Internet Info 1997 December/Internet_Info_CD-ROM_Walnut_Creek_December_1997.iso/drafts/draft_ietf_q_t/draft-ietf-snmpv3-usec-01.txt

Text File | 1997-06-19 | 118KB | 3,319 lines

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

                             18 June 1997


                            U. Blumenthal
                       IBM T. J. Watson Research
                           [e-mail]

                              B. Wijnen
                       IBM T. J. Watson Research
                          [e-mail]


                    <draft-ietf-snmpv3-usec-01.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 (USEC) for SNMP
version 3 for use in the SNMP architecture [SNMP-ARCH].  This
document 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.

0.1 Issues
     - Do we indeed want to move all STATS counters to MPC, we
       have assumed so for now.
     - Do we need to do group mapping here and pass it back to MPC
       we have assumed so for now... but other documents do not pass
       groupName around.



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     - Do we want to check reportableFlag to determine if caching
       of securityData is needed or not.

0.2 Change Log

   [version 1.2]
     - changed (simplified) time sync in section 3 item 7.
     - added usecUserMiId
     - cleaned up text
     - defined IV "salt" generation
     - removed Statistics counters (now in MPC) and reportPDU
       generation (now in MPC)
     - Removed auth and des MIBs which are now merged into USEC MIB
     - specified where cachedSecurityData needs to be discarded
     - added abtract 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.

   [version 1.1]
     - removed <securityCookie>.
     - added <securityIdentity>, <securityCachedData>.
     - added abstract function interface description of
       inter-module communications.
     - modified IV generation process to accomodate 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 timestamp is ahead of our notion of their clock).

   [version 1.0]
     - first version posted to the v3editors 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
   is composed of multiple subsystems:
     1) a message processing and control subsystem,
     2) a security subsystem,
     3) an access control subsystem, and
     4) orangelets.

   It is important to understand the SNMP architecture and the
   terminology of the architecture to understand where the 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 [SNMPv3-USEC] 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.
   So the description of Keyed-MD5 and CBC-DES are in separate sections.
   That way it shows that they are supposed to be self-contained
   pieces that 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 SNMPv3 security model
   should provide protection are:

   - Modification of Information
     The modification threat is the danger that some unauthorized entity
     may alter in-transit SNMPv3 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
     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.



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   Two secondary threats are also identified.  The security protocols
   defined in this memo provide 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 SNMPv3 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 SNMPv3 security protocol need
   not protect against.  The security protocols defined in this memo do
   not provide protection against:

   - Denial of Service
     An SNMPv3 security protocol need 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
     In addition, an SNMPv3 security protocol need not attempt to
     address traffic analysis attacks.  Indeed, many traffic patterns
     are predictable - agents may be managed on a regular basis by a
     relatively small number of management stations - and therefore
     there is no significant advantage afforded by protecting against
     traffic analysis.

1.2.  Goals and Constraints

   Based on the foregoing account of threats in the SNMP network
   management environment, the goals of this SNMPv3 security model are
   as follows.

   1) The protocol should provide for verification that each received
      SNMPv3 message has not been modified during its transmission
      through the network in such a way that an unauthorized management
      operation might result.

   2) The protocol should provide for verification of the identity of



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      the user on whose behalf a received SNMPv3 message claims to have
      been generated.

   3) The protocol should provide for detection of received SNMPv3
      messages, which request or contain management information, whose
      time of generation was not recent.

   4) The protocol should provide, when necessary, that the contents of
      each received SNMPv3 message are protected from disclosure.

   In addition to the principal goal of supporting secure network
   management, the design of this SNMPv3 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 an SNMPv3
   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.

   For the protocols specified in this memo, it is not possible to
   assure the specific originator of a received SNMPv3 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



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   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.  Implementation Organization

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

   - The timeliness module must provide for:

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

   - The authentication module must provide for:

     - Data Integrity,

     - Data Origin Authentication

   - The privacy module must provide for

     - Protection against disclosure of the message payload.

   The timeliness module is fixed for this 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 time values in an SNMPv3
   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 the
   time 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



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   authentication protocols may be defined as new needs arise.

   This User-based Security model prescribes that 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
   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.

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

   This 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 engine.  For messages with a GET, GETNEXT,
   GETBULK, SET or INFORM request as the payload, the receiver of such
   messages is authoritative.  For messages with a SNMPv2-TRAP,
   RESPONSE  or REPORT as the payload, the sender is authoritative.

1.5.2   The following mechanisms are used:

   - To protect against the threat of message delay or replay (to an
     extent greater than can occur through normal operation), a set of
     time (at the authoritative source) indicators and a request-id are
     included in each message generated.  An SNMPv3 engine evaluates
     the time indicators to determine if a received message is recent.
     An SNMPv3 engine may evaluate the time 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 SNMPv3 engine
     uses received authentic messages to advance its notion of time at
     the remote authoritative source.  An SNMPv3 engine also evaluates
     the request-id in received Response messages and discards messages
     which do not correspond to outstanding requests.

     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



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     receiver) when the receiver has 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
     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 time (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 SNMPv3 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 SNMPv3 engine cannot be
     replayed to/as-if-from another SNMPv3 engine.

     Included in each message is an identifier unique to the SNMPv3
     engine associated with the sender or intended recipient of the
     message.  Also, each message containing a Response PDU contains a
     request-id which associates the message to a recently generated
     request.

     A Report message sent by one SNMPv3 engine to a second SNMPv3
     engine can potentially be replayed to another SNMPv3 engine.
     However, Report messages do not request or contain 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 time (at the authoritative source) by less than the
     correct amount.

   - detecting messages which were not recently generated.

     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
     request-id; if the request-id does not match that of a recently
     generated request, then the message is not considered to be
     authentic.

     A Report message sent by an SNMPv3 engine can potentially be
     replayed at a later time to an SNMPv3 engine which has not
     recently communicated with that source engine.  However, Report
     messages do not request or contain management information, and



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     thus, goal #3 in Section 1.2 above is met; further, Report
     messages can at most cause the receiver to advance its notion of
     time (at the authoritative source) by less than the correct
     amount.

   This memo allows the same user to be defined on multiple SNMPv3
   engines.  Each SNMPv3 engine maintains a value, snmpEngineID,
   which uniquely identifies the engine.  This value is included in
   each message sent to/from the engine that is authoritative (see
   section 1.5.1).  On receipt of a message, an authoritative engine
   checks the value to ensure it is the intended recipient, and a
   non-authoritative engine uses the value to ensure that the message
   is processed using the correct state information.

