Diffie-Helman USM Key Management Information Base and Textual Convention
draft-stjohns-snmpv3-dhkeychange-mib-01

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                         Diffie-Helman USM Key
           Management Information Base and Textual Convention
              draft-stjohns-snmpv3-dhkeychange-mib-01.txt

                      Fri Aug  6 13:39:41 PDT 1999

                           Michael C. StJohns
                              Excite@Home
                         stjohns@corp.home.net

Status of this Memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.

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Copyright (c) The Internet Society 1998.  All Rights Reserved.

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

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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.

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Table of Contents

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

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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
        RFC 1155 [2], RFC 1212 [3] and RFC 1215 [4]. The second version,
        called SMIv2, is described in RFC 1902 [5], RFC 1903 [6] and RFC
        1904 [7].

    o   Message protocols for transferring management information. The
        first version of the SNMP message protocol is called SNMPv1 and
        described in 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 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.

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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 it 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.

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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.

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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 "9908060000Z"  -- 6 August 1999, Midnight
    ORGANIZATION "@Home Network"
    CONTACT-INFO "Author: Mike StJohns
                  Postal: Excite@Home
                          425 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."
    ::= { 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 from usmDHParameters, p is the prime from usmDHParameters, and

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    xa is a new random integer selected by the agent in the interval
    2^(l-1) <= xa < p-1.  'l' is the optional privateValueLength from
    usmDHParameters in bits.  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) <= xa < 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.

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        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, anytime usmDHParameters changes, all values of
    type DHKeyChange will change and new random numbers MUST be
    generated 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

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    }

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.

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    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."
    INDEX   { usmDHKickstartIndex }
    ::= {usmDHKickstartTable 1 }

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

usmDHKickstartIndex OBJECT-TYPE

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    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.

    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 =   [unspecified]
    "
    ::= { 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

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    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, 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;

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        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:

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         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

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    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 }

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END

4.  References

[1]  Harrington, D., Presuhn, R., and B. Wijnen, "An Architecture for
     Describing SNMP Management Frameworks", RFC 2271, Cabletron
     Systems, Inc., BMC Software, Inc., IBM T. J. Watson Research,
     January 1998

[2]  Rose, M., and K. McCloghrie, "Structure and Identification of
     Management Information for TCP/IP-based Internets", RFC 1155,
     Performance Systems International, Hughes LAN Systems, May 1990

[3]  Rose, M., and K. McCloghrie, "Concise MIB Definitions", RFC 1212,
     Performance Systems International, Hughes LAN Systems, March 1991

[4]  M. Rose, "A Convention for Defining Traps for use with the SNMP",
     RFC 1215, Performance Systems International, March 1991

[5]  Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Structure
     of Management Information for Version 2 of the Simple Network
     Management Protocol (SNMPv2)", RFC 1902, SNMP Research,Inc., Cisco
     Systems, Inc., Dover Beach Consulting, Inc., International Network
     Services, January 1996.

[6]  Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Textual
     Conventions for Version 2 of the Simple Network Management Protocol
     (SNMPv2)", RFC 1903, SNMP Research, Inc., Cisco Systems, Inc.,
     Dover Beach Consulting, Inc., International Network Services,
     January 1996.

[7]  Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Conformance
     Statements for Version 2 of the Simple Network Management Protocol
     (SNMPv2)", RFC 1904, SNMP Research, Inc., Cisco Systems, Inc.,
     Dover Beach Consulting, Inc., International Network Services,
     January 1996.

[8]  Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple Network
     Management Protocol", RFC 1157, SNMP Research, Performance Systems
     International, Performance Systems International, MIT Laboratory
     for Computer Science, May 1990.

[9]  Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
     "Introduction to Community-based SNMPv2", RFC 1901, SNMP Research,
     Inc., Cisco Systems, Inc., Dover Beach Consulting, Inc.,
     International Network Services, 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, SNMP Research, Inc., Cisco Systems, Inc.,
     Dover Beach Consulting, Inc., International Network Services,
     January 1996.

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[11] Case, J., Harrington D., Presuhn R., and B. Wijnen, "Message
     Processing and Dispatching for the Simple Network Management
     Protocol (SNMP)", RFC 2272, SNMP Research, Inc., Cabletron Systems,
     Inc., BMC Software, Inc., IBM T. J. Watson Research, January 1998.

[12] Blumenthal, U., and B. Wijnen, "User-based Security Model (USM) for
     version 3 of the Simple Network Management Protocol (SNMPv3)", RFC
     2274, IBM T. J. Watson Research, January 1998.

[13] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Protocol
     Operations for Version 2 of the Simple Network Management Protocol
     (SNMPv2)", RFC 1905, SNMP Research, Inc., Cisco Systems, Inc.,
     Dover Beach Consulting, Inc., International Network Services,
     January 1996.

[14] Levi, D., Meyer, P., and B. Stewart, "SNMPv3 Applications", RFC
     2273, SNMP Research, Inc., Secure Computing Corporation, Cisco
     Systems, January 1998

[15] Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based Access
     Control Model (VACM) for the Simple Network Management Protocol
     (SNMP)", RFC 2275, IBM T. J. Watson Research, BMC Software, Inc.,
     Cisco Systems, Inc., January 1998

[16] Bradner, S., "Key words for use in RFCs to Indicate Requirement
     Levels", RFC2119, Harvard University, March 1997

[17] "Diffie-Hellman Key-Agreement Standard, Version 1.4", PKCS #3, RSA
     Laboratories, November 1993

[18] Harkins, D., and Carrel, D., "The Internet Key Exchange", RFC 2409,
     cisco Systems, Inc., November 1988

[19] Eastlake, D., Crocker, S., and Schiller, J., "Randomness
     Recommendations for Security", RFC 1750, DEC, Cybercash, MIT,
     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

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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.  Copyright Section

Copyright (C) The Internet Society 1998. 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 implmentation 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

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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.

8.  Author's Address

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

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

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