<pre>Network Working Group                                        M. St. Johns
Request for Comments: 2786                                    Excite@Home
Category: Experimental                                         March 2000


                         <span class="h1">Diffie-Helman USM Key</span>
           <span class="h1">Management Information Base and Textual Convention</span>

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

IESG Note

   This document specifies an experimental MIB. Readers, implementers
   and users of this MIB should be aware that in the future the IETF may
   charter an IETF Working Group to develop a standards track MIB to
   address the same problem space that this MIB addresses.  It is quite
   possible that an incompatible standards track MIB may result from
   that effort.

Abstract

   This memo defines an experimental portion of the Management
   Information Base (MIB) for use with network management protocols in
   the Internet community.  In particular, it defines a textual
   convention for doing Diffie-Helman key agreement key exchanges and a
   set of objects which extend the usmUserTable to permit the use of a
   DH key exchange in addition to the key change method described in
   [<a href="#ref-12" title="&quot;User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)&quot;">12</a>]. In otherwords, this MIB adds the possibility of forward secrecy
   to the USM model.  It also defines a set of objects that can be used
   to kick start security on an SNMPv3 agent when the out of band path
   is authenticated, but not necessarily private or confidential.

   The KeyChange textual convention described in [<a href="#ref-12" title="&quot;User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)&quot;">12</a>] permits secure key
   changes, but has the property that if a third-party has knowledge of
   the original key (e.g. if the agent was manufactured with a standard
   default key) and could capture all SNMP exchanges, the third-party
   would know the new key.  The Diffie-Helman key change described here





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   limits knowledge of the new key to the agent and the manager making
   the change.  In otherwords, this process adds forward secrecy to the
   key change process.

   The recommendation in [<a href="#ref-12" title="&quot;User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)&quot;">12</a>] is that the usmUserTable be populated out
   of band - e.g. not via SNMP.  If the number of agents to be
   configured is small, this can be done via a console port and
   manually.  If the number of agents is large, as is the case for a
   cable modem system, the manual approach doesn't scale well.  The
   combination of the two mechanisms specified here - the DH key change
   mechanism, and the DH key ignition mechanism - allows managable use
   of SNMPv3 USM in a system of millions of devices.

   This memo specifies a MIB module in a manner that is compliant to the
   SNMP SMIv2[5][<a href="#ref-6" title="&quot;Textual Conventions for SMIv2&quot;">6</a>][7].  The set of objects is consistent with the SNMP
   framework and existing SNMP standards and is intended for use with
   the SNMPv3 User Security Model MIB and other security related MIBs.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [<a href="#ref-16" title="&quot;Key words for use in RFCs to Indicate Requirement Levels&quot;">16</a>].

   This memo is a private submission by the author, but is applicable to
   the SNMPv3 working group within the Internet Engineering Task Force.
   Comments are solicited and should be addressed to the the author.

Table of Contents

   <a href="#section-1">1</a> The SNMP Management Framework .................................   <a href="#page-2">2</a>
   <a href="#section-1.1">1.1</a> Structure of the MIB ........................................   <a href="#page-3">3</a>
   <a href="#section-2">2</a> Theory of Operation ...........................................   <a href="#page-4">4</a>
   <a href="#section-2.1">2.1</a> Diffie-Helman Key Changes ...................................   <a href="#page-4">4</a>
   <a href="#section-2.2">2.2</a> Diffie-Helman Key Ignition ..................................   <a href="#page-4">4</a>
   <a href="#section-3">3</a> Definitions ...................................................   <a href="#page-6">6</a>
   <a href="#section-4">4</a> References ....................................................  <a href="#page-17">17</a>
   <a href="#section-5">5</a> Security Considerations .......................................  <a href="#page-18">18</a>
   <a href="#section-6">6</a> Intellectual Property .........................................  <a href="#page-19">19</a>
   <a href="#section-7">7</a> Author's Address ..............................................  <a href="#page-19">19</a>
   <a href="#section-8">8</a> Full Copyright Statement ......................................  <a href="#page-20">20</a>

<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>.  The SNMP Management Framework  </span> The SNMP Management Framework
   presently consists of five major components:

   o   An overall architecture, described in <a href="./rfc2271">RFC 2271</a> [<a href="#ref-1" title="&quot;An Architecture for Describing SNMP Management Frameworks&quot;">1</a>].

   o   Mechanisms for describing and naming objects and events for the
       purpose of management. The first version of this Structure of
       Management Information (SMI) is called SMIv1 and described in STD



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       16, <a href="./rfc1155">RFC 1155</a> [<a href="#ref-2" title="&quot;Structure and Identification of Management Information for TCP/IP-based Internets&quot;">2</a>], STD 16, <a href="./rfc1212">RFC 1212</a> [<a href="#ref-3" title="&quot;Concise MIB Definitions&quot;">3</a>] and <a href="./rfc1215">RFC 1215</a> [<a href="#ref-4" title="&quot;A Convention for Defining Traps for use with the SNMP&quot;">4</a>]. The
       second version, called SMIv2, is described in STD 58, <a href="./rfc2578">RFC 2578</a>
       [<a href="#ref-5" title="&quot;Structure of Management Information Version 2 (SMIv2)&quot;">5</a>], STD 58, <a href="./rfc2579">RFC 2579</a> [<a href="#ref-6" title="&quot;Textual Conventions for SMIv2&quot;">6</a>] and STD 58, <a href="./rfc2580">RFC 2580</a> [<a href="#ref-7" title="&quot;Conformance Statements for SMIv2&quot;">7</a>].

