Internet DRAFT - draft-ietf-opsawg-hmac-sha-2-usm-snmp
draft-ietf-opsawg-hmac-sha-2-usm-snmp
OPSAWG J. Merkle, Ed.
Internet-Draft Secunet Security Networks
Intended status: Standards Track M. Lochter
Expires: October 22, 2015 BSI
April 20, 2015
HMAC-SHA-2 Authentication Protocols in USM for SNMPv3
draft-ietf-opsawg-hmac-sha-2-usm-snmp-06
Abstract
This memo specifies new HMAC-SHA-2 authentication protocols for the
User-based Security Model (USM) for SNMPv3 defined in RFC 3414.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 22, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. The Internet-Standard Management Framework . . . . . . . . . 3
3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. The HMAC-SHA-2 Authentication Protocols . . . . . . . . . . . 3
4.1. Deviations from the HMAC-SHA-96 Authentication
Protocol . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Processing . . . . . . . . . . . . . . . . . . . . . . . 5
4.2.1. Processing an Outgoing Message . . . . . . . . . . . 5
4.2.2. Processing an Incoming Message . . . . . . . . . . . 6
5. Key Localization and Key Change . . . . . . . . . . . . . . . 6
6. Structure of the MIB Module . . . . . . . . . . . . . . . . . 6
7. Relationship to Other MIB Modules . . . . . . . . . . . . . . 7
7.1. Relationship to SNMP-USER-BASED-SM-MIB . . . . . . . . . 7
7.2. Relationship to SNMP-FRAMEWORK-MIB . . . . . . . . . . . 7
7.3. MIB modules required for IMPORTS . . . . . . . . . . . . 7
8. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9.1. Use of the HMAC-SHA-2 authentication protocols in USM . . 10
9.2. Cryptographic strength of the authentication protocols . 10
9.3. Derivation of keys from passwords . . . . . . . . . . . . 11
9.4. Access to the SNMP-USM-HMAC-SHA2-MIB . . . . . . . . . . 11
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
11.1. Normative References . . . . . . . . . . . . . . . . . . 12
11.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
This memo defines a portion of the Management Information Base (MIB)
for use with network management protocols. In particular it defines
additional authentication protocols for the User-based Security Model
(USM) for version 3 of the Simple Network Management Protocol
(SNMPv3) specified in RFC 3414 [RFC3414].
In RFC 3414, two different authentication protocols, HMAC-MD5-96 and
HMAC-SHA-96, are defined based on the hash functions MD5 and SHA-1,
respectively. This memo specifies new HMAC-SHA-2 authentication
protocols for USM using an HMAC based on the SHA-2 family of hash
functions [SHA] and truncated to 128 bits for SHA-224, to 192 bits
for SHA-256, to 256 bits for SHA-384, and to 384 bits for SHA-512.
These protocols are straightforward adaptations of the authentication
protocols HMAC-MD5-96 and HMAC-SHA-96 to the SHA-2 based HMAC.
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2. The Internet-Standard Management Framework
For a detailed overview of the documents that describe the current
Internet-Standard Management Framework, please refer to section 7 of
RFC 3410 [RFC3410].
Managed objects are accessed via a virtual information store, termed
the Management Information Base or MIB. MIB objects are generally
accessed through the Simple Network Management Protocol (SNMP).
Objects in the MIB are defined using the mechanisms defined in the
Structure of Management Information (SMI). This memo specifies a MIB
module that is compliant to the SMIv2, which is described in STD 58,
RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580
[RFC2580].
3. Conventions
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 BCP 14, RFC 2119
[RFC2119].
4. The HMAC-SHA-2 Authentication Protocols
This section describes the HMAC-SHA-2 authentication protocols. They
use the SHA-2 hash functions, which are described in FIPS PUB 180-4
[SHA] and RFC 6234 [RFC6234], in HMAC mode described in RFC 2104
[RFC2104] and RFC 6234, truncating the output to 128 bits for SHA-
224, 192 bits for SHA-256, 256 bits for SHA-384, and 384 bits for
SHA-512. RFC 6234 also provides source code for all the SHA-2
algorithms and HMAC (without truncation). It also includes test
harness and standard test vectors for all the defined hash functions
and HMAC examples.
