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

Diffie-Helman USM Key

Management Information Base and Textual Convention

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 © 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 [12]. 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 [12] 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 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 [12] 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][6][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 [16].

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

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

1. The SNMP Management Framework The SNMP Management Framework

presently consists of five major components:

   o   An overall architecture, described in RFC 2271 [1].
   
   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
       16, RFC 1155 [2], STD 16, RFC 1212 [3] and RFC 1215 [4]. The
       second version, called SMIv2, is described in STD 58, RFC 2578
       [5], STD 58, RFC 2579 [6] and STD 58, RFC 2580 [7].
   
   o   Message protocols for transferring management information. The
       first version of the SNMP message protocol is called SNMPv1 and
       described in STD 15, RFC 1157 [8]. A second version of the SNMP
       message protocol, which is not an Internet standards track
       protocol, is called SNMPv2c and described in RFC 1901 [9] and RFC
       1906 [10].  The third version of the message protocol is called
       SNMPv3 and described in RFC 1906 [10], RFC 2272 [11] and RFC 2274
       [12].
   
   o   Protocol operations for accessing management information. The
       first set of protocol operations and associated PDU formats is
       described in STD 15, RFC 1157 [8]. A second set of protocol
       operations and associated PDU formats is described in RFC 1905
       [13].
   
   o   A set of fundamental applications described in RFC 2273 [14] and
       the view-based access control mechanism described in RFC 2275
       [15].

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.

1.1. Structure of the MIB

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.
   
   o   The usmDHUserKeyTable augments and extends the usmUserTable
       defined in the SNMPv3 User-based Security Model MIB [12] 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.

2. Theory of Operation

2.1. Diffie-Helman Key Changes

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.

2.2. Diffie-Helman Key Ignition

[12] 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 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 [15] 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.

3. Definitions

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 RFC 2786."
    
    ::= { experimental 101 }  -- IANA DHKEY-CHANGE 101

-- Administrative assignments

usmDHKeyObjects OBJECT IDENTIFIER ::= { snmpUsmDHObjectsMIB 1 }

usmDHKeyConformance OBJECT IDENTIFIER ::= { snmpUsmDHObjectsMIB 2 }

-- Textual conventions

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) <= xa < 2^l < 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
    <= xa < 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 <> 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) <= xr < 2^l < 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 <> 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

-- 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, section 9.  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 RFC-2409, The Internet Key Exchange, Section 6.1, 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, RFC 2409, 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."
    ::= { 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

    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

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

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) <= r < p-1 < 2^l. If l is unspecified, then r is a random integer selected in the interval 0 <= r < 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, RFC 2409, 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, RFC2409;
            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.

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

        "-- Password-Based Cryptography Standard, PKCS#5v2.0;
            RSA Laboratories, March 1999
         -- Applied Cryptography, 2nd Ed.; B. Schneier,
            Counterpane Systems; John Wiley & 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.
             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          ''
        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,
    
                  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

4. References

   [1]  Harrington, D., Presuhn, R. and B. Wijnen, "An Architecture for
        Describing SNMP Management Frameworks", RFC 2571, April 1999.
   
   [2]  Rose, M. and K. McCloghrie, "Structure and Identification of
        Management Information for TCP/IP-based Internets", STD 16, RFC
        1155, May 1990.
   
   [3]  Rose, M. and K. McCloghrie, "Concise MIB Definitions", STD 16,
        RFC 1212, March 1991.
   
   [4]  Rose, M., "A Convention for Defining Traps for use with the
        SNMP", RFC 1215, March 1991.
   
   [5]  McCloghrie, K., Perkins, D., Schoenwaelder, J., Case,  J.,
        Rose, M. and S. Waldbusser, "Structure of Management Information
        Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
   
   [6]  McCloghrie, K., Perkins, D., Schoenwaelder, J., Case,  J.,
        Rose, M. and S. Waldbusser, "Textual Conventions for SMIv2", STD
        58, RFC 2579, April 1999.
   
   [7]  McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
        M. and S. Waldbusser, "Conformance Statements for SMIv2", STD
        58, RFC 2580, April 1999.
   
   [8]  Case, J., Fedor, M., Schoffstall, M. and J. Davin, "Simple
        Network Management Protocol", STD 15, RFC 1157, May 1990.
   
   [9]  Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
        "Introduction to Community-based SNMPv2", RFC 1901, January
        1996.
   
   [10] 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.
   
   [11] Case, J., Harrington D., Presuhn R. and B. Wijnen, "Message
        Processing and Dispatching for the Simple Network Management
        Protocol (SNMP)", RFC 2572, April 1999.
   
   [12] Blumenthal, U. and B. Wijnen, "User-based Security Model (USM)
        for version 3 of the Simple Network Management Protocol
        (SNMPv3)", RFC 2574, April 1999.
   
   [13] 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.
   
   [14] Levi, D., Meyer, P. and B. Stewart, "SNMPv3 Applications", RFC
        2573, April 1999.
   
   [15] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based Access
        Control Model (VACM) for the Simple Network Management Protocol
        (SNMP)", RFC 2575, April 1999.
   
   [16] Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

[17] "Diffie-Hellman Key-Agreement Standard, Version 1.4", PKCS #3,

RSA Laboratories, November 1993.

   [18] Harkins, D. and D. Carrel, "The Internet Key Exchange", RFC
        2409, November 1988.
   
   [19] Eastlake, D., Crocker, S. and J. Schiller, "Randomness
        Recommendations for Security", RFC 1750, December 1994.

5. Security Considerations

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.

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" [19].

6. Intellectual Property

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 BCP-11. 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.

7. Author's Address

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

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

9. Full Copyright Statement

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Acknowledgement

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