   o   Message protocols for transferring management information. The
       first version of the SNMP message protocol is called SNMPv1 and
       described in STD 15, <a href="./rfc1157">RFC 1157</a> [<a href="#ref-8" title="&quot;Simple Network Management Protocol&quot;">8</a>]. A second version of the SNMP
       message protocol, which is not an Internet standards track
       protocol, is called SNMPv2c and described in <a href="./rfc1901">RFC 1901</a> [<a href="#ref-9" title="&quot;Introduction to Community-based SNMPv2&quot;">9</a>] and <a href="./rfc1906">RFC</a>
       <a href="./rfc1906">1906</a> [<a href="#ref-10" title="&quot;Transport Mappings for Version 2 of the Simple Network Management Protocol (SNMPv2)&quot;">10</a>].  The third version of the message protocol is called
       SNMPv3 and described in <a href="./rfc1906">RFC 1906</a> [<a href="#ref-10" title="&quot;Transport Mappings for Version 2 of the Simple Network Management Protocol (SNMPv2)&quot;">10</a>], <a href="./rfc2272">RFC 2272</a> [<a href="#ref-11" title="&quot;Message Processing and Dispatching for the Simple Network Management Protocol (SNMP)&quot;">11</a>] and <a href="./rfc2274">RFC 2274</a>
       [<a href="#ref-12" title="&quot;User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)&quot;">12</a>].

   o   Protocol operations for accessing management information. The
       first set of protocol operations and associated PDU formats is
       described in STD 15, <a href="./rfc1157">RFC 1157</a> [<a href="#ref-8" title="&quot;Simple Network Management Protocol&quot;">8</a>]. A second set of protocol
       operations and associated PDU formats is described in <a href="./rfc1905">RFC 1905</a>
       [<a href="#ref-13" title="&quot;Protocol Operations for Version 2 of the Simple Network Management Protocol (SNMPv2)&quot;">13</a>].

   o   A set of fundamental applications described in <a href="./rfc2273">RFC 2273</a> [<a href="#ref-14" title="&quot;SNMPv3 Applications&quot;">14</a>] and
       the view-based access control mechanism described in <a href="./rfc2275">RFC 2275</a>
       [<a href="#ref-15" title="&quot;View-based Access Control Model (VACM) for the Simple Network Management Protocol (SNMP)&quot;">15</a>].

   Managed objects are accessed via a virtual information store, termed
   the Management Information Base or MIB.  Objects in the MIB are
   defined using the mechanisms defined in the SMI.

   This memo specifies a MIB module that is compliant to the SMIv2. A
   MIB conforming to the SMIv1 can be produced through the appropriate
   translations. The resulting translated MIB must be semantically
   equivalent, except where objects or events are omitted because no
   translation is possible (use of Counter64). Some machine readable
   information in SMIv2 will be converted into textual descriptions in
   SMIv1 during the translation process. However, this loss of machine
   readable information is not considered to change the semantics of the
   MIB.

<span class="h3"><a class="selflink" id="section-1.1" href="#section-1.1">1.1</a>.  Structure of the MIB</span>

   This MIB is structured into three groups and a single textual
   convention:

   o   The DHKeyChange textual convention defines the process for
       changing a secret key value via a Diffie-Helman key exchange.

   o   The usmDHPublicObjects group contains a single object which
       describes the public Diffie-Helman parameters required by any
       instance of a DHKeyChange typed object.



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   o   The usmDHUserKeyTable augments and extends the usmUserTable
       defined in the SNMPv3 User-based Security Model MIB [<a href="#ref-12" title="&quot;User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)&quot;">12</a>] by
       providing objects which permit the updating of the Authentication
       and Privacy keys for a row in this table through the use of a
       Diffie-Helman key exchange.

   o   The usmDHKickstartTable provides a mechanism for a management
       station to be able to agree upon a set of authentication and
       confidentiality keys and their associated row in the
       usmUserTable.

<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>.  Theory of Operation</span>

<span class="h3"><a class="selflink" id="section-2.1" href="#section-2.1">2.1</a>.  Diffie-Helman Key Changes</span>

   Upon row creation (in the usmUserTable), or object change (either of
   the object in the usmDHUserKeyTable or its associated value in the
   usmUserTable), the agent generates a random number.  From this random
   number, the agent uses the DH parameters and transforms to derive a
   DH public value which is then published to the associated MIB object.
   The management station reads one or more of the objects in the
   usmDHUserKeyTable to get the agent's DH public values.

   The management station generates a random number, derives a DH public
   value from that random number (as described in the DHKeyChange
   Textual Convention), and does an SNMP SET against the object in the
   usmDHUserKeyTable.  The set consists of the concatenation of the
   agent's derived DH public value and the manager's derived DH public
   value (to ensure the DHKeyChange object hasn't otherwise changed in
   the meantime).

   Upon successful completion of the set, the underlying key
   (authentication or confidentiality) for the associated object in the
   usmUserTable is changed to a key derived from the DH shared secret.
   Both the agent and the management station are able to calculate this
   value based on their knowledge of their own random number and the
   other's DH public number.

<span class="h3"><a class="selflink" id="section-2.2" href="#section-2.2">2.2</a>.  Diffie-Helman Key Ignition</span>

   [<a id="ref-12">12</a>] recommends that the usmUserTable be populated out of band, for
   example - manually.  This works reasonably well if there are a small
   number of agents, or if all the agents are using the same key
   material, and if the device is physically accessible for that action.
   It does not scale very well to the case of possibly millions of
   devices located in thousands of locations in hundreds of markets in





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   multiple countries.  In other words, it doesn't work well with a
   cable modem system, and may not work all that well with other large-
   scale consumer broadband IP offerings.

   The methods described in the objects under the usmDHKickstartGroup
   can be used to populate the usmUserTable in the circumstances where
   you may be able to provide at least limited integrity for the
   provisioning process, but you can't guarantee confidentiality.  In
   addition, as a side effect of using the DH exchange, the operational
   USM keys for each agent will differ from the operational USM keys for
   every other device in the system, ensuring that compromise of one
   device does not compromise the system as a whole.

   The vendor who implements these objects is expected to provide one or
   more usmSecurityNames which map to a set of accesses defined in the
   VACM [<a href="#ref-15" title="&quot;View-based Access Control Model (VACM) for the Simple Network Management Protocol (SNMP)&quot;">15</a>] tables.  For example, the vendor may provide a 'root' user
   who has access to the entire device for read-write, and 'operator'
   user who has access to the network specific monitoring objects and
   can also reset the device, and a 'customer' user who has access to a
   subset of the monitoring objects which can be used to help the
   customer debug the device in conjunction with customer service
   questions.

   To use, the system manager (the organization or individual who own
   the group of devices) generates one or more random numbers - R.  The
   manager derives the DH Public Numbers R' from these random numbers,
   associates the public numbers with a security name, and configures
   the agent with this association.  The configuration would be done
   either manually (in the case of a small number of devices), or via
   some sort of distributed configuration file.  The actual mechanism is
   outside the scope of this document.  The agent in turn generates a
   random number for each name/number pair, and publishes the DH Public
   Number derived from its random number in the usmDHKickstartTable
   along with the manager's public number and provided security name.

   Once the agent is initialized, an SNMP Manager can read the contents
   of the usmDHKickstartTable using the security name of 'dhKickstart'
   with no authentication.  The manager looks for one or more entries in
   this table where it knows the random number used to derive the
   usmDHKickstartMgrPublic number.  Given the manager's knowledge of the
   private random number, and the usmDHKickstartMyPublic number, the
   manager can calculate the DH shared secret.  From that shared secret,
   it can derive the operational authentication and confidentiality keys
   for the usmUserTable row which has the matching security name.  Given
   the keys and the security name, the manager can then use normal USM
   mechanisms to access the remainder of the agent's MIB space.





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<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>.  Definitions</span>

SNMP-USM-DH-OBJECTS-MIB DEFINITIONS ::= BEGIN

IMPORTS
    MODULE-IDENTITY, OBJECT-TYPE,
    -- OBJECT-IDENTITY,
    experimental, Integer32
        FROM SNMPv2-SMI
    TEXTUAL-CONVENTION
        FROM SNMPv2-TC
    MODULE-COMPLIANCE, OBJECT-GROUP
        FROM SNMPv2-CONF
    usmUserEntry
        FROM SNMP-USER-BASED-SM-MIB
    SnmpAdminString
        FROM SNMP-FRAMEWORK-MIB;

snmpUsmDHObjectsMIB MODULE-IDENTITY
    LAST-UPDATED "200003060000Z"  -- 6 March 2000, Midnight
    ORGANIZATION "Excite@Home"
    CONTACT-INFO "Author: Mike StJohns
                  Postal: Excite@Home
                          450 Broadway
                          Redwood City, CA 94063
                  Email:  stjohns@corp.home.net
                  Phone:  +1-650-556-5368"

    DESCRIPTION
        "The management information definitions for providing forward
    secrecy for key changes for the usmUserTable, and for providing a
    method for 'kickstarting' access to the agent via a Diffie-Helman
    key agreement."

    REVISION     "200003060000Z"
    DESCRIPTION
       "Initial version published as <a href="./rfc2786">RFC 2786</a>."


    ::= { experimental 101 }  -- IANA DHKEY-CHANGE 101

-- Administrative assignments

usmDHKeyObjects OBJECT IDENTIFIER ::= { snmpUsmDHObjectsMIB 1 }
usmDHKeyConformance OBJECT IDENTIFIER ::= { snmpUsmDHObjectsMIB 2 }

-- Textual conventions




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DHKeyChange ::=         TEXTUAL-CONVENTION
    STATUS              current
    DESCRIPTION
        "Upon initialization, or upon creation of a row containing an
    object of this type, and after any successful SET of this value, a
    GET of this value returns 'y' where y = g^xa MOD p, and where g is
    the base from usmDHParameters, p is the prime from
    usmDHParameters, and xa is a new random integer selected by the
    agent in the interval 2^(l-1) &lt;= xa &lt; 2^l &lt; p-1.  'l' is the
    optional privateValueLength from usmDHParameters in bits.  If 'l'
    is omitted, then xa (and xr below) is selected in the interval 0
    &lt;= xa &lt; p-1.  y is expressed as an OCTET STRING 'PV' of length 'k'
    which satisfies

              k
        y =  SUM   2^(8(k-i)) PV'i
             i=1

        where PV1,...,PVk are the octets of PV from first to last, and
        where PV1 &lt;&gt; 0.

