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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 5591

Network Working Group                                      D. Harrington
Internet-Draft                                 Huawei Technologies (USA)
Intended status: Standards Track                             W. Hardaker
Expires: May 5, 2009                                        Sparta, Inc.
                                                        November 1, 2008


                   Transport Security Model for SNMP
              draft-ietf-isms-transport-security-model-10

Status of This Memo

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   This Internet-Draft will expire on May 5, 2009.

Abstract

   This memo describes a Transport Security Model for the Simple Network
   Management Protocol.

   This memo also defines a portion of the Management Information Base
   (MIB) for monitoring and managing the Transport Security Model for
   SNMP.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  The Internet-Standard Management Framework . . . . . . . .  4



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     1.2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . .  4
     1.3.  Modularity . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.4.  Motivation . . . . . . . . . . . . . . . . . . . . . . . .  6
     1.5.  Constraints  . . . . . . . . . . . . . . . . . . . . . . .  6
   2.  How the Transport Security Model Fits in the Architecture  . .  6
     2.1.  Security Capabilities of this Model  . . . . . . . . . . .  7
       2.1.1.  Threats  . . . . . . . . . . . . . . . . . . . . . . .  7
       2.1.2.  Security Levels  . . . . . . . . . . . . . . . . . . .  7
     2.2.  Transport Sessions . . . . . . . . . . . . . . . . . . . .  8
     2.3.  Coexistence  . . . . . . . . . . . . . . . . . . . . . . .  8
       2.3.1.  Coexistence with Message Processing Models . . . . . .  8
       2.3.2.  Coexistence with Other Security Models . . . . . . . .  8
       2.3.3.  Coexistence with Transport Models  . . . . . . . . . .  9
   3.  Cached Information and References  . . . . . . . . . . . . . .  9
     3.1.  securityStateReference . . . . . . . . . . . . . . . . . .  9
     3.2.  tmStateReference . . . . . . . . . . . . . . . . . . . . . 10
       3.2.1.  Transport information  . . . . . . . . . . . . . . . . 10
       3.2.2.  securityName . . . . . . . . . . . . . . . . . . . . . 11
       3.2.3.  securityLevel  . . . . . . . . . . . . . . . . . . . . 11
       3.2.4.  Session Information  . . . . . . . . . . . . . . . . . 12
     3.3.  Transport Security Model Cached Information  . . . . . . . 12
       3.3.1.  securityStateReference . . . . . . . . . . . . . . . . 12
       3.3.2.  tmStateReference . . . . . . . . . . . . . . . . . . . 13
       3.3.3.  Prefixes and securityNames . . . . . . . . . . . . . . 13
   4.  Processing an Outgoing Message . . . . . . . . . . . . . . . . 13
     4.1.  Security Processing for an Outgoing Message  . . . . . . . 14
     4.2.  Elements of Procedure for Outgoing Messages  . . . . . . . 15
   5.  Processing an Incoming SNMP Message  . . . . . . . . . . . . . 16
     5.1.  Security Processing for an Incoming Message  . . . . . . . 16
     5.2.  Elements of Procedure for Incoming Messages  . . . . . . . 17
   6.  MIB Module Overview  . . . . . . . . . . . . . . . . . . . . . 18
     6.1.  Structure of the MIB Module  . . . . . . . . . . . . . . . 18
       6.1.1.  The snmpTsmStats Subtree . . . . . . . . . . . . . . . 18
       6.1.2.  The snmpTsmConfiguration Subtree . . . . . . . . . . . 18
     6.2.  Relationship to Other MIB Modules  . . . . . . . . . . . . 19
       6.2.1.  MIB Modules Required for IMPORTS . . . . . . . . . . . 19
   7.  MIB module definition  . . . . . . . . . . . . . . . . . . . . 19
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 24
     8.1.  MIB module security  . . . . . . . . . . . . . . . . . . . 24
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 25
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 26
     11.2. Informative References . . . . . . . . . . . . . . . . . . 27
   Appendix A.  Notification Tables Configuration . . . . . . . . . . 27
     A.1.  Transport Security Model Processing for Notifications  . . 29
   Appendix B.  Processing Differences between USM and Secure
                Transport . . . . . . . . . . . . . . . . . . . . . . 29



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     B.1.  USM and the RFC3411 Architecture . . . . . . . . . . . . . 30
     B.2.  Transport Subsystem and the RFC3411 Architecture . . . . . 30
   Appendix C.  Open Issues . . . . . . . . . . . . . . . . . . . . . 31
   Appendix D.  Change Log  . . . . . . . . . . . . . . . . . . . . . 31















































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1.  Introduction

   This memo describes a Transport Security Model for the Simple Network
   Management Protocol, for use with secure Transport Models in the
   Transport Subsystem [I-D.ietf-isms-tmsm].

   This memo also defines a portion of the Management Information Base
   (MIB) for monitoring and managing the Transport Security Model for
   SNMP.

   It is important to understand the SNMP architecture and the
   terminology of the architecture to understand where the Transport
   Security Model described in this memo fits into the architecture and
   interacts with other subsystems and models within the architecture.
   It is expected that reader will have also read and understood RFC3411
   [RFC3411], RFC3412 [RFC3412], RFC3413 [RFC3413], and RFC3418
   [RFC3418].

1.1.  The Internet-Standard Management Framework

   For a detailed overview of the documents that describe the current
   Internet-Standard Management Framework, please refer to section 7 of
   RFC 3410 [RFC3410].

   Managed objects are accessed via a virtual information store, termed
   the Management Information Base or MIB.  MIB objects are generally
   accessed through the Simple Network Management Protocol (SNMP).
   Objects in the MIB are defined using the mechanisms defined in the
   Structure of Management Information (SMI).  This memo specifies a MIB
   module that is compliant to the SMIv2, which is described in STD 58,
   RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580
   [RFC2580].

1.2.  Conventions

   For consistency with SNMP-related specifications, this document
   favors terminology as defined in STD62 rather than favoring
   terminology that is consistent with non-SNMP specifications that use
   different variations of the same terminology.  This is consistent
   with the IESG decision to not require the SNMPv3 terminology be
   modified to match the usage of other non-SNMP specifications when
   SNMPv3 was advanced to Full Standard.

   Authentication in this document typically refers to the English
   meaning of "serving to prove the authenticity of" the message, not
   data source authentication or peer identity authentication.

   The terms "manager" and "agent" are not used in this document,



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   because in the RFC 3411 architecture, all SNMP entities have the
   capability of acting as either manager or agent or both depending on
   the SNMP applications included in the engine.  Where distinction is
   required, the application names of Command Generator, Command
   Responder, Notification Originator, Notification Receiver, and Proxy
   Forwarder are used.  See "SNMP Applications" [RFC3413] for further
   information.

   While security protocols frequently refer to a user, the terminology
   used in RFC3411 [RFC3411] and in this memo is "principal".  A
   principal is the "who" on whose behalf services are provided or
   processing takes place.  A principal can be, among other things, an
   individual acting in a particular role; a set of individuals, with
   each acting in a particular role; an application or a set of
   applications, or a combination of these within an administrative
   domain.