The following protocols are defined:
usmHMAC128SHA224AuthProtocol: uses SHA-224 and truncates the
output to 128 bits (16 octets);
usmHMAC192SHA256AuthProtocol: uses SHA-256 and truncates the
output to 192 bits (24 octets);
usmHMAC256SHA384AuthProtocol: uses SHA-384 and truncates the
output to 256 bits (32 octets);
usmHMAC384SHA512AuthProtocol: uses SHA-512 and truncates the
output to 384 bits (48 octets).
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Implementations conforming to this specification MUST support
usmHMAC192SHA256AuthProtocol and SHOULD support
usmHMAC384SHA512AuthProtocol. The protocols
usmHMAC128SHA224AuthProtocol and usmHMAC256SHA384AuthProtocol are
OPTIONAL.
4.1. Deviations from the HMAC-SHA-96 Authentication Protocol
All the HMAC-SHA-2 authentication protocols are straightforward
adaptations of the HMAC-MD5-96 and HMAC-SHA-96 authentication
protocols. Precisely, they differ from the HMAC-MD5-96 and HMAC-
SHA-96 authentication protocols in the following aspects:
o The SHA-2 hash function is used to compute the message digest in
the HMAC computation according to RFC 2104 and RFC 6234, as
opposed to the MD5 hash function [RFC1321] and SHA-1 hash function
[SHA] used in HMAC-MD5-96 and HMAC-SHA-96, respectively.
Consequently, the length of the message digest prior to truncation
is 224 bits for SHA-224 based protocol, 256 bits for SHA-256 based
protocol, 384 bits for SHA-384 based protocol, and 512 bits for
SHA-512 based protocol.
o The resulting message digest (output of HMAC) is truncated to
* 16 octets for usmHMAC128SHA224AuthProtocol
* 24 octets for usmHMAC192SHA256AuthProtocol
* 32 octets for usmHMAC256SHA384AuthProtocol
* 48 octets for usmHMAC384SHA512AuthProtocol
as opposed to the truncation to 12 octets in HMAC-MD5-96 and HMAC-
SHA-96.
o The user's secret key to be used when calculating a digest MUST
be:
* 28 octets long and derived with SHA-224 for the SHA-224 based
protocol usmHMAC128SHA224AuthProtocol
* 32 octets long and derived with SHA-256 for the SHA-256 based
protocol usmHMAC192SHA256AuthProtocol
* 48 octets long and derived with SHA-384 for the SHA-384 based
protocol usmHMAC256SHA384AuthProtocol
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* 64 octets long and derived with SHA-512 for the SHA-512 based
protocol usmHMAC384SHA512AuthProtocol
as opposed to the keys being 16 and 20 octets long in HMAC-MD5-96
and HMAC-SHA-96, respectively.
4.2. Processing
This section describes the procedures for the HMAC-SHA-2
authentication protocols. The descriptions are based on the
definition of services and data elements defined for HMAC-SHA-96 in
RFC 3414 with the deviations listed in Section 4.1.
4.2.1. Processing an Outgoing Message
Values of constants M (the length of the secret key in octets) and N
(the length of the MAC output in octets) used below, are:
usmHMAC128SHA224AuthProtocol: M=28, N=16;
usmHMAC192SHA256AuthProtocol: M=32, N=24;
usmHMAC256SHA384AuthProtocol: M=48, N=32;
usmHMAC384SHA512AuthProtocol: M=64, N=48.
correspondingly.
This section describes the procedure followed by an SNMP engine
whenever it must authenticate an outgoing message using one of the
authentication protocols defined above.
1. The msgAuthenticationParameters field is set to serialization,
according to the rules in RFC 3417 [RFC3417], of an OCTET STRING
containing N zero octets.
2. From the secret authKey of M octets, calculate the HMAC-SHA-2
digest over it according to RFC 6234. Take the first N octets of
the final digest - this is the Message Authentication Code (MAC).
3. Replace the msgAuthenticationParameters field with the MAC
obtained in the previous step.
4. The authenticatedWholeMsg is then returned to the caller together
with statusInformation indicating success.
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4.2.2. Processing an Incoming Message
Values of the constants M and N are the same as in Section 4.2.1, and
are selected based on which authentication protocol is configured for
the given USM usmUser Table entry.
This section describes the procedure followed by an SNMP engine
whenever it must authenticate an incoming message using one of the
HMAC-SHA-2 authentication protocols.
1. If the digest received in the msgAuthenticationParameters field
is not N octets long, then an failure and an errorIndication
(authenticationError) is returned to the calling module.
2. The MAC received in the msgAuthenticationParameters field is
saved.
3. The digest in the msgAuthenticationParameters field is replaced
by the N zero octets.
4. Using the secret authKey, the HMAC is calculated over the
wholeMsg.
5. N first octets of the above HMAC are taken as the computed MAC
value.
6. The msgAuthenticationParameters field is replaced with the MAC
value that was saved in step 2.
7. The newly calculated MAC is compared with the MAC saved in step
2. If they do not match, then a failure and an errorIndication
(authenticationFailure) are returned to the calling module.
8. The authenticatedWholeMsg and statusInformation indicating
success are then returned to the caller.
5. Key Localization and Key Change
For any of the protocols defined in Section 4, key localization and
key change SHALL be performed according to RFC 3414 using the SHA-2
hash function applied in the respective protocol.
6. Structure of the MIB Module
The MIB module specified in this memo does not define any managed
objects, subtrees, notifications or tables, but only object
identities (for authentication protocols) under a subtree of an
existing MIB.
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7. Relationship to Other MIB Modules
7.1. Relationship to SNMP-USER-BASED-SM-MIB
RFC 3414 specifies the MIB module for the User-based Security Model
(USM) for SNMPv3 (SNMP-USER-BASED-SM-MIB), which defines
authentication protocols for USM based on the hash functions MD5 and
SHA-1, respectively. The following MIB module defines new HMAC-SHA2
authentication protocols for USM based on the SHA-2 hash functions
[SHA]. The use of the HMAC-SHA2 authentication protocols requires
the usage of the objects defined in the SNMP-USER-BASED-SM-MIB.
7.2. Relationship to SNMP-FRAMEWORK-MIB
RFC 3411 [RFC3411] specifies the SNMP-FRAMEWORK-MIB, which defines a
subtree snmpAuthProtocols for SNMP authentication protocols. The
following MIB module defines new authentication protocols in the
snmpAuthProtocols subtree.
7.3. MIB modules required for IMPORTS
The following MIB module IMPORTS definitions from SNMPv2-SMI
[RFC2578] and SNMP-FRAMEWORK-MIB [RFC3411].
8. Definitions
SNMP-USM-HMAC-SHA2-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-IDENTITY,
snmpModules FROM SNMPv2-SMI -- [RFC2578]
snmpAuthProtocols FROM SNMP-FRAMEWORK-MIB; -- [RFC3411]
snmpUsmHmacSha2MIB MODULE-IDENTITY
LAST-UPDATED "201503090000Z" -- 9th Mar 2015, midnight
-- RFC Ed.: replace with publication date & remove this line
ORGANIZATION "SNMPv3 Working Group"
CONTACT-INFO "WG email: OPSAWG@ietf.org
Subscribe:
https://www.ietf.org/mailman/listinfo/opsawg
Editor: Johannes Merkle
secunet Security Networks
postal: Mergenthaler Allee 77
D-65760 Eschborn
Germany
phone: +49 20154543091
email: johannes.merkle@secunet.com
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Co-Editor: Manfred Lochter
Bundesamt fuer Sicherheit in der
Informationstechnik (BSI)
postal: Postfach 200363
D-53133 Bonn
Germany
phone: +49 228 9582 5643
email: manfred.lochter@bsi.bund.de"
DESCRIPTION "Definitions of Object Identities needed
for the use of HMAC-SHA2 by SNMP's User-based
Security Model.
Copyright (c) 2014 IETF Trust and the persons identified
as authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with
or without modification, is permitted pursuant to, and
subject to the license terms contained in, the Simplified
BSD License set forth in Section 4.c of the IETF Trust's
Legal Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info)."
REVISION "201503090000Z" -- 9th Mar 2015, midnight
-- RFC Ed.: replace with publication date & remove this line
DESCRIPTION "Initial version, published as RFC TBD"
-- RFC Ed.: replace TBD with actual RFC number & remove this line
::= { snmpModules nn } -- nn to be assigned by IANA
-- RFC Ed.: replace nn with actual number assigned by IANA & remove
-- this comment
usmHMAC128SHA224AuthProtocol OBJECT-IDENTITY
STATUS current
DESCRIPTION "The Authentication Protocol
usmHMAC128SHA224AuthProtocol uses HMAC-SHA-224 and
truncates output to 128 bits."