    A successful SET consists of the value 'y' expressed as an OCTET
    STRING as above concatenated with the value 'z'(expressed as an
    OCTET STRING in the same manner as y) where z = g^xr MOD p, where
    g, p and l are as above, and where xr is a new random integer
    selected by the manager in the interval 2^(l-1) &lt;= xr &lt; 2^l &lt;
    p-1. A SET to an object of this type will fail with the error
    wrongValue if the current 'y' does not match the 'y' portion of
    the value of the varbind for the object. (E.g. GET yout, SET
    concat(yin, z), yout &lt;&gt; yin).

    Note that the private values xa and xr are never transmitted from
    manager to device or vice versa, only the values y and z.
    Obviously, these values must be retained until a successful SET on
    the associated object.

    The shared secret 'sk' is calculated at the agent as sk = z^xa MOD
    p, and at the manager as sk = y^xr MOD p.

    Each object definition of this type MUST describe how to map from
    the shared secret 'sk' to the operational key value used by the
    protocols and operations related to the object.  In general, if n
    bits of key are required, the author suggests using the n
    right-most bits of the shared secret as the operational key value."
    REFERENCE
        "-- Diffie-Hellman Key-Agreement Standard, PKCS #3;
            RSA Laboratories, November 1993"
    SYNTAX              OCTET STRING



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-- Diffie Hellman public values

usmDHPublicObjects      OBJECT IDENTIFIER ::= { usmDHKeyObjects 1 }

usmDHParameters OBJECT-TYPE
    SYNTAX  OCTET STRING
    MAX-ACCESS read-write
    STATUS  current
    DESCRIPTION
        "The public Diffie-Hellman parameters for doing a Diffie-Hellman
    key agreement for this device.  This is encoded as an ASN.1
    DHParameter per PKCS #3, <a href="#section-9">section 9</a>.  E.g.

        DHParameter ::= SEQUENCE {
           prime   INTEGER,   -- p
           base    INTEGER,   -- g
           privateValueLength  INTEGER OPTIONAL }


    Implementors are encouraged to use either the values from
    Oakley Group 1  or the values of from Oakley Group 2 as specified
    in <a href="./rfc2409">RFC-2409</a>, The Internet Key Exchange, <a href="#section-6.1">Section 6.1</a>, 6.2 as the
    default for this object.  Other values may be used, but the
    security properties of those values MUST be well understood and
    MUST meet the requirements of PKCS #3 for the selection of
    Diffie-Hellman primes.

        In addition, any time usmDHParameters changes, all values of
    type DHKeyChange will change and new random numbers MUST be
    generated by the agent for each DHKeyChange object."
    REFERENCE
        "-- Diffie-Hellman Key-Agreement Standard, PKCS #3,
            RSA Laboratories, November 1993
         -- The Internet Key Exchange, <a href="./rfc2409">RFC 2409</a>, November 1998,
            Sec 6.1, 6.2"
    ::= { usmDHPublicObjects 1 }

usmDHUserKeyTable OBJECT-TYPE
    SYNTAX  SEQUENCE OF UsmDHUserKeyEntry
    MAX-ACCESS not-accessible
    STATUS  current
    DESCRIPTION
        "This table augments and extends the usmUserTable and provides
    4 objects which exactly mirror the objects in that table with the
    textual convention of 'KeyChange'.  This extension allows key
    changes to be done in a manner where the knowledge of the current
    secret plus knowledge of the key change data exchanges (e.g. via
    wiretapping)  will not reveal the new key."



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    ::= { usmDHPublicObjects 2 }

usmDHUserKeyEntry OBJECT-TYPE
    SYNTAX  UsmDHUserKeyEntry
    MAX-ACCESS not-accessible
    STATUS  current
    DESCRIPTION
        "A row of DHKeyChange objects which augment or replace the
    functionality of the KeyChange objects in the base table row."
    AUGMENTS { usmUserEntry }
    ::= {usmDHUserKeyTable 1 }

UsmDHUserKeyEntry ::= SEQUENCE {
        usmDHUserAuthKeyChange          DHKeyChange,
    usmDHUserOwnAuthKeyChange   DHKeyChange,
        usmDHUserPrivKeyChange          DHKeyChange,
        usmDHUserOwnPrivKeyChange       DHKeyChange
        }

usmDHUserAuthKeyChange OBJECT-TYPE
    SYNTAX  DHKeyChange
    MAX-ACCESS read-create
    STATUS  current
    DESCRIPTION
        "The object used to change any given user's Authentication Key
    using a Diffie-Hellman key exchange.

    The right-most n bits of the shared secret 'sk', where 'n' is the
    number of bits required for the protocol defined by
    usmUserAuthProtocol, are installed as the operational
    authentication key for this row after a successful SET."
    ::= { usmDHUserKeyEntry 1 }

usmDHUserOwnAuthKeyChange OBJECT-TYPE
    SYNTAX  DHKeyChange
    MAX-ACCESS read-create
    STATUS  current
    DESCRIPTION
        "The object used to change the agents own Authentication Key
    using a Diffie-Hellman key exchange.