   Each SNMPv3 engine maintains two values, engineBoots and engineTime,
   which taken together provide an indication of time at that engine.
   Both of these values are included in an authenticated message sent
   to/received from that engine. On receipt, the values are checked to
   ensure that the indicated time 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 SNMPv3 engine to generate a message which an authoritative
   engine will accept as authentic, and to verify that a message
   received from that authoritative engine is authentic, such an engine
   must first achieve time synchronization with the authoritative
   engine.



























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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.  SNMPv3 Users

   Management operations using this security model make use of a defined
   set of user identities.  For any SNMPv3 user on whose behalf
   management operations are authorized at a particular SNMPv3 engine,
   that engine must have knowledge of that user.  An SNMPv3 engine that
   wishes to communicate with another SNMPv3 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.

   <miId>
     A human-readable string representing a (security) model
     independent identity for this user.

   <groupName>
     A string representing the group that the user belongs to.

   <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 engines. Not visible via
     remote access.

   <authKeyChange>
     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.




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   <privKey>
     If messages sent on behalf of this user can be en/decrypted, the
     (private) privacy key for use with the privacy protocol. Note that
     a user's privacy key will normally be different at different
     authoritative engines. Not visible via remote access.

   <privKeyChange>
     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 SNMPv3 engine maintains three objects:

   - snmpEngineID, which is an identifier unique among all SNMPv3
     engines in (at least) an administrative domain;

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

   - engineTime, which is the number of seconds since engineBoots was
     last incremented.

   Each SNMPv3 engine is always authoritative with respect to these
   objects in its own engine.  It is the responsibility of a non-
   authoritative SNMPv3 engine to synchronize with the authoritative
   engine, as appropriate.

   An authoritative SNMPv3 engine is required to maintain the values of
   its snmpEngineID and engineBoots in non-volatile storage.

2.2.1.  snmpEngineID

   The engineID value contained in an authenticated message is used to
   defeat attacks in which messages from one engine to another engine
   are replayed to a different engine.

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

2.2.2.  engineBoots and engineTime

   The engineBoots and engineTime values contained in an authenticated
   message are used to defeat attacks in which messages are replayed
   when they are no longer valid.  Through use of engineBoots and
   engineTime, there is no requirement for an SNMPv3 engine to have a



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   non-volatile clock which ticks (i.e., increases with the passage of
   time) even when the engine is powered off.  Rather, each time an
   SNMPv3 engine re-boots, it retrieves, increments, and then stores
   engineBoots in non-volatile storage, and resets engineTime to zero.

   When an SNMPv3 engine is first installed, it sets its local values
   of engineBoots and engineTime to zero.  If engineTime ever
   reaches its maximum value (2147483647), then engineBoots is
   incremented as if the engine has re-booted and engineTime is reset to
   zero and starts incrementing again.

   Each time an authoritative SNMPv3 engine re-boots, any SNMPv3 engines
   holding that authoritative engine's values of engineBoots and
   engineTime need to re-synchronize prior to sending correctly
   authenticated messages to that authoritative 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 engine, when sent by an authoritative engine which has
   re-booted since the receiving engine last (re-)synchronized.

   If an authoritative SNMPv3 engine is ever unable to determine its
   latest engineBoots value, then it must set its engineBoots value to
   0xffffffff.

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

   In order to reset an engine whose engineBoots 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 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 engine (see
   section 5.1.1) in order to proceed with authentic communications,
   has occurred when the non-authoritative engine has obtained local
   values of engineBoots and engineTime from the authoritative engine
   that are within the authoritative engine's time window.  To remain
   synchronized, the local values must remain within the authoritative
   engine's time window and thus must be kept loosely synchronized
   with the values stored at the authoritative engine.



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   In addition to keeping a local version of engineBoots and engineTime,
   a non-authoritative engine must also keep one other local variable,
   latestReceivedEngineTime.  This value records the highest value of
   engineTime that was received by the non-authoritative engine from
   the authoritative engine and is used to eliminate the possibility
   of replaying messages that would prevent the non-authoritative
   engine's notion of the engineTime from advancing.

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

2.4.  SNMPv3 Messages Using this Model

   The syntax of an SNMPv3 message using this security model adheres
   to the message format defined in the SNMP Architecture document
   [SNMP-ARCH]. 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 parameters
              engineID
                  OCTET STRING (SIZE(12)),
              engineBoots
                  Unsigned32 (0..4294967295),
              engineTime
                  Unsigned32 (0..2147483647),
              userName
                  OCTET STRING (SIZE(1..16)),
              authParameters
                  OCTET STRING,
              privParameters
                  OCTET STRING,
          }
      END

   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 usecUserTable).

   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 usecUserTable).



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2.5  Input and Output of the User-based Security Module

   This section describes the inputs and outputs that the User-based
   Security module expects and produces when the Message Processing
   and Control module (MPC) invokes the User-base Security module for
   services.

2.5.1 Input and Output when generating an SNMPv3 Message

   When the Message Processing and Control module (MPC) invokes the
   User-based Security module to secure an outgoing SNMPv3 message,
   there are two possibilities:

   a) A new request is generated.  The abstract service interface is:

        generateRequestMsg(version, msgID, mms, msgFlags,
                           securityModel, securityParameters,
                           LoS, miId, engineID, scopedPDU)

   b) A response is generated.  The abtract service interface is:

        generateResponseMsg(version, msgID, mms, msgFlags,
                            securityModel, securityParameters,
                            scopedPDU, cachedSecurityDataReference)

   Where:

     version
      This is the version number for the SNMP message.
      This data is not used by the USEC module.
      It is part of the globalData of the message.
     msgID
      This is the msgID to be generated.
      This data is not used by the USEC module.
      It is part of the globalData of the message.
     mms
      This is the maximum message size.
      This data is not used by the USEC module.
      It is part of the globalData of the message.
     msgFlags
      This is the field containing the msgFlags.
      This data is not used by the USEC module.
      It is part of the globalData of the message.
      It should be consistent with the LoS that is passed.
     securityModel
      This is the securityModel in use. Should be the USEC model.
      This data is not used by the USEC module.
      It is part of the globalData of the message.
     securityParameters
      These are the security parameters. They will be filled in



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      by the User-based Security module.
     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.
     scopedPDU
      this is the message payload. The data is opaque as far as the
      User-based Security module is concerned.
     miId
      this is the (security) model independent Identifier.
      Together with the engineID it identifies a row in the
      usecUserTable that is to be used for securing the message.
     engineID
      the engineID of the authoritative SNMP engine to which the
      request is to be sent.
     cachedSecurityDataReference
      A handle/reference to cached security data to be used when
      securing an outgoing response. This is the handle/reference
      that was generated by the USEC module when the incoming
      request was processed.

   Upon completion of the process, the User-based Security module
   returns either and error indication or the completed message
   with privacy and authentication applied if such was requested
   by the Level of Security (LoS) flags passed.

   The abstract service interface is:

      returnGeneratedMsg(wholeMsg, wholeMsgLen, statusCode)

   Where:
     wholeMsg
      this is fully encoded and secured message ready to be sent on
      the wire.
     wholeMsgLen
      this is the length of the encoded and secured message wholeMsg.
     statusCode
      this is the indicator of whether the encoding and securing of
      the message was successful, and if not it is an indication of
      the problem.

2.5.2 Input and Output when receiving an SNMPv3 Message

   The Message Processing and Control module (MPC) invokes the
   User-based Security module to verify proper security of an incoming
   SNMPv3 message. The abstract service interface is:

      processMsg(version, msgID, mms, msgFlags,
                 securityModel, securityParameters,
                 LoS, wholeMsg, wholeMsgLen)




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   Where:

     version
      This is the version number for the SNMP message.
      This data is not used by the USEC module.
      It is part of the globalData of the message.
     msgID
      This is the msgID to be generated.
      This data is not used by the USEC module.
      It is part of the globalData of the message.
     mms
      This is the maximum message size.
      This data is not used by the USEC module.
      It is part of the globalData of the message.
     msgFlags
      This is the field containing the msgFlags.
      This data is not used by the USEC module.
      It is part of the globalData of the message.
      It should be consistent with the LoS that is passed.
     securityModel
      This is the securityModel in use. Should be the USEC model.
      This data is not used by the USEC module.
      It is part of the globalData of the message.
     securityParameters
      These are the security parameters. They will be filled in
      by the User-based Security module.
     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
      this is the complete message as it was received by the Message
      Processing and Control module (MPC).
     wholeMsgLen
      this is the length of the wholeMsg as received on the wire.

   Upon completion of the process, the User-based Security module
   returns a statusCode and in case of success authenticated and
   decrypted data. The abstract service interface is:

      returnMsg(miId, groupName, cachedSecurityDataReference,
                scopedPDUmms, scopedPDU, statusCode)

   Where:

     miId
      this is an Security Model-independent Identifier that identifies
      an entry in the usecUserTable. It is to be used later when a
      response message must be secured.
     groupName
      this is the group to which the user belongs. The User-based



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      Security module retrieves this information from the usecUserTable.
     cachedSecurityDataReference
      cached security data to be used when securing a possible outgoing
      response to this request.  Will have to be released explicitly
      by the MPC or the application.
     scopedPDUmms
      this is the maximum message size that a possible response PDU
      may use. The User-based Security module calculates this size such
      that there is always space available for any security parameters
      that need to be added to the response message.
     scopedPDU
      this is the message payload.  The data is opaque as far as the
      User-based Security module is concerned.  But if the data was
      encrypted because privacy protection was in effect, then upon
      return from the User-based Security module the data will have
      been decrypted.
     statusCode
      this is an indicator of whether the message was parsed,
      authenticated and possibly decrypted successfully. If
      it was not - it indicates what the problem was.


































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3.  Elements of Procedure

   This section describes the security related procedures followed by
   an SNMPv3 engine when processing SNMPv3 messages according to the
   User-based Security model.

3.1.  Processing an Outgoing Message

   This section describes the procedure followed by an SNMPv3 engine
   whenever it generates a message containing a management operation
   (either a request, a response, a notification, or a report) on
   behalf of a user, with a particular Level of Security (LoS).

   1)  - If any cachedSecurityDataReference is passed, then
         information concerning the user is extracted from the
         cachedSecurityData. The cachedSecurityData can now be
         discarded.
       - Otherwise, based on the miId, information concerning the user
         at the destination engineID is extracted from the Local
         (security) Configuration Datastore (LCD, usecUserTable).
         If information about the user is absent from the LCD,
         then an error indication (unknownSecurityIdentity) 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)  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.
       The abstract service interface is:

           encryptMsg(cryptKey, scopedPDU)

         Where:

         cryptKey
           The user's usecUserPrivKey. This is the secret key
           that can be used by the encryption algorithm.
         scopedPDU
           The data to be encrypted.



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       Upon completion the privacy module returns:

           returnEncryptedMsg(encryptedPDU, privParameters, statusCode)

         encryptedPDU
           The encrypted scopedPDU (encoded as an octet string).
         privParameters
           The privacy parameters (encoded as an octet string) that
           need to be sent in the outgoing message.
         statusCode
           The indicator of whether the PDU was encrypted successfully
           and if not, it indicates what went wrong.

       If an error indication is returned by the privacy module then
       the message cannot be sent and the error indication 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.

   5)  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 into the privParameters field of the
       securityParameters and the scopedPDU serves as the payload of
       the message being prepared.

   6)  The engineID is encoded as an octet string into the <engineID>
       field of the securityParameters.

   7)  If the Level of Security (LoS) specifies that the message is to
       be authenticated, then the current values of engineBoots, and
       engineTime corresponding to engineID from the LCD are used.
       Otherwise, a zero value is used for engineBoots and engineTime.
       The values are encoded as Unsigned32 into the engineBoots and
       engineTime fields of the securityParameters.

   8)  The userName is encoded as an octet string into the userName
       field of the securityParameters.

   9)  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.  The abstract service interface is:

            authMsg(authKey, wholeMsg)

          authKey
            The user's usecUserAuthKey. This is the secret key



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            that can be used by the authentication algorithm.
          wholeMsg
            the message to be authenticated.

       Upon completion the authentication module returns:

            returnAuthMsg(wholeMsg, statusCode)

          wholeMsg
            Same as in input, but with authParameters properly filled.
          statusCode
            The indicator of whether the message was successfully
            processed by the authentication module.

