|
Network Working Group Request for Comments: 2786 Category: Experimental |
M. St. Johns Excite@Home March 2000 |
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 © The Internet Society (2000). All Rights Reserved.
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.
This memo defines an experimental portion of the Management Information Base (MIB) for use with network management protocols in the Internet community. In particular, it defines a textual convention for doing Diffie-Helman key agreement key exchanges and a set of objects which extend the usmUserTable to permit the use of a DH key exchange in addition to the key change method described in [12]. In otherwords, this MIB adds the possibility of forward secrecy to the USM model. It also defines a set of objects that can be used to kick start security on an SNMPv3 agent when the out of band path is authenticated, but not necessarily private or confidential.
The KeyChange textual convention described in [12] permits secure key changes, but has the property that if a third-party has knowledge of the original key (e.g. if the agent was manufactured with a standard default key) and could capture all SNMP exchanges, the third-party would know the new key. The Diffie-Helman key change described here
limits knowledge of the new key to the agent and the manager making the change. In otherwords, this process adds forward secrecy to the key change process.
The recommendation in [12] is that the usmUserTable be populated out of band - e.g. not via SNMP. If the number of agents to be configured is small, this can be done via a console port and manually. If the number of agents is large, as is the case for a cable modem system, the manual approach doesn't scale well. The combination of the two mechanisms specified here - the DH key change mechanism, and the DH key ignition mechanism - allows managable use of SNMPv3 USM in a system of millions of devices.
This memo specifies a MIB module in a manner that is compliant to the SNMP SMIv2[5][6][7]. The set of objects is consistent with the SNMP framework and existing SNMP standards and is intended for use with the SNMPv3 User Security Model MIB and other security related MIBs.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [16].
This memo is a private submission by the author, but is applicable to the SNMPv3 working group within the Internet Engineering Task Force. Comments are solicited and should be addressed to the the author.
1 The SNMP Management Framework
1.1 Structure of the MIB
2 Theory of Operation
2.1 Diffie-Helman Key Changes
2.2 Diffie-Helman Key Ignition
3 Definitions
4 References
5 Security Considerations
6 Intellectual Property
7 Author's Address
8 Full Copyright Statement
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].
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.
This MIB is structured into three groups and a single textual convention:
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.
[12] recommends that the usmUserTable be populated out of band, for example - manually. This works reasonably well if there are a small number of agents, or if all the agents are using the same key material, and if the device is physically accessible for that action. It does not scale very well to the case of possibly millions of devices located in thousands of locations in hundreds of markets in
multiple countries. In other words, it doesn't work well with a cable modem system, and may not work all that well with other large- scale consumer broadband IP offerings.
The methods described in the objects under the usmDHKickstartGroup can be used to populate the usmUserTable in the circumstances where you may be able to provide at least limited integrity for the provisioning process, but you can't guarantee confidentiality. In addition, as a side effect of using the DH exchange, the operational USM keys for each agent will differ from the operational USM keys for every other device in the system, ensuring that compromise of one device does not compromise the system as a whole.
The vendor who implements these objects is expected to provide one or more usmSecurityNames which map to a set of accesses defined in the VACM [15] tables. For example, the vendor may provide a 'root' user who has access to the entire device for read-write, and 'operator' user who has access to the network specific monitoring objects and can also reset the device, and a 'customer' user who has access to a subset of the monitoring objects which can be used to help the customer debug the device in conjunction with customer service questions.
To use, the system manager (the organization or individual who own the group of devices) generates one or more random numbers - R. The manager derives the DH Public Numbers R' from these random numbers, associates the public numbers with a security name, and configures the agent with this association. The configuration would be done either manually (in the case of a small number of devices), or via some sort of distributed configuration file. The actual mechanism is outside the scope of this document. The agent in turn generates a random number for each name/number pair, and publishes the DH Public Number derived from its random number in the usmDHKickstartTable along with the manager's public number and provided security name.
Once the agent is initialized, an SNMP Manager can read the contents of the usmDHKickstartTable using the security name of 'dhKickstart' with no authentication. The manager looks for one or more entries in this table where it knows the random number used to derive the usmDHKickstartMgrPublic number. Given the manager's knowledge of the private random number, and the usmDHKickstartMyPublic number, the manager can calculate the DH shared secret. From that shared secret, it can derive the operational authentication and confidentiality keys for the usmUserTable row which has the matching security name. Given the keys and the security name, the manager can then use normal USM mechanisms to access the remainder of the agent's MIB space.