    The right-most n bits of the shared secret 'sk', where 'n' is the
    number of bits required for the protocol defined by
    usmUserAuthProtocol, are installed as the operational
    authentication key for this row after a successful SET."
    ::= { usmDHUserKeyEntry 2 }

usmDHUserPrivKeyChange OBJECT-TYPE



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    SYNTAX  DHKeyChange
    MAX-ACCESS read-create
    STATUS  current
    DESCRIPTION
        "The object used to change any given user's Privacy Key using
    a Diffie-Hellman key exchange.

    The right-most n bits of the shared secret 'sk', where 'n' is the
    number of bits required for the protocol defined by
    usmUserPrivProtocol, are installed as the operational privacy key
    for this row after a successful SET."
    ::= { usmDHUserKeyEntry 3 }

usmDHUserOwnPrivKeyChange OBJECT-TYPE
    SYNTAX  DHKeyChange
    MAX-ACCESS read-create
    STATUS  current
    DESCRIPTION
        "The object used to change the agent's own Privacy Key using a
    Diffie-Hellman key exchange.

    The right-most n bits of the shared secret 'sk', where 'n' is the
    number of bits required for the protocol defined by
    usmUserPrivProtocol, are installed as the operational privacy key
    for this row after a successful SET."
    ::= { usmDHUserKeyEntry 4 }

usmDHKickstartGroup OBJECT IDENTIFIER ::= { usmDHKeyObjects 2 }

usmDHKickstartTable OBJECT-TYPE
    SYNTAX      SEQUENCE OF UsmDHKickstartEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "A table of mappings between zero or more Diffie-Helman key
    agreement values and entries in the usmUserTable.  Entries in this
    table are created by providing the associated device with a
    Diffie-Helman public value and a usmUserName/usmUserSecurityName
    pair during initialization. How these values are provided is
    outside the scope of this MIB, but could be provided manually, or
    through a configuration file.  Valid public value/name pairs
    result in the creation of a row in this table as well as the
    creation of an associated row (with keys derived as indicated) in
    the usmUserTable.  The actual access the related usmSecurityName
    has is dependent on the entries in the VACM tables.  In general,
    an implementor will specify one or more standard security names
    and will provide entries in the VACM tables granting various
    levels of access to those names.  The actual content of the VACM



<span class="grey">St. Johns                     Experimental                     [Page 10]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-11" ></span>
<span class="grey"><a href="./rfc2786">RFC 2786</a>                 Diffie-Helman USM Key                March 2000</span>


    table is beyond the scope of this MIB.

    Note: This table is expected to be readable without authentication
    using the usmUserSecurityName 'dhKickstart'.  See the conformance
    statements for details."
    ::= { usmDHKickstartGroup 1 }

usmDHKickstartEntry OBJECT-TYPE
    SYNTAX      UsmDHKickstartEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION

        "An entry in the usmDHKickstartTable.  The agent SHOULD either
    delete this entry or mark it as inactive upon a successful SET of
    any of the KeyChange-typed objects in the usmUserEntry or upon a
    successful SET of any of the DHKeyChange-typed objects in the
    usmDhKeyChangeEntry where the related usmSecurityName (e.g. row of
    usmUserTable or row of ushDhKeyChangeTable) equals this entry's
    usmDhKickstartSecurityName.  In otherwords, once you've changed
    one or more of the keys for a row in usmUserTable with a
    particular security name, the row in this table with that same
    security name is no longer useful or meaningful."

    INDEX   { usmDHKickstartIndex }
    ::= {usmDHKickstartTable 1 }

UsmDHKickstartEntry ::= SEQUENCE  {
        usmDHKickstartIndex     Integer32,
        usmDHKickstartMyPublic  OCTET STRING,
        usmDHKickstartMgrPublic OCTET STRING,
        usmDHKickstartSecurityName      SnmpAdminString
        }

usmDHKickstartIndex OBJECT-TYPE
    SYNTAX      Integer32  (1..2147483647)
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "Index value for this row."
    ::= { usmDHKickstartEntry 1 }

usmDHKickstartMyPublic OBJECT-TYPE
    SYNTAX      OCTET STRING
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        "The agent's Diffie-Hellman public value for this row.  At



<span class="grey">St. Johns                     Experimental                     [Page 11]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-12" ></span>
<span class="grey"><a href="./rfc2786">RFC 2786</a>                 Diffie-Helman USM Key                March 2000</span>


    initialization, the agent generates a random number and derives
    its public value from that number.  This public value is published
    here.  This public value 'y' equals g^r MOD p where g is the from
    the set of Diffie-Hellman parameters, p is the prime from those
    parameters, and r is a random integer selected by the agent in the
    interval 2^(l-1) &lt;= r &lt; p-1 &lt; 2^l.  If l is unspecified, then r is
    a random integer selected in the interval 0 &lt;= r &lt; p-1

    The public value is expressed as an OCTET STRING 'PV' of length
    'k' which satisfies

              k
        y =  SUM   2^(8(k-i)) PV'i
             i = 1

        where PV1,...,PVk are the octets of PV from first to last, and
        where PV1 != 0.


