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Versions: 00 01 02 03 RFC 2264

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

                             14 July 1997


                            U. Blumenthal
                       IBM T. J. Watson Research
                           uri@watson.ibm.com

                              B. Wijnen
                       IBM T. J. Watson Research
                          wijnen@vnet.ibm.com


                     <draft-ietf-snmpv3-usm-00.txt>


                          Status of this Memo

This document is an Internet-Draft.  Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups.  Note that other groups may also distribute
working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time.  It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as ``work in progress.''

To learn the current status of any Internet-Draft, please check the
``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow
Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe),
ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim).


                          Abstract

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











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0.  Issues and Change Log

0.1.  Current Open Issues
      - Is it OK to use MD5 for KeyChange Algorithm ??
      - Improve acknowledgements and sync it up with other documents
      - Should the USM define checking such that a received Response
        messages used the same or better LoS than the Request message
        that this is a response to.
        In section 3.1 step 9, we return a completed outgoing message
        to the calling module (Message Processing). We believe it is
        the Message Processing Subsystem that should cache information
        about outgoing messages regarding msgID and such so that a
        possible Response Message can be mapped to an outstanding
        request. At the same time that piece of code can then ensure
        that the same securityModel and the same (or better??) LoS
        has been used for the Response Message. So in step 9 we do
        not save any cachedSecurityData for outgoing messages.
      - Can you all please review section 3.1 steps 7a and 7b to
        ensure that we have the timeliness checking and the
        automagic timeliness sync up correct? Quite some text changed
        in this writeup compared to what we used to see in SNMPv2u
        and SNMPv2*. I think the current text is much better and
        makes things simpler. But we need to make sure we cover
        everything.

0.2.  Change Log

   [version 1.8]
     - Add reference to RFC2119 about use of SHOULD and MUST
     - paginate and generate table of contents
     - posted as I-D <draft-ietf-snmpv3-usm-00.txt> on 15 July 1997

   [version 1.7]
     - Changed the KeyChange description so it allows for other
       hash algorithms instead of MD5. If in the future the MD5 gets
       replaced by another Authentication -- algorithm, then it seems
       we also need to use that new algorithm to -- calculate the
       digest during KeyChange.
     - Updated the password to key code fragment to cater for the
       variable length of the snmpEngineID.
     - Added issue on cacheing of data on outgoing messages and one
       on required review of timeliness handling.

   [version 1.4 - version 1.6]
     - Editorial changes because of internal review by authors
     - Adapt to latest list of Primitive names and parameters
     - Change USEC to USM
     - Changes based on comments from Jeff Case.
     - Checked MIB with SMICng

   [version 1.3]



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     - Too many changes have taken place, so marking it was skipped
       The most important changes are listed here.
       However, changes that just split text on different lines
       and changes like different capitalization of words/terms
       has not been listed. Also changes to fit new terms and such
       have not been listed.
     - Split/Join some lines to ensure we stay within 72 columns
       as required by RFC guidelines.
     - Addressed Dave Perkins comments:
       1) Section 1.3, last para's, timeliness was left off. -done
       2) Section 1.5.1, the operations need to be made general, since
          additional one may be added later.  - done
       3) Section 1.5.2, the field "request-id" is used throughout
          this section when it should be field "msgID"  - done
       4) The document must allow the value of engineID in the
          security to be a zero length string. There are several
          places that are affected by this change. An actual value is
          never needed, since secrets are never the same on different
          agents (see your paper).  - done
       5) Last sentence of description for object usmUserCloneFrom is
          not correct, since the object has a OID data type - done
     - Removed groupName from usmUserTable.
       Now done in Access Control as agreed at 2nd interim
     - Stats counters back in this document as agreed at 2nd interim
     - Use AutonomousType for usmUserPrivProtocol and
       usmUserAuthProtocol. Also use OBJECT-IDENTITY for the
       protocol OIDs (John Flick).
     - Changed "SNMPv3 engine" to "SNMP engine" at various places
     - added appendix with sample encoding of securityParameters
     - cleanup elements of procedure to use consistent terms
     - fix up some problems in elements of procedure
     - Do not use IMPLIED on usmUserTable as agreed at 2nd interim.
       For one thing, SNMPv1 cannot handle it.
     - cleanup section 2.3 and 3.3 step 7b based on comments by
       Dave Levi.

   [version 1.2]
     - changed (simplified) time sync in section 3 item 7.
     - added usmUserMiId
     - cleaned up text
     - defined IV "salt" generation
     - removed Statistics counters (now in MPC) and Report PDU
       generation (now in MPC)
     - Removed auth and DES MIBs which are now merged into
       User-based Security MIB
     - specified where cachedSecurityData needs to be discarded
     - added abstract service interface definitions
     - removed section on error reporting (is MPC responsibility)
     - removed auth/priv protocol definitions, they are in ARCH now
     - removed MIB definitions for snmpEngineID, Time, Boots. They
       are in ARCH now.



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   [version 1.1]
     - removed <securityCookie>.
     - added <securityIdentity>, <securityCachedData>.
     - added abstract function interface description of
       inter-module communications.
     - modified IV generation process to accommodate messages produced
       faster than one-per-second (still open).
     - always update the clock regardless of whether incoming message
       was Report or not (if the message was properly authenticated
       and its time-stamp is ahead of our notion of their clock).

   [version 1.0]
     - first version posted to the SNMPv3 editor's mailing list.
     - based on v2adv slides, v2adv items and issues list and on
       RFC1910 and SNMPv2u and SNMPv2* documents.
     - various iterations were done by the authors via private email.





































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1.  Introduction

   The Architecture for describing Internet Management Frameworks
   [SNMP-ARCH] is composed of multiple subsystems:

     1) a Message Processing Subsystem,
     2) a Security Subsystem,
     3) an Access Control Subsystem,

   Applications make use of the services of these subsystems.

   It is important to understand the SNMP architecture and the
   terminology of the architecture to understand where the Security
   Model described in this document fits into the architecture and
   interacts with other subsystems within the architecture.  The
   reader is expected to have read and understood the description of
   the SNMP architecture, as defined in [SNMP-ARCH].

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

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

1.1.  Threats

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

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

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

   - Masquerade



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

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

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

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

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

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

1.2.  Goals and Constraints

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

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



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

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

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

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

   1) When the requirements of effective management in times of
      network stress are inconsistent with those of security, the
      design should prefer the former.

   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 key
      management protocols).

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

1.3.  Security Services

   The security services necessary to support the goals of this SNMP
   Security Model are as follows:

   - Data Integrity
     is the provision of the property that data has not been altered
     or destroyed in an unauthorized manner, nor have data sequences
     been altered to an extent greater than can occur non-maliciously.

   - Data Origin Authentication
     is the provision of the property that the claimed identity of
     the user on whose behalf received data was originated is
     corroborated.

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

   - Message timeliness and limited replay protection
     is the provision of the property that a message whose generation
     time is outside of a specified time window is not accepted.
     Note that message reordering is not dealt with and can occur in



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     normal conditions too.

   For the protocols specified in this memo, it is not possible to
   assure the specific originator of a received SNMP message; rather,
   it is the user on whose behalf the message was originated that is
   authenticated.

   For these protocols, it not possible to obtain data integrity
   without data origin authentication, nor is it possible to obtain
   data origin authentication without data integrity.  Further,
   there is no provision for data confidentiality without both data
   integrity and data origin authentication.

   The security protocols used in this memo are considered acceptably
   secure at the time of writing.  However, the procedures allow for
   new authentication and privacy methods to be specified at a future
   time if the need arises.

1.4.  Module Organization

   The security protocols defined in this memo are split in three
   different modules and each has its specific responsibilities such
   that together they realize the goals and security services
   described above:

   - The authentication module MUST provide for:

     - Data Integrity,

     - Data Origin Authentication

   - The timeliness module MUST provide for:

     - Protection against message delay or replay (to an extent
       greater than can occur through normal operation)

   - The privacy module MUST provide for

     - Protection against disclosure of the message payload.

   The timeliness module is fixed for the User-based Security Model
   while there is provision for multiple authentication and/or
   privacy modules, each of which implements a specific authentication
   or privacy protocol respectively.

1.4.1.  Timeliness Module

   Section 3 (Elements of Procedure) uses the timeliness values in an
   SNMP message to do timeliness checking.  The timeliness check is
   only performed if authentication is applied to the message.  Since
   the complete message is checked for integrity, we can assume that



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   the timeliness values in a message that passes the authentication
   module are trustworthy.

1.4.2.  Authentication Protocol

   Section 6 describes the Keyed-MD5 authentication protocol which
   is the first authentication protocol to be used with the
   User-based Security Model.  In the future additional or
   replacement authentication protocols may be defined as new
   needs arise.

   The User-based Security Model prescribes that, if authentication
   is used, then the complete message is checked for integrity in
   the authentication module.

   For a message to be authenticated, it needs to pass authentication
   check by the authentication module and the timeliness check which
   is a fixed part of this User-based Security model.

1.4.3.  Privacy Protocol

   Section 7 describes the CBC-DES Symmetric Encryption Protocol
   which is the first privacy protocol to be used with the
   User-based Security Model.  In the future additional or
   replacement privacy protocols may be defined as new needs arise.

   The User-based Security Model prescribes that the scopedPDU
   is protected from disclosure when a message is sent with privacy.

   The User-based Security Model also prescribes that a message
   needs to be authenticated if privacy is in use.

1.5.  Protection against Message Replay, Delay and Redirection

1.5.1.  Authoritative SNMP engine

   In order to protect against message replay, delay and redirection,
   one of the SNMP engines involved in each communication is
   designated to be the authoritative SNMP engine.  When an SNMP
   message contains a payload which expects a response (for example
   a Get, GetNext, GetBulk, Set or Inform PDU), then the receiver of
   such messages is authoritative.  When an SNMP message contains a
   payload which does not expect a response (for example an
   SNMPv2-Trap, Response or Report PDU), then the sender of such a
   message is authoritative.

1.5.2.  Mechanisms

   The following mechanisms are used:

   - To protect against the threat of message delay or replay (to an



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     extent greater than can occur through normal operation), a set
     of timeliness (at the authoritative source) indicators and a
     msgID are included in each message generated.  An SNMP engine
     evaluates the timeliness indicators to determine if a received
     message is recent.  An SNMP engine may evaluate the timeliness
     indicators to ensure that a received message is at least as
     recent as the last message it received from the same source.
     A non-authoritative SNMP engine uses received authentic messages
     to advance its notion of the timeliness indicators at the remote
     authoritative source.  An SNMP engine also evaluates the msgID in
     received Response messages and discards those Response messages
     which do not correspond to an outstanding Request message.

     These mechanisms provide for the detection of messages whose
     time of generation was not recent in all but one circumstance;
     this circumstance is the delay or replay of a Report message
     (sent to a receiver) when the receiver has not recently
     communicated with the source of the Report message.  In this
     circumstance, the detection guarantees only that the Report
     message is more recent than the last communication between
     source and destination of the Report message.
     However, Report messages do not request or contain sensitive
     management information, and thus, goal #3 in Section 1.2 above
     is met; further, Report messages can at most cause the receiver
     to advance its notion of the timeliness indicators (at the source)
     by less than the proper amount.

     This protection against the threat of message delay or replay
     does not imply nor provide any protection against unauthorized
     deletion or suppression of messages.  Also, an SNMP engine may
     not be able to detect message reordering if all the messages
     involved are sent within the Time Window interval.  Other
     mechanisms defined independently of the security protocol can
     also be used to detect the re-ordering replay, deletion, or
     suppression of messages containing Set operations (e.g., the
     MIB variable snmpSetSerialNo [RFC1907]).

   - verifying that a message sent to/from one SNMP engine cannot
     be replayed to/as-if-from another SNMP engine.

     Included in each message is an identifier unique to the SNMP
     engine associated with the sender or intended recipient of the
     message.  Also, each message containing a Response PDU contains
     a msgID which associates the message with a recently generated
     Request message.

     A Report message sent by one SNMP engine to a second SNMP
     engine can potentially be replayed to another SNMP engine but
     that is not considered a threat (see above);

   - detecting messages which were not recently generated.



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     A set of time indicators are included in the message, indicating
     the time of generation.  Messages (other than those containing
     Report PDUs) without recent time indicators are not considered
     authentic.  In addition, messages containing Response PDUs have
     a msgID; if the msgID does not match that of a recently
     generated Request message, then the message is not considered
     to be authentic.

     A Report message sent by an SNMP engine can potentially be
     replayed at a later time to an SNMP engine which has not
     recently communicated with that source engine, which is
     not a threat (see above).