SNMP-USM-DH-OBJECTS-MIB DEFINITIONS ::= BEGIN
-- 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;
DESCRIPTION
"The management information definitions for providing forward
secrecy for key changes for the usmUserTable, and for providing a
method for 'kickstarting' access to the agent via a Diffie-Helman
key agreement."
REVISION "200003060000Z"
DESCRIPTION
"Initial version published as RFC 2786."
::= { experimental 101 } -- IANA DHKEY-CHANGE 101
-- Administrative assignments
usmDHKeyObjects OBJECT IDENTIFIER ::= { snmpUsmDHObjectsMIB 1 }
usmDHKeyConformance OBJECT IDENTIFIER ::= { snmpUsmDHObjectsMIB 2 }
-- Textual conventions
DHKeyChange ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION
"Upon initialization, or upon creation of a row containing an
object of this type, and after any successful SET of this value, a
GET of this value returns 'y' where y = g^xa MOD p, and where g is
the base from usmDHParameters, p is the prime from
usmDHParameters, and xa is a new random integer selected by the
agent in the interval 2^(l-1) <= xa < 2^l < p-1. 'l' is the
optional privateValueLength from usmDHParameters in bits. If 'l'
is omitted, then xa (and xr below) is selected in the interval 0
<= xa < p-1. y is expressed as an OCTET STRING 'PV' of length 'k'
which satisfies
k
y = SUM 2^(8(k-i)) PV'i
i=1
where PV1,...,PVk are the octets of PV from first to last, and where PV1 <> 0.
A successful SET consists of the value 'y' expressed as an OCTET STRING as above concatenated with the value 'z'(expressed as an
OCTET STRING in the same manner as y) where z = g^xr MOD p, where
g, p and l are as above, and where xr is a new random integer
selected by the manager in the interval 2^(l-1) <= xr < 2^l <
p-1. A SET to an object of this type will fail with the error
wrongValue if the current 'y' does not match the 'y' portion of
the value of the varbind for the object. (E.g. GET yout, SET
concat(yin, z), yout <> yin).
Note that the private values xa and xr are never transmitted from manager to device or vice versa, only the values y and z. Obviously, these values must be retained until a successful SET on the associated object.
The shared secret 'sk' is calculated at the agent as sk = z^xa MOD
p, and at the manager as sk = y^xr MOD p.
Each object definition of this type MUST describe how to map from
the shared secret 'sk' to the operational key value used by the
protocols and operations related to the object. In general, if n
bits of key are required, the author suggests using the n
right-most bits of the shared secret as the operational key value."
REFERENCE
"-- Diffie-Hellman Key-Agreement Standard, PKCS #3;
RSA Laboratories, November 1993"
SYNTAX OCTET STRING
-- Diffie Hellman public values
usmDHPublicObjects OBJECT IDENTIFIER ::= { usmDHKeyObjects 1 }
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 }
::= { usmDHPublicObjects 2 }
::= {usmDHUserKeyTable 1 }
UsmDHUserKeyEntry ::= SEQUENCE {
usmDHUserAuthKeyChange DHKeyChange,
usmDHUserOwnAuthKeyChange DHKeyChange,
usmDHUserPrivKeyChange DHKeyChange,
usmDHUserOwnPrivKeyChange DHKeyChange
}
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 }
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 }
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 }
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 }
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 }
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
}
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Index value for this row."
::= { usmDHKickstartEntry 1 }
SYNTAX OCTET STRING
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The agent's Diffie-Hellman public value for this row. At
initialization, the agent generates a random number and derives its public value from that number. This public value is published here. This public value 'y' equals g^r MOD p where g is the from the set of Diffie-Hellman parameters, p is the prime from those parameters, and r is a random integer selected by the agent in the interval 2^(l-1) <= r < p-1 < 2^l. If l is unspecified, then r is a random integer selected in the interval 0 <= r < p-1
The public value is expressed as an OCTET STRING 'PV' of length 'k' which satisfies
k
y = SUM 2^(8(k-i)) PV'i
i = 1
where PV1,...,PVk are the octets of PV from first to last, and
where PV1 != 0.
The following DH parameters (Oakley group #2, RFC 2409, sec 6.1, 6.2) are used for this object:
g = 2
p = FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE65381
FFFFFFFF FFFFFFFF
l=1024
"
REFERENCE
"-- Diffie-Hellman Key-Agreement Standard, PKCS#3v1.4;
RSA Laboratories, November 1993
-- The Internet Key Exchange, RFC2409;
Harkins, D., Carrel, D.; November 1998"
::= { usmDHKickstartEntry 2 }
SYNTAX OCTET STRING
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The manager's Diffie-Hellman public value for this row. Note that this value is not set via the SNMP agent, but may be set via some out of band method, such as the device's configuration file.
The manager calculates this value in the same manner and using the same parameter set as the agent does. E.g. it selects a random
number 'r', calculates y = g^r mod p and provides 'y' as the
public number expressed as an OCTET STRING. See
usmDHKickstartMyPublic for details.
When this object is set with a valid value during initialization, a row is created in the usmUserTable with the following values:
usmUserEngineID localEngineID
usmUserName [value of usmDHKickstartSecurityName]
usmUserSecurityName [value of usmDHKickstartSecurityName]
usmUserCloneFrom ZeroDotZero
usmUserAuthProtocol usmHMACMD5AuthProtocol
usmUserAuthKeyChange -- derived from set value
usmUserOwnAuthKeyChange -- derived from set value
usmUserPrivProtocol usmDESPrivProtocol
usmUserPrivKeyChange -- derived from set value
usmUserOwnPrivKeyChange -- derived from set value
usmUserPublic ''
usmUserStorageType permanent
usmUserStatus active
A shared secret 'sk' is calculated at the agent as sk =
mgrPublic^r mod p where r is the agents random number and p is the
DH prime from the common parameters. The underlying privacy key
for this row is derived from sk by applying the key derivation
function PBKDF2 defined in PKCS#5v2.0 with a salt of 0xd1310ba6,
and iterationCount of 500, a keyLength of 16 (for
usmDESPrivProtocol), and a prf (pseudo random function) of
'id-hmacWithSHA1'. The underlying authentication key for this row
is derived from sk by applying the key derivation function PBKDF2
with a salt of 0x98dfb5ac , an interation count of 500, a
keyLength of 16 (for usmHMAC5AuthProtocol), and a prf of
'id-hmacWithSHA1'. Note: The salts are the first two words in the
ks0 [key schedule 0] of the BLOWFISH cipher from 'Applied
Cryptography' by Bruce Schnier - they could be any relatively
random string of bits.
The manager can use its knowledge of its own random number and the
agent's public value to kickstart its access to the agent in a
secure manner. Note that the security of this approach is
directly related to the strength of the authorization security of
the out of band provisioning of the managers public value
(e.g. the configuration file), but is not dependent at all on the
strength of the confidentiality of the out of band provisioning
data."
REFERENCE
"-- Password-Based Cryptography Standard, PKCS#5v2.0; RSA Laboratories, March 1999
-- Applied Cryptography, 2nd Ed.; B. Schneier,
Counterpane Systems; John Wiley & Sons, 1996"
::= { usmDHKickstartEntry 3 }
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
STATUS current
DESCRIPTION
"The compliance statement for this module."
MODULE
GROUP usmDHKeyMIBBasicGroup
DESCRIPTION
"This group MAY be implemented by any agent which
implements the usmUserTable and which wishes to provide the
ability to change user and agent authentication and privacy
keys via Diffie-Hellman key exchanges."
GROUP usmDHKeyParamGroup
DESCRIPTION
"This group MUST be implemented by any agent which
implements a MIB containing the DHKeyChange Textual
Convention defined in this module."
GROUP usmDHKeyKickstartGroup
DESCRIPTION
"This group MAY be implemented by any agent which
implements the usmUserTable and which wishes the ability to
populate the USM table based on out-of-band provided DH
ignition values.
Any agent implementing this group is expected to provide preinstalled entries in the vacm tables as follows:
In the usmUserTable: This entry allows access to the system and dhKickstart groups
usmUserEngineID localEngineID
usmUserName 'dhKickstart'
usmUserSecurityName 'dhKickstart'
usmUserCloneFrom ZeroDotZero
usmUserAuthProtocol none
usmUserAuthKeyChange ''
usmUserOwnAuthKeyChange ''
usmUserPrivProtocol none
usmUserPrivKeyChange ''
usmUserOwnPrivKeyChange ''
usmUserPublic ''
usmUserStorageType permanent
usmUserStatus active
In the vacmSecurityToGroupTable: This maps the initial user into the accessible objects.
vacmSecurityModel 3 (USM)
vacmSecurityName 'dhKickstart'
vacmGroupName 'dhKickstart'
vacmSecurityToGroupStorageType permanent
vacmSecurityToGroupStatus active
In the vacmAccessTable: Group name to view name translation.
vacmGroupName 'dhKickstart'
vacmAccessContextPrefix ''
vacmAccessSecurityModel 3 (USM)
vacmAccessSecurityLevel noAuthNoPriv
vacmAccessContextMatch exact
vacmAccessReadViewName 'dhKickRestricted'
vacmAccessWriteViewName ''
vacmAccessNotifyViewName 'dhKickRestricted'
vacmAccessStorageType permanent
vacmAccessStatus active
In the vacmViewTreeFamilyTable: Two entries to allow the initial entry to access the system and kickstart groups.