   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].

1.3.  Modularity

   The reader is expected to have read and understood the description of
   the SNMP architecture, as defined in [RFC3411], and the architecture
   extension specified in "Transport Subsystem for the Simple Network
   Management Protocol" [I-D.ietf-isms-tmsm], which enables the use of
   external "lower layer transport" protocols to provide message
   security, tied into the SNMP architecture through the Transport
   Subsystem.  The Transport Security Model is designed to work with
   such lower-layer secure Transport Models.

   In keeping with the RFC 3411 design decisions to use self-contained
   documents, this memo includes the elements of procedure plus
   associated MIB objects which are needed for processing the Transport
   Security Model for SNMP.  These MIB objects SHOULD NOT be referenced
   in other documents.  This allows the Transport Security Model to be
   designed and documented as independent and self-contained, having no
   direct impact on other modules, and allowing this module to be
   upgraded and supplemented as the need arises, and to move along the
   standards track on different time-lines from other modules.

   This modularity of specification is not meant to be interpreted as
   imposing any specific requirements on implementation.







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1.4.  Motivation

   This memo describes a Security Model to make use of Transport Models
   that use lower layer secure transports and existing and commonly
   deployed security infrastructures.  This Security Model is designed
   to meet the security and operational needs of network administrators,
   maximize usability in operational environments to achieve high
   deployment success and at the same time minimize implementation and
   deployment costs to minimize the time until deployment is possible.

1.5.  Constraints

   The design of this SNMP Security Model is also influenced by the
   following constraints:

   1.  In times of network stress, the security protocol and its
       underlying security mechanisms SHOULD NOT depend solely upon the
       ready availability of other network services (e.g., Network Time
       Protocol (NTP) or Authentication, Authorization, and Accounting
       (AAA) protocols).

   2.  When the network is not under stress, the Security Model and its
       underlying security mechanisms MAY depend upon the ready
       availability of other network services.

   3.  It may not be possible for the Security Model to determine when
       the network is under stress.

   4.  A Security Model should require no changes to the SNMP
       architecture.

   5.  A Security Model should require no changes to the underlying
       security protocol.

2.  How the Transport Security Model Fits in the Architecture

   The Transport Security Model is designed to fit into the RFC3411
   architecture as a Security Model in the Security Subsystem, and to
   utilize the services of a secure Transport Model.

   For incoming messages, a secure Transport Model will pass a
   tmStateReference cache, described later.  To maintain RFC3411
   modularity, the Transport Model will not know which securityModel
   will process the incoming message; the Message Processing Model will
   determine this.  If the Transport Security Model is used with a non-
   secure Transport Model, then the cache will not exist or not be
   populated with security parameters, which will cause the Transport
   Security Model to return an error (see section 5.2)



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   The Transport Security Model will create the securityName and
   securityLevel to be passed to applications, and verify that the
   tmTransportSecurityLevel reported by the Transport Model is at least
   as strong as the securityLevel requested by the Message Processing
   Model.

   For outgoing messages, the Transport Security Model will create a
   tmStateReference cache (or use an existing one), and pass the
   tmStateReference to the specified Transport Model.

2.1.  Security Capabilities of this Model

2.1.1.  Threats

   The Transport Security Model is compatible with the RFC3411
   architecture, and provides protection against the threats identified
   by the RFC 3411 architecture.  However, the Transport Security Model
   does not provide security mechanisms such as authentication and
   encryption itself, so it SHOULD always be used with a Transport Model
   that provides appropriate security.  Which threats are addressed and
   how they are mitigated depends on the Transport Model.

2.1.2.  Security Levels

   The RFC 3411 architecture recognizes three levels of security:

      - without authentication and without privacy (noAuthNoPriv)

      - with authentication but without privacy (authNoPriv)

      - with authentication and with privacy (authPriv)

   The model-independent securityLevel parameter is used to request
   specific levels of security for outgoing messages, and to assert that
   specific levels of security were applied during the transport and
   processing of incoming messages.

   The transport layer algorithms used to provide security SHOULD NOT be
   exposed to the Transport Security Model, as the Transport Security
   Model has no mechanisms by which it can test whether an assertion
   made by a Transport Model is accurate.

   The Transport Security Model trusts that the underlying secure
   transport connection has been properly configured to support security
   characteristics at least as strong as reported in
   tmTransportSecurityLevel.





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2.2.  Transport Sessions

   The Transport Security Model does not work with transport sessions
   directly.  Instead the transport-related state is associated with a
   unique combination of transportDomain, transportAddress, securityName
   and securityLevel, and referenced via the tmStateReference parameter.
   How and if this is mapped to a particular transport or channel is the
   responsibility of the Transport Subsystem.

2.3.  Coexistence

   In the RFC3411 architecture, a Message Processing Model determines
   which Security Model should be called.  As of this writing, IANA has
   registered four Message Processing Models (SNMPv1, SNMPv2c, SNMPv2u/
   SNMPv2*, and SNMPv3) and three other Security Models (SNMPv1,
   SNMPv2c, and the User-based Security Model).

2.3.1.  Coexistence with Message Processing Models

   The SNMPv1 and SNMPv2c message processing described in RFC3584 (BCP
   74) [RFC3584] always selects the SNMPv1(1) and SNMPv2c(2) Security
   Models.  Since there is no mechanism defined in RFC3584 to select an
   alternative Security Model, SNMPv1 and SNMPv2c messages cannot use
   the Transport Security Model.  Such messages can still be conveyed
   over a secure transport protocol, but the Transport Security Model
   will not be invoked.

   The SNMPv2u/SNMPv2* Message Processing Model is a historic artifact
   for which there is no existing IETF specification.

   The SNMPv3 message processing defined in RFC3412 [RFC3412], extracts
   the securityModel from the msgSecurityModel field of an incoming
   SNMPv3Message.  When this value is transportSecurityModel(YY),
   security processing is directed to the Transport Security Model.  For
   an outgoing message to be secured using the Transport Security Model,
   the application should specify a securityModel parameter value of
   transportSecurityModel(YY) in the sendPdu ASI.

   [-- NOTE to RFC editor: replace YY with actual IANA-assigned number,
   and remove this note. ]

2.3.2.  Coexistence with Other Security Models

   The Transport Security Model uses its own MIB module for processing
   to maintain independence from other Security Models.  This allows the
   Transport Security Model to coexist with other Security Models, such
   as the User-based Security Model.




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2.3.3.  Coexistence with Transport Models

   The Transport Security Model may work with multiple Transport Models,
   but the RFC3411 application service interfaces (ASIs) do not carry a
   value for the Transport Model.  The MIB module defined in this memo
   allows an administrator to configure whether or not TSM prepends a
   transport model prefix to the securityName.  This will allow SNMP
   applications to consider transport model as a factor when making
   decisions, such as access control, notification generation, and proxy
   forwarding.

3.  Cached Information and References

   When performing SNMP processing, there are two levels of state
   information that may need to be retained: the immediate state linking
   a request-response pair, and potentially longer-term state relating
   to transport and security.

   The RFC3411 architecture uses caches to maintain the short-term
   message state, and uses references in the ASIs to pass this
   information between subsystems.

   This document defines the requirements for a cache to handle the
   longer-term transport state information, using a tmStateReference
   parameter to pass this information between subsystems.

   To simplify the elements of procedure, the release of state
   information is not always explicitly specified.  As a general rule,
   if state information is available when a message being processed gets
   discarded, the state related to that message SHOULD also be
   discarded.  If state information is available when a relationship
   between engines is severed, such as the closing of a transport
   session, the state information for that relationship SHOULD also be
   discarded.

   Since the contents of a cache are meaningful only within an
   implementation, and not on-the-wire, the format of the cache is
   implementation-specific.

3.1.  securityStateReference

   The securityStateReference parameter is defined in RFC3411.  Its
   primary purpose is to provide a mapping between a request and the
   corresponding response.  This cache is not accessible to Transport
   Models, and an entry is typically only retained for the lifetime of a
   request-response pair of messages.





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3.2.  tmStateReference

   For each transport session, information about the transport security
   is stored in a cache.  The tmStateReference parameter is used to pass
   model-specific and mechanism-specific parameters between the
   Transport subsystem and transport-aware Security Models.

   The tmStateReference cache will typically remain valid for the
   duration of the transport session, and hence may be used for several
   messages.

   Since this cache is only used within an implementation, and not on-
   the-wire, the precise contents and format are implementation-
   dependent.  However, for interoperability between Transport Models
   and transport-aware Security Models, entries in this cache must
   include at least the following fields:

      transportDomain

      transportAddress

      tmSecurityName

      tmRequestedSecurityLevel

      tmTransportSecurityLevel

      tmSameSecurity

      tmSessionID

3.2.1.  Transport information

   Information about the source of an incoming SNMP message is passed up
   from the Transport subsystem as far as the Message Processing
   subsystem.  However these parameters are not included in the
   processIncomingMsg ASI defined in RFC3411, and hence this information
   is not directly available to the Security Model.

   A transport-aware Security Model might wish to take account of the
   transport protocol and originating address when authenticating the
   request, and setting up the authorization parameters.  It is
   therefore necessary for the Transport Model to include this
   information in the tmStateReference cache, so that it is accessible
   to the Security Model.






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   o  transportDomain: the transport protocol (and hence the Transport
      Model) used to receive the incoming message

   o  transportAddress: the source of the incoming message.

   The ASIs used for processing an outgoing message all include explicit
   transportDomain and transportAddress parameters.  The values within
   the securityStateReference cache might override these parameters for
   outgoing messages.

3.2.2.  securityName

   There are actually three distinct "identities" that can be identified
   during the processing of an SNMP request over a secure transport:

   o  transport principal: the transport-authenticated identity, on
      whose behalf the secure transport connection was (or should be)
      established.  This value is transport-, mechanism- and
      implementation- specific, and is only used within a given
      Transport Model.

   o  tmSecurityName: a human-readable name (in snmpAdminString format)
      representing this transport identity.  This value is transport-
      and implementation-specific, and is only used (directly) by the
      Transport and Security Models.

   o  securityName: a human-readable name (in snmpAdminString format)
      representing the SNMP principal in a model-independent manner.

   The transport principal may or may not be the same as the
   tmSecurityName.  Similarly, the tmSecurityName may or may not be the
   same as the securityName as seen by the Application and Access
   Control subsystems.  In particular, a non-transport-aware Security
   Model will ignore tmSecurityName completely when determining the SNMP
   securityName.

   However it is important that the mapping between the transport
   principal and the SNMP securityName (for transport-aware Security
   Models) is consistent and predictable, to allow configuration of
   suitable access control and the establishment of transport
   connections.

3.2.3.  securityLevel

   There are two distinct issues relating to security level as applied
   to secure transports.  For clarity, these are handled by separate
   fields in the tmStateReference cache:




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   o  tmTransportSecurityLevel: an indication from the Transport Model
      of the level of security offered by this session.  The Security
      Model can use this to ensure that incoming messages were suitably
      protected before acting on them.

   o  tmRequestedSecurityLevel: an indication from the Security Model of
      the level of security required to be provided by the transport
      protocol.  The Transport Model can use this to ensure that
      outgoing messages will not be sent over an insufficiently secure
      session.

3.2.4.  Session Information

   For security reasons, if a secure transport session is closed between
   the time a request message is received and the corresponding response
   message is sent, then the response message SHOULD be discarded, even
   if a new session has been established.  The SNMPv3 WG decided that
   this should be a SHOULD architecturally, and it is a security-model-
   specific decision whether to REQUIRE this.

   o  tmSameSecurity: this flag is used by a transport-aware Security
      Model to indicate whether the Transport Model MUST enforce this
      restriction.

   o  tmSessionID: in order to verify whether the session has changed,
      the Transport Model must be able to compare the session used to
      receive the original request with the one to be used to send the
      response.  This typically requires some form of session
      identifier.  This value is only ever used by the Transport Model,
      so the format and interpretation of this field are model-specific
      and implementation-dependent.

   When processing an outgoing message, if tmSameSecurity is true, then
   the tmSessionID MUST match the current transport session, otherwise
   the message MUST be discarded, and the dispatcher notified that
   sending the message failed.

3.3.  Transport Security Model Cached Information

   The Transport Security Model has specific responsibilities regarding
   the cached information.

3.3.1.  securityStateReference

   The Transport Security Model adds the tmStateReference received from
   the processIncomingMsg ASI to the securityStateReference.  This
   tmStateReference can then be retrieved during the generateResponseMsg
   ASI, so that it can be passed back to the Transport Model.



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   The Transport Security Model REQUIRES that the security parameters
   used for a response are the same as those used for the corresponding
   request.  This security model sets the tmSameSecurity flag to true in
   the tmStateReference before passing it to the transport model.

3.3.2.  tmStateReference

   For outgoing messages, the Transport Security Model uses parameters
   provided by the SNMP application to lookup or create a
   tmStateReference.  This security model uses the tmStateReference
   stored as part of the securityStateReference when appropriate.

   For incoming messages, the Transport Security Model uses parameters
   provided in the tmStateReference cache to determine the securityName,
   and to verify adequate security levels.

3.3.3.  Prefixes and securityNames

   The SNMP-VIEW-BASED-ACM-MIB [RFC3415], the SNMP-TARGET-MIB module
   [RFC3413], and other MIB modules contain objects to configure
   security parameters for use by applications such as access control,
   notification generation, and proxy forwarding.

   IANA maintains a registry for transport domains and the corresponding
   prefix.

   If snmpTsmConfigurationUsePrefix is set to true then all
   securityNames provided by, or provided to, the Transport Security
   Model MUST include a valid transport domain prefix.

   If snmpTsmConfigurationUsePrefix is set to false then all
   securityNames provided by, or provided to, the Transport Security
   Model MUST NOT include a transport domain prefix.