       If an error indication is returned by the authentication module,
       then the message cannot be sent and the error indication is
       returned to the calling module.

   10) 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.

   11) The completed message is returned to the calling module with
       the statusCode set to success.

3.2.  Processing an Incoming Message

   This section describes the procedure followed by an SNMPv3 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
       formated according to the securityParameters defined in section
       2.4, then the snmpInASNParseErrs counter [RFC1907] is
       incremented, and an error indication (ASNParseError) is returned
       to the calling module.

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

   3)  If the engineID field contained in the securityParameters is
       unknown then:

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

       - an error indication (unknownEngineID) is returned to the
         calling module.




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   4)  Information about the value of the userName and engineID
       fields is extracted from the Local (security) Configuration
       Database (LCD, usecUserTable).  If no information is
       available for this user, then an error indication
       (unknownSecurityIdentity) 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 and an error indication (unsupportedLoS) 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. The abstract service interface is:

           authIncomingMsg(authKey, authParameters, wholeMsg)

         authKey
           The user's (secret) usecUserAuthKey
         authParameters
           the authParameters from the incoming message.
         wholeMsg
           the message to be authenticated.

       The authentication module returns:

           returnAuthIncomingMsg(wholeMsg, statusCode)

       If the message is not authentic according to the authentication
       protocol module (i.e. it returns an error indication), then the
       error indication is returned to the calling module.

       Otherwise, the authenticated wholeMsg is used for further
       processing.

   7)  If the LoS field indicates an authenticated message, then
       the local values of engineBoots and engineTime corresponding to
       the value of the engineID field are extracted from the
       Local (security) Configuration Database (LCD).

       a) If the engineID value is the same as the snmpEngineID of
          the processing SNMPv3 engine (meaning that this is the
          authoritative 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 engineBoots is 0xffffffff;

           - the engineBoots field differs from the local value of



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             engineBoots; or,

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

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

       b) If the engineID value is not the same as the snmpEngineID of
          the processing SNMPv3 engine (meaning that this engine is not
          the authoritative engine), then:

          - if at least one of the following conditions is true:

            - the engineBoots field is greater than the local value
              of engineBoots; or,

            - the engineBoots field is equal to the local value of
              engineBoots and the engineTime field is greater than
              the value of latestReceivedEngineTime,

            then the LCD entry corresponding to the value of the
            engineID field is updated, by setting the local value of
            engineBoots from the engineBoots field, the local value
            latestReceivedEngineTime from the engineTime field, and
            the local value of engineTime from the engineTime field.

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

            - the local value of engineBoots is 0xffffffff;

            - the engineBoots field is less than the local value of
              engineBoots; or,

            - the engineBoots field is equal to the local value of
              engineBoots and the engineTime field is more than 150
              seconds less than the local notion of engineTime.

            If the message is considered to be outside of the Time
            Window then an error indication (notInTimeWindow) is
            returned to the calling module;
            however, time synchronization procedures may be invoked.
            Note that this procedure allows for engineBoots in the
            message to be greater than the local value of engineBoots
            to allow for received messages to be accepted as authentic
            when received from an authoritative SNMPv3 engine that
            has re-booted since the receiving SNMPv3 engine last
            (re-)synchronized.




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   8)  If the LoS field indicates that the message was protected from
       disclosure, then the octet sequence representing the scopedPDU
       is decrypted according to the user's privacy protocol to obtain
       a serialized scopedPDUs value.  Otherwise the data component is
       assumed to directly contain the scopedPDUs value. To do the
       decryption, a call is made to the privacy module that implements
       the user's privacy protocol.  The abstract service interface is:

           decryptMsg(cryptKey, privParameters, encryptedPDU)

         cryptKey
           The user's secret usecUserPrivKey
         privParameters
           The privParameters field from the securityParameters from
           the incoming message.
         encryptedPDU
           the data to be decrypted

       The privacy module returns:

           returnDecryptedMsg(scopedPDU, statusCode)

         scopedPDU
           The decrypted scopedPDU.
         statusCode
           The indicator whether the message was successfully decrypted.

       If an error indication is returned by the privacy module, then
       the error indication is returned to the calling module.

   9)  The scopedPDU-MMS is calculated.

   10) The groupName is retrieved from the usecUserTable

   11) The miId is retrieved from the usecUserTable

   12) The securityData is cached, so that a possible response to
       this message can use the same authentication and privacy
       secrets.  Information to be saved/cached is as follows:

          usecUserName,
          usecUserAuthProto, usecUserAuthKey,
          usecUserPrivProto, usecUserPrivKey

-- Editor's note:
   If we assume SNMPv3, then we could check the reportableFlag and if
   it is not set, then we do not need to cache any security data
   because then there is no response possible. Do we want to do that?
-- End Editor's note.

   13) The statusCode is set to success and a return is made to the



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       calling module according to this abstract service interface:

          returnMsg(miId, groupName, cachedSecurityDataReference,
                    scopedPDUmms, scopedPDU, statusCode)


















































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4.  Discovery

   This security model requires that a discovery process obtains
   sufficient information about other SNMP engines in order to
   communicate with them.  Discovery requires the SNMP manager to
   learn the engine's snmpEngineID value before communication may
   proceed.  This may be accomplished by formulating a get-request
   communication with the LoS set to noAuth/noPriv, the userName set
   to "public", the snmpEngineID set to all zeros (binary), and the
   varBindList left empty.  The response to this message will be a
   report PDU that contains the snmpEngineID within the
   securityParameters field (and containing the snmpUnknownEngineIDs
   counter in the varBindList).
   If authenticated communication is required then the discovery
   process may invoke the procedure described in Section 2.3 to
   synchronize the timers.






































