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LinuxDig.com Request For Comments

RFC Number : 2786

Title : Diffie-Helman USM Key Management Information Base and Textual Convention.






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





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

The recommendation in [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



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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.



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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





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

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

The vendor who implements these objects is expected to provide one or
more usmSecurityNames which map to a set of accesses defined in the
VACM [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 '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




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DHKeyChange ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION
'Upon initialization, or upon creation of a row containing an
object of this type, and after any successful SET of this value, a
GET of this value returns 'y' where y = g^xa MOD p, and where g is
the base from usmDHParameters, p is the prime from
usmDHParameters, and xa is a new random integer selected by the
agent in the interval 2^(l-1) <= 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



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-- Diffie Hellman public values

usmDHPublicObjects OBJECT IDENTIFIER ::= { usmDHKeyObjects 1 }

usmDHParameters OBJECT-TYPE
SYNTAX OCTET STRING
MAX-ACCESS read-write
STATUS current
DESCRIPTION
'The public Diffie-Hellman parameters for doing a Diffie-Hellman
key agreement for this device. This is encoded as an ASN.1
DHParameter per PKCS #3, 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.'



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::= { usmDHPublicObjects 2 }

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

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

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

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

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

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

usmDHUserPrivKeyChange OBJECT-TYPE



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

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

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

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

usmDHKickstartGroup OBJECT IDENTIFIER ::= { usmDHKeyObjects 2 }

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



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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



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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.




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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



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'-- 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.



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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 ''



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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,



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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.






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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.




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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










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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]




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