   The tmSecurityName in the tmStateReference stored as part of the
   securityStateReference does not contain a prefix.

4.  Processing an Outgoing Message

   An error indication may return an OID and value for an incremented
   counter and a value for securityLevel, and values for contextEngineID
   and contextName for the counter, and the securityStateReference if
   the information is available at the point where the error is
   detected.







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4.1.  Security Processing for an Outgoing Message

   This section describes the procedure followed by the Transport
   Security Model.

   The parameters needed for generating a message are supplied to the
   Security Model by the Message Processing Model via the
   generateRequestMsg() or the generateResponseMsg() ASI.  The Transport
   Subsystem architectural extension has added the transportDomain,
   transportAddress, and tmStateReference parameters to the original
   RFC3411 ASIs.

    statusInformation =                -- success or errorIndication
          generateRequestMsg(
          IN   messageProcessingModel  -- typically, SNMP version
          IN   globalData              -- message header, admin data
          IN   maxMessageSize          -- of the sending SNMP entity
          IN   transportDomain         -- (NEW) specified by application
          IN   transportAddress        -- (NEW) specified by application
          IN   securityModel           -- for the outgoing message
          IN   securityEngineID        -- authoritative SNMP entity
          IN   securityName            -- on behalf of this principal
          IN   securityLevel           -- Level of Security requested
          IN   scopedPDU               -- message (plaintext) payload
          OUT  securityParameters      -- filled in by Security Module
          OUT  wholeMsg                -- complete generated message
          OUT  wholeMsgLength          -- length of generated message
          OUT  tmStateReference        -- (NEW)  transport info
               )






















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  statusInformation = -- success or errorIndication
          generateResponseMsg(
          IN   messageProcessingModel  -- typically, SNMP version
          IN   globalData              -- message header, admin data
          IN   maxMessageSize          -- of the sending SNMP entity
          IN   transportDomain         -- (NEW) specified by application
          IN   transportAddress        -- (NEW) specified by application
          IN   securityModel           -- for the outgoing message
          IN   securityEngineID        -- authoritative SNMP entity
          IN   securityName            -- on behalf of this principal
          IN   securityLevel           -- Level of Security requested
          IN   scopedPDU               -- message (plaintext) payload
          IN   securityStateReference  -- reference to security state
                                       -- information from original
                                       -- request
          OUT  securityParameters      -- filled in by Security Module
          OUT  wholeMsg                -- complete generated message
          OUT  wholeMsgLength          -- length of generated message
          OUT  tmStateReference        -- (NEW) transport info
               )

4.2.  Elements of Procedure for Outgoing Messages

   1) If there is a securityStateReference (Response or Report message),
   then this security model uses the cached information rather than the
   information provided by the ASI.  Extract the securityName and
   securityLevel and tmStateReference from the securityStateReference
   cache.  Set the tmRequestedSecurityLevel to the value of the
   extracted securityLevel.  Set the tmSameSecurity parameter in the
   tmStateReference cache to true.  The cachedSecurityData for this
   message can now be discarded.

   2) If there is no securityStateReference then create a
   tmStateReference cache with tmRequestedSecurityLevel set to the value
   of securityLevel, the tmSecurityName set to securityName, and
   tmSameSecurity set to false.

   If the snmpTsmConfigurationUsePrefix object is set to true, then use
   the transportDomain to look up the corresponding prefix.  (Since the
   securityStateReference stores the tmStateReference with the
   unprefixed tmSecurityName for the incoming message, prefix stripping
   only occurs when we are not using the securityStateReference).

   a.  If the prefix lookup fails for any reason, then the
       snmpTsmUnknownPrefixes counter is incremented, an error
       indication is returned to the calling module, and message
       processing stops.




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       If the lookup succeeds, but the prefix returned does not match
       the prefix in the securityName, or there is no prefix in the
       securityName, then the snmpTsmInvalidPrefixes counter is
       incremented, an error indication is returned to the calling
       module, and message processing stops.

       Strip the transport-specific prefix and trailing ':' character
       (ASCII 0x3a) from the tmSecurityName.

   3) Set securityParameters to a zero-length OCTET STRING ('0400').

   4) Combine the message parts into a wholeMsg and calculate
   wholeMsgLength.

   5) The wholeMsg, wholeMsgLength, securityParameters and
   tmStateReference are returned to the calling Message Processing Model
   with the statusInformation set to success.

5.  Processing an Incoming SNMP Message

   An error indication may return an OID and value for an incremented
   counter and a value for securityLevel, and values for contextEngineID
   and contextName for the counter, and the securityStateReference if
   the information is available at the point where the error is
   detected.

5.1.  Security Processing for an Incoming Message

   This section describes the procedure followed by the Transport
   Security Model whenever it receives an incoming message from a
   Message Processing Model.  The ASI from a Message Processing Model to
   the Security Subsystem for a received message is:



















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   statusInformation =  -- errorIndication or success
                            -- error counter OID/value if error
   processIncomingMsg(
   IN   messageProcessingModel    -- typically, SNMP version
   IN   maxMessageSize            -- from the received message
   IN   securityParameters        -- from the received message
   IN   securityModel             -- from the received message
   IN   securityLevel             -- from the received message
   IN   wholeMsg                  -- as received on the wire
   IN   wholeMsgLength            -- length as received on the wire
   IN   tmStateReference          -- (NEW) from the Transport Model
   OUT  securityEngineID          -- authoritative SNMP entity
   OUT  securityName              -- identification of the principal
   OUT  scopedPDU,                -- message (plaintext) payload
   OUT  maxSizeResponseScopedPDU  -- maximum size sender can handle
   OUT  securityStateReference    -- reference to security state
    )                         -- information, needed for response

5.2.  Elements of Procedure for Incoming Messages

   1) Set the securityEngineID to the local snmpEngineID.

   2) If tmStateReference does not refer to a cache containing values
   for transportDomain, transportAddress, tmSecurityName and
   tmTransportSecurityLevel, then the snmpTsmInvalidCaches counter is
   incremented, an error indication is returned to the calling module,
   and Security Model processing stops for this message.

   3) Copy the tmSecurityName to securityName.

   If the snmpTsmConfigurationUsePrefix object is set to true, then use
   the transportDomain to look up the corresponding prefix.

   a.  If the prefix lookup fails for any reason, then the
       snmpTsmUnknownPrefixes counter is incremented and an error
       indication is returned to the calling module, and message
       processing stops.

       If the lookup succeeds, but the prefix length is less than one or
       greater than four octets, then the snmpTsmInvalidPrefixes counter
       is incremented, an error indication is returned to the calling
       module, and message processing stops.

       Set the securityName to be the concatenation of the prefix, a ':'
       character (ASCII 0x3a) and the tmSecurityName.