    The following DH parameters (Oakley group #2, <a href="./rfc2409">RFC 2409</a>, sec 6.1,
    6.2) are used for this object:

    g = 2
    p = FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
        29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
        EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
        E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
        EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE65381
        FFFFFFFF FFFFFFFF
    l=1024
    "
    REFERENCE
        "-- Diffie-Hellman Key-Agreement Standard, PKCS#3v1.4;
            RSA Laboratories, November 1993
         -- The Internet Key Exchange, <a href="./rfc2409">RFC2409</a>;
            Harkins, D., Carrel, D.; November 1998"
    ::= { usmDHKickstartEntry 2 }

usmDHKickstartMgrPublic OBJECT-TYPE
    SYNTAX      OCTET STRING
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION

        "The manager's Diffie-Hellman public value for this row.  Note
    that this value is not set via the SNMP agent, but may be set via
    some out of band method, such as the device's configuration file.




<span class="grey">St. Johns                     Experimental                     [Page 12]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-13" ></span>
<span class="grey"><a href="./rfc2786">RFC 2786</a>                 Diffie-Helman USM Key                March 2000</span>


    The manager calculates this value in the same manner and using the
    same parameter set as the agent does.  E.g. it selects a random
    number 'r', calculates y = g^r mod p and provides 'y' as the
    public number expressed as an OCTET STRING.  See
    usmDHKickstartMyPublic for details.

    When this object is set with a valid value during initialization,
    a row is created in the usmUserTable with the following values:

    usmUserEngineID             localEngineID
    usmUserName                 [value of usmDHKickstartSecurityName]
    usmUserSecurityName         [value of usmDHKickstartSecurityName]
    usmUserCloneFrom            ZeroDotZero
    usmUserAuthProtocol         usmHMACMD5AuthProtocol
    usmUserAuthKeyChange        -- derived from set value
    usmUserOwnAuthKeyChange     -- derived from set value
    usmUserPrivProtocol         usmDESPrivProtocol
    usmUserPrivKeyChange        -- derived from set value
    usmUserOwnPrivKeyChange     -- derived from set value
    usmUserPublic               ''
    usmUserStorageType          permanent
    usmUserStatus               active

    A shared secret 'sk' is calculated at the agent as sk =
    mgrPublic^r mod p where r is the agents random number and p is the
    DH prime from the common parameters.  The underlying privacy key
    for this row is derived from sk by applying the key derivation
    function PBKDF2 defined in PKCS#5v2.0 with a salt of 0xd1310ba6,
    and iterationCount of 500, a keyLength of 16 (for
    usmDESPrivProtocol), and a prf (pseudo random function) of
    'id-hmacWithSHA1'.  The underlying authentication key for this row
    is derived from sk by applying the key derivation function PBKDF2
    with a salt of 0x98dfb5ac , an interation count of 500, a
    keyLength of 16 (for usmHMAC5AuthProtocol), and a prf of
    'id-hmacWithSHA1'.  Note: The salts are the first two words in the
    ks0 [key schedule 0] of the BLOWFISH cipher from 'Applied
    Cryptography' by Bruce Schnier - they could be any relatively
    random string of bits.

    The manager can use its knowledge of its own random number and the
    agent's public value to kickstart its access to the agent in a
    secure manner.  Note that the security of this approach is
    directly related to the strength of the authorization security of
    the out of band provisioning of the managers public value
    (e.g. the configuration file), but is not dependent at all on the
    strength of the confidentiality of the out of band provisioning
    data."
    REFERENCE



<span class="grey">St. Johns                     Experimental                     [Page 13]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-14" ></span>
<span class="grey"><a href="./rfc2786">RFC 2786</a>                 Diffie-Helman USM Key                March 2000</span>


        "-- Password-Based Cryptography Standard, PKCS#5v2.0;
            RSA Laboratories, March 1999
         -- Applied Cryptography, 2nd Ed.; B. Schneier,
            Counterpane Systems; John Wiley &amp; Sons, 1996"
    ::= { usmDHKickstartEntry 3 }

usmDHKickstartSecurityName OBJECT-TYPE
    SYNTAX      SnmpAdminString
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        "The usmUserName and usmUserSecurityName in the usmUserTable
    associated with this row.  This is provided in the same manner and
    at the same time as the usmDHKickstartMgrPublic value -
    e.g. possibly manually, or via the device's configuration file."
    ::= { usmDHKickstartEntry 4 }

-- Conformance Information

usmDHKeyMIBCompliances  OBJECT IDENTIFIER ::= { usmDHKeyConformance 1 }
usmDHKeyMIBGroups       OBJECT IDENTIFIER ::= { usmDHKeyConformance 2 }

-- Compliance statements

usmDHKeyMIBCompliance   MODULE-COMPLIANCE
    STATUS      current
    DESCRIPTION
        "The compliance statement for this module."
    MODULE
        GROUP usmDHKeyMIBBasicGroup
        DESCRIPTION
        "This group MAY be implemented by any agent which
        implements the usmUserTable and which wishes to provide the
        ability to change user and agent authentication and privacy
        keys via Diffie-Hellman key exchanges."

        GROUP usmDHKeyParamGroup
        DESCRIPTION
            "This group MUST be implemented by any agent which
        implements a MIB containing the DHKeyChange Textual
        Convention defined in this module."

        GROUP usmDHKeyKickstartGroup
        DESCRIPTION
            "This group MAY be implemented by any agent which
        implements the usmUserTable and which wishes the ability to
        populate the USM table based on out-of-band provided DH
        ignition values.



<span class="grey">St. Johns                     Experimental                     [Page 14]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-15" ></span>
<span class="grey"><a href="./rfc2786">RFC 2786</a>                 Diffie-Helman USM Key                March 2000</span>


             Any agent implementing this group is expected to provide
        preinstalled entries in the vacm tables as follows:

             In the usmUserTable: This entry allows access to the
        system and dhKickstart groups

        usmUserEngineID         localEngineID
        usmUserName             'dhKickstart'
        usmUserSecurityName     'dhKickstart'
        usmUserCloneFrom        ZeroDotZero
        usmUserAuthProtocol     none
        usmUserAuthKeyChange    ''
        usmUserOwnAuthKeyChange ''
        usmUserPrivProtocol     none
        usmUserPrivKeyChange    ''
        usmUserOwnPrivKeyChange ''
        usmUserPublic           ''
        usmUserStorageType      permanent
        usmUserStatus           active

            In the vacmSecurityToGroupTable: This maps the initial
        user into the accessible objects.

        vacmSecurityModel               3 (USM)
        vacmSecurityName                'dhKickstart'
        vacmGroupName                   'dhKickstart'
        vacmSecurityToGroupStorageType  permanent
        vacmSecurityToGroupStatus       active

            In the vacmAccessTable: Group name to view name translation.

        vacmGroupName                   'dhKickstart'
    vacmAccessContextPrefix             ''
        vacmAccessSecurityModel         3 (USM)
        vacmAccessSecurityLevel         noAuthNoPriv
        vacmAccessContextMatch          exact
        vacmAccessReadViewName          'dhKickRestricted'
        vacmAccessWriteViewName         ''
        vacmAccessNotifyViewName        'dhKickRestricted'
        vacmAccessStorageType           permanent
        vacmAccessStatus                active

            In the vacmViewTreeFamilyTable: Two entries to allow the
        initial entry to access the system and kickstart groups.

        vacmViewTreeFamilyViewName      'dhKickRestricted'
        vacmViewTreeFamilySubtree       1.3.6.1.2.1.1  (system)
        vacmViewTreeFamilyMask          ''



<span class="grey">St. Johns                     Experimental                     [Page 15]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-16" ></span>
<span class="grey"><a href="./rfc2786">RFC 2786</a>                 Diffie-Helman USM Key                March 2000</span>


        vacmViewTreeFamilyType          1
        vacmViewTreeFamilyStorageType   permanent
        vacmViewTreeFamilyStatus        active

        vacmViewTreeFamilyViewName      'dhKickRestricted'
        vacmViewTreeFamilySubtree         (usmDHKickstartTable OID)
        vacmViewTreeFamilyMask          ''
        vacmViewTreeFamilyType          1
        vacmViewTreeFamilyStorageType   permanent
        vacmViewTreeFamilyStatus        active
        "

        OBJECT usmDHParameters
        MIN-ACCESS      read-only
        DESCRIPTION
            "It is compliant to implement this object as read-only for
        any device."

    ::= { usmDHKeyMIBCompliances 1 }

-- Units of Compliance

usmDHKeyMIBBasicGroup OBJECT-GROUP
    OBJECTS     {
                  usmDHUserAuthKeyChange,
                  usmDHUserOwnAuthKeyChange,
                  usmDHUserPrivKeyChange,
                  usmDHUserOwnPrivKeyChange
                }
    STATUS      current
    DESCRIPTION
        ""
    ::= { usmDHKeyMIBGroups 1 }

usmDHKeyParamGroup OBJECT-GROUP
    OBJECTS     {
                  usmDHParameters
                }
    STATUS      current
    DESCRIPTION
        "The mandatory object for all MIBs which use the DHKeyChange
    textual convention."
    ::= { usmDHKeyMIBGroups 2 }

usmDHKeyKickstartGroup OBJECT-GROUP
    OBJECTS     {
                  usmDHKickstartMyPublic,
                  usmDHKickstartMgrPublic,



<span class="grey">St. Johns                     Experimental                     [Page 16]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-17" ></span>
<span class="grey"><a href="./rfc2786">RFC 2786</a>                 Diffie-Helman USM Key                March 2000</span>


                  usmDHKickstartSecurityName
                }
    STATUS      current
    DESCRIPTION
        "The objects used for kickstarting one or more SNMPv3 USM
    associations via a configuration file or other out of band,
    non-confidential access."
    ::= { usmDHKeyMIBGroups 3 }


END

<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>.  References</span>

   [<a id="ref-1">1</a>]  Harrington, D., Presuhn, R. and B. Wijnen, "An Architecture for
        Describing SNMP Management Frameworks", <a href="./rfc2571">RFC 2571</a>, April 1999.

   [<a id="ref-2">2</a>]  Rose, M. and K. McCloghrie, "Structure and Identification of
        Management Information for TCP/IP-based Internets", STD 16, <a href="./rfc1155">RFC</a>
        <a href="./rfc1155">1155</a>, May 1990.

   [<a id="ref-3">3</a>]  Rose, M. and K. McCloghrie, "Concise MIB Definitions", STD 16,
        <a href="./rfc1212">RFC 1212</a>, March 1991.

   [<a id="ref-4">4</a>]  Rose, M., "A Convention for Defining Traps for use with the
        SNMP", <a href="./rfc1215">RFC 1215</a>, March 1991.