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5.  Definitions

SNMP-USEC-MIB DEFINITIONS ::= BEGIN

IMPORTS
    MODULE-IDENTITY, OBJECT-TYPE, snmpModules  FROM SNMPv2-SMI
    TEXTUAL-CONVENTION, TestAndIncr,
    RowStatus, StorageType                     FROM SNMPv2-TC
    MODULE-COMPLIANCE, OBJECT-GROUP            FROM SNMPv2-CONF,
    SnmpAdminString, SnmpLoS, SnmpEngineID,
    SnmpSecurityModel,
    imfAuthMD5Protocol, imfNoPrivProtocol      FROM IMF-MIB;

snmpUsecMIB MODULE-IDENTITY
    LAST-UPDATED "9706180000Z"     -- 18 June 1997, midnight
    ORGANIZATION "SNMPv3 Working Group"
    CONTACT-INFO "WG-email:   [e-mail]
                  Subscribe:  [e-mail]
                              In msg body:  subscribe snmpv3

                  Chair:      Russ Mundy
                              Trusted Information Systems
                  postal:     3060 Washington Rd
                              Glenwood MD 21738
                  email:      [e-mail]
                  phone:      [phone]

                  Co-editor   Uri Blumenthal
                              IBM T. J. Watson Research
                  postal:     30 Saw Mill River Pkwy,
                              Hawthorne, NY 10532
                              USA
                  email:      [e-mail]
                  phone:      [phone]

                  Co-editor:  Bert Wijnen
                              IBM T. J. Watson Research
                  postal:     Schagen 33
                              3461 GL Linschoten
                              Netherlands
                  email:      [e-mail]
                  phone:      [phone]
                 "

    DESCRIPTION  "The management information definitions for the
                  SNMPv3 User-based Security model.
                 "
    ::= { snmpModules 99 }  -- to be assigned

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




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snmpUsecAdmin           OBJECT IDENTIFIER ::= { snmpUsecMIB 1 }
snmpUsecMIBObjects      OBJECT IDENTIFIER ::= { snmpUsecMIB 2 }
snmpUsecMIBConformance  OBJECT IDENTIFIER ::= { snmpUsecMIB 3 }

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

UserName ::=     TEXTUAL-CONVENTION
    STATUS       current
    DESCRIPTION "A string representing the name of a user for use in
                 accordance with the SNMP User-based Security model.
                "
    SYNTAX       SnmpAdminString (SIZE(1..16))


-- Editor's note:
-- A real issue is whether the fact that MD5 is used in the following
-- TC is OK. It might be better to use 3DES for 3DES and IDEA for IDEA.
-- End Editor's note

KeyChange ::=    TEXTUAL-CONVENTION
    STATUS       current
    DESCRIPTION
         "Every definition of an object with this syntax must identify
          a protocol, P, and a secret key, K.  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,
          imfAuthMD5Protocol 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



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                temporary variable, and the result is input to the MD5
                hash algorithm 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 MD5
             hash algorithm to produce a digest value;
           - 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.

             i.e.,

                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

-- *******************************************************************

-- The valid users for the User-based Security model ******************

usecUser         OBJECT IDENTIFIER ::= { snmpUsecMIBObjects 1 }

usecUserTable    OBJECT-TYPE
    SYNTAX       SEQUENCE OF UsecUserEntry
    MAX-ACCESS   not-accessible
    STATUS       current
    DESCRIPTION "The table of users configured in the SNMP engine's
                 Local (security) Configuration Datastore (LCD)."
    ::= { usecUser 1 }

usecUserEntry    OBJECT-TYPE
    SYNTAX       UsecUserEntry
    MAX-ACCESS   not-accessible



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    STATUS       current
    DESCRIPTION "A user configured in the SNMP engine's Local
                 (security) Configuration Datastore (LCD) for
                 the User-based Security model.
                "
    INDEX       { usecUserEngineID,
                  IMPLIED usecUserName
                }
    ::= { usecUserTable 1 }

UsecUserEntry ::= SEQUENCE {
    usecUserEngineID         SnmpEngineID,
    usecUserName             UserName,
    usecUserMiId             SnmpAdminString,
    usecUserGroupName        SnmpAdminString,
    usecUserCloneFrom        RowPointer,
    usecUserAuthProtocol     OBJECT IDENTIFIER,
    usecUserAuthKeyChange    KeyChange,
--  usecUserAuthKey          OCTET STRING, not visible
    usecUserAuthPublic       OCTET STRING,
    usecUserPrivProtocol     OBJECT IDENTIFIER,
    usecUserPrivKeyChange    KeyChange,
--  usecUserPrivKey          OCTET STRING, not visible
    usecUserPrivPublic       OCTET STRING,
    usecUserStorageType      StorageType,
    usecUserStatus           RowStatus
}

usecUserEngineID 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.

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

usecUserName     OBJECT-TYPE
    SYNTAX       UserName
    MAX-ACCESS   not-accessible
    STATUS       current
    DESCRIPTION "A string representing the name of the user.  This is
                 the (User-based security) model dependent identity.
                "
    ::= { usecUserEntry 2 }



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usecUserMiId     OBJECT-TYPE
    SYNTAX       SnmpAdminString
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION "A string representing the (security) model independent
                 identity for this user.

                 The default mapping for the User-based Security model
                 is that the miId is the same as the userName.
                "
    ::= { usecUserEntry 3 }

usecUserGroupName OBJECT-TYPE
    SYNTAX       SnmpAdminString
    MAX-ACCESS   read-write
    STATUS       current
    DESCRIPTION "A string representing the group to which the user
                 belongs.  A group name of zero length indicates
                 that the user is not [perhaps yet] a member of any
                 group, possibly because the entry has not yet been
                 completely configured.  Users which are not a part
                 of any group are effectively disabled to perform any
                 SNMP operations.
                "
    DEFVAL      { ''H } -- the empty string
    ::= { usecUserEntry 4 }

usecUserCloneFrom OBJECT-TYPE
    SYNTAX       RowPointer
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION "A pointer to another conceptual row in this
                 usecUserTable.  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 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 agent.
                 The cloning process fails with an 'inconsistentName'
                 error if the conceptual row representing the
                 clone-from user is not in an active state when the
                 cloning process is invoked.




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                 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 zero length string is
                 returned.
                "
    ::= { usecUserEntry 5 }

usecUserAuthProtocol OBJECT-TYPE
    SYNTAX       OBJECT IDENTIFIER
    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
                 usecUserEngineID, 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      { imfAuthMD5Protocol }
    ::= { usecUserEntry 6 }

usecUserAuthKeyChange 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
                 usecUserEngineID, to be modified via a one-way
                 function.

                 The associated protocol is the usecUserAuthProtocol.
                 The associated secret key is the user's secret
                 authentication key (usecUserAuthKey).

                 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 usecUserCloneFrom.
                "
    DEFVAL      { ''H }    -- the empty string



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    ::= { usecUserEntry 7 }

usecUserAuthPublic    OBJECT-TYPE
    SYNTAX       OCTET STRING -- for MD5 (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 key,
                 and later read to determine whether the change of
                 the secrets was effected.
                "
    DEFVAL      { ''H }  -- the empty string
    ::= { usecUserEntry 8 }

usecUserPrivProtocol OBJECT-TYPE
    SYNTAX       OBJECT IDENTIFIER
    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
                 usecUserEngineID, 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      { imfNoPrivProtocol }
    ::= { usecUserEntry 9 }

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

                 The associated protocol is the usecUserPrivProtocol.
                 The associated secret key is the user's secret
                 encryption key (usecUserPrivKey).

                 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



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                 through a set operation on the corresponding value
                 of usecUserCloneFrom.
                "
    DEFVAL      { ''H }    -- the empty string
    ::= { usecUserEntry 10 }

usecUserPrivPublic    OBJECT-TYPE
    SYNTAX       OCTET STRING -- for DES (SIZE(0..16))
    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 key,
                 and later read to determine whether the change of
                 the secrets was effected.
                "
    DEFVAL      { ''H }  -- the empty string
    ::= { usecUserEntry 11 }

usecUserStorageType OBJECT-TYPE
    SYNTAX       StorageType
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION "The storage type for this conceptual row."
    DEFVAL      { nonVolatile }
    ::= { usecUserEntry 12 }

usecUserStatus 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 usecUserStatus column is 'notReady'.

                 For those columnar objects which permit write-access,
                 their value in an existing conceptual row can be
                 changed irrespective of the value of usecUserStatus
                 for that row.
                "
    ::= { usecUserEntry 13 }


usecUserSecretSpinLock  OBJECT-TYPE
    SYNTAX       TestAndIncr
    MAX-ACCESS   read-write
    STATUS       current
    DESCRIPTION "An advisory lock used to allow several cooperating
                 SNMPv3 engines, all acting in a manager role, to
                 coordinate their use of facilities to alter secrets
                 in the usecUserTable.



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                "
    ::= { usecUser 2 }

--Editor's note
Is it enough to have just one spin-lock for such a table where
several secrets can be modified? Can the protocol ensure the
consistency? Should it?
--End editor's note

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

snmpUsecMIBCompliances
                 OBJECT IDENTIFIER ::= { snmpUsecMIBConformance 1 }
snmpUsecMIBGroups
                 OBJECT IDENTIFIER ::= { snmpUsecMIBConformance 2 }

-- Compliance statements

snmpUsecMIBCompliance MODULE-COMPLIANCE
    STATUS       current
    DESCRIPTION "The compliance statement for SNMP engines which
                 implement the SNMP USEC MIB.
                "

    MODULE       -- this module
        MANDATORY-GROUPS { snmpUsecMIBBasicGroup }

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

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

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

    ::= { snmpUsecMIBCompliances 1 }

-- Units of compliance

snmpUsecMIBBasicGroup OBJECT-GROUP
    OBJECTS     {
                  usecUserMiId,
                  usecUserGroupName,
                  usecUserCloneFrom,
                  usecUserAuthProtocol,
                  usecUserAuthKeyChange,
                  usecUserAuthPublic,



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                  usecUserPrivProtocol,
                  usecUserPrivKeyChange,
                  usecUserPrivPublic,
                  usecUserStorageType,
                  usecUserStatus
                }
    STATUS       current
    DESCRIPTION "A collection of objects providing for configuration
                 of an SNMP engine which implements the SNMP
                 User-based Security model.
                "
    ::= { snmpUsecMIBGroups 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.
   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 SNMPv3 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 SNMPv3
     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 SNMPv3 engines
     authorized to originate messages on behalf of the appropriate
     user.

   - In order to not expose the shared secrets (keys) at all SNMPv3
     engines in case one of the engines is compromised, such secrets
     (keys) are localized for each authoritative SNMPv3 engine, see
     [Localized-Key].

6.1.1.  Digest Authentication Protocol

   The Digest Authentication Protocol defined in this memo provides for:

   - verifying 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 a message.  The digest is computed
     by the originator of the message, transmitted with the message, and
     verified by the recipient of the message.

   - verifying the user on whose behalf the message was generated.

     A secret value known only to SNMPv3 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
     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 SNMPv3 message



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   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.  SNMPv3 Users

   Authentication using this Digest Authentication protocol makes use
   of a defined set of user identities.  For any SNMPv3 user on whose
   behalf a message must be authenticated at a particular SNMPv3 engine,
   that engine must have knowledge of that user.  An SNMPv3 engine that
   wishes to communicate with another SNMPv3 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.  EngineID

   The engineID value contained in an authenticated message specifies
   the authoritative SNMPv3 engine for that particular message.
   (see the definition of engineID in the SNMP Architecture document
   [SNMP-ARCH]).

   The user's (private) authentication key is normally different at
   each authoritative SNMPv3 engine and so the snmpEngineID is used
   to select the proper key for the authentication process.

6.2.3.  SNMPv3 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
   are intact and have not been tampered with.

6.2.4  Input and Output of the MD5 Authentication Module




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

6.2.4.1  Input and Output when generating an SNMPv3 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. The abstract service interface is:

          authMsg(authKey, wholeMsg)

   Where:

          authKey
            The secret key to be used by the authentication algorithm.
          wholeMsg
            the message to be authenticated.

   Upon completion the authentication module returns information.
   The abstract service interface is:

        returnAuthMsg(wholeMsg, statusCode)

   Where:

        wholeMsg
          Same as in input, but with authParameters properly filled.
        statusCode
          The indicator of whether the message was successfully
          processed or not.

   Note, that <authParameters> is filled by the authentication module
   and this field should be already present in the <wholeMsg> before
   the MAC is generated.

6.2.4.2  Input and Output when receiving an SNMPv3 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. The abstract service interface is:

        authIncomingMsg(authKey, authParameters, wholeMsg)

   Where:

        authKey
          The secret key to be used by the authentication algorithm.
        authParameters
          the authParameters from the incoming message.



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        wholeMsg
          the message to be authenticated.

   Upon completion the authentication module returns information.
   The abstract service interface is:

        returnAuthIncomingMsg(wholeMsg, statusCode)

        wholeMsg
          Same as in input, data has been authenticated.
        statusCode
          The indicator of whether the message was successfully
          processed or not.

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 SNMPv3 engine
   whenever it must authenticate an outgoing message using the
   imfAuthMD5Protocol.

   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 a statusCode of success.

