rfc1352.txt
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Network Working Group J. Galvin
Request for Comments: 1352 Trusted Information Systems, Inc.
K. McCloghrie
Hughes LAN Systems, Inc.
J. Davin
MIT Laboratory for Computer Science
July 1992
SNMP Security Protocols
Status of this Memo
This document specifies an IAB standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "IAB
Official Protocol Standards" for the standardization state and status
of this protocol. Distribution of this memo is unlimited.
Table of Contents
1. Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1 Threats . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 Goals and Constraints . . . . . . . . . . . . . . . . . . . 5
2.3 Security Services . . . . . . . . . . . . . . . . . . . . . 6
2.4 Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4.1 Message Digest Algorithm . . . . . . . . . . . . . . . . . 7
2.4.2 Symmetric Encryption Algorithm . . . . . . . . . . . . . . 8
3. SNMP Party . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Digest Authentication Protocol . . . . . . . . . . . . . . . 11
4.1 Generating a Message . . . . . . . . . . . . . . . . . . . 14
4.2 Receiving a Message . . . . . . . . . . . . . . . . . . . . 15
5. Symmetric Privacy Protocol . . . . . . . . . . . . . . . . . 16
5.1 Generating a Message . . . . . . . . . . . . . . . . . . . 17
5.2 Receiving a Message . . . . . . . . . . . . . . . . . . . . 18
6. Clock and Secret Distribution . . . . . . . . . . . . . . . 19
6.1 Initial Configuration . . . . . . . . . . . . . . . . . . 20
6.2 Clock Distribution . . . . . . . . . . . . . . . . . . . . 22
6.3 Clock Synchronization . . . . . . . . . . . . . . . . . . . 24
6.4 Secret Distribution . . . . . . . . . . . . . . . . . . . . 26
6.5 Crash Recovery . . . . . . . . . . . . . . . . . . . . . . 28
7. Security Considerations . . . . . . . . . . . . . . . . . . 30
7.1 Recommended Practices . . . . . . . . . . . . . . . . . . . 30
7.2 Conformance . . . . . . . . . . . . . . . . . . . . . . . 33
7.3 Protocol Correctness . . . . . . . . . . . . . . . . . . . . 34
7.3.1 Clock Monotonicity Mechanism . . . . . . . . . . . . . . . 35
7.3.2 Data Integrity Mechanism . . . . . . . . . . . . . . . . . 36
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RFC 1352 SNMP Security Protocols July 1992
7.3.3 Data Origin Authentication Mechanism . . . . . . . . . . . 36
7.3.4 Restricted Administration Mechanism . . . . . . . . . . . 36
7.3.5 Ordered Delivery Mechanism . . . . . . . . . . . . . . . 37
7.3.6 Message Timeliness Mechanism . . . . . . . . . . . . . . . 38
7.3.7 Selective Clock Acceleration Mechanism . . . . . . . . . . 38
7.3.8 Confidentiality Mechanism . . . . . . . . . . . . . . . . 39
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 39
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 40
10. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 41
1. Abstract
The Simple Network Management Protocol (SNMP) specification [1]
allows for the protection of network management operations by a
variety of security protocols. The SNMP administrative model
described in [2] provides a framework for securing SNMP network
management. In the context of that framework, this memo defines
protocols to support the following three security services:
o data integrity,
o data origin authentication, and
o data confidentiality.
Please send comments to the SNMP Security Developers mailing list
(snmp-sec-dev@tis.com).
2. Introduction
In the model described in [2], each SNMP party is, by definition,
associated with a single authentication protocol. The authentication
protocol provides a mechanism by which SNMP management communications
transmitted by the party may be reliably identified as having
originated from that party. The authentication protocol defined in
this memo also reliably determines that the message received is the
message that was sent.
Similarly, each SNMP party is, by definition, associated with a
single privacy protocol. The privacy protocol provides a mechanism by
which SNMP management communications transmitted to said party are
protected from disclosure. The privacy protocol in this memo
specifies that only authenticated messages may be protected from
disclosure.
These protocols are secure alternatives to the so-called "trivial"
protocol defined in [1].
Galvin, McCloghrie, & Davin [Page 2]
RFC 1352 SNMP Security Protocols July 1992
USE OF THE TRIVIAL PROTOCOL ALONE DOES NOT CONSTITUTE SECURE
NETWORK MANAGEMENT. THEREFORE, A NETWORK MANAGEMENT SYSTEM THAT
IMPLEMENTS ONLY THE TRIVIAL PROTOCOL IS NOT CONFORMANT TO THIS
SPECIFICATION.
The Digest Authentication Protocol is described in Section 4. It
provides a data integrity service by transmitting a message digest --
computed by the originator and verified by the recipient -- with each
SNMP message. The data origin authentication service is provided by
prefixing the message with a secret value known only to the
originator and recipient, prior to computing the digest. Thus, data
integrity is supported explicitly while data origin authentication is
supported implicitly in the verification of the digest.