   This memo allows the same user to be defined on multiple SNMP
   engines.  Each SNMP engine maintains a value, snmpEngineID,
   which uniquely identifies the SNMP engine.  This value is included
   in each message sent to/from the SNMP engine that is authoritative
   (see section 1.5.1).  On receipt of a message, an authoritative
   SNMP engine checks the value to ensure that it is the intended
   recipient, and a non-authoritative SNMP engine uses the value to
   ensure that the message is processed using the correct state
   information.

   Each SNMP engine maintains two values, snmpEngineBoots and
   snmpEngineTime, which taken together provide an indication of
   time at that SNMP engine.  Both of these values are included in
   an authenticated message sent to/received from that SNMP engine.
   On receipt, the values are checked to ensure that the indicated
   timeliness value is within a Time Window of the current time.
   The Time Window represents an administrative upper bound on
   acceptable delivery delay for protocol messages.

   For an SNMP engine to generate a message which an authoritative
   SNMP engine will accept as authentic, and to verify that a message
   received from that authoritative SNMP engine is authentic, such an
   SNMP engine must first achieve timeliness synchronization with the
   authoritative SNMP engine. See section 2.3.
















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2.  Elements of the Model

   This section contains definitions required to realize the security
   model defined by this memo.

2.1.  User-based Security Model Users

   Management operations using this Security Model make use of a
   defined set of user identities.  For any user on whose behalf
   management operations are authorized at a particular SNMP engine,
   that SNMP engine must have knowledge of that user.  An SNMP engine
   that wishes to communicate with another SNMP engine must also have
   knowledge of a user known to that engine, including knowledge of
   the applicable attributes of that user.

   A user and its attributes are defined as follows:

   userName
     A string representing the name of the user.

   securityName
     A human-readable string representing the user in a format that
     is Security Model independent.

   authProtocol
     An indication of whether messages sent on behalf of this user can
     be authenticated, and if so, the type of authentication protocol
     which is used.  One such protocol is defined in this memo: the
     Digest Authentication Protocol.

   authKey
     If messages sent on behalf of this user can be authenticated,
     the (private) authentication key for use with the authentication
     protocol.  Note that a user's authentication key will normally
     be different at different authoritative SNMP engines.
     The authKey is not accessible via SNMP.

   authKeyChange and authOwnKeyChange
     The only way to remotely update the authentication key.  Does
     that in a secure manner, so that the update can be completed
     without the need to employ privacy protection.

   privProtocol
     An indication of whether messages sent on behalf of this user
     can be protected from disclosure, and if so, the type of privacy
     protocol which is used.  One such protocol is defined in this
     memo: the DES-based Encryption Protocol.

   privKey
     If messages sent on behalf of this user can be en/decrypted,
     the (private) privacy key for use with the privacy protocol.



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     Note that a user's privacy key will normally be different at
     different authoritative SNMP engines. The privKey is not
     accessible via SNMP.

   privKeyChange and privOwnKeyChange
     The only way to remotely update the encryption key. Does that
     in a secure manner, so that the update can be completed without
     the need to employ privacy protection.


2.2.  Replay Protection

   Each SNMP engine maintains three objects:

   - snmpEngineID, which (at least within an administrative domain)
     uniquely and unambiguously identifies an SNMP engine.

   - snmpEngineBoots, which is a count of the number of times the
     SNMP engine has re-booted/re-initialized since snmpEngineID
     was last configured; and,

   - snmpEngineTime, which is the number of seconds since the
     snmpEngineBoots counter was last incremented.

   Each SNMP engine is always authoritative with respect to these
   objects in its own SNMP entity.  It is the responsibility of a
   non-authoritative SNMP engine to synchronize with the
   authoritative SNMP engine, as appropriate.

   An authoritative SNMP engine is required to maintain the values of
   its snmpEngineID and snmpEngineBoots in non-volatile storage.

2.2.1.  authEngineID

   The authEngineID value contained in an authenticated message is
   used to defeat attacks in which messages from one SNMP engine to
   another SNMP engine are replayed to a different SNMP engine.
   It represents the snmpEngineID at the authoritative SNMP engine
   involved in the exchange of the message.

   When an authoritative SNMP engine is first installed, it sets its
   local value of snmpEngineID according to a enterprise-specific
   algorithm (see the definition of the Textual Convention for
   SnmpEngineID in the SNMP Architecture document [SNMP-ARCH]).

2.2.2.  authEngineBoots and authEngineTime

   The authEngineBoots and authEngineTime values contained in an
   authenticated message are used to defeat attacks in which messages
   are replayed when they are no longer valid.  They represent the
   snmpEngineBoots and snmpEngineTime values at the authoritative



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   SNMP engine involved in the exchange of the message.

   Through use of snmpEngineBoots and snmpEngineTime, there is no
   requirement for an SNMP engine to have a non-volatile clock which
   ticks (i.e., increases with the passage of time) even when the
   SNMP engine is powered off.  Rather, each time an SNMP engine
   re-boots, it retrieves, increments, and then stores snmpEngineBoots
   in non-volatile storage, and resets snmpEngineTime to zero.

   When an SNMP engine is first installed, it sets its local values
   of snmpEngineBoots and snmpEngineTime to zero.  If snmpEngineTime
   ever reaches its maximum value (2147483647), then snmpEngineBoots
   is incremented as if the SNMP engine has re-booted and
   snmpEngineTime is reset to zero and starts incrementing again.

   Each time an authoritative SNMP engine re-boots, any SNMP engines
   holding that authoritative SNMP engine's values of snmpEngineBoots
   and snmpEngineTime need to re-synchronize prior to sending
   correctly authenticated messages to that authoritative SNMP engine
   (see Section 2.3 for (re-)synchronization procedures).  Note,
   however, that the procedures do provide for a notification to be
   accepted as authentic by a receiving SNMP engine, when sent by an
   authoritative SNMP engine which has re-booted since the receiving
   SNMP engine last (re-)synchronized.

   If an authoritative SNMP engine is ever unable to determine its
   latest snmpEngineBoots value, then it must set its snmpEngineBoots
   value to 0xffffffff.

   Whenever the local value of snmpEngineBoots has the value
   0xffffffff, it latches at that value and an authenticated message
   always causes an notInTimeWindow authentication failure.

   In order to reset an SNMP engine whose snmpEngineBoots value has
   reached the value 0xffffffff, manual intervention is required.
   The engine must be physically visited and re-configured, either
   with a new snmpEngineID value, or with new secret values for the
   authentication and privacy protocols of all users known to that
   SNMP engine.

2.2.3.  Time Window

   The Time Window is a value that specifies the window of time in
   which a message generated on behalf of any user is valid.  This
   memo specifies that the same value of the Time Window, 150 seconds,
   is used for all users.

2.3.  Time Synchronization

   Time synchronization, required by a non-authoritative SNMP engine
   in order to proceed with authentic communications, has occurred



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   when the non-authoritative SNMP engine has obtained a local notion
   of the authoritative SNMP engine's values of snmpEngineBoots and
   snmpEngineTime from the authoritative SNMP engine.  These values
   must be (and remain) within the authoritative SNMP engine's Time
   Window.  So the local notion of the authoritative SNMP engine's
   values must be kept loosely synchronized with the values stored
   at the authoritative SNMP engine.  In addition to keeping a local
   copy of snmpEngineBoots and snmpEngineTime from the authoritative
   SNMP engine, a non-authoritative SNMP engine must also keep one
   local variable, latestReceivedEngineTime.  This value records the
   highest value of snmpEngineTime that was received by the
   non-authoritative SNMP engine from the authoritative SNMP engine
   and is used to eliminate the possibility of replaying messages
   that would prevent the non-authoritative SNMP engine's notion of
   the snmpEngineTime from advancing.

   A non-authoritative SNMP engine must keep local notions of these
   values for each authoritative SNMP engine with which it wishes to
   communicate.  Since each authoritative SNMP engine is uniquely
   and unambiguously identified by its value of snmpEngineID, the
   non-authoritative SNMP engine may use this value as a key in
   order to cache its local notions of these values.

   Time synchronization occurs as part of the procedures of receiving
   an SNMP message (Section 3.2, step 7b). As such, no explicit time
   synchronization procedure is required by a non-authoritative SNMP
   engine.  Note, that whenever the local value of snmpEngineID is
   changed (e.g., through discovery) or when secure communications
   are first established with an authoritative SNMP engine, the local
   values of snmpEngineBoots and latestReceivedEngineTime should be
   set to zero.  This will cause the time synchronization to occur
   when the next authentic message is received.






















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2.4.  SNMP Messages Using this Security Model

   The syntax of an SNMP message using this Security Model adheres
   to the message format defined in the version-specific Message
   Processing Model document (for example [SNMP-MP]).
   The securityParameters in the message are defined as an
   OCTET STRING. The format of that OCTET STRING for the User-based
   Security Model is as follows:

      securityParameters ::=
          SEQUENCE {
              -- global User-based security parameters
              authEngineID
                  OCTET STRING (SIZE(12)),
              authEngineBoots
                  Unsigned32 (0..4294967295),
              authEngineTime
                  Unsigned32 (0..2147483647),
              userName
                  OCTET STRING (SIZE(1..16)),
              -- authentication protocol specific parameters
              authParameters
                  OCTET STRING,
              -- privacy protocol specific parameters
              privParameters
                  OCTET STRING,
          }
      END

   The authEngineID is the snmpEngineID of the authoritative SNMP
   engine involved in the exchange of the message.

   The authEngineBoots is the snmpEngineBoots value at the
   authoritative SNMP engine involved in the exchange of the message.

   The authEngineTime is the snmpEngineTime value at the
   authoritative SNMP engine involved in the exchange of the message.

   The authParameters are defined by the authentication protocol in
   use for the message (as defined by the authProtocol column in
   the user's entry in the usmUserTable).

   The privParameters are defined by the privacy protocol in
   use for the message (as defined by the privProtocol column in
   the user's entry in the usmUserTable).

   See appendix A.4 for en example of the encoding.

2.5.  Services provided by the User-based Security Model

   This section describes the services provided by the User-based



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   Security Model with their inputs and outputs.

   The services are described as primitives of an abstract service
   interface and the inputs and outputs are described as abstract
   data elements as they are passed in these abstract service
   interface primitives.


2.5.1.  Services for Generating an Outgoing SNMP Message

   When the Message Processing (MP) Subsystem invokes the User-based
   Security module to secure an outgoing SNMP message, it must use
   the appropriate service as provided by the Security module.  These
   two services are provided:

     1) A service to generate a Request message.

     2) A service to generate a Response message.

   Upon completion of the process, the User-based Security module
   returns statusInformation and, if the process was successful,
   the completed message with privacy and authentication applied
   if such was requested by the specified Level of Security (LoS).

   The abstract service interface primitives are:

    generateRequestMsg(
        messageProcessingModel      -- typically, SNMP version
        msgID                       -- for the outgoing message
        mms                         -- of the sending SNMP entity
        msgFlags                    -- for the outgoing message
        securityParameters          -- filled in by Security Module
        securityModel               -- for the outgoing message
        securityName                -- on behalf of this principal
        LoS                         -- Level of Security requested
        snmpEngineID                -- authoritative SNMP entity
        scopedPDU                   -- message (plaintext) payload
        )

    generateResponseMsg(
        messageProcessingModel      -- typically, SNMP version
        msgID                       -- for the outgoing message
        mms                         -- of the sending SNMP entity
        msgFlags                    -- for the outgoing message
        securityParameters          -- filled in by Security Module
        securityModel               -- for the outgoing message
        scopedPDU                   -- message (plaintext) payload
        securityStateReference      -- reference to security state
                                    -- information, as received in
        )                           -- processPdu primitive




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    returnGeneratedMsg(
        wholeMsg                    -- complete generated message
        wholeMsgLength              -- length of the generated message
        statusInformation           -- errorIndication or success
        )

   Where:

    messageProcessingModel
      The SNMP version number for the message to be generated.
      This data is not used by the User-based Security module.
      It is part of the globalData of the message.
    msgID
      The msgID for the message to be generated.
      This data is not used by the User-based Security module.
      It is part of the globalData of the message.
    mms
      The maximum message size to be included as mms in the message.
      This data is not used by the User-based Security module.
      It is part of the globalData of the message.
    msgFlags
      The msgFlags to be included in the message.
      This data is not used by the User-based Security module.
      It is part of the globalData of the message.
      It should be consistent with the LoS that is passed.
    securityParameters
      These are the security parameters. They will be filled in
      by the User-based Security module.
    securityModel
      The securityModel in use.
      Should be the User-based Security Model.
      This data is not used by the User-based Security module.
      It is part of the globalData of the message.
    securityName
      Together with the snmpEngineID it identifies a row in the
      usmUserTable that is to be used for securing the message.
      The securityName has a format that is independent of the
      Security Model.
    LoS
      The Level of Security (LoS) from which the User-based Security
      module determines if the message needs to be protected from
      disclosure and if the message needs to be authenticated.
    snmpEngineID
      The snmpEngineID of the authoritative SNMP engine to which the
      Request message is to be sent or from which the Response
      message originates.  In case of a response the snmpEngineID
      is implied to be the processing SNMP engine's snmpEngineID.
    scopedPDU
      The message payload.  The data is opaque as far as the
      User-based Security Model is concerned.
    securityStateReference



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      A handle/reference to cached security data to be used when
      securing an outgoing Response message.  This is the exact same
      handle/reference as it was generated by the User-based Security
      module when processing the incoming Request message to which
      this is the Response message.

    wholeMsg
      The fully encoded and secured message ready for sending on
      the wire.
    wholeMsgLength
      The length of the encoded and secured message (wholeMsg).
    statusInformation
      An indication of whether the encoding and securing of the
      message was successful.  If not it is an indication of the
      problem.