REFERENCE "- Krawczyk, H., Bellare, M., and R. Canetti, HMAC:
Keyed-Hashing for Message Authentication, RFC 2104.
- National Institute of Standards and Technology,
Secure Hash Standard (SHS), FIPS PUB 180-4, 2012."
::= { snmpAuthProtocols aa } -- aa to be assigned by IANA
-- RFC Ed.: replace aa with actual number assigned by IANA & remove
-- this comment
usmHMAC192SHA256AuthProtocol OBJECT-IDENTITY
STATUS current
DESCRIPTION "The Authentication Protocol
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usmHMAC192SHA256AuthProtocol uses HMAC-SHA-256 and
truncates output to 192 bits."
REFERENCE "- Krawczyk, H., Bellare, M., and R. Canetti, HMAC:
Keyed-Hashing for Message Authentication, RFC 2104.
- National Institute of Standards and Technology,
Secure Hash Standard (SHS), FIPS PUB 180-4, 2012."
::= { snmpAuthProtocols bb } -- bb to be assigned by IANA
-- RFC Ed.: replace bb with actual number assigned by IANA & remove
-- this comment
usmHMAC256SHA384AuthProtocol OBJECT-IDENTITY
STATUS current
DESCRIPTION "The Authentication Protocol
usmHMAC256SHA384AuthProtocol uses HMAC-SHA-384 and
truncates output to 256 bits."
REFERENCE "- Krawczyk, H., Bellare, M., and R. Canetti, HMAC:
Keyed-Hashing for Message Authentication, RFC 2104.
- National Institute of Standards and Technology,
Secure Hash Standard (SHS), FIPS PUB 180-4, 2012."
::= { snmpAuthProtocols cc } -- cc to be assigned by IANA
-- RFC Ed.: replace cc with actual number assigned by IANA & remove
-- this comment
usmHMAC384SHA512AuthProtocol OBJECT-IDENTITY
STATUS current
DESCRIPTION "The Authentication Protocol
usmHMAC384SHA512AuthProtocol uses HMAC-SHA-512 and
truncates output to 384 bits."
REFERENCE "- Krawczyk, H., Bellare, M., and R. Canetti, HMAC:
Keyed-Hashing for Message Authentication, RFC 2104.
- National Institute of Standards and Technology,
Secure Hash Standard (SHS), FIPS PUB 180-4, 2012."
::= { snmpAuthProtocols dd } -- dd to be assigned by IANA
-- RFC Ed.: replace dd with actual number assigned by IANA & remove
-- this comment
END
9. Security Considerations
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9.1. Use of the HMAC-SHA-2 authentication protocols in USM
The security considerations of RFC 3414 also apply to the HMAC-SHA-2
authentication protocols defined in this document.
9.2. Cryptographic strength of the authentication protocols
At the time of publication of this document, all of the HMAC-SHA-2
authentication protocols provide a very high level of security. The
security of each HMAC-SHA-2 authentication protocol depends on the
parameters used in the corresponding HMAC computation, which are the
length of the key (if the key has maximum entropy), the size of the
hash function's internal state, and the length of the truncated MAC.
For the HMAC-SHA-2 authentication protocols these values are as
follows (values are given in bits).
+------------------------------+---------+----------------+---------+
| Protocol | Key | Size of | MAC |
| | length | internal state | length |
+------------------------------+---------+----------------+---------+
| usmHMAC128SHA224AuthProtocol | 224 | 256 | 128 |
| usmHMAC192SHA256AuthProtocol | 256 | 256 | 192 |
| usmHMAC256SHA384AuthProtocol | 384 | 512 | 256 |
| usmHMAC384SHA512AuthProtocol | 512 | 512 | 384 |
+------------------------------+---------+----------------+---------+
Table 1: HMAC parameters of the HMAC-SHA-2 authentication protocols
The security of the HMAC scales with both the key length and the size
of the internal state: longer keys render key guessing attacks more
difficult, and a larger internal state decreases the success
probability of MAC forgeries based on internal collisions of the hash
function.
The role of the truncated output length is more complicated:
according to [BCK], there is a trade-off in that "by outputting less
bits the attacker has less bits to predict in a MAC forgery but, on
the other hand, the attacker also learns less about the output of the
compression function from seeing the authentication tags computed by
legitimate parties"; thus, truncation weakens the HMAC against
forgery by guessing, but at the same time strengthens it against
chosen message attacks aiming at MAC forgery based on internal
collisions or at key guessing. RFC 2104 and [BCK] allow truncation
to any length that is not less than half the size of the internal
state.