   4) Compare the value of tmTransportSecurityLevel in the
   tmStateReference cache to the value of the securityLevel parameter



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   passed in the processIncomingMsg ASI.  If securityLevel specifies
   privacy (Priv), and tmTransportSecurityLevel specifies no privacy
   (noPriv), or securityLevel specifies authentication (auth) and
   tmTransportSecurityLevel specifies no authentication (noAuth) was
   provided by the Transport Model, then the
   snmpTsmInadequateSecurityLevels counter is incremented, and an error
   indication (unsupportedSecurityLevel) together with the OID and value
   of the incremented counter is returned to the calling module.
   Transport Security Model processing stops for this message.

   5) The security data is cached as cachedSecurityData, so that a
   possible response to this message will use the same security
   parameters.  Then securityStateReference is set for subsequent
   reference to this cached data.  For Transport Security Model, the
   securityStateReference includes a reference to the tmStateReference
   cache.

   6) The scopedPDU component is extracted from the wholeMsg.

   7) The maxSizeResponseScopedPDU is calculated.  This is the maximum
   size allowed for a scopedPDU for a possible Response message.

   8) The statusInformation is set to success and a return is made to
   the calling module passing back the OUT parameters as specified in
   the processIncomingMsg ASI.

6.  MIB Module Overview

   This MIB module provides objects for use only by the Transport
   Security Model.  It defines a configuration scalar and related error
   counters.

6.1.  Structure of the MIB Module

   Objects in this MIB module are arranged into subtrees.  Each subtree
   is organized as a set of related objects.  The overall structure and
   assignment of objects to their subtrees, and the intended purpose of
   each subtree, is shown below.

6.1.1.  The snmpTsmStats Subtree

   This subtree contains error counters specific to the Transport
   Security Model.

6.1.2.  The snmpTsmConfiguration Subtree

   This subtree contains a configuration object that enables
   administrators to specify if they want a transport domain prefix



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   prepended to securityNames for use by applications.

6.2.  Relationship to Other MIB Modules

   Some management objects defined in other MIB modules are applicable
   to an entity implementing the Transport Security Model.  In
   particular, it is assumed that an entity implementing the Transport
   Security Model will implement the SNMP-FRAMEWORK-MIB [RFC3411], the
   SNMP-TARGET-MIB [RFC3413], the SNMP-VIEW-BASED-ACM-MIB [RFC3415], and
   the SNMPv2-MIB [RFC3418].  These are not needed to implement the
   SNMP-TSM-MIB.

6.2.1.  MIB Modules Required for IMPORTS

   The following MIB module imports items from [RFC2578], [RFC2579], and
   [RFC2580].

7.  MIB module definition


 SNMP-TSM-MIB DEFINITIONS ::= BEGIN

 IMPORTS
     MODULE-IDENTITY, OBJECT-TYPE,
     mib-2, Counter32
       FROM SNMPv2-SMI
     MODULE-COMPLIANCE, OBJECT-GROUP
       FROM SNMPv2-CONF
     TruthValue
        FROM SNMPv2-TC
     ;

 snmpTsmMIB MODULE-IDENTITY
     LAST-UPDATED "200807100000Z"
     ORGANIZATION "ISMS Working Group"
     CONTACT-INFO "WG-EMail:   isms@lists.ietf.org
                   Subscribe:  isms-request@lists.ietf.org

                   Chairs:
                     Juergen Quittek
                     NEC Europe Ltd.
                     Network Laboratories
                     Kurfuersten-Anlage 36
                     69115 Heidelberg
                     Germany
                     +49 6221 90511-15
                     quittek@netlab.nec.de




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                     Juergen Schoenwaelder
                     Jacobs University Bremen
                     Campus Ring 1
                     28725 Bremen
                     Germany
                     +49 421 200-3587
                     j.schoenwaelder@iu-bremen.de

                   Editor:
                     David Harrington
                     Huawei Technologies USA
                     1700 Alma Dr.
                     Plano TX 75075
                     USA
                     +1 603-436-8634
                     ietfdbh@comcast.net

                     Wes Hardaker
                     Sparta, Inc.
                     P.O. Box 382
                     Davis, CA  95617
                     USA
                     +1 530 792 1913
                     ietf@hardakers.net
                  "
     DESCRIPTION "The Transport Security Model MIB

                  In keeping with the RFC 3411 design decisions
                  to use self-contained documents, the RFC which
                  contains the definition of this MIB module also
                  includes the elements of procedure which are
                  needed for processing the Transport Security
                  Model for SNMP. These MIB objects
                  SHOULD NOT be modified via other subsystems
                  or models defined in other document..
                  This allows the Transport Security Model
                  for SNMP to be designed and documented as
                  independent and self- contained, having no
                  direct impact on other modules, and this
                  allows this module to be upgraded and
                  supplemented as the need arises, and to
                  move along the standards track on different
                  time-lines from other modules.

                  Copyright (C) The IETF Trust (2008). This
                  version of this MIB module is part of RFC XXXX;
                  see the RFC itself for full legal notices.
 -- NOTE to RFC editor: replace XXXX with actual RFC number



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 --                     for this document and remove this note
                 "

     REVISION    "200807100000Z"
     DESCRIPTION "The initial version, published in RFC XXXX.
 -- NOTE to RFC editor: replace XXXX with actual RFC number
 --                     for this document and remove this note
                 "

     ::= { mib-2 xxxx }
 -- RFC Ed.: replace xxxx with IANA-assigned number and
 --          remove this note

 -- ---------------------------------------------------------- --
 -- subtrees in the SNMP-TSM-MIB
 -- ---------------------------------------------------------- --

 snmpTsmNotifications OBJECT IDENTIFIER ::= { snmpTsmMIB 0 }
 snmpTsmMIBObjects    OBJECT IDENTIFIER ::= { snmpTsmMIB 1 }
 snmpTsmConformance   OBJECT IDENTIFIER ::= { snmpTsmMIB 2 }

 -- -------------------------------------------------------------
 -- Objects
 -- -------------------------------------------------------------

 -- Statistics for the Transport Security Model


 snmpTsmStats         OBJECT IDENTIFIER ::= { snmpTsmMIBObjects 1 }

 snmpTsmInvalidCaches OBJECT-TYPE
     SYNTAX       Counter32
     MAX-ACCESS   read-only
     STATUS       current
     DESCRIPTION "The number of incoming messages dropped because the
                  tmStateReference referred to an invalid cache.
                 "
     ::= { snmpTsmStats 1 }

 snmpTsmInadequateSecurityLevels OBJECT-TYPE
     SYNTAX       Counter32
     MAX-ACCESS   read-only
     STATUS       current
     DESCRIPTION "The number of incoming messages dropped because
                  the securityLevel asserted by the transport model was
                  less than the securityLevel requested by the
                  application.
                 "



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     ::= { snmpTsmStats 2 }

 snmpTsmUnknownPrefixes OBJECT-TYPE
     SYNTAX       Counter32
     MAX-ACCESS   read-only
     STATUS       current
     DESCRIPTION "The number of messages dropped because
                  snmpTsmConfigurationUsePrefix was set to true and
                  there is no known prefix for the specified transport
                  domain.
                 "
     ::= { snmpTsmStats 3 }

 snmpTsmInvalidPrefixes OBJECT-TYPE
     SYNTAX       Counter32
     MAX-ACCESS   read-only
     STATUS       current
     DESCRIPTION "The number of messages dropped because
                  the securityName associated with an outgoing message
                  did not contain a valid transport domain prefix.
                 "
     ::= { snmpTsmStats 4 }