2.5.2.  Services for Processing an Incoming SNMP Message

   When the Message Processing (MP) Subsystem invokes the User-based
   Security module to verify proper security of an incoming message,
   it must use the service provided for an incoming message.

   Upon completion of the process, the User-based Security module
   returns statusInformation and, if the process was successful,
   the additional data elements for further processing of the message.

   The abstract service interface primitives are:

    processMsg(
        messageProcessingModel      -- typically, SNMP version
        msgID                       -- of the received message
        mms                         -- of the sending SNMP entity
        msgFlags                    -- for the received message
        securityParameters          -- for the received message
        securityModel               -- for the received message
        LoS                         -- Level of Security
        wholeMsg                    -- as received on the wire
        wholeMsgLength              -- length as received on the wire
        )

    returnProcessedMsg(
        securityName                -- identification of the principal
        scopedPDU,                  -- message (plaintext) payload
        maxSizeResponseScopedPDU    -- maximum size of the Response PDU
        securityStateReference      -- reference to security state
                                    -- information, needed for response
        statusInformation           -- errorIndication or success
        )                           -- error counter OID/value if error

   Where:



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    messageProcessingModel
      The SNMP version number as received in the message.
      This data is not used by the User-based Security module.
      It is part of the globalData of the message.
    msgID
      The msgID as received in the message.
      This data is not used by the User-based Security module.
      It is part of the globalData of the message.
    mms
      The maximum message size as received in the message.
      It is part of the globalData of the message.
      The USM module uses this information to calculate the
      maxSizeResponseScopedPDU that it returns upon completion.
    msgFlags
      The msgFlags as received in the message.
      This data is not used by the User-based Security module.
      It is part of the globalData of the message.
      It should be consistent with the LoS that is passed.
    securityParameters
      These are the security parameters as received in the message.
    securityModel
      The securityModel in use.
      Should be the User-based Security Model.
      This data is not used by the User-based Security module.
      It is part of the globalData of the message.
    LoS
      The Level of Security (LoS) from which the User-based Security
      module determines if the message needs to be protected from
      disclosure and if the message needs to be authenticated.
    wholeMsg
      The whole message as it was received.
    wholeMsgLength
      The length of the message as it was received (wholeMsg).

    securityName
      The security name representing the user on whose behalf the
      message was received.  The securityName has a format that is
      independent of the Security Model.
    scopedPDU
      The message payload.  The data is opaque as far as the
      User-based Security Model is concerned.
    maxSizeResponseScopedPDU
      The maximum size of a scopedPDU to be included in a possible
      Response message.  The User-base Security module calculates
      this size based on the mms (as received in the message) and
      the space required for the message header (including the
      securityParameters) for such a Response message.
    securityStateReference
      A handle/reference to cached security data to be used when
      securing an outgoing Response message.  When the Message



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      Processing Subsystem calls the User-based Security module to
      generate a response to this incoming message it must pass this
      handle/reference.
    statusInformation
      An indication of whether the process was successful or not.
      If not, then the statusInformation includes the OID and the
      value of the error counter that was incremented.















































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3.  Elements of Procedure

   This section describes the security related procedures followed by
   an SNMP engine when processing SNMP messages according to the
   User-based Security Model.

3.1.  Generating an Outgoing SNMP Message

   This section describes the procedure followed by an SNMP engine
   whenever it generates a message containing a management operation
   (like a request, a response, a notification, or a report) on
   behalf of a user, with a particular Level of Security (LoS).

   1)  a) If any securityStateReference is passed (Response message),
          then information concerning the user is extracted from the
          cachedSecurityData.  The snmpEngineID and the Level of
          Security (LoS) are extracted from the cachedSecurityData.
          The cachedSecurityData can now be discarded.

          Otherwise,

       b) based on the securityName, information concerning the
          user at the destination snmpEngineID is extracted from
          the Local Configuration Datastore (LCD, usmUserTable).
          If information about the user is absent from the LCD,
          then an error indication (unknownSecurityName) is
          returned to the calling module.

   2)  If the Level of Security (LoS) specifies that the message
       is to be protected from disclosure, but the user does not
       support both an authentication and a privacy protocol then
       the message cannot be sent.  An error indication
       (unsupportedLoS) is returned to the calling module.

   3)  If the Level of Security (LoS) specifies that the message
       is to be authenticated, but the user does not support an
       authentication protocol, then the message cannot be sent.
       An error indication (unsupportedLoS) is returned to the
       calling module.

   4)  a) If the Level of Security (LoS) specifies that the
          message is to be protected from disclosure, then the
          octet sequence representing the serialized scopedPDU
          is encrypted according to the user's privacy protocol.
          To do so a call is made to the privacy module that
          implements the user's privacy protocol according to
          the abstract service interface primitive:

           encryptData(
               cryptKey           -- user's privKey
               dataToEncrypt)     -- serialized scopedPDU



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          The user's private privKey is the secret key that can
          be used by the encryption algorithm. The serialized
          scopedPDU is the data that must be encrypted.

          Upon completion the privacy module returns the result
          according to the abstract service interface primitive:

           returnEncryptedData(
               encryptedData       -- serialized encryptedPDU
               privParameters      -- serialized privParameters
               statusInformation)  -- success or failure


          The encryptedPDU represents the encrypted scopedPDU,
          encoded as an OCTET STRING.
          The privParameters represents the privacy parameters,
          encoded as an OCTET STRING.
          The statusInformation indicates if the scopedPDU was
          encrypted successfully or not.

          If the privacy module returns failure, then the message
          cannot be sent and an error indication (encryptionFailure)
          is returned to the calling module.

          If the privacy module returns success, then the
          privParameters field is put into the securityParameters
          and the encryptedPDU serves as the payload of the message
          being prepared.

          Otherwise,

       b) If the Level of Security (LoS) specifies that the message
          is not to be protected from disclosure, then the NULL
          string is encoded as an OCTET STRING and put into the
          privParameters field of the securityParameters and the
          plaintext scopedPDU serves as the payload of the message
          being prepared.

   5)  The snmpEngineID is encoded as an OCTET STRING into the
       authEngineID field of the securityParameters.

   6)  a) If the Level of Security (LoS) specifies that the message
          is to be authenticated, then the current values of
          snmpEngineBoots and snmpEngineTime corresponding to the
          snmpEngineID from the LCD are used.

          Otherwise,

       b) If this is a Response message, then the current value of
          snmpEngineBoots and snmpEngineTime corresponding to the



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          local snmpEngineID from the LCD are used.

          Otherwise,

       c) If this is a Request message, then a zero value is used
          for both snmpEngineBoots and snmpEngineTime.

       The values are encoded as Unsigned32 into the authEngineBoots
       and authEngineTime fields of the securityParameters.

   7)  The userName is encoded as an OCTET STRING into the userName
       field of the securityParameters.

   8)  a) If the Level of Security (LoS) specifies that the message
          is to be authenticated, the message is authenticated
          according to the user's authentication protocol.
          To do so a call is made to the authentication module that
          implements the user's authentication protocol according to
          the abstract service interface primitive:

           authenticateOutgoingMsg(
               authKey       -- the user's authKey
               wholeMsg)     -- the complete serialized message

          The user's private authKey is the secret key that can
          be used by the authentication algorithm.
          The wholeMsg is the complete serialized message that
          must be authenticated.

          Upon completion the authentication module returns the result
          according to the abstract service interface primitive:

           returnAuthenticatedOutgoingMsg(
               wholeMsg            -- secured serialized message
               statusInformation)  -- success or failure

          The wholeMsg is the same as the input given to the
          authenticateOutgoingMsg service, but with authParameters
          properly filled in.
          The statusInformation indicates if the message was
          successfully processed by the authentication module or not.

          If the authentication module returns failure, then the
          message cannot be sent and an error indication
          (authenticationFailure) is returned to the calling module.

          If the authentication module returns success, then the
          authParameters field is put into the securityParameters
          and the wholeMsg represents the serialization of the
          authenticated message being prepared.




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          Otherwise,

       b) If the Level of Security (LoS) specifies that the message
          is not to be authenticated then the NULL string is encoded
          as an OCTET STRING into the authParameters field of the
          securityParameters.  The wholeMsg is now serialized and
          then represents the unauthenticated message being prepared.

   9)  The completed message with its length is returned to the
       calling module with the statusInformation set to success.
       This is done according to the following abstract service
       interface primitive:

         returnGeneratedMsg(
             wholeMsg            -- LoS secured serialized message
             wholeMsgLength      -- length of message
             statusInformation)  -- success

3.2.  Processing an Incoming SNMP Message

   This section describes the procedure followed by an SNMP engine
   whenever it receives a message containing a management operation
   on behalf of a user, with a particular Level of Security (LoS).

   1)  If the received securityParameters is not the serialization
       (according to the conventions of [RFC1906]) of an OCTET STRING
       formatted according to the securityParameters defined in
       section 2.4, then the snmpInASNParseErrs counter [RFC1907] is
       incremented, and an error indication (parseError) together
       with the OID and value of the incremented counter is returned
       to the calling module.

   2)  The values of the security parameter fields are extracted from
       the securityParameters.

   3)  If the value of the authEngineID contained in the
       securityParameters is unknown then:

       a) a manager that performs discovery may optionally create a
          new entry in its Local Configuration Datastore (LCD)
          and continue processing;

          or

       b) the usmStatsUnknownEngineIDs counter is incremented, and
          an error indication (unknownEngineID) together with the
          OID and value of the incremented counter is returned to
          the calling module.

   4)  Information about the value of the userName and authEngineID
       fields is extracted from the Local Configuration Datastore



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       (LCD, usmUserTable).  If no information is available for
       the user, then the usmStatsUnknownUserNames counter is
       incremented and an error indication (unknownSecurityName)
       together with the OID and value of the incremented counter
       is returned to the calling module.

   5)  If the information about the user indicates that it does not
       support the Level of Security indicated by the LoS parameter,
       then the usmStatsUnsupportedLoS counter is incremented and
       an error indication (unsupportedLoS) together with the OID
       and value of the incremented counter is returned to the
       calling module.

   6)  If the Level of Security (LoS) specifies that the message
       is to be authenticated, then the message is authenticated
       according to the user's authentication protocol.
       To do so a call is made to the authentication module that
       implements the user's authentication protocol according to
       the abstract service interface primitive:

           authenticateIncomingMsg(
               authKey        -- the user's authKey
               authParameters -- as received on the wire
               wholeMsg)      -- as received on the wire

       The user's private authKey is the secret key that can
       be used by the authentication algorithm.
       The authParameters and the wholeMsg are passed as received
       on the wire.

       Upon completion the authentication module returns the result
       according to the abstract service interface primitive:

           returnAuthenticatedIncomingMsg(
               wholeMsg            -- authenticated serialized message
               statusInformation)  -- success or failure

       The wholeMsg is the same as the input given to the
       authenticateIncomingMsg service.
       The statusInformation indicates if the message was successfully
       authenticated by the authentication module or not.

       If the authentication module returns failure, then the message
       cannot trusted, so the usmStatsWrongDigests counter is
       incremented and an error indication (authenticationFailure)
       together with the OID and value of the incremented counter is
       returned to the calling module.

       If the authentication module returns success, then the message
       is authentic and can be trusted so processing continues.




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   7)  If the Level of Security (LoS) indicates an authenticated
       message, then the local values of snmpEngineBoots and
       snmpEngineTime corresponding to the value of the authEngineID
       field are extracted from the Local Configuration Datastore.

       a) If the extracted value of authEngineID is the same as
          the value of SnmpEngineID of the processing SNMP engine
          (meaning this is the authoritative SNMP engine), then
          if any of the following conditions is true, then the
          message is considered to be outside of the Time Window:

           - the local value of snmpEngineBoots is 0xffffffff;

           - the value of the authEngineBoots field differs from
             the local value of snmpEngineBoots; or,

           - the value of the authEngineTime field differs from
             the local notion of snmpEngineTime by more than
             +/- 150 seconds.