6.3.2  Processing an Incoming Message

   This section describes the procedure followed by an SNMPv3 engine
   whenever it must authenticate an incoming message using the
   imfAuthMD5Protocol.

   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



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       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 (authenticationError) is returned to the calling
       module.

   7)  The wholeMsg (excluding the appended secret key) and a
       statusCode of 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.
   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 is in combination with a time value is used to
     create the en/decryption key and the initialization vector.
     The secret value is shared by all SNMPv3 engines authorized to
     originate messages on behalf of the appropriate user.

   - In order to not expose the shared secrets (keys) at all SNMPv3
     engines in case one of the engines is compromised, such secrets
     (keys) are localized for each authoritative SNMPv3 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
   SNMPv3 message is encrypted and included as part of the message
   sent to the recipient.

   This memo requires that if data confidentiality is supported by
   an SNMPv3 engine, this engine must implement at least the Data
   Encryption Standard (DES) in the Cipher Block Chaining mode of
   operation.

   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
   (see [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].



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   - There is a specification of a validation test suite for the DES
     [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 IV for two different packets encrypted
   by the same key, are not the same (i.e. 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 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 a random 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 as an octet-string.  The "salt" integer is incremented by one
   and wraps when it reaches the maximum value.

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

   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.

7.1.1.2  Data Encryption.

   The data to be encrypted is treated as sequence of octets. Its



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   length should be an integral multiple of 8 - and if not, the
   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 sequence to be decrypted is not an
   integral multiple of 8 octets, the processing of the octet sequence
   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.  SNMPv3 Users

   Data En/Decryption using this Symmetric Encryption Protocol makes use
   of a defined set of user identities.  For any SNMPv3 user on whose
   behalf a message must be en/decrypted at a particular SNMPv3 engine,
   that engine must have knowledge of that user.  An SNMPv3 engine that
   wishes to communicate with another SNMPv3 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>
     An octet string representing the name of the user.



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

7.2.2.  EngineID

   The engineID value contained in an authenticated message specifies
   the authoritative SNMPv3 engine for that particular message.
   (see the definition of engineID in the SNMP Architecture document
   [SNMP-ARCH]).

   The user's (private) privacy key is normally different at
   each authoritative SNMPv3 engine and so the snmpEngineID is used
   to select the proper key for the authentication process.

7.2.3.  SNMPv3 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  Input and Output of 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  Input and Output when generating an SNMPv3 Message

   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. The abstract service interface is:

        encryptMsg(cryptKey, scopedPDU)

   Where:

        cryptKey
          The secret key to be used by the encryption algorithm.
        scopedPDU
          The data to be encrypted.

   Upon completion the privacy module returns information.
   The abstract service interface is:

        returnEncryptedMsg(encryptedPDU, privParameters, statusCode)
   Where:
        encryptedPDU
          The encrypted scopedPDU (encoded as an octet string).
        privParameters
          The privacy parameters (encoded as an octet string) that



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          need to be sent in the outgoing message.
        statusCode
          The indicator of whether the PDU was encrypted successfully
          and if not, it indicates what went wrong.

7.2.4.2  Input and Output when receiving an SNMPv3 Message

   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. The abstract service interface is:

         decryptMsg(cryptKey, privParameters, encryptedPDU)

   Where:

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

   Upon completion the privacy module returns information.
   The abstract service interface is:

         returnDecryptedMsg(scopedPDU, statusCode)

   Where:

         scopedPDU
           The decrypted scopedPDU.
         statusCode
           The indicator whether the message was successfully decrypted.

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 SNMPv3 engine
   whenever it must encrypt part of an outgoing message using the
   imfPrivDESProtocol.

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

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



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   2)  The scopedPDU is encrypted (as described in 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 a statusCode of
       success is returned to the caller.

7.3.2  Processing an Incoming Message

   This section describes the procedure followed by an SNMPv3 engine
   whenever it must decrypt part of an incoming message using the
   imfPrivDESProtocol.

   1)  If the privParameters field is not an 8-byte octet string,
       then an error indication (privacyError) 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 7.1.1.1).

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

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

   6)  The decrypted scopedPDU and a statusCode of 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:      [e-mail]
   phone:      [phone]

   Co-editor:  Bert Wijnen
               IBM T. J. Watson Research
   postal:     Schagen 33
               3461 GL Linschoten
               Netherlands
   email:      [e-mail]
   phone:      [phone]

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.

   - A management station must discard SNMPv3 responses for which
     neither the msgID nor the request-id component or the represented
     management information corresponds to any currently outstanding
     request.

     Although it would be typical for a management station 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).

   - A management station must generate unpredictable msgIDs and
     request-ids in authenticated messages in order to protect against
     the possibility of message duplication (malicious or otherwise).
     For example, start operations with msgID and/or request-id 0 is
     not a good idea. Initializing them with a pseudorandom number
     and then incrementing by one would be acceptable.

   - A management station 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 agent, a
     management station should delay sending successive messages to the
     managed agent until a positive acknowledgement is received for the
     previous message or until the previous message expires.

     No message ordering is imposed by the SNMPv3. 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 agent, 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, a management station 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
     specifically defined for use with SNMPv2 set operations in order
     to provide a mechanism to ensure the processing of SNMPv2 messages
     occurs in a specific order.

   - The frequency with which the secrets of an SNMPv3 user should be
     changed is indirectly related to the frequency of their use.




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     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 the
     communication paths, more caution is prudent.

10.2  Defining Users

   The mechanisms defined in this document employ the notion of "users"
   which map into "groups" and such "groups" have access rights.
   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 a manager station application or set
   of manager station 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)
   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.




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   Since it is infeasible for human users to maintain different
   passwords for every engine, but security requirements strongly
   discourage having the same key for more than one engine, SNMPv3
   employs a compromise proposed in [Localized-key].
   It derives the user keys for the SNMPv3 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 SNMPv3 engine from
   any combination of user's keys on SNMPv3 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 SNMPv3 implementation" based on the User-base
   Security model, an SNMPv3 implementation:

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

   - must, to the maximum extent possible, prohibit access to the
     secret(s) of each user about which it maintains information in a
     Local (security) Configuration Database (LCD) under all
     circumstances except as required to generate and/or validate
     SNMPv3 messages with respect to that user.

   - must implement the SNMP USEC MIB.

   In addition, an authoritative SNMPv3 engine must provide initial
   configuration in accordance with Appendix A.1.