 -- -------------------------------------------------------------
 -- Configuration
 -- -------------------------------------------------------------

 -- Configuration for the Transport Security Model


 snmpTsmConfiguration   OBJECT IDENTIFIER ::= { snmpTsmMIBObjects 2 }

 snmpTsmConfigurationUsePrefix OBJECT-TYPE
     SYNTAX      TruthValue
     MAX-ACCESS  read-write
     STATUS      current
     DESCRIPTION "If this object is set to true then securityNames
                  passing to and from the application are expected to
                  contain a transport domain specific prefix. If this
                  object is set to true then a domain specific prefix
                  will be added by the TSM to the securityName for
                  incoming messages and removed from the securityName
                  when processing outgoing messages. Transport domains
                  and prefixes are maintained in a registry by IANA.
                  This object SHOULD persist across system reboots.
                 "
     DEFVAL { false }
     ::= { snmpTsmConfiguration 1 }



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 -- -------------------------------------------------------------
 -- snmpTsmMIB - Conformance Information
 -- -------------------------------------------------------------

 snmpTsmCompliances OBJECT IDENTIFIER ::= { snmpTsmConformance 1 }

 snmpTsmGroups      OBJECT IDENTIFIER ::= { snmpTsmConformance 2 }

 -- -------------------------------------------------------------
 -- Compliance statements
 -- -------------------------------------------------------------

 snmpTsmCompliance MODULE-COMPLIANCE
     STATUS      current
     DESCRIPTION "The compliance statement for SNMP engines that support
                  the SNMP-TSM-MIB
                 "
     MODULE
         MANDATORY-GROUPS { snmpTsmGroup }
     ::= { snmpTsmCompliances 1 }

 -- -------------------------------------------------------------
 -- Units of conformance
 -- -------------------------------------------------------------
 snmpTsmGroup OBJECT-GROUP
     OBJECTS {
         snmpTsmInvalidCaches,
         snmpTsmInadequateSecurityLevels,
         snmpTsmUnknownPrefixes,
         snmpTsmInvalidPrefixes,
         snmpTsmConfigurationUsePrefix
     }
     STATUS      current
     DESCRIPTION "A collection of objects for maintaining
                  information of an SNMP engine which implements
                  the SNMP Transport Security Model.
                 "

     ::= { snmpTsmGroups 2 }


 END









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8.  Security Considerations

   This document describes a Security Model, compatible with the RFC3411
   architecture, that permits SNMP to utilize security services provided
   through an SNMP Transport Model.  The Transport Security Model relies
   on Transport Models for mutual authentication, binding of keys,
   confidentiality and integrity.

   The Transport Security Model relies on secure Transport Models to
   provide an authenticated principal identifier and an assertion of
   whether authentication and privacy are used during transport.  This
   Security Model SHOULD always be used with Transport Models that
   provide adequate security, but "adequate security" is a configuration
   and/or run-time decision of the operator or management application.
   The security threats and how these threats are mitigated should be
   covered in detail in the specifications of the Transport Models and
   the underlying secure transports.

   An authenticated principal identifier (securityName) is used in SNMP
   applications, for purposes such as access control, notification
   generation, and proxy forwarding.  This security model supports
   multiple transport models.  Operators might judge some transports to
   be more secure than others, so this security model can be configured
   to prepend a prefix to the securityName to indicate the transport
   model used to authenticate the principal.  Operators can use the
   prefixed securityName when making application decisions about levels
   of access.

8.1.  MIB module security

   There are a number of management objects defined in this MIB module
   with a MAX-ACCESS clause of read-write and/or read-create.  Such
   objects may be considered sensitive or vulnerable in some network
   environments.  The support for SET operations in a non-secure
   environment without proper protection can have a negative effect on
   network operations.  These are the tables and objects and their
   sensitivity/vulnerability:

   o  The snmpTsmConfigurationUsePrefix object could be modified,
      creating a denial of service or authorizing SNMP messages that
      would not have previously been authorized by an Access Control
      Model (e.g. the VACM).

   Some of the readable objects in this MIB module (i.e., objects with a
   MAX-ACCESS other than not-accessible) may be considered sensitive or
   vulnerable in some network environments.  It is thus important to
   control even GET and/or NOTIFY access to these objects and possibly
   to even encrypt the values of these objects when sending them over



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   the network via SNMP.  These are the tables and objects and their
   sensitivity/vulnerability:

   o  All the counters in this module refer to configuration errors and
      do not expose sensitive information.

   SNMP versions prior to SNMPv3 did not include adequate security.
   Even if the network itself is secure (for example by using IPsec),
   even then, there is no control as to who on the secure network is
   allowed to access and GET/SET (read/change/create/delete) the objects
   in this MIB module.

   It is RECOMMENDED that implementers consider the security features as
   provided by the SNMPv3 framework (see [RFC3410] section 8), including
   full support for the USM and Transport Security Model cryptographic
   mechanisms (for authentication and privacy).

   Further, deployment of SNMP versions prior to SNMPv3 is NOT
   RECOMMENDED.  Instead, it is RECOMMENDED to deploy SNMPv3 and to
   enable cryptographic security.  It is then a customer/operator
   responsibility to ensure that the SNMP entity giving access to an
   instance of this MIB module is properly configured to give access to
   the objects only to those principals (users) that have legitimate
   rights to indeed GET or SET (change/create/delete) them.

9.  IANA Considerations

   IANA is requested to assign:

   1.  an SMI number under mib-2, for the MIB module in this document,

   2.  a value, preferably 4, to identify the Transport Security Model,
       in the Security Models registry at
       http://www.iana.org/assignments/snmp-number-spaces.  This should
       result in the following table of values:

   Value   Description                         References
   -----   -----------                         ----------
     0     reserved for 'any'                  [RFC3411]
     1     reserved for SNMPv1                 [RFC3411]
     2     reserved for SNMPv2c                [RFC3411]
     3     User-Based Security Model (USM)     [RFC3411]
     YY    Transport Security Model (TSM)      [RFCXXXX]

   -- NOTE to RFC editor: replace XXXX with actual RFC number
   --                     for this document and remove this note
   -- NOTE to RFC editor: replace YY with actual IANA-assigned number,
                          throughout this document and remove this note.



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10.  Acknowledgements

   The editors would like to thank Jeffrey Hutzelman for sharing his SSH
   insights, and Dave Shield for an outstanding job wordsmithing the
   existing document to improve organization and clarity.

   Additionally, helpful document reviews were received from: Juergen
   Schoenwaelder.

11.  References

11.1.  Normative References

   [RFC2119]             Bradner, S., "Key words for use in RFCs to
                         Indicate Requirement Levels", BCP 14, RFC 2119,
                         March 1997.