          If the message is considered to be outside of the Time
          Window then the usmStatsNotInTimeWindows counter is
          incremented and an error indication (notInTimeWindow)
          together with the OID and value of the incremented counter
          is returned to the calling module.

       b) If the extracted value of authEngineID is not the same as
          the value snmpEngineID of the processing SNMP engine
          (meaning this is not the authoritative SNMP engine), then:

          1) if at least one of the following conditions is true:

             - the extracted value of the authEngineBoots field is
               greater than the local notion of the value of
               snmpEngineBoots; or,

             - the extracted value of the authEngineBoots field is
               equal to the local notion of the value of
               snmpEngineBoots and the extracted value of
               authEngineTime field is greater than the value of
               latestReceivedEngineTime,

             then the LCD entry corresponding to the extracted value
             of the authEngineID field is updated, by setting:

                - the local notion of the value of snmpEngineBoots
                  to the value of the authEngineBoots field,
                - the local notion of the value of snmpEngineTime
                  to the value of the authEngineTime field, and
                - the latestReceivedEngineTime to the value of the
                  authEngineTime field.



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          2) if any of the following conditions is true, then the
             message is considered to be outside of the Time Window:

             - the local notion of the value of snmpEngineBoots is
               0xffffffff;

             - the value of the authEngineBoots field is less than
               the local notion of the value of snmpEngineBoots; or,

             - the value of the authEngineBoots field is equal to
               the local notion of the value of snmpEngineBoots
               and the value of the authEngineTime field is more
               than 150 seconds less than the local notion of
               of the value of snmpEngineTime.

             If the message is considered to be outside of the Time
             Window then an error indication (notInTimeWindow) is
             returned to the calling module;

             Note that this means that a too old (possibly replayed)
             message has been detected and is deemed unauthentic.

             Note that this procedure allows for the value of
             authEngineBoots in the message to be greater than the
             local notion of the value of snmpEngineBoots to allow
             for received messages to be accepted as authentic when
             received from an authoritative SNMP engine that has
             re-booted since the receiving SNMP engine last
             (re-)synchronized.

   8)  a) If the Level of Security (LoS) indicates that the message
          was protected from disclosure, then the OCTET STRING
          representing the encryptedPDU is decrypted according to
          the user's privacy protocol to obtain an unencrypted
          serialized scopedPDU value.
          To do so a call is made to the privacy module that
          implements the user's privacy protocol according to
          the abstract service interface primitive:

           decryptData(
               decryptKey          -- user's privKey
               privParameters      -- as received on the wire
               encryptedData)      -- encryptedPDU received on wire

          The user's private privKey is the secret key that can
          be used by the decryption algorithm.  The serialized
          encryptedPDU is the data that must be decrypted.

          Upon completion the privacy module returns the result
          according to the abstract service interface primitive:



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           returnDecryptedData(
               decryptedData       -- serialized decrypted scopedPDU
               statusInformation)  -- success or failure

          The statusInformation indicates if the scopedPDU was
          decrypted successfully or not.

          If the privacy module returns failure, then the message can
          not be processed, so the usmStatsDecryptionErrors counter
          is incremented and an error indication (encryptionFailure)
          together with the OID and value of the incremented counter
          is returned to the calling module.

          If the privacy module returns success, then the decrypted
          scopedPDU is the message payload to be returned to the
          calling module.

          Otherwise,

       b) The scopedPDU component is assumed to be in plain text
          and is the message payload to be returned to the calling
          module.

   9)  The maxSizeResponseScopedPDU is calculated.  This is the
       maximum size allowed for a scopedPDU for a possible Response
       message.  Provision is made for a message header that allows
       the same Level of Security as the received Request.

   10) The securityName for the user is retrieved from the
       usmUserTable.

   11) The security data is cached as cachedSecurityData, so that a
       possible response to this message can and will use the same
       authentication and privacy secrets, the same Level of Security
       and the same authEngineID.  Information to be saved/cached is
       as follows:

          usmUserName, LoS
          usmUserAuthProtocol, usmUserAuthKey
          usmUserPrivProtocol, usmUserPrivKey
          authEngineID

   12) The statusInformation is set to success and a return is made
       to the calling module according to this abstract service               interface primitive:

         returnProcessedMsg(
           securityName             -- identification of the principal
           scopedPDU,               -- message (plaintext) payload
           maxSizeResponseScopedPDU -- maximum size of the Response PDU
           securityStateReference   -- reference to security state



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                                    -- information, needed for response
           statusInformation        -- errorIndication or success
           )                        -- error counter OID/value if error



















































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4.  Discovery

   The User-based Security Model requires that a discovery process
   obtains sufficient information about other SNMP engines in order
   to communicate with them.  Discovery requires an non-authoritative
   SNMP engine to learn the authoritative SNMP engine's snmpEngineID
   value before communication may proceed.  This may be accomplished
   by generating a Request message with a Level of Security (LoS) of
   noAuthNoPriv, a userName of "initial", an authEngineID value of
   zero length or all zeroes (binary), and the varBindList left empty.
   The response to this message will be a Report message containing
   the snmpEngineID of the authoritative SNMP engine as the value of
   the authEngineID field within the securityParameters field.  It
   also contains a Report PDU with the usmStatsUnknownEngineIDs
   counter in the varBindList.

   If authenticated communication is required, then the discovery
   process should also establish time synchronization with the
   authoritative SNMP engine.  This may be accomplished by sending an
   authenticated Request message with the value of authEngineID set
   to the newly learned snmpEngineID and with the values of
   authEngineBoots and authEngineTime set to zero.
   The response to this authenticated message will be a Report message
   containing the up to date values of the authoritative SNMP engine's
   snmpEngineBoots and snmpEngineTime as the value of the
   authEngineBoots and authEngineTime fields respectively.  It also
   contains the usmStatsNotInTimeWindows counter in the varBindList
   of the Report PDU.  The time synchronization then happens
   automatically as part of the procedures in section 3.2 step 7b.
   See also section 2.3.
























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5.  Definitions

SNMP-USER-BASED-SM-MIB DEFINITIONS ::= BEGIN

IMPORTS
    MODULE-IDENTITY, OBJECT-TYPE,
    OBJECT-IDENTITY,
    snmpModules, Counter32                FROM SNMPv2-SMI
    TEXTUAL-CONVENTION, TestAndIncr,
    RowStatus, RowPointer,
    StorageType, AutonomousType           FROM SNMPv2-TC
    MODULE-COMPLIANCE, OBJECT-GROUP       FROM SNMPv2-CONF
    SnmpAdminString, SnmpLoS,
    SnmpEngineID, SnmpSecurityModel,
    snmpAuthProtocols, snmpPrivProtocols  FROM SNMP-FRAMEWORK-MIB;

snmpUsmMIB MODULE-IDENTITY
    LAST-UPDATED "9707140000Z"            -- 14 July 1997, midnight
    ORGANIZATION "SNMPv3 Working Group"
    CONTACT-INFO "WG-email:   snmpv3@tis.com
                  Subscribe:  majordomo@tis.com
                              In msg body:  subscribe snmpv3

                  Chair:      Russ Mundy
                              Trusted Information Systems
                  postal:     3060 Washington Rd
                              Glenwood MD 21738
                              USA
                  email:      mundy@tis.com
                  phone:      +1-301-854-6889

                  Co-editor   Uri Blumenthal
                              IBM T. J. Watson Research
                  postal:     30 Saw Mill River Pkwy,
                              Hawthorne, NY 10532
                              USA
                  email:      uri@watson.ibm.com
                  phone:      +1-914-784-7964

                  Co-editor:  Bert Wijnen
                              IBM T. J. Watson Research
                  postal:     Schagen 33
                              3461 GL Linschoten
                              Netherlands
                  email:      wijnen@vnet.ibm.com
                  phone:      +31-348-432-794
                 "

    DESCRIPTION  "The management information definitions for the
                  SNMP User-based Security Model.
                 "



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    ::= { snmpModules 9 }     -- to be verified with IANA

-- Administrative assignments ****************************************

usmAdmin          OBJECT IDENTIFIER ::= { snmpUsmMIB 1 }
usmMIBObjects     OBJECT IDENTIFIER ::= { snmpUsmMIB 2 }
usmMIBConformance OBJECT IDENTIFIER ::= { snmpUsmMIB 3 }

-- Identification of Authentication and Privacy Protocols ************

usmNoAuthProtocol OBJECT-IDENTITY
    STATUS        current
    DESCRIPTION  "No Authentication Protocol."
    ::= { snmpAuthProtocols 1 }

usmMD5AuthProtocol OBJECT-IDENTITY
    STATUS        current
    DESCRIPTION  "The Keyed MD5 Digest Authentication Protocol."
    REFERENCE    "Rivest, R., Message Digest Algorithm MD5, RFC1321."
    ::= { snmpAuthProtocols 2 }

usmNoPrivProtocol OBJECT-IDENTITY
    STATUS        current
    DESCRIPTION  "No Privacy Protocol."
    ::= { snmpPrivProtocols 1 }

usmDESPrivProtocol OBJECT-IDENTITY
    STATUS        current
    DESCRIPTION  "The CBC-DES Symmetric Encryption Protocol."
    REFERENCE    "- Data Encryption Standard, National Institute of
                    Standards and Technology.  Federal Information
                    Processing Standard (FIPS) Publication 46-1.
                    Supersedes FIPS Publication 46,
                    (January, 1977; reaffirmed January, 1988).

                  - Data Encryption Algorithm, American National
                    Standards Institute.  ANSI X3.92-1981,
                    (December, 1980).

                  - DES Modes of Operation, National Institute of
                    Standards and Technology.  Federal Information
                    Processing Standard (FIPS) Publication 81,
                    (December, 1980).

                  - Data Encryption Algorithm - Modes of Operation,
                    American National Standards Institute.
                    ANSI X3.106-1983, (May 1983).
                 "
    ::= { snmpPrivProtocols 2 }

-- Textual Conventions ***********************************************



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-- Editor's note:
-- If in the future the MD5 gets replaced by another Authentication
-- algorithm, then it seems we also need to use that new algorithm to
-- calculate the digest during KeyChange. So this TC has been changed
-- End Editor's note

KeyChange ::=     TEXTUAL-CONVENTION
   STATUS         current
   DESCRIPTION
         "Every definition of an object with this syntax must identify
          a protocol, P, a secret key, K, and a hash algorithm, H.
          The object's value is a manager-generated, partially-random
          value which, when modified, causes the value of the secret
          key, K, to be modified via a one-way function.

          The value of an instance of this object is the concatenation
          of two components: a 'random' component and a 'delta'
          component.  The lengths of the random and delta components
          are given by the corresponding value of the protocol, P;
          if P requires K to be a fixed length, the length of both the
          random and delta components is that fixed length; if P
          allows the length of K to be variable up to a particular
          maximum length, the length of the random component is that
          maximum length and the length of the delta component is any
          length less than or equal to that maximum length.
          For example, usmMD5AuthProtocol requires K to be a fixed
          length of 16 octets.  Other protocols may define other
          sizes, as deemed appropriate.

