rfc1446.txt

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          Network Working Group                                J. Galvin
          Request for Comments: 1446         Trusted Information Systems
                                                           K. McCloghrie
                                                      Hughes LAN Systems
                                                              April 1993


                                Security Protocols
                               for version 2 of the
                   Simple Network Management Protocol (SNMPv2)


          Status of this Memo

          This RFC specifes 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 Introduction ..........................................    2
          1.1 A Note on Terminology ...............................    3
          1.2 Threats .............................................    4
          1.3 Goals and Constraints ...............................    5
          1.4 Security Services ...................................    6
          1.5 Mechanisms ..........................................    7
          1.5.1 Message Digest Algorithm ..........................    8
          1.5.2 Symmetric Encryption Algorithm ....................    9
          2 SNMPv2 Party ..........................................   11
          3 Digest Authentication Protocol ........................   14
          3.1 Generating a Message ................................   16
          3.2 Receiving a Message .................................   18
          4 Symmetric Privacy Protocol ............................   21
          4.1 Generating a Message ................................   21
          4.2 Receiving a Message .................................   22
          5 Clock and Secret Distribution .........................   24
          5.1 Initial Configuration ...............................   25
          5.2 Clock Distribution ..................................   28
          5.3 Clock Synchronization ...............................   29
          5.4 Secret Distribution .................................   31
          5.5 Crash Recovery ......................................   34
          6 Security Considerations ...............................   37
          6.1 Recommended Practices ...............................   37
          6.2 Conformance .........................................   39
          6.3 Protocol Correctness ................................   42




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          RFC 1446        Security Protocols for SNMPv2       April 1993


          6.3.1 Clock Monotonicity Mechanism ......................   43
          6.3.2 Data Integrity Mechanism ..........................   43
          6.3.3 Data Origin Authentication Mechanism ..............   44
          6.3.4 Restricted Administration Mechanism ...............   44
          6.3.5 Message Timeliness Mechanism ......................   45
          6.3.6 Selective Clock Acceleration Mechanism ............   46
          6.3.7 Confidentiality Mechanism .........................   47
          7 Acknowledgements ......................................   48
          8 References ............................................   49
          9 Authors' Addresses ....................................   51








































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          RFC 1446        Security Protocols for SNMPv2       April 1993


          1.  Introduction

          A network management system contains: several (potentially
          many) nodes, each with a processing entity, termed an agent,
          which has access to management instrumentation; at least one
          management station; and, a management protocol, used to convey
          management information between the agents and management
          stations.  Operations of the protocol are carried out under an
          administrative framework which defines both authentication and
          authorization policies.

          Network management stations execute management applications
          which monitor and control network elements.  Network elements
          are devices such as hosts, routers, terminal servers, etc.,
          which are monitored and controlled through access to their
          management information.

          In the Administrative Model for SNMPv2 document [1], each
          SNMPv2 party is, by definition, associated with a single
          authentication protocol and a single privacy protocol.  It is
          the purpose of this document, Security Protocols for SNMPv2,
          to define one such authentication and one such privacy
          protocol.

          The authentication protocol provides a mechanism by which
          SNMPv2 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.

          The privacy protocol provides a mechanism by which SNMPv2
          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 [2].

               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.






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          RFC 1446        Security Protocols for SNMPv2       April 1993


          The Digest Authentication Protocol is described in Section 3.
          It provides a data integrity service by transmitting a message
          digest - computed by the originator and verified by the
          recipient - with each SNMPv2 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 4.  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 5.3 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 5.4 presents
          one such strategy that is particularly suited to the demands
          of SNMP network management.


          1.1.  A Note on Terminology

          For the purpose of exposition, the original Internet-standard
          Network Management Framework, as described in RFCs 1155, 1157,
          and 1212, is termed the SNMP version 1 framework (SNMPv1).
          The current framework is termed the SNMP version 2 framework
          (SNMPv2).








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          RFC 1446        Security Protocols for SNMPv2       April 1993


          1.2.  Threats

          Several of the classical threats to network protocols are
          applicable to the network management problem and therefore
          would be applicable to any SNMPv2 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 SNMPv2 security
          protocol should provide protection are:


          Modification of Information
               The SNMPv2 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 SNMPv2 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 SNMPv2 protocol is based upon a connectionless
               transport service which may operate over any subnetwork
               service.  The re-ordering, delay or replay of messages
               can and does occur through the natural operation of many
               such subnetwork 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 subnetwork service, in order to effect
               unauthorized management operations.





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          RFC 1446        Security Protocols for SNMPv2       April 1993


          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 SNMPv2 is used to create new SNMPv2 parties [1]
               on which subsequent secure operation might be based.
               Protecting against the disclosure threat may also be
               required as a matter of local policy.

          There are at least two threats that a SNMPv2 security protocol
          need not protect against.  The security protocols defined in
          this memo do not provide protection against:

          Denial of Service
               A SNMPv2 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.

          Traffic Analysis
               In addition, a SNMPv2 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.


          1.3.  Goals and Constraints

          Based on the foregoing account of threats in the SNMP network
          management environment, the goals of a SNMPv2 security
          protocol are enumerated below.

          (1)  The protocol should provide for verification that each
               received SNMPv2 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 SNMPv2
               message.