   [RFC2578]             McCloghrie, K., Ed., Perkins, D., Ed., and J.
                         Schoenwaelder, Ed., "Structure of Management
                         Information Version 2 (SMIv2)", STD 58,
                         RFC 2578, April 1999.

   [RFC2579]             McCloghrie, K., Ed., Perkins, D., Ed., and J.
                         Schoenwaelder, Ed., "Textual Conventions for
                         SMIv2", STD 58, RFC 2579, April 1999.

   [RFC2580]             McCloghrie, K., Perkins, D., and J.
                         Schoenwaelder, "Conformance Statements for
                         SMIv2", STD 58, RFC 2580, April 1999.

   [RFC3411]             Harrington, D., Presuhn, R., and B. Wijnen, "An
                         Architecture for Describing Simple Network
                         Management Protocol (SNMP) Management
                         Frameworks", STD 62, RFC 3411, December 2002.

   [RFC3412]             Case, J., Harrington, D., Presuhn, R., and B.
                         Wijnen, "Message Processing and Dispatching for
                         the Simple Network Management Protocol (SNMP)",
                         STD 62, RFC 3412, December 2002.

   [RFC3413]             Levi, D., Meyer, P., and B. Stewart, "Simple
                         Network Management Protocol (SNMP)
                         Applications", STD 62, RFC 3413, December 2002.

   [I-D.ietf-isms-tmsm]  Harrington, D. and J. Schoenwaelder, "Transport
                         Subsystem for the Simple Network Management
                         Protocol (SNMP)", draft-ietf-isms-tmsm-14 (work
                         in progress), October 2008.



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11.2.  Informative References

   [RFC3410]             Case, J., Mundy, R., Partain, D., and B.
                         Stewart, "Introduction and Applicability
                         Statements for Internet-Standard Management
                         Framework", RFC 3410, December 2002.

   [RFC3414]             Blumenthal, U. and B. Wijnen, "User-based
                         Security Model (USM) for version 3 of the
                         Simple Network Management Protocol (SNMPv3)",
                         STD 62, RFC 3414, December 2002.

   [RFC3415]             Wijnen, B., Presuhn, R., and K. McCloghrie,
                         "View-based Access Control Model (VACM) for the
                         Simple Network Management Protocol (SNMP)",
                         STD 62, RFC 3415, December 2002.

   [RFC3418]             Presuhn, R., "Management Information Base (MIB)
                         for the Simple Network Management Protocol
                         (SNMP)", STD 62, RFC 3418, December 2002.

   [RFC3584]             Frye, R., Levi, D., Routhier, S., and B.
                         Wijnen, "Coexistence between Version 1, Version
                         2, and Version 3 of the Internet-standard
                         Network Management Framework", BCP 74,
                         RFC 3584, August 2003.

Appendix A.  Notification Tables Configuration

   The SNMP-TARGET-MIB and SNMP-NOTIFICATION-MIB [RFC3413] are used to
   configure notification originators with the destinations to which
   notifications should be sent.

   Most of the configuration is security-model-independent and
   transport-model-independent.

   The values we will use in the examples for the five model-independent
   security and transport parameters are:

      transportDomain = snmpSSHDomain

      transportAddress = 192.0.2.1:162

      securityModel = Transport Security Model

      securityName = sampleUser





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      securityLevel = authPriv

   The following example will configure the Notification Originator to
   send informs to a Notification Receiver at host 192.0.2.1 port 162
   using the securityName "sampleUser".  The columns marked with a "*"
   are the items that are Security Model or Transport Model specific.

   The configuration for the "sampleUser" settings in the SNMP-VIEW-
   BASED-ACM-MIB objects are not shown here for brevity.  First we
   configure which type of notification should be sent for this taglist
   (toCRTag).  In this example, we choose to send an Inform.
     snmpNotifyTable row:
          snmpNotifyName                 CRNotif
          snmpNotifyTag                  toCRTag
          snmpNotifyType                 inform
          snmpNotifyStorageType          nonVolatile
          snmpNotifyColumnStatus         createAndGo

   Then we configure a transport address to which notifications
   associated with this taglist should be sent, and we specify which
   snmpTargetParamsEntry should be used (toCR) when sending to this
   transport address.
          snmpTargetAddrTable row:
             snmpTargetAddrName              toCRAddr
         *   snmpTargetAddrTDomain           snmpSSHDomain
             snmpTargetAddrTAddress          192.0.2.1:162
             snmpTargetAddrTimeout           1500
             snmpTargetAddrRetryCount        3
             snmpTargetAddrTagList           toCRTag
             snmpTargetAddrParams            toCR   (must match below)
             snmpTargetAddrStorageType       nonVolatile
             snmpTargetAddrColumnStatus      createAndGo


   Then we configure which principal at the host should receive the
   notifications associated with this taglist.  Here we choose
   "sampleUser", who uses the Transport Security Model.
         snmpTargetParamsTable row:
             snmpTargetParamsName            toCR
             snmpTargetParamsMPModel         SNMPv3
         *   snmpTargetParamsSecurityModel   TransportSecurityModel
             snmpTargetParamsSecurityName    "sampleUser"
             snmpTargetParamsSecurityLevel   authPriv
             snmpTargetParamsStorageType     nonVolatile
             snmpTargetParamsRowStatus       createAndGo






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A.1.  Transport Security Model Processing for Notifications

   The Transport Security Model is called using the generateRequestMsg()
   ASI, with the following parameters (* are from the above tables):

    statusInformation =                -- success or errorIndication
          generateRequestMsg(
          IN   messageProcessingModel  -- *snmpTargetParamsMPModel
          IN   globalData              -- message header, admin data
          IN   maxMessageSize          -- of the sending SNMP entity
          IN   transportDomain         -- *snmpTargetAddrTDomain
          IN   transportAddress        -- *snmpTargetAddrTAddress
          IN   securityModel           -- *snmpTargetParamsSecurityModel
          IN   securityEngineID        -- immaterial; TSM will ignore.
          IN   securityName            -- snmpTargetParamsSecurityName
          IN   securityLevel           -- *snmpTargetParamsSecurityLevel
          IN   scopedPDU               -- message (plaintext) payload
          OUT  securityParameters      -- filled in by Security Module
          OUT  wholeMsg                -- complete generated message
          OUT  wholeMsgLength          -- length of generated message
          OUT  tmStateReference        -- reference to transport info
               )

   The Transport Security Model will determine the Transport Model based
   on the snmpTargetAddrTDomain.  The selected Transport Model will
   select the appropriate transport connection using the
   snmpTargetAddrTAddress, snmpTargetParamsSecurityName, and
   snmpTargetParamsSecurityLevel.

Appendix B.  Processing Differences between USM and Secure Transport

   USM and secure transports differ in the processing order and
   responsibilities within the RFC3411 architecture.  While the steps
   are the same, they occur in a different order, and may be done by
   different subsystems.  The following lists illustrate the difference
   in the flow and the responsibility for different processing steps for
   incoming messages when using USM and when using a secure transport.
   (These lists are simplified for illustrative purposes, and do not
   represent all details of processing.  Transport Models must provide
   the detailed elements of procedure.)