   [<a id="ref-5">5</a>]  McCloghrie, K., Perkins, D., Schoenwaelder, J., Case,  J.,
        Rose, M. and S. Waldbusser, "Structure of Management Information
        Version 2 (SMIv2)", STD 58, <a href="./rfc2578">RFC 2578</a>, April 1999.

   [<a id="ref-6">6</a>]  McCloghrie, K., Perkins, D., Schoenwaelder, J., Case,  J.,
        Rose, M. and S. Waldbusser, "Textual Conventions for SMIv2", STD
        58, <a href="./rfc2579">RFC 2579</a>, April 1999.

   [<a id="ref-7">7</a>]  McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
        M. and S. Waldbusser, "Conformance Statements for SMIv2", STD
        58, <a href="./rfc2580">RFC 2580</a>, April 1999.

   [<a id="ref-8">8</a>]  Case, J., Fedor, M., Schoffstall, M. and J. Davin, "Simple
        Network Management Protocol", STD 15, <a href="./rfc1157">RFC 1157</a>, May 1990.

   [<a id="ref-9">9</a>]  Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
        "Introduction to Community-based SNMPv2", <a href="./rfc1901">RFC 1901</a>, January
        1996.






<span class="grey">St. Johns                     Experimental                     [Page 17]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-18" ></span>
<span class="grey"><a href="./rfc2786">RFC 2786</a>                 Diffie-Helman USM Key                March 2000</span>


   [<a id="ref-10">10</a>] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Transport
        Mappings for Version 2 of the Simple Network Management Protocol
        (SNMPv2)", <a href="./rfc1906">RFC 1906</a>, January 1996.

   [<a id="ref-11">11</a>] Case, J., Harrington D., Presuhn R. and B. Wijnen, "Message
        Processing and Dispatching for the Simple Network Management
        Protocol (SNMP)", <a href="./rfc2572">RFC 2572</a>, April 1999.

   [<a id="ref-12">12</a>] Blumenthal, U. and B. Wijnen, "User-based Security Model (USM)
        for version 3 of the Simple Network Management Protocol
        (SNMPv3)", <a href="./rfc2574">RFC 2574</a>, April 1999.

   [<a id="ref-13">13</a>] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Protocol
        Operations for Version 2 of the Simple Network Management
        Protocol (SNMPv2)", <a href="./rfc1905">RFC 1905</a>, January 1996.

   [<a id="ref-14">14</a>] Levi, D., Meyer, P. and B. Stewart, "SNMPv3 Applications", <a href="./rfc2573">RFC</a>
        <a href="./rfc2573">2573</a>, April 1999.

   [<a id="ref-15">15</a>] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based Access
        Control Model (VACM) for the Simple Network Management Protocol
        (SNMP)", <a href="./rfc2575">RFC 2575</a>, April 1999.

   [<a id="ref-16">16</a>] Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.

   [<a id="ref-17">17</a>] "Diffie-Hellman Key-Agreement Standard, Version 1.4", PKCS #3,
        RSA Laboratories, November 1993.

   [<a id="ref-18">18</a>] Harkins, D. and D. Carrel, "The Internet Key Exchange", <a href="./rfc2409">RFC</a>
        <a href="./rfc2409">2409</a>, November 1988.

   [<a id="ref-19">19</a>] Eastlake, D., Crocker, S. and J. Schiller, "Randomness
        Recommendations for Security", <a href="./rfc1750">RFC 1750</a>, December 1994.

<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>.  Security Considerations</span>

   Objects in the usmDHUserKeyTable should be considered to have the
   same security sensitivity as the objects of the KeyChange type in
   usmUserTable and should be afforded the same level of protection.
   Specifically, the VACM should not grant more or less access to these
   objects than it grants to the usmUserTable KeyChange object.

   The improper selection of parameters for use with Diffie-Hellman key
   changes may adversely affect the security of the agent.  Please see
   the body of the MIB for specific recommendations or requirements on
   the selection of the DH parameters.




<span class="grey">St. Johns                     Experimental                     [Page 18]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-19" ></span>
<span class="grey"><a href="./rfc2786">RFC 2786</a>                 Diffie-Helman USM Key                March 2000</span>


   An unauthenticated DH exchange is subject to "man-in-the-middle"
   attacks.  The use of the DH exchange in any specific environment
   should balance risk versus threat.

   Good security from a DH exchange requires a good source of random
   numbers.  If your application cannot provide a reasonable source of
   randomness, do not use a DH exchange.  For more information, see
   "Randomness Recommendations for Security" [<a href="#ref-19" title="&quot;Randomness Recommendations for Security&quot;">19</a>].

<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>.  Intellectual Property</span>

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in <a href="https://www.rfc-editor.org/bcp/bcp11">BCP-11</a>.  Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.

<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>.  Author's Address</span>

   Michael C. StJohns
   Excite@Home
   450 Broadway
   Redwood City, CA 94063
   USA

   Phone: +1-650-556-5368
   EMail: stjohns@corp.home.net










<span class="grey">St. Johns                     Experimental                     [Page 19]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-20" ></span>
<span class="grey"><a href="./rfc2786">RFC 2786</a>                 Diffie-Helman USM Key                March 2000</span>


<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>.  Full Copyright Statement</span>

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















St. Johns                     Experimental                     [Page 20]
</pre>