the so-called "trivial"
   protocol defined in [1].




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RFC 1352                SNMP Security Protocols                July 1992


      USE OF THE TRIVIAL PROTOCOL ALONE DOES NOT CONSTITUTE SECURE
      NETWORK MANAGEMENT. THEREFORE, A NETWORK MANAGEMENT SYSTEM THAT
      IMPLEMENTS ONLY THE TRIVIAL PROTOCOL IS NOT CONFORMANT TO THIS
      SPECIFICATION.

   The Digest Authentication Protocol is described in Section 4.  It
   provides a data integrity service by transmitting a message digest --
   computed by the originator and verified by the recipient -- with each
   SNMP message. The data origin authentication service is provided by
   prefixing the message with a secret value known only to the
   originator and recipient, prior to computing the digest. Thus, data
   integrity is supported explicitly while data origin authentication is
   supported implicitly in the verification of the digest.

   The Symmetric Privacy Protocol is described in Section 5. It protects
   messages from disclosure by encrypting their contents according to a
   secret cryptographic key known only to the originator and recipient.
   The additional functionality afforded by this protocol is assumed to
   justify its additional computational cost.

   The Digest Authentication Protocol depends on the existence of
   loosely synchronized clocks between the originator and recipient of a
   message. The protocol specification makes no assumptions about the
   strategy by which such clocks are synchronized. Section 6.3 presents
   one strategy that is particularly suited to the demands of SNMP
   network management.

   Both protocols described here require the sharing of secret
   information between the originator of a message and its recipient.
   The protocol specifications assume the existence of the necessary
   secrets. The selection of such secrets and their secure distribution
   to appropriate parties may be accomplished by a variety of
   strategies. Section 6.4 presents one such strategy that is
   particularly suited to the demands of SNMP network management.

2.1   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 protocol. 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 any SNMP security protocol should
   provide protection are:





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RFC 1352                SNMP Security Protocols                July 1992


   Modification of Information.
      The SNMP protocol provides the means for management stations to
      interrogate and to manipulate the value of objects in a managed
      agent.  The modification threat is the danger that some party may
      alter in-transit messages generated by an authorized party in such
      a way as to effect unauthorized management operations, including
      falsifying the value of an object.

   Masquerade.
      The SNMP administrative model includes an access control model.
      Access control necessarily depends on knowledge of the origin of a
      message.  The masquerade threat is the danger that management
      operations not authorized for some party may be attempted by that
      party by assuming the identity of another party that has the
      appropriate authorizations.

   Two secondary threats are also identified. The security protocols
   defined in this memo do provide protection against:

   Message Stream Modification.
      The SNMP protocol is based upon connectionless transport services.
      The message stream modification threat is the danger that messages
      may be arbitrarily re-ordered, delayed or replayed to effect
      unauthorized management operations.  This threat may arise either
      by the work of a malicious attacker or by the natural operation of
      a subnetwork service.

   Disclosure.
      The disclosure threat is the danger of eavesdropping on the
      exchanges between managed agents and a management station.
      Protecting against this threat is mandatory when the SNMP is used
      to administer private parameters on which its security is based.
      Protecting against the disclosure threat may also be required as a
      matter of local policy.

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

   Denial of Service.
      A SNMP security protocol need not attempt to address the broad
      range of attacks by which service to authorized parties 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.





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RFC 1352                SNMP Security Protocols                July 1992


   Traffic Analysis.
      In addition, a SNMP security protocol need not attempt to address
      traffic analysis attacks.  Indeed, many traffic patterns are
      predictable -- agents may be managed on a regular basis by a
      relatively small number of management stations -- and therefore
      there is no significant advantage afforded by protecting against
      traffic analysis.

2.2   Goals and Constraints

   Based on the foregoing account of threats in the SNMP network
   management environment, the goals of a SNMP security protocol are
   enumerated below.

    1. The protocol should provide for verification that each
       received SNMP message has not been modified during
       its transmission through the network in such a way that
       an unauthorized management operation might result.

    2. The protocol should provide for verification of the
       identity of the originator of each received SNMP
       message.

    3. The protocol should provide that the apparent time of
       generation for each received SNMP message is recent.

    4. The protocol should provide that the apparent time of
       generation for each received SNMP message is
       subsequent to that for all previously delivered messages
       of similar origin.

    5. The protocol should 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 any SNMP security protocol is also
   influenced by the following constraints:

    1. When the requirements of effective management in times
       of network stress are inconsistent with those of security,
       the former are preferred.

    2. Neither the security protocol nor its underlying security
       mechanisms should depend upon the ready availability
       of other network services (e.g., Network Time Protocol
       (NTP) or secret/key management protocols).




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RFC 1352                SNMP Security Protocols                July 1992


    3. A security mechanism should entail no changes to the
       basic SNMP network management philosophy.

2.3   Security Services

   The security services necessary to support the goals of a SNMP
   security protocol are as follows.

   Data Integrity   is the provision of the property that data
       and data sequences have not been altered or destroyed
       in an unauthorized manner.

   Data Origin Authentication    is the provision of the
       property that the claimed origin of received data is
       corroborated.

   Data Confidentiality   is the provision of the property that
       information is not made available or disclosed to
       unauthorized individuals, entities, or processes.

      The protocols specified in this memo require both data
      integrity and data origin authentication to be used at all
      times. For these protocols, it is not possible to realize data