vacmViewTreeFamilyViewName 'dhKickRestricted'
vacmViewTreeFamilySubtree 1.3.6.1.2.1.1 (system)
vacmViewTreeFamilyMask ''
vacmViewTreeFamilyType 1
vacmViewTreeFamilyStorageType permanent
vacmViewTreeFamilyStatus active
vacmViewTreeFamilyViewName 'dhKickRestricted'
vacmViewTreeFamilySubtree (usmDHKickstartTable OID)
vacmViewTreeFamilyMask ''
vacmViewTreeFamilyType 1
vacmViewTreeFamilyStorageType permanent
vacmViewTreeFamilyStatus active
"
OBJECT usmDHParameters
MIN-ACCESS read-only
DESCRIPTION
"It is compliant to implement this object as read-only for
any device."
::= { usmDHKeyMIBCompliances 1 }
-- Units of Compliance
OBJECTS {
usmDHUserAuthKeyChange,
usmDHUserOwnAuthKeyChange,
usmDHUserPrivKeyChange,
usmDHUserOwnPrivKeyChange
}
STATUS current
DESCRIPTION
""
::= { usmDHKeyMIBGroups 1 }
OBJECTS {
usmDHParameters
}
STATUS current
DESCRIPTION
"The mandatory object for all MIBs which use the DHKeyChange
textual convention."
::= { usmDHKeyMIBGroups 2 }
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 }
[1] Harrington, D., Presuhn, R. and B. Wijnen, "An Architecture for Describing SNMP Management Frameworks", RFC 2571, April 1999.
[2] Rose, M. and K. McCloghrie, "Structure and Identification of Management Information for TCP/IP-based Internets", STD 16, RFC 1155, May 1990.
[3] Rose, M. and K. McCloghrie, "Concise MIB Definitions", STD 16, RFC 1212, March 1991.
[4] Rose, M., "A Convention for Defining Traps for use with the SNMP", RFC 1215, March 1991.
[5] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose, M. and S. Waldbusser, "Structure of Management Information Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
[6] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose, M. and S. Waldbusser, "Textual Conventions for SMIv2", STD 58, RFC 2579, April 1999.
[7] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose, M. and S. Waldbusser, "Conformance Statements for SMIv2", STD 58, RFC 2580, April 1999.
[8] Case, J., Fedor, M., Schoffstall, M. and J. Davin, "Simple Network Management Protocol", STD 15, RFC 1157, May 1990.
[9] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Introduction to Community-based SNMPv2", RFC 1901, January 1996.
[10] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Transport Mappings for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1906, January 1996.
[11] Case, J., Harrington D., Presuhn R. and B. Wijnen, "Message Processing and Dispatching for the Simple Network Management Protocol (SNMP)", RFC 2572, April 1999.
[12] Blumenthal, U. and B. Wijnen, "User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)", RFC 2574, April 1999.
[13] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Protocol Operations for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1905, January 1996.
[14] Levi, D., Meyer, P. and B. Stewart, "SNMPv3 Applications", RFC 2573, April 1999.
[15] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based Access Control Model (VACM) for the Simple Network Management Protocol (SNMP)", RFC 2575, April 1999.
[16] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[17] "Diffie-Hellman Key-Agreement Standard, Version 1.4", PKCS #3, RSA Laboratories, November 1993.
[18] Harkins, D. and D. Carrel, "The Internet Key Exchange", RFC 2409, November 1988.
[19] Eastlake, D., Crocker, S. and J. Schiller, "Randomness Recommendations for Security", RFC 1750, December 1994.
Objects in the usmDHUserKeyTable should be considered to have the same security sensitivity as the objects of the KeyChange type in usmUserTable and should be afforded the same level of protection. Specifically, the VACM should not grant more or less access to these objects than it grants to the usmUserTable KeyChange object.
The improper selection of parameters for use with Diffie-Hellman key changes may adversely affect the security of the agent. Please see the body of the MIB for specific recommendations or requirements on the selection of the DH parameters.
An unauthenticated DH exchange is subject to "man-in-the-middle" attacks. The use of the DH exchange in any specific environment should balance risk versus threat.
Good security from a DH exchange requires a good source of random numbers. If your application cannot provide a reasonable source of randomness, do not use a DH exchange. For more information, see "Randomness Recommendations for Security" [19].
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.
Michael C. StJohns
Excite@Home
450 Broadway
Redwood City, CA 94063
USA
Phone: +1-650-556-5368
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