          When an instance of this object is modified to have a new
          value by the management protocol, the agent generates a new
          value of K as follows:

           - a temporary variable is initialized to the existing value
             of K;
           - if the length of the delta component is greater than 16
             bytes, then:
              - the random component is appended to the value of the
                temporary variable, and the result is input to the
                the hash algorithm H to produce a digest value, and
                the temporary variable is set to this digest value;
              - the value of the temporary variable is XOR-ed with
                the first (next) 16-bytes of the delta component to
                produce the first (next) 16-bytes of the new value
                of K.
              - the above two steps are repeated until the unused
                portion of the delta component is 16 bytes or less,
           - the random component is appended to the value of the
             temporary variable, and the result is input to the
             hash algorithm H to produce a digest value;



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           - this digest value, truncated if necessary to be the same
             length as the unused portion of the delta component, is
             XOR-ed with the unused portion of the delta component to
             produce the (final portion of the) new value of K.

             for example, using MD5 as the hash algorithm H:

              iterations = (lenOfDelta - 1)/16; /* integer division */
              temp = keyOld;
              for (i = 0; i < iterations; i++) {
                  temp = MD5 (temp || random);
                  keyNew[i*16 .. (i*16)+15] =
                         temp XOR delta[i*16 .. (i*16)+15];
              }
              temp = MD5 (temp || random);
              keyNew[i*16 .. lenOfDelta-1] =
                     temp XOR delta[i*16 .. lenOfDelta-1];

          The value of an object with this syntax, whenever it is
          retrieved by the management protocol, is always the zero
          length string.
         "
    SYNTAX       OCTET STRING

-- Statistics for the User-based Security Model **********************

usmStats         OBJECT IDENTIFIER ::= { usmMIBObjects 1 }

usmStatsUnsupportedLoS OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION "The total number of packets received by the SNMP
                 engine which were dropped because they requested
                 a Level of Security (LoS) that was unknown to the
                 SNMP engine or otherwise unavailable.
                "
    ::= { usmStats 1 }

usmStatsNotInTimeWindows OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION "The total number of packets received by the SNMP
                 engine which were dropped because they appeared
                 outside of the authoritative SNMP engine's window.
                "
    ::= { usmStats 2 }

usmStatsUnknownUserNames OBJECT-TYPE
    SYNTAX       Counter32



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    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION "The total number of packets received by the SNMP
                 engine which were dropped because they referenced a
                 user that was not known to the SNMP engine.
                "
    ::= { usmStats 3 }

usmStatsUnknownEngineIDs OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION "The total number of packets received by the SNMP
                 engine which were dropped because they referenced an
                 snmpEngineID that was not known to the SNMP engine.
                "
    ::= { usmStats 4 }

usmStatsWrongDigests OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION "The total number of packets received by the SNMP
                 engine which were dropped because they didn't
                 contain the expected digest value.
                "
    ::= { usmStats 5 }

usmStatsDecryptionErrors OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION "The total number of packets received by the SNMP
                 engine which were dropped because they could not be
                 decrypted.
                "
    ::= { usmStats 6 }

-- The usmUser Group ************************************************

usmUser          OBJECT IDENTIFIER ::= { usmMIBObjects 2 }

usmUserSpinLock  OBJECT-TYPE
    SYNTAX       TestAndIncr
    MAX-ACCESS   read-write
    STATUS       current
    DESCRIPTION "An advisory lock used to allow several cooperating
                 Command Generator Applications to coordinate their
                 use of facilities to alter secrets in the
                 usmUserTable.
                "



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    ::= { usmUser 1 }

-- The table of valid users for the User-based Security Model ********

usmUserTable     OBJECT-TYPE
    SYNTAX       SEQUENCE OF UsmUserEntry
    MAX-ACCESS   not-accessible
    STATUS       current
    DESCRIPTION "The table of users configured in the SNMP engine's
                 Local Configuration Datastore (LCD)."
    ::= { usmUser 2 }

usmUserEntry     OBJECT-TYPE
    SYNTAX       UsmUserEntry
    MAX-ACCESS   not-accessible
    STATUS       current
    DESCRIPTION "A user configured in the SNMP engine's Local
                 Configuration Datastore (LCD) for the User-based
                 Security Model.
                "
    INDEX       { usmUserEngineID,
                  usmUserName
                }
    ::= { usmUserTable 1 }

UsmUserEntry ::= SEQUENCE
    {
        usmUserEngineID         SnmpEngineID,
        usmUserName             SnmpAdminString,
        usmUserSecurityName     SnmpAdminString,
        usmUserCloneFrom        RowPointer,
        usmUserAuthProtocol     AutonomousType,
        usmUserAuthKeyChange    KeyChange,
        usmUserOwnAuthKeyChange KeyChange,
        usmUserPrivProtocol     AutonomousType,
        usmUserPrivKeyChange    KeyChange,
        usmUserOwnPrivKeyChange KeyChange,
        usmUserPublic           OCTET STRING,
        usmUserStorageType      StorageType,
        usmUserStatus           RowStatus
    }

usmUserEngineID  OBJECT-TYPE
    SYNTAX       SnmpEngineID
    MAX-ACCESS   not-accessible
    STATUS       current
    DESCRIPTION "An SNMP engine's administratively-unique identifier.

                 In a simple agent, this value is always that agent's
                 own snmpEngineID value.




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                 The value can also take the value of the snmpEngineID
                 of a remote SNMP engine with which this user can
                 communicate.
                "
    ::= { usmUserEntry 1 }

usmUserName      OBJECT-TYPE
    SYNTAX       SnmpAdminString (SIZE(1..16))
    MAX-ACCESS   not-accessible
    STATUS       current
    DESCRIPTION "A human readable string representing the name of
                 the user.

                 This is the (User-based Security) Model dependent
                 security ID.
                "
    ::= { usmUserEntry 2 }

usmUserSecurityName OBJECT-TYPE
    SYNTAX       SnmpAdminString
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION "A human readable string representing the user in
                 Security Model independent format.

                 The default transformation of the User-based Security
                 Model dependent security ID to the securityName and
                 vice versa is the identity function so that the
                 securityName is the same as the userName.
                "
    ::= { usmUserEntry 3 }

usmUserCloneFrom OBJECT-TYPE
    SYNTAX       RowPointer
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION "A pointer to another conceptual row in this
                 usmUserTable.  The user in this other conceptual
                 row is called the clone-from user.

                 When a new user is created (i.e., a new conceptual
                 row is instantiated in this table), the privacy and
                 authentication parameters of the new user are cloned
                 from its clone-from user.

                 The first time an instance of this object is set by
                 a management operation (either at or after its
                 instantiation), the cloning process is invoked.
                 Subsequent writes are successful but invoke no
                 action to be taken by the receiver.
                 The cloning process fails with an 'inconsistentName'



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                 error if the conceptual row representing the
                 clone-from user is not in an active state when the
                 cloning process is invoked.

                 Cloning also causes the initial values of the secret
                 authentication key and the secret encryption key of
                 the new user to be set to the same value as the
                 corresponding secret of the clone-from user.

                 When this object is read, the ZeroDotZero OID
                 is returned.
                "
    ::= { usmUserEntry 4 }

usmUserAuthProtocol OBJECT-TYPE
    SYNTAX       AutonomousType
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION "An indication of whether messages sent on behalf of
                 this user to/from the SNMP engine identified by
                 usmUserEngineID, can be authenticated, and if so,
                 the type of authentication protocol which is used.

                 An instance of this object is created concurrently
                 with the creation of any other object instance for
                 the same user (i.e., as part of the processing of
                 the set operation which creates the first object
                 instance in the same conceptual row).  Once created,
                 the value of an instance of this object can not be
                 changed.
                "
    DEFVAL      { usmMD5AuthProtocol }
    ::= { usmUserEntry 5 }

usmUserAuthKeyChange OBJECT-TYPE
    SYNTAX       KeyChange   -- typically (SIZE (0..32))
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION "An object, which when modified, causes the secret
                 authentication key used for messages sent on behalf
                 of this user to/from the SNMP engine identified by
                 usmUserEngineID, to be modified via a one-way
                 function.

                 The associated protocol is the usmUserAuthProtocol.
                 The associated secret key is the user's secret
                 authentication key (authKey). The associated hash
                 algorithm is the algorithm used by the user's
                 usmUserAuthProtocol.

                 When creating a new user, it is an 'inconsistentName'



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                 error for a Set operation to refer to this object
                 unless it is previously or concurrently initialized
                 through a set operation on the corresponding value
                 of usmUserCloneFrom.
                "
    DEFVAL      { ''H }    -- the empty string
    ::= { usmUserEntry 6 }

usmUserOwnAuthKeyChange OBJECT-TYPE
    SYNTAX       KeyChange  -- typically (SIZE (0..32))
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION "Behaves exactly as usmUserAuthKeyChange, with one
                 notable difference: in order for the Set operation
                 to succeed, the usmUserName of the operation
                 requester must match the usmUserName that
                 indexes the row which is targeted by this
                 operation.

                 The idea here is that access to this column can be
                 public, since it will only allow a user to change
                 his own secret authentication key (authKey).
                "
    DEFVAL      { ''H }    -- the empty string
    ::= { usmUserEntry 7 }

usmUserPrivProtocol OBJECT-TYPE
    SYNTAX       AutonomousType
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION "An indication of whether messages sent on behalf of
                 this user to/from the SNMP engine identified by
                 usmUserEngineID, can be protected from disclosure,
                 and if so, the type of privacy protocol which is used.

                 An instance of this object is created concurrently
                 with the creation of any other object instance for
                 the same user (i.e., as part of the processing of
                 the set operation which creates the first object
                 instance in the same conceptual row).  Once created,
                 the value of an instance of this object can not be
                 changed.
                "
    DEFVAL      { usmNoPrivProtocol }
    ::= { usmUserEntry 8 }

usmUserPrivKeyChange OBJECT-TYPE
    SYNTAX       KeyChange  -- typically (SIZE (0..32))
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION "An object, which when modified, causes the secret



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                 encryption key used for messages sent on behalf
                 of this user to/from the SNMP engine identified by
                 usmUserEngineID, to be modified via a one-way
                 function.

                 The associated protocol is the usmUserPrivProtocol.
                 The associated secret key is the user's secret
                 privacy key (privKey). The associated hash
                 algorithm is the algorithm used by the user's
                 usmUserAuthProtocol.

                 When creating a new user, it is an 'inconsistentName'
                 error for a set operation to refer to this object
                 unless it is previously or concurrently initialized
                 through a set operation on the corresponding value
                 of usmUserCloneFrom.
                "
    DEFVAL      { ''H }    -- the empty string
    ::= { usmUserEntry 9 }

usmUserOwnPrivKeyChange OBJECT-TYPE
    SYNTAX       KeyChange  -- typically (SIZE (0..32))
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION "Behaves exactly as usmUserPrivKeyChange, with one
                 notable difference: in order for the Set operation
                 to succeed, the usmUserName of the operation
                 requester must match the usmUserName that indexes
                 the row which is targeted by this operation.

                 The idea here is that access to this column can be
                 public, since it will only allow a user to change
                 his own secret privacy key (privKey).
                "
    DEFVAL      { ''H }    -- the empty string
    ::= { usmUserEntry 10 }

usmUserPublic    OBJECT-TYPE
    SYNTAX       OCTET STRING (SIZE(0..32))
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION "A publicly-readable value which is written as part
                 of the procedure for changing a user's secret
                 authentication and/or privacy key, and later read to
                 determine whether the change of the secret was
                 effected.
                "
    DEFVAL      { ''H }  -- the empty string
    ::= { usmUserEntry 11 }

usmUserStorageType OBJECT-TYPE



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    SYNTAX       StorageType
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION "The storage type for this conceptual row.

                 Conceptual rows having the value 'permanent'
                 must allow write-access at a minimum to:

                 - usmUserAuthKeyChange, usmUserOwnAuthKeyChange
                   and usmUserPublic for a user who employs
                   authentication, and
                 - usmUserPrivKeyChange, usmUserOwnPrivKeyChange
                   and usmUserPublic for a user who employs
                   privacy.

                 Note that any user who employs authentication or
                 privacy must allow its secret(s) to be updated and
                 thus cannot be 'readOnly'.
                "
    DEFVAL      { nonVolatile }
    ::= { usmUserEntry 12 }

usmUserStatus    OBJECT-TYPE
    SYNTAX       RowStatus
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION "The status of this conceptual row.

                 Until instances of all corresponding columns are
                 appropriately configured, the value of the
                 corresponding instance of the usmUserStatus column
                 is 'notReady'.

                 In particular, a newly created row cannot be made
                 active until the corresponding usmUserCloneFrom,
                 usmUserAuthKeyChange, usmUserOwnAuthKeyChange,
                 usmUserPrivKeyChange and usmUserOwnPrivKeyChange
                 have all been set.

                 The value of this object has no effect on whether
                 other objects in this conceptual row can be modified.
                "
    ::= { usmUserEntry 13 }

-- Conformance Information *******************************************

usmMIBCompliances OBJECT IDENTIFIER ::= { usmMIBConformance 1 }
usmMIBGroups      OBJECT IDENTIFIER ::= { usmMIBConformance 2 }

-- Compliance statements




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usmMIBCompliance MODULE-COMPLIANCE
    STATUS       current
    DESCRIPTION "The compliance statement for SNMP engines which
                 implement the SNMP-USER-BASED-SM-MIB.
                "

    MODULE       -- this module
        MANDATORY-GROUPS { usmMIBBasicGroup }

        OBJECT           usmUserAuthProtocol
        MIN-ACCESS       read-only
        DESCRIPTION     "Write access is not required."

        OBJECT           usmUserPrivProtocol
        MIN-ACCESS       read-only
        DESCRIPTION     "Write access is not required."