Further discussion of the security of the HMAC construction is given
in RFC 2104.
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9.3. Derivation of keys from passwords
If secret keys to be used for HMAC-SHA-2 authentication protocols are
derived from passwords, the derivation SHOULD be performed using the
password-to-key algorithm from Appendix A.1 of RFC 3414 with MD5
being replaced by the SHA-2 hash function H used in the HMAC-SHA-2
authentication protocol. Specifically, the password is converted
into the required secret key by the following steps:
o forming a string of length 1,048,576 octets by repeating the value
of the password as often as necessary, truncating accordingly, and
using the resulting string as the input to the hash function H.
The resulting digest, termed "digest1", is used in the next step.
o a second string is formed by concatenating digest1, the SNMP
engine's snmpEngineID value, and digest1. This string is used as
input to the hash function H.
9.4. Access to the SNMP-USM-HMAC-SHA2-MIB
The SNMP-USM-HMAC-SHA2-MIB module defines OBJECT IDENTIFIER values
for use in other MIB modules. It does not define any objects that
can be accessed. As such, the SNMP-USM-HMAC-SHA2-MIB does not, by
itself, have any effect on the security of the Internet.
The values defined in this module are expected to be used with the
usmUserTable defined in the SNMP-USER-BASED-SM-MIB [RFC3414]. The
considerations in Section 11.5 of RFC 3414 should be taken into
account.
10. IANA Considerations
IANA is requested to assign an OID for
+--------------------+-------------------------+
| Descriptor | OBJECT IDENTIFIER value |
+--------------------+-------------------------+
| snmpUsmHmacSha2MIB | { snmpModules nn } |
+--------------------+-------------------------+
Table 2: OID of MIB
with nn appearing in the MIB module definition in Section 8.
Furthermore, IANA is requested to assign a value in the
SnmpAuthProtocols registry for each of the following protocols.
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+------------------------------+-------+-----------+
| Description | Value | Reference |
+------------------------------+-------+-----------+
| usmHMAC128SHA224AuthProtocol | aa | RFC YYYY |
| usmHMAC192SHA256AuthProtocol | bb | RFC YYYY |
| usmHMAC256SHA384AuthProtocol | cc | RFC YYYY |
| usmHMAC384SHA512AuthProtocol | dd | RFC YYYY |
+------------------------------+-------+-----------+
Table 3: Code points assigned to HMAC-SHA-2 authentication protocols
-- RFC Ed.: replace YYYY with actual RFC number and remove this line
with aa, bb, cc, etc. appearing in the MIB module definition in
Section 8.
11. References
11.1. Normative References
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, February
1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management Information
Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
[RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Textual Conventions for SMIv2", STD
58, RFC 2579, April 1999.
[RFC2580] McCloghrie, K., Perkins, D., and J. Schoenwaelder,
"Conformance Statements for SMIv2", STD 58, RFC 2580,
April 1999.
[RFC3414] Blumenthal, U. and B. Wijnen, "User-based Security Model
(USM) for version 3 of the Simple Network Management
Protocol (SNMPv3)", STD 62, RFC 3414, December 2002.
[SHA] National Institute of Standards and Technology, "Secure
Hash Standard (SHS)", FIPS PUB 180-4, March 2012.
[RFC6234] Eastlate 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234, May 2011.
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11.2. Informative References
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992.
[RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
December 2002.
[RFC3417] Presuhn, R., "Transport Mappings for the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3417, December
2002.
[BCK] Bellare, M., Canetti, R., and H. Krawczyk, "Keyed Hash
Functions for Message Authentication", Advances in
Cryptology - CRYPTO 99, Lecture Notes in Computer Science
1109, Springer Verlag, 1996.
Authors' Addresses
Johannes Merkle (editor)
Secunet Security Networks
Mergenthaler Allee 77
65760 Eschborn
Germany
Phone: +49 201 5454 3091
EMail: johannes.merkle@secunet.com
Manfred Lochter
BSI
Postfach 200363
53133 Bonn
Germany
Phone: +49 228 9582 5643
EMail: manfred.lochter@bsi.bund.de
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