| Rfc | 7860 |
|---|
| Title | HMAC-SHA-2 Authentication Protocols in User-Based Security Model
(USM) for SNMPv3 |
|---|
| Author | J. Merkle, Ed., M. Lochter |
|---|
| Date | April 2016 |
|---|
| Format: | TXT, HTML |
|---|
| Obsoletes | RFC7630 |
|---|
| Status: | PROPOSED STANDARD |
|---|
|
Internet Engineering Task Force (IETF) J. Merkle, Ed.
Request for Comments: 7860 Secunet Security Networks
Obsoletes: 7630 M. Lochter
Category: Standards Track BSI
ISSN: 2070-1721 April 2016
HMAC-SHA-2 Authentication Protocols in
User-Based Security Model (USM) for SNMPv3
Abstract
This document specifies several authentication protocols based on the
SHA-2 hash functions for the User-based Security Model (USM) for
SNMPv3 defined in RFC 3414. It obsoletes RFC 7630, in which the MIB
MODULE-IDENTITY value was incorrectly specified.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7860.
Copyright Notice
Copyright (c) 2016 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.
1. Introduction
Within the Architecture for describing Simple Network Management
Protocol (SNMP) Management Frameworks [RFC3411], the User-based
Security Model (USM) [RFC3414] for SNMPv3 is defined as a Security
Subsystem within an SNMP engine. 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 a Hashed Message Authentication Code (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.
This document obsoletes RFC 7630, in which the MIB MODULE-IDENTITY
value was incorrectly specified.
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,
[RFC2578], STD 58, [RFC2579] and STD 58, [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, which
use the SHA-2 hash functions (described in FIPS PUB 180-4 [SHA] and
RFC 6234 [RFC6234]) in the HMAC mode (described in [RFC2104] and
[RFC6234]), 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).
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. Specifically, 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 the 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 the SHA-224-based protocol, 256 bits for the
SHA-256-based protocol, 384 bits for the SHA-384-based protocol,
and 512 bits for the 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
* 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 specified for HMAC-SHA-96 in
RFC 3414 with the deviations listed in Section 4.1.
Values of constants M (the length of the secret key in octets) and N
(the length of the Message Authentication Code (MAC) output in
octets), and the hash function H used below are:
usmHMAC128SHA224AuthProtocol: M=28, N=16, H=SHA-224;
usmHMAC192SHA256AuthProtocol: M=32, N=24, H=SHA-256;
usmHMAC256SHA384AuthProtocol: M=48, N=32, H=SHA-384;
usmHMAC384SHA512AuthProtocol: M=64, N=48, H=SHA-512.
4.2.1. Processing an Outgoing Message
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. Values of the constants M
and N, and the hash function H are as defined in Section 4.2 and are
selected based on which authentication protocol is configured for the
given USM usmUser Table entry.
1. The msgAuthenticationParameters field is set to the serialization
of an OCTET STRING containing N zero octets; it is serialized
according to the rules in [RFC3417].
2. Using the secret authKey of M octets, the HMAC is calculated over
the wholeMsg according to RFC 6234 with hash function H.
3. The N first octets of the above HMAC are taken as the computed
MAC value.
4. The msgAuthenticationParameters field is replaced with the MAC
obtained in the previous step.
5. The authenticatedWholeMsg is then returned to the caller together
with the statusInformation indicating success.
4.2.2. Processing an Incoming Message
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. Values of the constants M and
N, and the hash function H are as defined in Section 4.2 and are
selected based on which authentication protocol is configured for the
given USM usmUser Table entry.
1. If the digest received in the msgAuthenticationParameters field
is not N octets long, then a failure and an errorIndication
(authenticationError) are 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 of M octets, the HMAC is calculated over
the wholeMsg according to RFC 6234 with hash function H.
5. The 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 [RFC3414] using the same
SHA-2 hash function as in the HMAC-SHA-2 authentication protocol.
6. Structure of the MIB Module
The MIB module specified in this memo does not define any managed
objects, subtrees, notifications, or tables; rather, it only defines
object identities (for authentication protocols) under a subtree of
an existing MIB.