    ::= { usmMIBCompliances 1 }

-- Units of compliance

usmMIBBasicGroup OBJECT-GROUP
    OBJECTS     {
                  usmStatsUnsupportedLoS,
                  usmStatsNotInTimeWindows,
                  usmStatsUnknownUserNames,
                  usmStatsUnknownEngineIDs,
                  usmStatsWrongDigests,
                  usmStatsDecryptionErrors,
                  usmUserSpinLock,
                  usmUserSecurityName,
                  usmUserCloneFrom,
                  usmUserAuthProtocol,
                  usmUserAuthKeyChange,
                  usmUserOwnAuthKeyChange,
                  usmUserPrivProtocol,
                  usmUserPrivKeyChange,
                  usmUserOwnPrivKeyChange,
                  usmUserPublic,
                  usmUserStorageType,
                  usmUserStatus
                }
    STATUS       current
    DESCRIPTION "A collection of objects providing for configuration
                 of an SNMP engine which implements the SNMP
                 User-based Security Model.
                "
    ::= { usmMIBGroups 1 }

END




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6.  MD5 Authentication Protocol

   This section describes the Keyed-MD5 authentication protocol.
   This protocol is the first authentication protocol defined for
   the User-based Security Model.

   This protocol is identified by usmMD5AuthProtocol.

   Over time, other authentication protocols may be defined either
   as a replacement of this protocol or in addition to this protocol.

6.1.  Mechanisms

   - In support of data integrity, a message digest algorithm is
     required.  A digest is calculated over an appropriate portion
     of an SNMP message and included as part of the message sent
     to the recipient.

   - In support of data origin authentication and data integrity,
     a secret value is both inserted into, and appended to, the
     SNMP message prior to computing the digest; the inserted value
     is overwritten prior to transmission, and the appended value
     is not transmitted.  The secret value is shared by all SNMP
     engines authorized to originate messages on behalf of the
     appropriate user.

   - In order to not expose the shared secrets (keys) at all SNMP
     engines in case one of the SNMP engines is compromised, such
     secrets (keys) are localized for each authoritative SNMP
     engine, see [Localized-Key].

6.1.1.  Digest Authentication Protocol

   The Digest Authentication Protocol defined in this memo provides
   for:

   - verification of the integrity of a received message
     (i.e., the message received is the message sent).

     The integrity of the message is protected by computing a digest
     over an appropriate portion of the message.  The digest is
     computed by the originator of the message, transmitted with the
     message, and verified by the recipient of the message.

   - verification of the user on whose behalf the message was
     generated.

     A secret value known only to SNMP engines authorized to generate
     messages on behalf of a user is both inserted into, and appended
     to, the message prior to the digest computation.  Thus, the
     verification of the user is implicit with the verification of the



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     digest.  Note that the use of two copies of the secret, one near
     the start and one at the end, is recommended by [KEYED-MD5].

   This protocol uses the MD5 [MD5] message digest algorithm.
   A 128-bit digest is calculated over the designated portion of an
   SNMP message and included as part of the message sent to the
   recipient.  The size of both the digest carried in a message and
   the private authentication key (the secret) is 16 octets.

6.2.  Elements of the Digest Authentication Protocol

   This section contains definitions required to realize the
   authentication module defined by this memo.

6.2.1.  Users

   Authentication using this Digest Authentication protocol makes use
   of a defined set of userNames.  For any user on whose behalf a
   message must be authenticated at a particular SNMP engine, that
   SNMP engine must have knowledge of that user.  An SNMP engine that
   wishes to communicate with another SNMP engine must also have
   knowledge of a user known to that engine, including knowledge of
   the applicable attributes of that user.

   A user and its attributes are defined as follows:

   <userName>
     A string representing the name of the user.
   <authKey>
     A user's secret key to be used when calculating a digest.

6.2.2.  authEngineID

   The authEngineID value contained in an authenticated message
   specifies the authoritative SNMP engine for that particular
   message (see the definition of SnmpEngineID in the SNMP
   Architecture document [SNMP-ARCH]).

   The user's (private) authentication key is normally different at
   each authoritative SNMP engine and so the snmpEngineID is used
   to select the proper key for the authentication process.

6.2.3.  SNMP Messages Using this Authentication Protocol

   Messages using this authentication protocol carry an authParameters
   field as part of the securityParameters.  For this protocol, the
   authParameters field is the serialized OCTET STRING representing
   the MD5 digest of the wholeMsg.

   The digest is calculated over the wholeMsg so if a message is
   authenticated, that also means that all the fields in the message



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   are intact and have not been tampered with.

6.2.4.  Services provided by the MD5 Authentication Module

   This section describes the inputs and outputs that the MD5
   Authentication module expects and produces when the User-based
   Security module calls the MD5 Authentication module for services.

6.2.4.1.  Services for Generating an Outgoing SNMP Message

   This MD5 authentication protocol assumes that the selection of the
   authKey is done by the caller and that the caller passes the
   secret key to be used.

   Upon completion the authentication module returns statusInformation
   and, if the message digest was correctly calculated, the wholeMsg
   with the digest inserted at the proper place.

   The abstract service interfaces are:

     authenticateOutgoingMsg(
         authKey                     -- secret key for authentication
         wholeMsg                    -- complete message
         )

     returnAuthenticatedOutgoingMsg(
         wholeMsg                    -- complete authenticated message
         statusInformation           -- success or errorIndication
         )

   Where:

     authKey
       The secret key to be used by the authentication algorithm.
     wholeMsg
       The message to be authenticated on input or the authenticated
       message (including inserted digest) on output.
     statusInformation
       An indication of whether the authentication process was
       successful.  If not it is an indication of the problem.

   Note, that authParameters field is filled by the authentication
   module and this field should be already present in the wholeMsg
   before the Message Authentication Code (MAC) is generated.

6.2.4.2.  Services for Processing an Incoming SNMP Message

   This MD5 authentication protocol assumes that the selection of the
   authKey is done by the caller and that the caller passes
   the secret key to be used.




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   Upon completion the authentication module returns statusInformation
   and, if the message digest was correctly calculated, the wholeMsg
   as it was processed.

   The abstract service interfaces are:

     authenticateIncomingMsg(
         authKey                     -- secret key for authentication
         authParameters              -- filled in by service provider
         wholeMsg                    -- as received on the wire
         )

     returnAuthenticatedIncomingMsg(
         wholeMsg                    -- complete authenticated message
         statusInformation           -- success or errorIndication
         )

   Where:

     authKey
       The secret key to be used by the authentication algorithm.
     authParameters
       The authParameters from the incoming message.
     wholeMsg
       The message to be authenticated on input and the authenticated
       message on output.




























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6.3.  Elements of Procedure

   This section describes the procedures for the Keyed-MD5
   authentication protocol.

6.3.1.  Processing an Outgoing Message

   This section describes the procedure followed by an SNMP engine
   whenever it must authenticate an outgoing message using the
   usmMD5AuthProtocol.

   1)  The authParameters field is set to the serialization according
       to the rules in [RFC1906] of an OCTET STRING representing the
       secret (localized) authKey.

   2)  The secret (localized) authKey is then appended to the end of
       the wholeMsg.

   3)  The MD5-Digest is calculated according to [MD5]. Then the
       authParameters field is replaced with the calculated digest.

   4)  The wholeMsg (excluding the appended secret key) is then
       returned to the caller together with statusInformation
       indicating success.

6.3.2.  Processing an Incoming Message

   This section describes the procedure followed by an SNMP engine
   whenever it must authenticate an incoming message using the
   usmMD5AuthProtocol.

   1)  If the digest received in the authParameters field is not
       16 octets long, then an error indication (authenticationError)
       is returned to the calling module.

   2)  The digest received in the authParameters field is saved.

   3)  The digest in the authParameters field is replaced by the
       secret (localized) authKey.

   4)  The secret (localized) authKey is then appended to the end of
       the wholeMsg.

   5)  The MD5-Digest is calculated according to [MD5].
       The authParameters field is replaced with the digest value
       that was saved in step 2).

   6)  Then the newly calculated digest is compared with the digest
       saved in step 2). If the digests do not match, then an error
       indication (authenticationFailure) is returned to the calling
       module.



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   7)  The wholeMsg (excluding the appended secret key) and
       statusInformation indicating success are then returned to
       the caller.


















































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7.  DES Privacy Protocol

   This section describes the DES privacy protocol.
   This protocol is the first privacy protocol defined for the
   User-based Security Model.

   This protocol is identified by usmDESPrivProtocol.

   Over time, other privacy protocols may be defined either
   as a replacement of this protocol or in addition to this protocol.


7.1.  Mechanisms

   - In support of data confidentiality, an encryption algorithm is
     required.  An appropriate portion of the message is encrypted
     prior to being transmitted. The User-based Security Model
     specifies that the scopedPDU is the portion of the message
     that needs to be encrypted.

   - A secret value in combination with a timeliness value is used
     to create the en/decryption key and the initialization vector.
     The secret value is shared by all SNMP engines authorized to
     originate messages on behalf of the appropriate user.

   - In order to not expose the shared secrets (keys) at all SNMP
     engines in case one of the SNMP engines is compromised, such
     secrets (keys) are localized for each authoritative SNMP engine,
     see [Localized-Key].

7.1.1.  Symmetric Encryption Protocol

   The Symmetric Encryption Protocol defined in this memo provides
   support for data confidentiality.  The designated portion of an
   SNMP message is encrypted and included as part of the message
   sent to the recipient.

   Two organizations have published specifications defining the DES:
   the National Institute of Standards and Technology (NIST)
   [DES-NIST] and the American National Standards Institute
   [DES-ANSI].  There is a companion Modes of Operation specification
   for each definition ([DESO-NIST] and [DESO-ANSI], respectively).

   The NIST has published three additional documents that implementors
   may find useful.

   - There is a document with guidelines for implementing and using
     the DES, including functional specifications for the DES and
     its modes of operation [DESG-NIST].

   - There is a specification of a validation test suite for the DES



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     [DEST-NIST].  The suite is designed to test all aspects of the
     DES and is useful for pinpointing specific problems.

   - There is a specification of a maintenance test for the DES
     [DESM-NIST].  The test utilizes a minimal amount of data and
     processing to test all components of the DES.  It provides a
     simple yes-or-no indication of correct operation and is useful
     to run as part of an initialization step, e.g., when a computer
     re-boots.

7.1.1.1.  DES key and Initialization Vector.

   The first 8 bytes of the 16-byte secret (private privacy key) are
   used as a DES key.  Since DES uses only 56 bits, the Least
   Significant Bit in each byte is disregarded.

   The Initialization Vector for encryption is obtained using the
   following procedure.

   The last 8 bytes of the 16-byte secret (private privacy key)
   are used as pre-IV.

   In order to ensure that the IV for two different packets encrypted
   by the same key, are not the same (i.e. the IV does not repeat) we
   need to "salt" the pre-IV with something unique per packet.
   An 8-byte octet string is used as the "salt".  The concatenation
   of the generating SNMP engine's 32-bit snmpEngineBoots and a local
   32-bit integer, that the encryption engine maintains, is input to
   the "salt".  The 32-bit integer is initialized to an arbitrary
   value at boot time.
   The 32-bit snmpEngineBoots is converted to the first 4 bytes
   (Most Significant Byte first) of our "salt".  The 32-bit integer
   is then converted to the last 4 bytes (Most Significant Byte first)
   of our "salt".  The resulting "salt" is then XOR-ed with the
   pre-IV. The 8-byte "salt" is then put into the privParameters
   field encoded as an OCTET STRING.  The "salt" integer is then
   modified.  We recommend that it be incremented by one and wrap
   when it reaches the maximum value.

   How exactly the value of the "salt" (and thus of the IV) varies,
   is an implementation issue, as long as the measures are taken to
   avoid producing a duplicate IV.

   The "salt" must be placed in the privParameters field to enable the
   receiving entity to compute the correct IV and to decrypt the
   message.

7.1.1.2.  Data Encryption.

   The data to be encrypted is treated as sequence of octets. Its
   length should be an integral multiple of 8 - and if t is not, the



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   data is padded at the end as necessary.  The actual pad value
   is irrelevant.

   The data is encrypted in Cipher Block Chaining mode.
   The plaintext is divided into 64-bit blocks.

   The plaintext for each block is XOR-ed with the ciphertext
   of the previous block, the result is encrypted and the output
   of the encryption is the ciphertext for the block.
   This procedure is repeated until there are no more plaintext
   blocks.

   For the very first block, the Initialization Vector is used
   instead of the ciphertext of the previous block.

7.1.1.3.  Data Decryption

   Before decryption, the encrypted data length is verified.
   If the length of the OCTET STRING to be decrypted is not an
   integral multiple of 8 octets, the decryption process is halted
   and an appropriate exception noted.  When decrypting, the padding
   is ignored.