   Implementation of a Privacy Protocol (the 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.


[SNMP-ARCH] The SNMPv3 Working Group, Harrington, D., Wijnen, B.,
     "An Architecture for describing Internet Management Frameworks",
     draft-ietf-snmpv3-next-gen-arch-02.txt, June 1997.

[SNMPv3-MPC] The SNMPv3 Working Group, Wijnen, B., Harrington, D.,
     "Message Processing and Control Model for version 3 of the Simple
     Network Management Protocol (SNMPv3)",
     draft-ietf-snmpv3-mpc-01.txt, June 1997.

[SNMPv3-ACM] The SNMPv3 Working Group, Wijnen, B., Harrington, D.,
     "Access Control Model for Version 3 of the Simple Network
     Management Protocol (SNMPv3)", draft-ietf-snmpv3-acm-00.txt,
     June 1997.

[SNMPv3-USEC] The SNMPv3 Working Group, Blumenthal, U., Wijnen, B.
     "User-Based Security Model for version 3 of the Simple Network
     Management Protocol (SNMPv3)",
     draft-ietf-snmpv3-usec-01.txt, June 1997.

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




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

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

[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.   Engine Installation Parameters

During installation, an SNMPv3 engine acting in an authoritative role
is configured with several parameters.  These include:

(1) 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).

    With these configured parameters, the SNMPv3 engine instantiates
    the following usecUserEntry in the usecUserTable:

                              no privacy support  privacy support
                              ------------------  ---------------
      usecUserEngineID        localEngineID       localEngineID
      usecUserName            "public"            "public"
      usecUserMiId            "public"            "public"
      usecUserGroupName       "public"            "public"
      usecUserCloseFrom       ZeroDotZero         ZeroDotZero
      usecUserAuthProtocol    imfAuthMD5Protocol  imfAuthMD5Protocol
      usecUserAuthKeyChange   ""                  ""
      usecUserAuthPublic      ""                  ""
      usecUserPrivProtocol    none                imfPrivDESProtocol
      usecUserPrivKeyChange   ""                  ""
      usecUserrivhPublic      ""                  ""
      usecUserStorageType     permanent           permanent
      usecUserStatus          active              active








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A.2.   Password to Key Algorithm

The following code fragment 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 [RFC1321]

void password_to_key(
   u_char *password,    /* IN */
   u_int   passwordlen, /* IN */
   u_char *engineID,    /* IN  - ptr to 12 octet long snmpEngineID  */
   u_char *key)         /* OUT - caller's pointer to 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];
      }
      MDupdate (&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                  */
   /*****************************************************/
   memcpy(password_buf, key, 16);
   memcpy(password_buf+16, engineID, 12);
   memcpy(password_buf+28, key, 16);

   MD5Init(&MD);
   MDupdate(&MD, password_buf, 44);
   MD5Final(key, &MD);

   return;
}



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A.3.   Password to Key Sample

   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 engine's engineID 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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Table of Contents

0.1 Issues                                                             1
0.2 Change Log                                                         2
1.  Introduction                                                       3
1.1.  Threats                                                          3
1.2.  Goals and Constraints                                            4
1.3.  Security Services                                                5
1.4.  Implementation Organization                                      6
1.4.1.  Timeliness Module                                              6
1.4.2.  Authentication Protocol                                        6
1.4.3.  Privacy Protocol                                               7
1.5  Protection against Message Replay, Delay and Redirection          7
1.5.1   Authoritative SNMP Engine                                      7
1.5.2   The following mechanisms are used:                             7
2.  Elements of the Model                                             10
2.1.  SNMPv3 Users                                                    10
2.2.  Replay Protection                                               11
2.2.1.  snmpEngineID                                                  11
2.2.2.  engineBoots and engineTime                                    11
   2.3 for (re-)synchronization procedures).  Note, however, that the 12
2.2.3.  Time Window                                                   12
2.3.  Time Synchronization                                            12
2.4.  SNMPv3 Messages Using this Model                                13
2.5  Input and Output of the User-based Security Module               14
2.5.1 Input and Output when generating an SNMPv3 Message              14
2.5.2 Input and Output when receiving an SNMPv3 Message               15
3.  Elements of Procedure                                             18
3.1.  Processing an Outgoing Message                                  18
3.2.  Processing an Incoming Message                                  20
       2.4, then the snmpInASNParseErrs counter [RFC1907] is          20
4.  Discovery                                                         25
5.  Definitions                                                       26
6.  MD5 Authentication Protocol                                       36
6.1  Mechanisms                                                       36
6.1.1.  Digest Authentication Protocol                                36
6.2  Elements of the Digest Authentication Protocol                   37
6.2.1.  SNMPv3 Users                                                  37
6.2.2.  EngineID                                                      37
6.2.3.  SNMPv3 Messages Using this Authentication Protocol            37
6.2.4  Input and Output of the MD5 Authentication Module              37
6.2.4.1  Input and Output when generating an SNMPv3 Message           38
6.2.4.2  Input and Output when receiving an SNMPv3 Message            38
6.3  Elements of Procedure                                            39
6.3.1  Processing an Outgoing Message                                 39
6.3.2  Processing an Incoming Message                                 39
7.  DES Privacy Protocol                                              41
7.1  Mechanisms                                                       41
7.1.1.  Symmetric Encryption Protocol                                 41
7.1.1.1  DES key and Initialization Vector.                           42
7.1.1.2  Data Encryption.                                             42
7.1.1.3  Data Decryption                                              43
7.2  Elements of the DES Privacy Protocol                             43
7.2.1.  SNMPv3 Users                                                  43
7.2.2.  EngineID                                                      44
7.2.3.  SNMPv3 Messages Using this Privacy Protocol                   44
7.2.4  Input and Output of the DES Privacy Module                     44
7.2.4.1  Input and Output when generating an SNMPv3 Message           44
7.2.4.2  Input and Output when receiving an SNMPv3 Message            45
7.3  Elements of Procedure.                                           45
7.3.1  Processing an Outgoing Message                                 45
       7.1.1.1).                                                      45
7.3.2  Processing an Incoming Message                                 46
8.  Editor's Addresses                                                47
9.  Acknowledgements                                                  47
A.1.   Engine Installation Parameters                                 53
A.2.   Password to Key Algorithm                                      54
A.3.   Password to Key Sample                                         55



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