The Symmetric Privacy Protocol is described in Section 5. It protects
messages from disclosure by encrypting their contents according to a
secret cryptographic key known only to the originator and recipient.
The additional functionality afforded by this protocol is assumed to
justify its additional computational cost.
The Digest Authentication Protocol depends on the existence of
loosely synchronized clocks between the originator and recipient of a
message. The protocol specification makes no assumptions about the
strategy by which such clocks are synchronized. Section 6.3 presents
one strategy that is particularly suited to the demands of SNMP
network management.
Both protocols described here require the sharing of secret
information between the originator of a message and its recipient.
The protocol specifications assume the existence of the necessary
secrets. The selection of such secrets and their secure distribution
to appropriate parties may be accomplished by a variety of
strategies. Section 6.4 presents one such strategy that is
particularly suited to the demands of SNMP network management.
2.1 Threats
Several of the classical threats to network protocols are applicable
to the network management problem and therefore would be applicable
to any SNMP security protocol. Other threats are not applicable to
the network management problem. This section discusses principal
threats, secondary threats, and threats which are of lesser
importance.
The principal threats against which any SNMP security protocol should
provide protection are:
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RFC 1352 SNMP Security Protocols July 1992
Modification of Information.
The SNMP protocol provides the means for management stations to
interrogate and to manipulate the value of objects in a managed
agent. The modification threat is the danger that some party may
alter in-transit messages generated by an authorized party in such
a way as to effect unauthorized management operations, including
falsifying the value of an object.
Masquerade.
The SNMP administrative model includes an access control model.
Access control necessarily depends on knowledge of the origin of a
message. The masquerade threat is the danger that management
operations not authorized for some party may be attempted by that
party by assuming the identity of another party that has the
appropriate authorizations.
Two secondary threats are also identified. The security protocols
defined in this memo do provide protection against:
Message Stream Modification.
The SNMP protocol is based upon connectionless transport services.
The message stream modification threat is the danger that messages
may be arbitrarily re-ordered, delayed or replayed to effect
unauthorized management operations. This threat may arise either
by the work of a malicious attacker or by the natural operation of
a subnetwork service.
Disclosure.
The disclosure threat is the danger of eavesdropping on the
exchanges between managed agents and a management station.
Protecting against this threat is mandatory when the SNMP is used
to administer private parameters on which its security is based.
Protecting against the disclosure threat may also be required as a
matter of local policy.
There are at least two threats that a SNMP security protocol need not
protect against. The security protocols defined in this memo do not
provide protection against:
Denial of Service.
A SNMP security protocol need not attempt to address the broad
range of attacks by which service to authorized parties is denied.
Indeed, such denial-of-service attacks are in many cases
indistinguishable from the type of network failures with which any
viable network management protocol must cope as a matter of
course.
Galvin, McCloghrie, & Davin [Page 4]
RFC 1352 SNMP Security Protocols July 1992
Traffic Analysis.
In addition, a SNMP security protocol need not attempt to address
traffic analysis attacks. Indeed, many traffic patterns are
predictable -- agents may be managed on a regular basis by a
relatively small number of management stations -- and therefore
there is no significant advantage afforded by protecting against
traffic analysis.
2.2 Goals and Constraints
Based on the foregoing account of threats in the SNMP network
management environment, the goals of a SNMP security protocol are
enumerated below.
1. The protocol should provide for verification that each
received SNMP message has not been modified during
its transmission through the network in such a way that
an unauthorized management operation might result.
2. The protocol should provide for verification of the
identity of the originator of each received SNMP
message.
3. The protocol should provide that the apparent time of
generation for each received SNMP message is recent.
4. The protocol should provide that the apparent time of
generation for each received SNMP message is
subsequent to that for all previously delivered messages
of similar origin.
5. The protocol should provide, when necessary, that the
contents of each received SNMP message are protected
from disclosure.
In addition to the principal goal of supporting secure network
management, the design of any SNMP security protocol is also
influenced by the following constraints:
1. When the requirements of effective management in times
of network stress are inconsistent with those of security,
the former are preferred.
2. Neither the security protocol nor its underlying security
mechanisms should depend upon the ready availability
of other network services (e.g., Network Time Protocol
(NTP) or secret/key management protocols).
Galvin, McCloghrie, & Davin [Page 5]
RFC 1352 SNMP Security Protocols July 1992
3. A security mechanism should entail no changes to the
basic SNMP network management philosophy.
2.3 Security Services
The security services necessary to support the goals of a SNMP
security protocol are as follows.
Data Integrity is the provision of the property that data
and data sequences have not been altered or destroyed
in an unauthorized manner.
Data Origin Authentication is the provision of the
property that the claimed origin of received data is
corroborated.
Data Confidentiality is the provision of the property that
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