   The first ciphertext block is decrypted, the decryption output is
   XOR-ed with the Initialization Vector, and the result is the first
   plaintext block.

   For each subsequent block, the ciphertext block is decrypted,
   the decryption output is XOR-ed with the previous ciphertext
   block and the result is the plaintext block.

7.2.  Elements of the DES Privacy Protocol

   This section contains definitions required to realize the privacy
   module defined by this memo.

7.2.1.  Users

   Data en/decryption using this Symmetric Encryption Protocol makes
   use of a defined set of userNames.  For any user on whose behalf
   a message must be en/decrypted at a particular SNMP engine, that
   SNMP engine must have knowledge of that user.  An SNMP engine that
   wishes to communicate with another SNMP engine must also have
   knowledge of a user known to that SNMP engine, including knowledge
   of the applicable attributes of that user.

   A user and its attributes are defined as follows:

   <userName>
     An octet string representing the name of the user.
   <privKey>



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     A user's secret key to be used as input for the DES key and IV.

7.2.2.  authEngineID

   The authEngineID value contained in an authenticated message
   specifies the authoritative SNMP engine for that particular
   message (see the definition of SnmpEngineID in the SNMP
   Architecture document [SNMP-ARCH]).

   The user's (private) privacy key is normally different at
   each authoritative SNMP engine and so the snmpEngineID is used
   to select the proper key for the en/decryption process.

7.2.3.  SNMP Messages Using this Privacy Protocol

   Messages using this privacy protocol carry a privParameters
   field as part of the securityParameters. For this protocol, the
   privParameters field is the serialized octet string representing
   the "salt" that was used to create the IV.

7.2.4.  Services provided by the DES Privacy Module

   This section describes the inputs and outputs that the DES Privacy
   module expects and produces when the User-based Security module
   invokes the DES Privacy module for services.

7.2.4.1.  Services for Encrypting Outgoing Data

   This DES privacy protocol assumes that the selection of the
   privKey is done by the caller and that the caller passes
   the secret key to be used.

   Upon completion the privacy module returns statusInformation
   and, if the encryption process was successful, the encryptedPDU
   and the privParameters encoded as an OCTET STRING.

   The abstract service interface primitives are:

     encryptData(
         encryptKey                  -- secret key for encryption
         dataToEncrypt               -- data to encrypt (scopedPDU)
         )

     returnEncryptedData(
         encryptedData               -- encrypted data (encryptedPDU)
         privParameters              -- filled in by service provider
         statusInformation           -- success or errorIndication
         )

   Where:




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     encryptKey
       The secret key to be used by the encryption algorithm.
     dataToEncrypt
       The data that must be encrypted.

     encryptedData
       The encrypted data upon successful completion.
     privParameters
       The privParameters encoded as an OCTET STRING.
     statusInformation
       An indication of the success or failure of the encryption
       process.  In case of failure, it is an indication of the
       error.

7.2.4.2.  Services for Decrypting Incoming Data

   This DES privacy protocol assumes that the selection of the
   privKey is done by the caller and that the caller passes
   the secret key to be used.

   Upon completion the privacy module returns statusInformation
   and, if the decryption process was successful, the scopedPDU
   in plain text.

   The abstract service interface primitives are:

     decryptData(
         decryptKey                  -- secret key for decryption
         privParameters              -- as received on the wire
         encryptedData               -- encrypted data (encryptedPDU)

     returnDecryptedData(
         decryptedData               -- decrypted data (scopedPDU)
         statusInformation           -- success or errorIndication
         )

   Where:

     decryptKey
       The secret key to be used by the decryption algorithm.
     privParameters
       The "salt" to be used to calculate the IV.
     encryptedData
       The data to be decrypted.

     decryptedData
       The decrypted data.
     statusInformation
       An indication whether the data was successfully decrypted
       and if not an indication of the error.




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7.3.  Elements of Procedure.

   This section describes the procedures for the DES privacy protocol.

7.3.1.  Processing an Outgoing Message

   This section describes the procedure followed by an SNMP engine
   whenever it must encrypt part of an outgoing message using the
   usmDESPrivProtocol.

   1)  The secret (localized) cryptKey is used to construct the DES
       encryption key, the "salt" and the DES pre-IV (as described
       in section 7.1.1.1).

   2)  The privParameters field is set to the serialization according
       to the rules in [RFC1906] of an OCTET STRING representing the
       the "salt" string.

   2)  The scopedPDU is encrypted (as described in section 7.1.1.2)
       and the encrypted data is serialized according to the rules
       in [RFC1906] as an OCTET STRING.

   3)  The the serialized OCTET STRING representing the encrypted
       scopedPDU together with the privParameters and statusInformation
       indicating success is returned to the calling module.

7.3.2.  Processing an Incoming Message

   This section describes the procedure followed by an SNMP engine
   whenever it must decrypt part of an incoming message using the
   usmDESPrivProtocol.

   1)  If the privParameters field is not an 8-byte OCTET STRING,
       then an error indication (decryptionError) is returned to
       the calling module.

   2)  The "salt" is extracted from the privParameters field.

   3)  The secret (localized) cryptKey and the "salt" are then used
       to construct the DES decryption key and pre-IV (as described
       in section 7.1.1.1).

   4)  The encryptedPDU is then decrypted (as described in
       section 7.1.1.3).

   5)  If the encryptedPDU cannot be decrypted, then an error
       indication (decryptionError) is returned to the calling module.

   6)  The decrypted scopedPDU and statusInformation indicating
       success are returned to the calling module.




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8.  Editor's Addresses

   Co-editor   Uri Blumenthal
               IBM T. J. Watson Research
   postal:     30 Saw Mill River Pkwy,
               Hawthorne, NY 10532
               USA
   email:      uri@watson.ibm.com
   phone:      +1-914-784-7064

   Co-editor:  Bert Wijnen
               IBM T. J. Watson Research
   postal:     Schagen 33
               3461 GL Linschoten
               Netherlands
   email:      wijnen@vnet.ibm.com
   phone:      +31-348-432-794

9.  Acknowledgements

This document is based on the recommendations of the SNMP Security and
Administrative Framework Evolution team, comprised of

    David Harrington (Cabletron Systems Inc.)
    Jeff Johnson (Cisco)
    David Levi (SNMP Research Inc.)
    John Linn (Openvision)
    Russ Mundy (Trusted Information Systems) chair
    Shawn Routhier (Epilogue)
    Glenn Waters (Nortel)
    Bert Wijnen (IBM T. J. Watson Research)

Further a lot of "cut and paste" material comes from RFC1910 and from
earlier draft documents from the SNMPv2u and SNMPv2* series.

Further more a special thanks is due to the SNMPv3 WG, specifically:
    ....

















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10.  Security Considerations

10.1.  Recommended Practices

   This section describes practices that contribute to the secure,
   effective operation of the mechanisms defined in this memo.

   - An SNMP engine must discard SNMP Response messages for which
     the msgID component does not correspond to any currently
     outstanding Request message.
     An SNMP Command Generator Application must discard any Response
     PDU for which the request-id component or the represented
     management information does not correspond to any currently
     outstanding Request PDU.

     Although it would be typical for an SNMP engine and an SNMP
     Command Generator Application to do this as a matter of course,
     when using these security protocols it is significant due to
     the possibility of message duplication (malicious or otherwise).

   - An SNMP engine must generate unpredictable msgIDs and an SNMP
     Command Generator or Notification Originator Application must
     generate unpredictable request-ids in authenticated messages in
     order to protect against the possibility of message duplication
     (malicious or otherwise).
     For example, starting operations with a msgID and/or request-id
     value of zero is not a good idea.  Initializing them with an
     unpredictable number (so they do not start out the same after
     each reboot) and then incrementing by one would be acceptable.

   - An SNMP engine should perform time synchronization using
     authenticated messages in order to protect against the
     possibility of message duplication (malicious or otherwise).

   - When sending state altering messages to a managed authoritative
     SNMP engine, a Command Generator Application should delay sending
     successive messages to that managed SNMP engine until a positive
     acknowledgement is received for the previous message or until
     the previous message expires.

     No message ordering is imposed by the SNMP. Messages may be
     received in any order relative to their time of generation and
     each will be processed in the ordered received.  Note that when
     an authenticated message is sent to a managed SNMP engine, it
     will be valid for a period of time of approximately 150 seconds
     under normal circumstances, and is subject to replay during this
     period.  Indeed, an SNMP engine and SNMP Command Generator
     Applications must cope with the loss and re-ordering of messages
     resulting from anomalies in the network as a matter of course.

     However, a managed object, snmpSetSerialNo [RFC1907], is



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     specifically defined for use with SNMP Set operations in order
     to provide a mechanism to ensure that the processing of SNMP
     messages occurs in a specific order.

   - The frequency with which the secrets of a User-based Security
     Model user should be changed is indirectly related to the
     frequency of their use.

     Protecting the secrets from disclosure is critical to the overall
     security of the protocols.  Frequent use of a secret provides a
     continued source of data that may be useful to a cryptanalyst in
     exploiting known or perceived weaknesses in an algorithm.
     Frequent changes to the secret avoid this vulnerability.

     Changing a secret after each use is generally regarded as the
     most secure practice, but a significant amount of overhead may
     be associated with that approach.

     Note, too, in a local environment the threat of disclosure may be
     less significant, and as such the changing of secrets may be less
     frequent.  However, when public data networks are used as the
     communication paths, more caution is prudent.

10.2  Defining Users

   The mechanisms defined in this document employ the notion of users
   on whose behalf messages are sent.  How "users" are defined is
   subject to the security policy of the network administration.
   For example, users could be individuals (e.g., "joe" or "jane"),
   or a particular role (e.g., "operator" or "administrator"), or a
   combination (e.g., "joe-operator", "jane-operator" or "joe-admin").
   Furthermore, a user may be a logical entity, such as an SNMP
   Application or a set of SNMP Applications, acting on behalf of an
   individual or role, or set of individuals, or set of roles,
   including combinations.

   Appendix A describes an algorithm for mapping a user "password" to
   a 16 octet value for use as either a user's authentication key or
   privacy key (or both).  Note however, that using the same password
   (and therefore the same key) for both authentication and privacy
   is very poor security practice and should be strongly discouraged.
   Passwords are often generated, remembered, and input by a human.
   Human-generated passwords may be less than the 16 octets required
   by the authentication and privacy protocols, and brute force
   attacks can be quite easy on a relatively short ASCII character
   set.  Therefore, the algorithm is Appendix A performs a
   transformation on the password.  If the Appendix A algorithm is
   used, SNMP implementations (and SNMP configuration applications)
   must ensure that passwords are at least 8 characters in length.

   Because the Appendix A algorithm uses such passwords (nearly)



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   directly, it is very important that they not be easily guessed.
   It is suggested that they be composed of mixed-case alphanumeric
   and punctuation characters that don't form words or phrases that
   might be found in a dictionary.  Longer passwords improve the
   security of the system.  Users may wish to input multiword
   phrases to make their password string longer while ensuring that
   it is memorable.

   Since it is infeasible for human users to maintain different
   passwords for every SNMP engine, but security requirements
   strongly discourage having the same key for more than one SNMP
   engine, the User-based Security Model employs a compromise
   proposed in [Localized-key].  It derives the user keys for the
   SNMP engines from user's password in such a way that it is
   practically impossible to either determine the user's password,
   or user's key for another SNMP engine from any combination of
   user's keys on SNMP engines.

   Note however, that if user's password is disclosed, key
   localization will not help and network security may be
   compromised in this case.

10.3.  Conformance

   To be termed a "Secure SNMP implementation" based on the
   User-based Security Model, an SNMP implementation MUST:

   - implement one or more Authentication Protocol(s). The MD5
     Authentication Protocol defined in this memo is one such
     protocol.

   - to the maximum extent possible, prohibit access to the
     secret(s) of each user about which it maintains information
     in a Local Configuration Datastore (LCD) under all
     circumstances except as required to generate and/or
     validate SNMP messages with respect to that user.

   - implement the SNMP-USER-BASE-SM-MIB.

   In addition, an authoritative SNMP engine SHOULD [RFC2119] provide
   initial configuration in accordance with Appendix A.1.

   Implementation of a Privacy Protocol (the DES Symmetric Encryption
   Protocol defined in this memo is one such protocol) is optional.










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11.  References

[RFC1902] The SNMPv2 Working Group, Case, J., McCloghrie, K.,
     Rose, M., and S., Waldbusser, "Structure of Management
     Information for Version  2 of the Simple Network Management
     Protocol (SNMPv2)", RFC 1905, January 1996.

[RFC1905] The SNMPv2 Working Group, Case, J., McCloghrie, K.,
     Rose, M., and S., Waldbusser, "Protocol Operations for
     Version 2 of the Simple Network Management Protocol (SNMPv2)",
     RFC 1905, January 1996.

[RFC1906] The SNMPv2 Working Group, Case, J., McCloghrie, K.,
     Rose, M., and S. Waldbusser, "Transport Mappings for
     Version 2 of the Simple Network Management Protocol (SNMPv2)",
     RFC 1906, January 1996.

[RFC1907] The SNMPv2 Working Group, Case, J., McCloghrie, K.,
     Rose, M., and S. Waldbusser, "Management Information Base for
     Version 2 of the Simple Network Management Protocol (SNMPv2)",
     RFC 1907 January 1996.

[RFC1908] The SNMPv2 Working Group, Case, J., McCloghrie, K.,
     Rose, M., and S. Waldbusser, "Coexistence between Version 1
     and Version 2 of the Internet-standard Network Management
     Framework", RFC 1908, January 1996.

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

[SNMP-ARCH] The SNMPv3 Working Group, Harrington, D., Wijnen, B.,
     "An Architecture for describing Internet Management Frameworks",
     draft-ietf-snmpv3-next-gen-arch-03.txt, July 1997.

[SNMP-v3MP] The SNMPv3 Working Group, Wijnen, B., Harrington, D.,
     Case, J., "Message Processing Model for version 3 of the Simple
     Network Management Protocol (SNMPv3)",
     draft-ietf-snmpv3-mpc-03.txt, July 1997.

[SNMP-ACM] The SNMPv3 Working Group, Wijnen, B., Harrington, D.,
     "View-based Access Control Model for the Simple Network
     Management Protocol (SNMP)",
     draft-ietf-snmpv3-acm-01.txt, July 1997.

[Localized-Key] U. Blumenthal, N. C. Hien, B. Wijnen
     "Key Derivation for Network Management Applications"
     IEEE Network Magazine, April/May issue, 1997.

[KEYED-MD5] Krawczyk, H.,
     "Keyed-MD5 for Message Authentication",
     Work in Progress, IBM, June 1995.



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[MD5] Rivest, R.,  "Message Digest Algorithm MD5",
     RFC 1321, April 1992.

[DES-NIST] Data Encryption Standard, National Institute of Standards
     and Technology.  Federal Information Processing Standard (FIPS)
     Publication 46-1.  Supersedes FIPS Publication 46, (January, 1977;
     reaffirmed January, 1988).

[DES-ANSI] Data Encryption Algorithm, American National Standards
     Institute.  ANSI X3.92-1981, (December, 1980).

[DESO-NIST] DES Modes of Operation, National Institute of Standards and
     Technology.  Federal Information Processing Standard (FIPS)
     Publication 81, (December, 1980).

[DESO-ANSI] Data Encryption Algorithm - Modes of Operation, American
     National Standards Institute.  ANSI X3.106-1983, (May 1983).

[DESG-NIST] Guidelines for Implementing and Using the NBS Data
     Encryption Standard, National Institute of Standards and
     Technology.  Federal Information Processing Standard (FIPS)
     Publication 74, (April, 1981).

[DEST-NIST] Validating the Correctness of Hardware Implementations of
     the NBS Data Encryption Standard, National Institute of Standards
     and Technology.  Special Publication 500-20.

[DESM-NIST] Maintenance Testing for the Data Encryption Standard,
     National Institute of Standards and Technology.
     Special Publication 500-61, (August, 1980).























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APPENDIX A - Installation

A.1.  SNMP engine Installation Parameters

During installation, an authoritative SNMP engine SHOULD (in the
meaning as defined in [RFC2119]) be configured with several initial
parameters.  These include:

(1) A security posture

    The choice of security posture determines if initial configuration
    is implemented and if so how.  One of three possible choices
    is selected:

          minimum-secure,
          semi-secure,
          very-secure (i.e. no-initial-configuration)

    In the case of a very-secure posture, there is no initial
    configuration, and so the following steps are irrelevant.

(2) one or more secrets

    These are the authentication/privacy secrets for the first user
    to be configured.

    One way to accomplish this is to have the installer enter a
    "password" for each required secret. The password is then
    algorithmically converted into the required secret by:

    - forming a string of length 1,048,576 octets by repeating the
      value of the password as often as necessary, truncating
      accordingly, and using the resulting string as the input to
      the MD5 algorithm [MD5].  The resulting digest, termed
      "digest1", is used in the next step.

    - a second string of length 44 octets is formed by concatenating
      digest1, the SNMPv3 engine's snmpEngineID value, and digest1.
      This string is used as input to the MD5 algorithm [MD5].

      The resulting digest is the required secret (see Appendix A.2).













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    With these configured parameters, the SNMP engine instantiates
    the following usmUserEntry in the usmUserTable:

                              no privacy support  privacy support
                              ------------------  ---------------
     usmUserEngineID          localEngineID       localEngineID
     usmUserName              "initial"           "initial"
     usmUserSecurityName      "initial"           "initial"
     usmUserCloneFrom         ZeroDotZero         ZeroDotZero
     usmUserAuthProtocol      usmMD5AuthProtocol  usmMD5AuthProtocol
     usmUserAuthKeyChange     ""                  ""
     usmUserOwnAuthKeyChange  ""                  ""
     usmUserPrivProtocol      none                usmDESPrivProtocol
     usmUserPrivKeyChange     ""                  ""
     usmUserOwnPrivKeyChange  ""                  ""
     usmUserPublic            ""                  ""
     usmUserStorageType       anyValidStorageType anyValidStorageType
     usmUserStatus            active              active


A.2.  Password to Key Algorithm

   The following code fragment (section A.2.1) demonstrates the
   password to key algorithm which can be used when mapping a password
   to an authentication or privacy key. The calls to MD5 are as
   documented in [RFC1321].

   An example of the results of a correct implementation is provided
   (section A.2.2) whihc an implementer can use to check if his
   implementation produces the same result.
























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A.2.1.  Password to Key Sample Code

void password_to_key(
   u_char *password,    /* IN */
   u_int   passwordlen, /* IN */
   u_char *engineID,    /* IN  - pointer to snmpEngineID  */
   u_int   engineLength /* IN  - length of snmpEngineID */
   u_char *key)         /* OUT - pointer to caller 16-byte buffer */
{
   MD5_CTX     MD;
   u_char     *cp, password_buf[64];
   u_long      password_index = 0;
   u_long      count = 0, i;

   MD5Init (&MD);   /* initialize MD5 */

   /**********************************************/
   /* Use while loop until we've done 1 Megabyte */
   /**********************************************/
   while (count < 1048576) {
      cp = password_buf;
      for (i = 0; i < 64; i++) {
          /*************************************************/
          /* Take the next byte of the password, wrapping  */
          /* to the beginning of the password as necessary.*/
          /*************************************************/
          *cp++ = password[password_index++ % passwordlen];
      }
      MD5Update (&MD, password_buf, 64);
      count += 64;
   }
   MD5Final (key, &MD);          /* tell MD5 we're done */

   /*****************************************************/
   /* Now localize the key with the engineID and pass   */
   /* through MD5 to produce final key                  */
   /* May want to ensure that engineLength <= 32,       */
   /* otherwise need to use a buffer larger than 64     */
   /*****************************************************/
   memcpy(password_buf, key, 16);
   memcpy(password_buf+16, engineID, engineLength);
   memcpy(password_buf+engineLength, key, 16);

   MD5Init(&MD);
   MD5Update(&MD, password_buf, 32+engineLength);
   MD5Final(key, &MD);

   return;
}





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A.3.  Password to Key Sample Results

   The following shows a sample output of the password to key
   algorithm.

   With a password of "maplesyrup" the output of the password to key
   algorithm before the key is localized with the SNMP engine's
   snmpEngineID is:

      '9f af 32 83 88 4e 92 83 4e bc 98 47 d8 ed d9 63'H

   After the intermediate key (shown above) is localized with the
   snmpEngineID value of:

      '00 00 00 00 00 00 00 00 00 00 00 02'H

   the final output of the password to key algorithm is:

      '52 6f 5e ed 9f cc e2 6f 89 64 c2 93 07 87 d8 2b'H



































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A.4.  Sample encoding of securityParameters

   The securityParameters in an SNMP message are represented as
   an OCTET STRING. This OCTET STRING should be considered opaque
   outside a specific Security Model.

   The User-based Security Model defines the contents of the OCTET
   STRING as a SEQUENCE (see section 2.4).

   Given these two properties, the following is an example of the
   securityParameters for the User-based Security Model, encoded
   as an OCTET STRING:

     04 <length>
     30 <length>
     04 <length> <authEngineID>
     02 <length> <authEngineBoots>
     02 <length> <authEngineTime>
     04 <length> <userName>
     04 10       <MD5-digest>
     04 08       <salt>

   Here is the example once more. but now with real values (except
   for the digest in authParameters and the salt in privParameters,
   which depend on variable data that we have not defined here):

     Hex Data                         Description
     --------------------------  --------------------------------
     04 39                       OCTET STRING, length 57
     30 37                       SEQUENCE, length 55
     04 0c 00000002 00000000     authEngineID:    IBM, IP, 9.132.3.1
           09840301
     02 01 01                    authEngineBoots: 1
     02 02 0101                  authEngineTime:  257
     04 04 62657274              userName:        bert
     04 10 01234567 89abcdef     authParameters:  sample value
           fedcba98 76543210
     04 08 01234567 89abcdef     privParameters:  sample value
















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Table of Contents

0.  Issues and Change Log                                              2
0.1.  Current Open Issues                                              2
0.2.  Change Log                                                       2
1.  Introduction                                                       5
1.1.  Threats                                                          5
1.2.  Goals and Constraints                                            6
1.3.  Security Services                                                7
1.4.  Module Organization                                              8
1.4.1.  Timeliness Module                                              8
1.4.2.  Authentication Protocol                                        9
1.4.3.  Privacy Protocol                                               9
1.5.  Protection against Message Replay, Delay and Redirection         9
1.5.1.  Authoritative SNMP engine                                      9
1.5.2.  Mechanisms                                                     9
2.  Elements of the Model                                             12
2.1.  User-based Security Model Users                                 12
2.2.  Replay Protection                                               13
2.2.1.  authEngineID                                                  13
2.2.2.  authEngineBoots and authEngineTime                            13
2.2.3.  Time Window                                                   14
2.3.  Time Synchronization                                            14
2.4.  SNMP Messages Using this Security Model                         16
2.5.  Services provided by the User-based Security Model              16
2.5.1.  Services for Generating an Outgoing SNMP Message              17
2.5.2.  Services for Processing an Incoming SNMP Message              19
3.  Elements of Procedure                                             22
3.1.  Generating an Outgoing SNMP Message                             22
3.2.  Processing an Incoming SNMP Message                             25
4.  Discovery                                                         31
5.  Definitions                                                       32
6.  MD5 Authentication Protocol                                       44
6.1.  Mechanisms                                                      44
6.1.1.  Digest Authentication Protocol                                44
6.2.  Elements of the Digest Authentication Protocol                  45
6.2.1.  Users                                                         45
6.2.2.  authEngineID                                                  45
6.2.3.  SNMP Messages Using this Authentication Protocol              45
6.2.4.  Services provided by the MD5 Authentication Module            46
6.2.4.1.  Services for Generating an Outgoing SNMP Message            46
6.2.4.2.  Services for Processing an Incoming SNMP Message            46
6.3.  Elements of Procedure                                           48
6.3.1.  Processing an Outgoing Message                                48
6.3.2.  Processing an Incoming Message                                48
7.  DES Privacy Protocol                                              50
7.1.  Mechanisms                                                      50
7.1.1.  Symmetric Encryption Protocol                                 50
7.1.1.1.  DES key and Initialization Vector.                          51
7.1.1.2.  Data Encryption.                                            51
7.1.1.3.  Data Decryption                                             52
7.2.  Elements of the DES Privacy Protocol                            52
7.2.1.  Users                                                         52



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7.2.2.  authEngineID                                                  53
7.2.3.  SNMP Messages Using this Privacy Protocol                     53
7.2.4.  Services provided by the DES Privacy Module                   53
7.2.4.1.  Services for Encrypting Outgoing Data                       53
7.2.4.2.  Services for Decrypting Incoming Data                       54
7.3.  Elements of Procedure.                                          55
7.3.1.  Processing an Outgoing Message                                55
7.3.2.  Processing an Incoming Message                                55
8.  Editor's Addresses                                                56
9.  Acknowledgements                                                  56
A.1.  SNMP engine Installation Parameters                             62
A.2.  Password to Key Algorithm                                       63
A.2.1.  Password to Key Sample Code                                   64
A.3.  Password to Key Sample Results                                  65
A.4.  Sample encoding of securityParameters                           66







































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