7. Relationship to Other MIB Modules
7.1. Relationship to SNMP-USER-BASED-SM-MIB
[RFC3414] specifies the MIB module for 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
[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,
mib-2 FROM SNMPv2-SMI -- RFC 2578
snmpAuthProtocols FROM SNMP-FRAMEWORK-MIB; -- RFC 3411
snmpUsmHmacSha2MIB MODULE-IDENTITY
LAST-UPDATED "201604180000Z" -- 18 April 2016, midnight
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
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 Authentication Protocols by SNMP's User-based Security
Model.
Copyright (c) 2016 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 "201604180000Z" -- 18 April 2016, midnight
DESCRIPTION
"Version correcting the MODULE-IDENTITY value,
published as RFC 7860"
REVISION "201510140000Z" -- 14 October 2015, midnight
DESCRIPTION
"Initial version, published as RFC 7630"
::= { mib-2 235 }
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 4 }
usmHMAC192SHA256AuthProtocol OBJECT-IDENTITY
STATUS current
DESCRIPTION "The Authentication Protocol
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 5 }
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 6 }
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 7 }
END
9. Security Considerations
9.1. Use of the HMAC-SHA-2 Authentication Protocols in USM
The security considerations of [RFC3414] 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.
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 forming a second string 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 has assigned an OID for the MIB as follows.
+--------------------+-------------------------+
| Descriptor | OBJECT IDENTIFIER value |
+--------------------+-------------------------+
| snmpUsmHmacSha2MIB | { mib-2 235 } |
+--------------------+-------------------------+
Table 2: OID of MIB
Furthermore, IANA has assigned a value in the SnmpAuthProtocols
registry for each of the following protocols.
+------------------------------+-------+-----------+
| Description | Value | Reference |
+------------------------------+-------+-----------+
| usmHMAC128SHA224AuthProtocol | 4 | RFC 7860 |
| usmHMAC192SHA256AuthProtocol | 5 | RFC 7860 |
| usmHMAC256SHA384AuthProtocol | 6 | RFC 7860 |
| usmHMAC384SHA512AuthProtocol | 7 | RFC 7860 |
+------------------------------+-------+-----------+
Table 3: Code Points Assigned to HMAC-SHA-2 Authentication Protocols
11. References
11.1. Normative References
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997,
<http://www.rfc-editor.org/info/rfc2104>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management Information
Version 2 (SMIv2)", STD 58, RFC 2578,
DOI 10.17487/RFC2578, April 1999,
<http://www.rfc-editor.org/info/rfc2578>.
[RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Textual Conventions for SMIv2",
STD 58, RFC 2579, DOI 10.17487/RFC2579, April 1999,
<http://www.rfc-editor.org/info/rfc2579>.
[RFC2580] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Conformance Statements for SMIv2",
STD 58, RFC 2580, DOI 10.17487/RFC2580, April 1999,
<http://www.rfc-editor.org/info/rfc2580>.
[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,
DOI 10.17487/RFC3414, December 2002,
<http://www.rfc-editor.org/info/rfc3414>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<http://www.rfc-editor.org/info/rfc6234>.
[SHA] National Institute of Standards and Technology, "Secure
Hash Standard (SHS)", FIPS PUB 180-4,
DOI 10.6028/NIST.FIPS.180-4, August 2015,
<http://nvlpubs.nist.gov/nistpubs/FIPS/
NIST.FIPS.180-4.pdf>.
11.2. Informative References
[BCK] Bellare, M., Canetti, R., and H. Krawczyk, "Keyed Hash
Functions for Message Authentication", Advances in
Cryptology - CRYPTO 96, Lecture Notes in Computer
Science 1109, Springer-Verlag Berlin Heidelberg,
DOI 10.1007/3-540-68697-5_1, 1996.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
DOI 10.17487/RFC1321, April 1992,
<http://www.rfc-editor.org/info/rfc1321>.
[RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410,
DOI 10.17487/RFC3410, December 2002,
<http://www.rfc-editor.org/info/rfc3410>.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
DOI 10.17487/RFC3411, December 2002,
<http://www.rfc-editor.org/info/rfc3411>.
[RFC3417] Presuhn, R., Ed., "Transport Mappings for the Simple
Network Management Protocol (SNMP)", STD 62, RFC 3417,
DOI 10.17487/RFC3417, December 2002,
<http://www.rfc-editor.org/info/rfc3417>.
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