   With USM, SNMPv1, and SNMPv2c Security Models, security processing
   starts when the Message Processing Model decodes portions of the
   ASN.1 message to extract header fields that are used to determine
   which Security Model should process the message to perform
   authentication, decryption, timeliness checking, integrity checking,
   and translation of parameters to model-independent parameters.  By
   comparison, a secure transport performs those security functions on



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   the message, before the ASN.1 is decoded.

   Step 6 cannot occur until after decryption occurs.  Step 6 and beyond
   are the same for USM and a secure transport.

B.1.  USM and the RFC3411 Architecture

   1) decode the ASN.1 header (Message Processing Model)

   2) determine the SNMP Security Model and parameters (Message
      Processing Model)

   3) verify securityLevel.  [Security Model]

   4) translate parameters to model-independent parameters (Security
      Model)

   5) authenticate the principal, check message integrity and
      timeliness, and decrypt the message.  [Security Model]

   6) determine the pduType in the decrypted portions (Message
      Processing Model), and

   7) pass on the decrypted portions with model-independent parameters.

B.2.  Transport Subsystem and the RFC3411 Architecture

   1) authenticate the principal, check integrity and timeliness of the
      message, and decrypt the message.  [Transport Model]

   2) translate parameters to model-independent parameters (Transport
      Model)

   3) decode the ASN.1 header (Message Processing Model)

   4) determine the SNMP Security Model and parameters (Message
      Processing Model)

   5) verify securityLevel [Security Model]

   6) determine the pduType in the decrypted portions (Message
      Processing Model), and

   7) pass on the decrypted portions with model-independent security
      parameters

   If a message is secured using a secure transport layer, then the
   Transport Model should provide the translation from the authenticated



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   identity (e.g., an SSH user name) to a human-friendly identifier in
   step 2.  The security model will provide a mapping from that
   identifier to a model-independent securityName.

Appendix C.  Open Issues



Appendix D.  Change Log

   From -09- to -10-

      snmpTsmInvalidPrefix -> snmpTsmInvalidPrefixes

      Improvements to the prefix handling text in the EOP

      Removed transform selection

      Removed translation table

      Removed option to disable transports.

      Removed references to the LCD.

      Removed modifications to the "Cached Information" section to keep
      this consistent with other ISMS documents.

      Eliminated most "Relationship to Other MIB modules" text.

      Significant text cleanup

   From -08- to -09-

      Added the transport domain specific prefix adding/removing support
      as agreed to within the ISMS WG.  The implementation is a bit
      different than what was originally discussed and is now housed
      entirely within this document and requires only a string
      allocation in the TM documents.  In the end this form greatly
      reduced the documentation and procedure complexity in most
      documents.

      Added the snmpTsmConfigurationUsePrefix scalar.

      Removed the snmpTsmLCDTable since it is no longer needed.

      Removed the snmpTsmLCDDomainTable since it is not needed with the
      prefix addition replaced the functionality.




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   From -07- to -08-

      Added tables to the MIB module to define a Transport Security
      Model-specific LCD, and updated the Elements of Procedure.  This
      was because references to an abstract LCD sort of owned by both
      the security model and the transport model were found confusing.

      Realized we referred to the MIB module in text as SNMP-TRANSPORT-
      SM-MIB, but SNMP-TSM-MIB in the module.  Changed all occurrences
      of SNMP-TRANSPORT-SM-MIB to SNMP-TSM-MIB, following RFC4181
      guidelines for naming.

      Updated Security Considerations to warn about writable objects,
      and added the new counter to the readable objects list.

      Changed snmpTsmLCDName to snmpTsmLCDTmSecurityName

   From -05- to -06-

      Fixed a bunch of editorial nits

      Fixed the note about terminology consistent with SNMPv3.

      Updated MIB assignment to by rfc4181 compatible

      Replaced tmSameSession with tmSameSecurity to eliminate session-
      matching from the security model.

      Eliminated all reference to the LCD from the Transport Security
      Model; the LCD is now TM-specific.

      Added tmTransportSecurityLevel and tmRequestedSecurityLevel to
      clarify incoming versus outgoing

   From -04- to -05-

      Removed check for empty securityParameters for incoming messages

      Added a note about terminology, for consistency with SNMPv3 rather
      than with RFC2828.

   From -03- to -04-

      Editorial changes requested by Tom Petch, to clarify behavior with
      SNMPv1/v2c

      Added early discussion of how TSM fits into the architecture to
      clarify behavior when RFC3584 security models are co-resident.



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      Editorial changes requested by Bert Wijnen, to eliminate version-
      specific discussions.

      Removed sections on version-specific message formats.

      Removed discussion of SNMPv3 in Motivation section.

      Added discussion of request/response session matching.

   From -02- to -03-

      Editorial changes suggested by Juergen Schoenwaelder

      Capitalized Transport Models, Security Models, and Message
      Processing Models, to be consistent with RFC341x conventions.

      Eliminated some text that duplicated RFC3412, especially in
      Elements of Procedure.

      Changed the encoding of msgSecurityParameters

      Marked the (NEW) fields added to existing ASIs

      Modified text intro discussing relationships to other MIB modules.

   From -01- to -02-

      Changed transportSecurityModel(4) to transportSecurityModel(YY),
      waiting for assignment

      cleaned up elements of procedure [todo]s

      use the same errorIndication as USM for unsupportedSecurityLevel

      fixed syntax of tsmInadequateSecurity counter

      changed the "can and will use" the same security parameters to
      "can use", to allow responses that have different security
      parameters than the request.

      removed "Relationship to the SNMP-FRAMEWORK-MIB"

      cleaned up "MIB Modules Required for IMPORTS"



   From -00- to -01-




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      made the Transport Model not know anything about the Security
      Model.

      modified the elements of procedure sections, given the
      implications of this change.

      simplified elements of procedure, removing most info specified in
      architecture/subsystem definitions.

      rethought the coexistence section

      noted the implications of the Transport Security Model on
      isAccessAllowed()

      modified all text related to the LCD.

      removed most of the MIB (now the TSM has no configuration
      parameters).

      added counters needed to support elements of procedure

      renamed MIB module, and registered under snmpModules

      updated IANA and Security Considerations

      updated references.

      modified the notification configurations.

   From SSHSM-04- to Transport-security-model-00

      added tsmUserTable

      updated Appendix - Notification Tables Configuration

      remove open/closed issue appendices

      changed tmSessionReference to tmStateReference













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Authors' Addresses

   David Harrington
   Huawei Technologies (USA)
   1700 Alma Dr. Suite 100
   Plano, TX 75075
   USA

   Phone: +1 603 436 8634
   EMail: dharrington@huawei.com


   Wes Hardaker
   Sparta, Inc.
   P.O. Box 382
   Davis, CA  95617
   US

   Phone: +1 530 792 1913
   EMail: ietf@hardakers.net































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