GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc2786

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

St. Johns Experimental [Page 1] RFC 2786 Diffie-Helman USM Key March 2000

 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

St. Johns Experimental [Page 2] RFC 2786 Diffie-Helman USM Key March 2000

     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.

St. Johns Experimental [Page 3] RFC 2786 Diffie-Helman USM Key March 2000

 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

St. Johns Experimental [Page 4] RFC 2786 Diffie-Helman USM Key March 2000

 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.

St. Johns Experimental [Page 5] RFC 2786 Diffie-Helman USM Key March 2000

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

St. Johns Experimental [Page 6] RFC 2786 Diffie-Helman USM Key March 2000

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

St. Johns Experimental [Page 7] RFC 2786 Diffie-Helman USM Key March 2000

– 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."

St. Johns Experimental [Page 8] RFC 2786 Diffie-Helman USM Key March 2000

  ::= { 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

St. Johns Experimental [Page 9] RFC 2786 Diffie-Helman USM Key March 2000

  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

St. Johns Experimental [Page 10] RFC 2786 Diffie-Helman USM Key March 2000

  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

St. Johns Experimental [Page 11] RFC 2786 Diffie-Helman USM Key March 2000

  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.

St. Johns Experimental [Page 12] RFC 2786 Diffie-Helman USM Key March 2000

  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

St. Johns Experimental [Page 13] RFC 2786 Diffie-Helman USM Key March 2000

      "-- 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.

St. Johns Experimental [Page 14] RFC 2786 Diffie-Helman USM Key March 2000

           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          ''

St. Johns Experimental [Page 15] RFC 2786 Diffie-Helman USM Key March 2000

      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,

St. Johns Experimental [Page 16] RFC 2786 Diffie-Helman USM Key March 2000

                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.

St. Johns Experimental [Page 17] RFC 2786 Diffie-Helman USM Key March 2000

 [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.

St. Johns Experimental [Page 18] RFC 2786 Diffie-Helman USM Key March 2000

 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

St. Johns Experimental [Page 19] RFC 2786 Diffie-Helman USM Key March 2000

9. Full Copyright Statement

 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]

/data/webs/external/dokuwiki/data/pages/rfc/rfc2786.txt · Last modified: 2000/03/14 20:41 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki