ISMS W. Hardaker
Internet-Draft Sparta, Inc.
Intended status: Standards Track September 1, 2009
Expires: March 5, 2010
Transport Layer Security Transport Model for SNMP
draft-ietf-isms-dtls-tm-00.txt
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Abstract
This document describes a Transport Model for the Simple Network
Management Protocol (SNMP), that uses either the Transport Layer
Security protocol or the Datagram Transport Layer Security (DTLS)
protocol. The TLS and DTLS protocols provide authentication and
privacy services for SNMP applications. This document describes how
the TLS Transport Model (TLSTM) implements the needed features of a
SNMP Transport Subsystem to make this protection possible in an
interoperable way.
This transport model is designed to meet the security and operational
needs of network administrators. The TLS mode can make use of TCP's
improved support for larger packet sizes and the DTLS mode provides
potentially superior operation in environments where a connectionless
(e.g. UDP or SCTP) transport is preferred. Both TLS and DTLS
integrate well into existing public keying infrastructures.
This document also defines a portion of the Management Information
Base (MIB) for use with network management protocols. In particular
it defines objects for managing the TLS Transport Model for SNMP.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Conventions . . . . . . . . . . . . . . . . . . . . . . . 7
2. The Transport Layer Security Protocol . . . . . . . . . . . . 8
2.1. SNMP requirements of (D)TLS . . . . . . . . . . . . . . . 8
3. How the TLSTM fits into the Transport Subsystem . . . . . . . 8
3.1. Security Capabilities of this Model . . . . . . . . . . . 10
3.1.1. Threats . . . . . . . . . . . . . . . . . . . . . . . 10
3.1.2. Message Protection . . . . . . . . . . . . . . . . . . 12
3.1.3. (D)TLS Sessions . . . . . . . . . . . . . . . . . . . 13
3.2. Security Parameter Passing . . . . . . . . . . . . . . . . 13
3.3. Notifications and Proxy . . . . . . . . . . . . . . . . . 14
4. Elements of the Model . . . . . . . . . . . . . . . . . . . . 15
4.1. X.509 Certificates . . . . . . . . . . . . . . . . . . . . 15
4.1.1. Provisioning for the Certificate . . . . . . . . . . . 15
4.2. Messages . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.3. SNMP Services . . . . . . . . . . . . . . . . . . . . . . 16
4.3.1. SNMP Services for an Outgoing Message . . . . . . . . 16
4.3.2. SNMP Services for an Incoming Message . . . . . . . . 17
4.4. (D)TLS Services . . . . . . . . . . . . . . . . . . . . . 18
4.4.1. Services for Establishing a Session . . . . . . . . . 18
4.4.2. (D)TLS Services for an Incoming Message . . . . . . . 20
4.4.3. (D)TLS Services for an Outgoing Message . . . . . . . 20
4.5. Cached Information and References . . . . . . . . . . . . 21
4.5.1. TLS Transport Model Cached Information . . . . . . . . 21
5. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 21
5.1. Procedures for an Incoming Message . . . . . . . . . . . . 22
5.1.1. DTLS Processing for Incoming Messages . . . . . . . . 22
5.1.2. Transport Processing for Incoming Messages . . . . . . 23
5.2. Procedures for an Outgoing Message . . . . . . . . . . . . 25
5.3. Establishing a Session . . . . . . . . . . . . . . . . . . 26
5.4. Closing a Session . . . . . . . . . . . . . . . . . . . . 28
6. MIB Module Overview . . . . . . . . . . . . . . . . . . . . . 29
6.1. Structure of the MIB Module . . . . . . . . . . . . . . . 29
6.2. Textual Conventions . . . . . . . . . . . . . . . . . . . 29
6.3. Statistical Counters . . . . . . . . . . . . . . . . . . . 29
6.4. Configuration Tables . . . . . . . . . . . . . . . . . . . 29
6.5. Relationship to Other MIB Modules . . . . . . . . . . . . 30
6.5.1. MIB Modules Required for IMPORTS . . . . . . . . . . . 30
7. MIB Module Definition . . . . . . . . . . . . . . . . . . . . 30
8. Operational Considerations . . . . . . . . . . . . . . . . . . 53
8.1. Sessions . . . . . . . . . . . . . . . . . . . . . . . . . 53
8.2. Notification Receiver Credential Selection . . . . . . . . 53
8.3. contextEngineID Discovery . . . . . . . . . . . . . . . . 54
9. Security Considerations . . . . . . . . . . . . . . . . . . . 54
9.1. Certificates, Authentication, and Authorization . . . . . 54
9.2. Use with SNMPv1/SNMPv2c Messages . . . . . . . . . . . . . 55
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9.3. MIB Module Security . . . . . . . . . . . . . . . . . . . 56
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 57
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 58
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 59
12.1. Normative References . . . . . . . . . . . . . . . . . . . 59
12.2. Informative References . . . . . . . . . . . . . . . . . . 60
Appendix A. (D)TLS Overview . . . . . . . . . . . . . . . . . . . 61
A.1. The (D)TLS Record Protocol . . . . . . . . . . . . . . . . 61
A.2. The (D)TLS Handshake Protocol . . . . . . . . . . . . . . 62
Appendix B. PKIX Certificate Infrastructure . . . . . . . . . . . 63
Appendix C. Target and Notificaton Configuration Example . . . . 64
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 66
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1. Introduction
It is important to understand the modular SNMPv3 architecture as
defined by [RFC3411] and enhanced by the Transport Subsystem
[I-D.ietf-isms-tmsm]. It is also important to understand the
terminology of the SNMPv3 architecture in order to understand where
the Transport Model described in this document fits into the
architecture and how it interacts with the other architecture
subsystems. For a detailed overview of the documents that describe
the current Internet-Standard Management Framework, please refer to
Section 7 of [RFC3410].
This document describes a Transport Model that makes use of the
Transport Layer Security (TLS) [RFC5246] and the Datagram Transport
Layer Security (DTLS) Protocol [RFC4347], within a transport
subsystem [I-D.ietf-isms-tmsm]. DTLS is the datagram variant of the
Transport Layer Security (TLS) protocol [RFC5246]. The Transport
Model in this document is referred to as the Transport Layer Security
Transport Model (TLSTM). TLS and DTLS take advantage of the X.509
public keying infrastructure [RFC5280]. This transport model is
designed to meet the security and operational needs of network
administrators, operate in both environments where a connectionless
(e.g. UDP or SCTP) transport is preferred and in environments where
large quantities of data need to be sent (e.g. over a TCP based
stream). Both TLS and DTLS integrate well into existing public
keying infrastructures.
This document also defines a portion of the Management Information
Base (MIB) for use with network management protocols. In particular
it defines objects for managing the TLS Transport Model for SNMP.
For a detailed overview of the documents that describe the current
Internet-Standard Management Framework, please refer to section 7 of
RFC [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]
The diagram shown below gives a conceptual overview of two SNMP
entities communicating using the TLS Transport Model. One entity
contains a Command Responder and Notification Originator application,
and the other a Command Generator and Notification Responder
application. It should be understood that this particular mix of
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application types is an example only and other combinations are
equally as legitimate.
+----------------------------------------------------------------+
| Network |
+----------------------------------------------------------------+
^ ^ ^ ^
|Notifications |Commands |Commands |Notifications
+---|---------------------|--------+ +--|---------------|-------------+
| V V | | V V |
| +------------+ +------------+ | | +-----------+ +----------+ |
| | (D)TLS | | (D)TLS | | | | (D)TLS | | (D)TLS | |
| | Service | | Service | | | | Service | | Service | |
| | (Client) | | (Server) | | | | (Client) | | (Server)| |
| +------------+ +------------+ | | +-----------+ +----------+ |
| ^ ^ | | ^ ^ |
| | | | | | | |
| +--+----------+ | | +-+--------------+ |
| +-----|---------+----+ | | +---|--------+----+ |
| | V |LCD | +-------+ | | | V |LCD | +--------+ |
| | +------+ +----+ | | | | | +------+ +----+ | | |
| | | DTLS | <---------->| Cache | | | | | DTLS | <---->| Cache | |
| | | TM | | | | | | | | TM | | | | |
| | +------+ | +-------+ | | | +------+ | +--------+ |
| |Transport Subsystem | ^ | | |Transport Sub. | ^ |
| +--------------------+ | | | +-----------------+ | |
| ^ +----+ | | ^ | |
| | | | | | | |
| v | | | V | |
| +-------+ +----------+ +-----+ | | | +-----+ +------+ +-----+ | |
| | | |Message | |Sec. | | | | | | | MP | |Sec. | | |
| | Disp. | |Processing| |Sub- | | | | |Disp.| | Sub- | |Sub- | | |
| | | |Subsystem | |sys. | | | | | | |system| |sys. | | |
| | | | | | | | | | | | | | | | | |
| | | | | |+---+| | | | | | | | |+---+| | |
| | | | +-----+ | || || | | | | | |+----+| || || | |
| | <--->|v3MP |<-->||TSM|<-+ | | | <-->|v3MP|<->|TSM|<-+ |
| | | | +-----+ | || || | | | | |+----+| || || |
| +-------+ | | |+---+| | | +-----+ | | |+---+| |
| ^ | | | | | | ^ | | | | |
| | +----------+ +-----+ | | | +------+ +-----+ |
| +-+------------+ | | +-+------------+ |
| ^ ^ | | ^ ^ |
| | | | | | | |
| v v | | V V |
| +-------------+ +--------------+ | | +-----------+ +--------------+ |
| | COMMAND | | NOTIFICATION | | | | COMMAND | | NOTIFICATION | |
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| | RESPONDER | | ORIGINATOR | | | | GENERATOR | | RESPONDER | |
| | application | | applications | | | |application| | application | |
| +-------------+ +--------------+ | | +-----------+ +--------------+ |
| SNMP entity | | SNMP entity |
+----------------------------------+ +--------------------------------+
1.1. Conventions
For consistency with SNMP-related specifications, this document
favors terminology as defined in STD62 rather than favoring
terminology that is consistent with non-SNMP specifications. This is
consistent with the IESG decision to not require the SNMPv3
terminology be modified to match the usage of other non-SNMP
specifications when SNMPv3 was advanced to Full Standard.
Authentication in this document typically refers to the English
meaning of "serving to prove the authenticity of" the message, not
data source authentication or peer identity authentication.
Large portions of this document simultaneously refer to both TLS and
DTLS when discussing TLSTM components that function equally with
either protocol. "(D)TLS" is used in these places to indicate that
the statement applies to either or both protocols as appropriate.
When a distinction between the protocols is needed they are referred
to independently through the use of "TLS" or "DTLS". The Transport
Model, however, is named "TLS Transport Model" and refers not to the
TLS or DTLS protocol but to the standard defined in this document,
which includes support for both TLS and DTLS.
The terms "manager" and "agent" are not used in this document,
because in the RFC 3411 architecture [RFC3411], all SNMP entities
have the capability of acting in either manager or agent or in both
roles depending on the SNMP application types supported in the
implementation. Where distinction is required, the application names
of Command Generator, Command Responder, Notification Originator,
Notification Receiver, and Proxy Forwarder are used. See "SNMP
Applications" [RFC3413] for further information.
Throughout this document, the terms "client" and "server" are used to
refer to the two ends of the (D)TLS transport connection. The client
actively opens the (D)TLS connection, and the server passively
listens for the incoming (D)TLS connection. Either SNMP entity may
act as client or as server, as discussed further below.
The User-Based Security Model (USM) [RFC3414] is a mandatory-to-
implement Security Model in STD 62. While (D)TLS and USM frequently
refer to a user, the terminology preferred in RFC3411 [RFC3411] and
in this memo is "principal". A principal is the "who" on whose
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behalf services are provided or processing takes place. A principal
can be, among other things, an individual acting in a particular
role; a set of individuals, with each acting in a particular role; an
application or a set of applications, or a combination of these
within an administrative domain.
Throughout this document, the term "session" is used to refer to a
secure association between two TLS Transport Models that permits the
transmission of one or more SNMP messages within the lifetime of the
session.
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 [RFC2119].
2. The Transport Layer Security Protocol
(D)TLS provides authentication, data message integrity, and privacy
at the transport layer. (See [RFC4347])
The primary goals of the TLS Transport Model are to provide privacy,
source authentication and data integrity between two communicating
SNMP entities. The TLS and DTLS protocols provide a secure transport
upon which the TLSTM is based. An overview of (D)TLS can be found in
section Appendix A. Please refer to [RFC4347] for a complete
description of the protocol.
2.1. SNMP requirements of (D)TLS
To properly support the SNMP over TLS Transport Model, the (D)TLS
implementation requires the following:
o The TLS Transport Model SHOULD always use authentication of both
the server and the client.
o At a minimum the TLS Transport Model MUST support authentication
of the Command Generator principals to guarantee the authenticity
of the securityName.
o The TLS Transport Model SHOULD support the message encryption to
protect sensitive data from eavesdropping attacks.
3. How the TLSTM fits into the Transport Subsystem
A transport model is a component of the Transport Subsystem. The TLS
Transport Model thus fits between the underlying (D)TLS transport
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layer and the message dispatcher [RFC3411] component of the SNMP
engine and the Transport Subsystem.
The TLS Transport Model will establish a session between itself and
the TLS Transport Model of another SNMP engine. The sending
transport model passes unprotected messages from the dispatcher to
(D)TLS to be protected, and the receiving transport model accepts
decrypted and authenticated/integrity-checked incoming messages from
(D)TLS and passes them to the dispatcher.
After a TLS Transport Model session is established, SNMP messages can
conceptually be sent through the session from one SNMP message
dispatcher to another SNMP message dispatcher. If multiple SNMP
messages are needed to be passed between two SNMP applications they
SHOULD be passed through the same session. A TLSTM implementation
engine MAY choose to close a (D)TLS session to conserve resources.
The TLS Transport Model of an SNMP engine will perform the
translation between (D)TLS-specific security parameters and SNMP-
specific, model-independent parameters.
The diagram below depicts where the TLS Transport Model fits into the
architecture described in RFC3411 and the Transport Subsystem:
+------------------------------+
| Network |
+------------------------------+
^ ^ ^
| | |
v v v
+-------------------------------------------------------------------+
| +--------------------------------------------------+ |
| | Transport Subsystem | +--------+ |
| | +-----+ +-----+ +-------+ +-------+ | | | |
| | | UDP | | SSH | |(D)TLS | . . . | other |<--->| Cache | |
| | | | | TM | | TM | | | | | | |
| | +-----+ +-----+ +-------+ +-------+ | +--------+ |
| +--------------------------------------------------+ ^ |
| ^ | |
| | | |
| Dispatcher v | |
| +--------------+ +---------------------+ +----------------+ | |
| | Transport | | Message Processing | | Security | | |
| | Dispatch | | Subsystem | | Subsystem | | |
| | | | +------------+ | | +------------+ | | |
| | | | +->| v1MP |<--->| | USM | | | |
| | | | | +------------+ | | +------------+ | | |
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| | | | | +------------+ | | +------------+ | | |
| | | | +->| v2cMP |<--->| | Transport | | | |
| | Message | | | +------------+ | | | Security |<--+ |
| | Dispatch <---->| +------------+ | | | Model | | |
| | | | +->| v3MP |<--->| +------------+ | |
| | | | | +------------+ | | +------------+ | |
| | PDU Dispatch | | | +------------+ | | | Other | | |
| +--------------+ | +->| otherMP |<--->| | Model(s) | | |
| ^ | +------------+ | | +------------+ | |
| | +---------------------+ +----------------+ |
| v |
| +-------+-------------------------+---------------+ |
| ^ ^ ^ |
| | | | |
| v v v |
| +-------------+ +---------+ +--------------+ +-------------+ |
| | COMMAND | | ACCESS | | NOTIFICATION | | PROXY | |
| | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | |
| | application | | | | applications | | application | |
| +-------------+ +---------+ +--------------+ +-------------+ |
| ^ ^ |
| | | |
| v v |
| +----------------------------------------------+ |
| | MIB instrumentation | SNMP entity |
+-------------------------------------------------------------------+
3.1. Security Capabilities of this Model
3.1.1. Threats
The TLS Transport Model provides protection against the threats
identified by the RFC 3411 architecture [RFC3411]:
1. Modification of Information - The modification threat is the
danger that some unauthorized entity may alter in-transit SNMP
messages generated on behalf of an authorized principal in such a
way as to effect unauthorized management operations, including
falsifying the value of an object.
(D)TLS provides verification that the content of each received
message has not been modified during its transmission through the
network, data has not been altered or destroyed in an
unauthorized manner, and data sequences have not been altered to
an extent greater than can occur non-maliciously.
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2. Masquerade - The masquerade threat is the danger that management
operations unauthorized for a given principal may be attempted by
assuming the identity of another principal that has the
appropriate authorizations.
The TLSTM provides for authentication of the Command Generator,
Command Responder, Notification Generator, Notification Responder
and Proxy Forwarder through the use of X.509 certificates.
The masquerade threat can be mitigated against by using an
appropriate Access Control Model (ACM) such as the View-based
Access Control Module (VACM) [RFC3415]. In addition, it is
important to authenticate and verify both the authenticated
identity of the (D)TLS client and the (D)TLS server to protect
against this threat. (See Section 9 for more detail.)
3. Message stream modification - The re-ordering, delay or replay of
messages can and does occur through the natural operation of many
connectionless transport services. The message stream
modification threat is the danger that messages may be
maliciously re-ordered, delayed or replayed to an extent which is
greater than can occur through the natural operation of
connectionless transport services, in order to effect
unauthorized management operations.
(D)TLS provides replay protection with a MAC that includes a
sequence number. Since UDP provides no sequencing ability DTLS
uses a sliding window protocol with the sequence number for
replay protection, see [RFC4347]. The technique used is similar
to that as in IPsec AH/ESP [RFC4302] [RFC4303], by maintaining a
bitmap window of received records. Records that are too old to
fit in the window and records that have previously been received
are silently discarded. The replay detection feature is
optional, since packet duplication can also occur naturally due
to routing errors and does not necessarily indicate an active
attack. Applications may conceivably detect duplicate packets
and accordingly modify their data transmission strategy.
4. Disclosure - The disclosure threat is the danger of eavesdropping
on the exchanges between SNMP engines. Protecting against this
threat may be required by local policy at the deployment site.
Symmetric cryptography (e.g., AES [AES], DES [DES] etc.) can be
used by (D)TLS for data privacy. The keys for this symmetric
encryption are generated uniquely for each session and are based
on a secret negotiated by another protocol (such as the (D)TLS
Handshake Protocol).
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5. Denial of Service - the RFC 3411 architecture [RFC3411] states
that denial of service (DoS) attacks need not be addressed by an
SNMP security protocol. However, datagram-based security
protocols like DTLS are susceptible to a variety of denial of
service attacks because it is more vulnerable to spoofed
messages.
In order to counter both of these attacks, DTLS borrows the
stateless cookie technique used by Photuris [RFC2522] and IKEv2
[RFC4306] and is described fully in section 4.2.1 of [RFC4347].
This mechanism, though, does not provide any defense against
denial of service attacks mounted from valid IP addresses. DTLS
Transport Model server implementations MUST support DTLS cookies.
Implementations are not required to perform the stateless cookie
exchange for every DTLS handshakes but in environments where
amplification could be an issue or has been detected it is
RECOMMENDED that the cookie exchange is utilized.
3.1.2. Message Protection
The RFC 3411 architecture recognizes three levels of security:
o without authentication and without privacy (noAuthNoPriv)
o with authentication but without privacy (authNoPriv)
o with authentication and with privacy (authPriv)
The TLS Transport Model determines from (D)TLS the identity of the
authenticated principal, and the type and address associated with an
incoming message, and the TLS Transport Model provides this
information to (D)TLS for an outgoing message.
When an application requests a session for a message, through the
cache, the application requests a security level for that session.
The TLS Transport Model MUST ensure that the (D)TLS session provides
security at least as high as the requested level of security. How
the security level is translated into the algorithms used to provide
data integrity and privacy is implementation-dependent. However, the
NULL integrity and encryption algorithms MUST NOT be used to fulfill
security level requests for authentication or privacy.
Implementations MAY choose to force (D)TLS to only allow
cipher_suites that provide both authentication and privacy to
guarantee this assertion.
If a suitable interface between the TLS Transport Model and the
(D)TLS Handshake Protocol is implemented to allow the selection of
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security level dependent algorithms, for example a security level to
cipher_suites mapping table, then different security levels may be
utilized by the application. However, different port numbers will
need to be used by at least one side of the connection to
differentiate between the (D)TLS sessions. This is the only way to
ensured proper selection of a session ID for an incoming (D)TLS
message.
The authentication, integrity and privacy algorithms used by the
(D)TLS Protocol [RFC4347] may vary over time as the science of
cryptography continues to evolve and the development of (D)TLS
continues over time. Implementers are encouraged to plan for changes
in operator trust of particular algorithms and implementations should
offer configuration settings for mapping algorithms to SNMPv3
security levels.
3.1.3. (D)TLS Sessions
(D)TLS sessions are opened by the TLS Transport Model during the
elements of procedure for an outgoing SNMP message. Since the sender
of a message initiates the creation of a (D)TLS session if needed,
the (D)TLS session will already exist for an incoming message.
Implementations MAY choose to instantiate (D)TLS sessions in
anticipation of outgoing messages. This approach might be useful to
ensure that a (D)TLS session to a given target can be established
before it becomes important to send a message over the (D)TLS
session. Of course, there is no guarantee that a pre-established
session will still be valid when needed.
DTLS sessions, when used over UDP, are uniquely identified within the
TLS Transport Model by the combination of transportDomain,
transportAddress, securityName, and requestedSecurityLevel associated
with each session. Each unique combination of these parameters MUST
have a locally-chosen unique dtlsSessionID associated for active
sessions. For further information see Section 4.4 and Section 5.
TLS and DTLS over SCTP sessions, on the other hand, do not require a
unique paring of attributes since their lower layer protocols (TCP
and SCTP) already provide adequate session framing.
3.2. Security Parameter Passing
For the (D)TLS server-side, (D)TLS-specific security parameters
(i.e., cipher_suites, X.509 certificate fields, IP address and port)
are translated by the TLS Transport Model into security parameters
for the TLS Transport Model and security model (i.e., securityLevel,
securityName, transportDomain, transportAddress). The transport-
related and (D)TLS-security-related information, including the
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authenticated identity, are stored in a cache referenced by
tmStateReference.
For the (D)TLS client-side, the TLS Transport Model takes input
provided by the dispatcher in the sendMessage() Abstract Service
Interface (ASI) and input from the tmStateReference cache. The
(D)TLS Transport Model converts that information into suitable
security parameters for (D)TLS and establishes sessions as needed.
The elements of procedure in Section 5 discuss these concepts in much
greater detail.
3.3. Notifications and Proxy
(D)TLS sessions may be initiated by (D)TLS clients on behalf of
command generators or notification originators. Command generators
are frequently operated by a human, but notification originators are
usually unmanned automated processes. The targets to whom
notifications should be sent is typically determined and configured
by a network administrator.
The SNMP-TARGET-MIB module [RFC3413] contains objects for defining
management targets, including transportDomain, transportAddress,
securityName, securityModel, and securityLevel parameters, for
Notification Generator, Proxy Forwarder, and SNMP-controllable
Command Generator applications. Transport domains and transport
addresses are configured in the snmpTargetAddrTable, and the
securityModel, securityName, and securityLevel parameters are
configured in the snmpTargetParamsTable. This document defines a MIB
module that extends the SNMP-TARGET-MIB's snmpTargetParamsTable to
specify a (D)TLS client-side certificate to use for the connection.
When configuring a (D)TLS target, the snmpTargetAddrTDomain and
snmpTargetAddrTAddress parameters in snmpTargetAddrTable should be
set to the snmpTLSDomain, snmpDTLSUDPDomain, or snmpDTLSSCTPDomain
object and an appropriate snmpTLSAddress, snmpDTLSUDPAddress or
snmpDTLSSCTPAddress value respectively. The snmpTargetParamsMPModel
column of the snmpTargetParamsTable should be set to a value of 3 to
indicate the SNMPv3 message processing model. The
snmpTargetParamsSecurityName should be set to an appropriate
securityName value and the tlstmParamsClientHashType and
tlstmParamsClientHashValue parameters of the tlstmParamsTable should
be set to values that refer to a locally held certificate to be used.
The tlstmAddrServerHashType and tlstmAddrServerHashValue must be set
to a hash value that refers to a locally held copy of the server's
presented identity certificate. Other parameters, for example
cryptographic configuration such as cipher suites to use, must come
from configuration mechanisms not defined in this document. The
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other needed configuration may be configured using SNMP or other
implementation-dependent mechanisms (for example, via a CLI). This
securityName defined in the snmpTargetParamsSecurityName column will
be used by the access control model to authorize any notifications
that need to be sent.
4. Elements of the Model
This section contains definitions required to realize the (D)TLS
Transport Model defined by this document.
4.1. X.509 Certificates
(D)TLS makes use of X.509 certificates for authentication of both
sides of the transport. This section discusses the use of
certificates in the TLSTM. An overview of X.509 certificate
infrastructure can be found in Appendix B.
4.1.1. Provisioning for the Certificate
Authentication using (D)TLS will require that SNMP entities are
provisioned with certificates, which are signed by trusted
certificate authorities. Furthermore, SNMP entities will most
commonly need to be provisioned with root certificates which
represent the list of trusted certificate authorities that an SNMP
entity can use for certificate verification. SNMP entities SHOULD
also be provisioned with a X.509 certificate revocation mechanism
which can be used to verify that a certificate has not been revoked.
The authenticated tmSecurityName of the principal is looked up using
the tlstmCertToSNTable. This table either:
o Maps a certificate's fingerprint hash type and value to a directly
specified tmSecurityName.
o Identifies a certificate issuer's fingerprint hash type and value
and allows child certificate's subjectAltName or CommonName to
directly used as the tmSecurityNome.
The certificate trust anchors, being either CA certificates or public
keys for use by self-signed certificates, must be installed through
an out of band trusted mechanism into the server and its authenticity
MUST be verified before access is granted. Implementations SHOULD
choose to discard any connections for which no potential
tlstmCertToSNTable mapping exists before performing certificate
verification to avoid expending computational resources associated
with certificate verification.
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The typical enterprise configuration will map a "subjectAltName"
component of the tbsCertificate to the TLSTM specific tmSecurityName.
Thus, the authenticated identity can be obtained by the TLS Transport
Model by extracting the subjectAltName(s) from the peer's certificate
and the receiving application will have an appropriate tmSecurityName
for use by components like an access control model. This setup
requires very little configuration: a single row in the
tlstmCertToSNTable referencing a certificate authority.
An example mapping setup can be found in Appendix C
This tmSecurityName may be later translated from a TLSTM specific
tmSecurityName to a SNMP engine securityName by the security model.
A security model, like the TSM security model, may perform an
identity mapping or a more complex mapping to derive the securityName
from the tmSecurityName offered by the TLS Transport Model.
4.2. Messages
As stated in Section 4.1.1 of [RFC4347], each DTLS record must fit
within a single DTLS datagram. The TLSTM SHOULD prohibit SNMP
messages from being sent that exceeds the maximum DTLS message size.
The TLSTM implementation SHOULD return an error when the DTLS message
size would be exceeded and the message won't be sent.
4.3. SNMP Services
This section describes the services provided by the (D)TLS Transport
Model with their inputs and outputs. The services are between the
Transport Model and the dispatcher.
The services are described as primitives of an abstract service
interface (ASI) and the inputs and outputs are described as abstract
data elements as they are passed in these abstract service
primitives.
4.3.1. SNMP Services for an Outgoing Message
The dispatcher passes the information to the TLS Transport Model
using the ASI defined in the transport subsystem:
statusInformation =
sendMessage(
IN destTransportDomain -- transport domain to be used
IN destTransportAddress -- transport address to be used
IN outgoingMessage -- the message to send
IN outgoingMessageLength -- its length
IN tmStateReference -- reference to transport state
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)
The abstract data elements passed as parameters in the abstract
service primitives are as follows:
statusInformation: An indication of whether the passing of the
message was successful. If not it is an indication of the
problem.
destTransportDomain: The transport domain for the associated
destTransportAddress. The Transport Model uses this parameter to
determine the transport type of the associated
destTransportAddress. This parameter may also be used by the
transport subsystem to route the message to the appropriate
Transport Model. This document specifies three TLS and DTLS based
Transport Domains for use: the snmpTLSDomain, the
snmpDTLSUDPDomain and the snmpDTLSSCTPDomain.
destTransportAddress: The transport address of the destination TLS
Transport Model in a format specified by the SnmpTLSAddress, the
SnmpDTLSUDPAddress or the SnmpDTLSSCTPAddress TEXTUAL-CONVENTIONs.
outgoingMessage: The outgoing message to send to (D)TLS for
encapsulation.
outgoingMessageLength: The length of the outgoing message.
tmStateReference: A handle/reference to tmSecurityData to be used
when securing outgoing messages.
4.3.2. SNMP Services for an Incoming Message
The TLS Transport Model processes the received message from the
network using the (D)TLS service and then passes it to the dispatcher
using the following ASI:
statusInformation =
receiveMessage(
IN transportDomain -- origin transport domain
IN transportAddress -- origin transport address
IN incomingMessage -- the message received
IN incomingMessageLength -- its length
IN tmStateReference -- reference to transport state
)
The abstract data elements passed as parameters in the abstract
service primitives are as follows:
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statusInformation: An indication of whether the passing of the
message was successful. If not it is an indication of the
problem.
transportDomain: The transport domain for the associated
transportAddress. This document specifies three TLS and DTLS
based Transport Domains for use: the snmpTLSDomain, the
snmpDTLSUDPDomain and the snmpDTLSSCTPDomain.
transportAddress: The transport address of the source of the
received message in a format specified by the SnmpTLSAddress, the
SnmpDTLSUDPAddress or the SnmpDTLSSCTPAddress TEXTUAL-CONVENTION.
incomingMessage: The whole SNMP message stripped of all (D)TLS
protection data.
incomingMessageLength: The length of the SNMP message after being
processed by (D)TLS.
tmStateReference: A handle/reference to tmSecurityData to be used by
the security model.
4.4. (D)TLS Services
This section describes the services provided by the (D)TLS Transport
Model with their inputs and outputs. These services are between the
TLS Transport Model and the (D)TLS transport layer. The following
sections describe services for establishing and closing a session and
for passing messages between the (D)TLS transport layer and the TLS
Transport Model.
4.4.1. Services for Establishing a Session
The TLS Transport Model provides the following ASI to describe the
data passed between the Transport Model and the (D)TLS transport
layer for session establishment.
statusInformation = -- errorIndication or success
openSession(
IN destTransportDomain -- transport domain to be used
IN destTransportAddress -- transport address to be used
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested
OUT tlsSessionID -- Session identifier for (D)TLS
)
The abstract data elements passed as parameters in the abstract
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service primitives are as follows:
statusInformation: An indication of whether the process was
successful or not. If not, then the status information will
include the error indication provided by (D)TLS.
destTransportDomain: The transport domain for the associated
destTransportAddress. The TLS Transport Model uses this parameter
to determine the transport type of the associated
destTransportAddress. This document specifies three TLS and DTLS
based Transport Domains for use: the snmpTLSDomain, the
snmpDTLSUDPDomain, and the snmpDTLSSCTPDomain.
destTransportAddress: The transport address of the destination TLS
Transport Model in a format specified by the SnmpTLSAddress, the
SnmpDTLSUDPAddress or the SnmpDTLSSCTPAddress TEXTUAL-CONVENTION.
securityName: The security name representing the principal on whose
behalf the message will be sent.
securityLevel: The level of security requested by the application.
dtlsSessionID: An implementation-dependent session identifier to
reference the specific (D)TLS session.
DTLS and UDP do not provide a session de-multiplexing mechanism and
it is possible that implementations will only be able to identify a
unique session based on a unique combination of source address,
destination address, source UDP port number and destination UDP port
number. Because of this, when establishing a new sessions
implementations MUST use a different UDP source port number for each
connection to a remote destination IP-address/port-number combination
to ensure the remote entity can properly disambiguate between
multiple sessions from a host to the same port on a server. TLS and
DTLS over SCTP provide session de-multiplexing so this restriction is
not needed for TLS or DTLS over SCTP implementations.
The procedural details for establishing a session are further
described in Section 5.3.
Upon completion of the process the TLS Transport Model returns status
information and, if the process was successful the dtlsSessionID.
Other implementation-dependent data from (D)TLS are also returned.
The dtlsSessionID is stored in an implementation- dependent manner
and tied to the tmSecurityData for future use of this session.
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4.4.2. (D)TLS Services for an Incoming Message
When the TLS Transport Model invokes the (D)TLS record layer to
verify proper security for the incoming message, it must use the
following ASI:
statusInformation = -- errorIndication or success
tlsRead(
IN tlsSessionID -- Session identifier for (D)TLS
IN wholeTlsMsg -- as received on the wire
IN wholeTlsMsgLength -- length as received on the wire
OUT incomingMessage -- the whole SNMP message from (D)TLS
OUT incomingMessageLength -- the length of the SNMP message
)
The abstract data elements passed as parameters in the abstract
service primitives are as follows:
statusInformation: An indication of whether the process was
successful or not. If not, then the status information will
include the error indication provided by (D)TLS.
tlsSessionID: An implementation-dependent session identifier to
reference the specific (D)TLS session. How the (D)TLS session ID
is obtained for each message is implementation-dependent. As an
implementation hint, for dtls over udp the TLS Transport Model can
examine incoming messages to determine the source IP address,
source port number, destination IP address, and destination port
number and use these values to look up the local tlsSessionID in
the list of active sessions.
wholeDtlsMsg: The whole message as received on the wire.
wholeDtlsMsgLength: The length of the message as it was received on
the wire.
incomingMessage: The whole SNMP message stripped of all (D)TLS
privacy and integrity data.
incomingMessageLength: The length of the SNMP message stripped of
all (D)TLS privacy and integrity data.
4.4.3. (D)TLS Services for an Outgoing Message
When the TLS Transport Model invokes the (D)TLS record layer to
encapsulate and transmit a SNMP message, it must use the following
ASI.
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statusInformation = -- errorIndication or success
tlsWrite(
IN tlsSessionID -- Session identifier for (D)TLS
IN outgoingMessage -- the message to send
IN outgoingMessageLength -- its length
)
The abstract data elements passed as parameters in the abstract
service primitives are as follows:
statusInformation: An indication of whether the process was
successful or not. If not, then the status information will
include the error indication provided by (D)TLS.
tlsSessionID: An implementation-dependent session identifier to
reference the specific (D)TLS session that the message should be
sent using.
outgoingMessage: The outgoing message to send to (D)TLS for
encapsulation.
outgoingMessageLength: The length of the outgoing message.
4.5. Cached Information and References
When performing SNMP processing, there are two levels of state
information that may need to be retained: the immediate state linking
a request-response pair, and potentially longer-term state relating
to transport and security. "Transport Subsystem for the Simple
Network Management Protocol" [I-D.ietf-isms-tmsm] defines general
requirements for caches and references.
4.5.1. TLS Transport Model Cached Information
The TLSTM has no specific responsibilities regarding the cached
information beyond those discussed in "Transport Subsystem for the
Simple Network Management Protocol" [I-D.ietf-isms-tmsm]
5. Elements of Procedure
Abstract service interfaces have been defined by RFC 3411 to describe
the conceptual data flows between the various subsystems within an
SNMP entity. The TLSTM uses some of these conceptual data flows when
communicating between subsystems. These RFC 3411-defined data flows
are referred to here as public interfaces.
To simplify the elements of procedure, the release of state
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information is not always explicitly specified. As a general rule,
if state information is available when a message gets discarded, the
message-state information should also be released. If state
information is available when a session is closed, the session state
information should also be released. Sensitive information, like
cryptographic keys, should be overwritten appropriately first prior
to being released.
An error indication may return an OID and value for an incremented
counter if the information is available at the point where the error
is detected.
5.1. Procedures for an Incoming Message
This section describes the procedures followed by the (D)TLS
Transport Model when it receives a (D)TLS protected packet. The
steps are broken into two different sections. Section 5.1.1
describes the needed steps for de-multiplexing multiple DTLS
sessions, which is specifically needed for DTLS over UDP sessions.
Section 5.1.2 describes the steps specific to transport processing
once the (D)TLS processing has been completed.
5.1.1. DTLS Processing for Incoming Messages
DTLS is significantly different in terms of session handling than
TCP-based session streams like SSH or TLS. The DTLS protocol, which
is datagram-based, does not have a session identifier when run over
UDP that allows implementations to determine through what session a
packet arrived. DTLS over SCTP and TLS over TCP streams have built
in session demultiplexing and thus the steps in this section are not
necessary for those protocol combinations. It is always critical,
however, that implementations be able to derive a tlsSessionID from
any demultiplexing process.
A process for de-multiplexing multiple DTLS sessions arriving over
UDP must be incorporated into the procedures for processing an
incoming message. The steps in this section describe how this can be
accomplished, although any implementation dependent method should be
suitable as long as the results are consistently deterministic. The
important output results from the steps in this process are the
transportDomain, the transportAddress, the wholeMessage, the
wholeMessageLength, and a unique implementation-dependent session
identifier (tlsSessionID).
This demultiplexing procedure assumes that upon session establishment
an entry in a local transport mapping table is created in the
Transport Model's Local Configuration Datastore (LCD). The transport
mapping table's entry should map a unique combination of the remote
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address, remote port number, local address and local port number to a
implementation-dependent tlsSessionID.
1) The TLS Transport Model examines the raw UDP message, in an
implementation-dependent manner. If the message is not a DTLS
message then it should be discarded. If the message is not a
(D)TLS Application Data message then the message should be
processed by the underlying DTLS framework as it is (for example)
a session initialization or session modification message and no
further steps below should be taken by the DTLS Transport.
2) The TLS Transport Model queries the LCD using the transport
parameters (source and destination addresses and ports) to
determine if a session already exists and its tlsSessionID.
3) If a matching entry in the LCD does not exist then the message is
discarded. Increment the tlstmSessionNoAvailableSessions counter
and stop processing the message.
Note that an entry would already exist if the client and server's
session establishment procedures had been successfully completed
(as described both above and in Section 5.3) even if no message
had yet been sent through the newly established session. An
entry may not exist, however, if a "rogue" message was routed to
the SNMP entity by mistake. An entry might also be missing
because of a "broken" session (see operational considerations).
4) Retrieve the tlsSessionID from the LCD.
5) The tlsWholeMsg, and the tlsSessionID are passed to DTLS for
integrity checking and decryption using the tlsRead() ASI.
6) If the message fails integrity checks or other (D)TLS security
processing then the tlstmDTLSProtectionErrors counter is
incremented, the message is discarded and processing of the
message is stopped.
7) The output of the tlsRead results in an incomingMessage and an
incomingMessageLength. These results and the tlsSessionID are
used below in the Section 5.1.2 to complete the processing of the
incoming message.
5.1.2. Transport Processing for Incoming Messages
The procedures in this section describe how the TLS Transport Model
should process messages that have already been properly extracted
from the (D)TLS stream.
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Create a tmStateReference cache for the subsequent reference and
assign the following values within it:
tmTransportDomain = snmpTLSDomain, snmpDTLSUDPDomain or
snmpDTLSSCTPDomain as appropriate.
tmTransportAddress = The address the message originated from,
determined in an implementation dependent way.
tmSecurityLevel = The derived tmSecurityLevel for the session, as
discussed in Section 3.1.2 and Section 5.3.
tmSecurityName = The derived tmSecurityName for the session as
discussed in and Section 5.3. This value MUST be constant during
the lifetime of the (D)TLS session.
tmSessionID = The tlsSessionID, which MUST be a unique session
identifier for this (D)TLS session. The contents and format of
this identifier are implementation dependent as long as it is
unique to the session. A session identifier MUST NOT be reused
until all references to it are no longer in use. The tmSessionID
is equal to the tlsSessionID discussed in Section 5.1.1.
tmSessionID refers to the session identifier when stored in the
tmStateReference and tlsSessionID refers to the session identifier
when stored in the LCD. They MUST always be equal when processing
a given session's traffic.
The wholeMessage and the wholeMessageLength are assigned values from
the incomingMessage and incomingMessageLength values from the (D)TLS
processing.
The TLS Transport Model passes the transportDomain, transportAddress,
wholeMessage, and wholeMessageLength to the dispatcher using the
receiveMessage ASI:
statusInformation =
receiveMessage(
IN transportDomain -- snmpTLSDomain, snmpDTLSUDPDomain,
-- or snmpDTLSSCTPDomain
IN transportAddress -- address for the received message
IN wholeMessage -- the whole SNMP message from (D)TLS
IN wholeMessageLength -- the length of the SNMP message
IN tmStateReference -- (NEW) transport info
)
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5.2. Procedures for an Outgoing Message
The dispatcher sends a message to the TLS Transport Model using the
following ASI:
statusInformation =
sendMessage(
IN destTransportDomain -- transport domain to be used
IN destTransportAddress -- transport address to be used
IN outgoingMessage -- the message to send
IN outgoingMessageLength -- its length
IN tmStateReference -- (NEW) transport info
)
This section describes the procedure followed by the TLS Transport
Model whenever it is requested through this ASI to send a message.
1) Extract tmSessionID, tmTransportAddress, tmSecurityName,
tmRequestedSecurityLevel. and tmSameSecurity from the
tmStateReference. Note: The tmSessionID value may be undefined
if session exists yet.
2) If tmSameSecurity is true and either tmSessionID is undefined or
refers to a session that is no longer open then increment the
tlstmSessionNoAvailableSessions counter, discard the message and
return the error indication in the statusInformation. Processing
of this message stops.
3) If tmSameSecurity is false and tmSessionID refers to a session
that is no longer available then an implementation SHOULD open a
new session using the openSession() ASI as described below in
step 4b. An implementation MAY choose to return an error to the
calling module.
4) If tmSessionID is undefined, then use tmTransportAddress,
tmSecurityName and tmRequestedSecurityLevel to see if there is a
corresponding entry in the LCD suitable to send the message over.
4a) If there is a corresponding LCD entry, then this session
will be used to send the message.
4b) If there is not a corresponding LCD entry, then open a
session using the openSession() ASI (discussed further in
Section 4.4.1). Implementations MAY wish to offer message
buffering to prevent redundant openSession() calls for the
same cache entry. If an error is returned from
OpenSession(), then discard the message, increment the
tlstmSessionOpenErrors, and return an error indication to
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the calling module.
5) Using either the session indicated by the tmSessionID if there
was one or the session resulting in the previous step, pass the
outgoingMessage to (D)TLS for encapsulation and transmission.
5.3. Establishing a Session
The TLS Transport Model provides the following primitive to establish
a new (D)TLS session (previously discussed in Section 4.4.1):
statusInformation = -- errorIndication or success
openSession(
IN destTransportDomain -- transport domain to be used
IN destTransportAddress -- transport address to be used
IN securityName -- on behalf of this principal
IN securityLevel -- Level of Security requested
OUT tlsSessionID -- Session identifier for (D)TLS
)
The following describes the procedure to follow to establish a SNMP
over (D)TLS session between SNMP engines to exchange SNMP messages.
This process is followed by any SNMP engine establishing a session
for subsequent use.
This MAY be done automatically for SNMP messages which are not
Response or Report messages.
(D)TLS provides no explicit manner for transmitting an identity the
client wishes to connect to during or prior to key exchange to
facilitate certificate selection at the server (e.g. at a
Notification Receiver). I.E., there is no available mechanism for
sending notifications to a specific principal at a given TCP, UDP or
SCTP port. Therefore, implementations MAY support responding with
multiple identities using separate TCP, UDP or SCTP port numbers to
indicate the desired principal or some other implementation-dependent
solution.
1) The client selects the appropriate certificate and cipher_suites
for the key agreement based on the tmSecurityName and the
tmRequestedSecurityLevel for the session. For sessions being
established as a result of a SNMP-TARGET-MIB based operation, the
certificate will potentially have been identified via the
tlstmParamsTable mapping and the cipher_suites will have to be
taken from system-wide or implementation-specific configuration.
Otherwise, the certificate and appropriate cipher_suites will
need to be passed to the openSession() ASI as supplemental
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information or configured through an implementation-dependent
mechanism. It is also implementation-dependent and possibly
policy-dependent how tmRequestedSecurityLevel will be used to
influence the security capabilities provided by the (D)TLS
session. However this is done, the security capabilities
provided by (D)TLS MUST be at least as high as the level of
security indicated by the tmRequestedSecurityLevel parameter.
The actual security level of the session should be reported in
the tmStateReference cache as tmSecurityLevel. For (D)TLS to
provide strong authentication, each principal acting as a Command
Generator SHOULD have its own certificate.
2) Using the destTransportDomain and destTransportAddress values,
the client will initiate the (D)TLS handshake protocol to
establish session keys for message integrity and encryption.
If the attempt to establish a session is unsuccessful, then
tlstmSessionOpenErrors is incremented, an error indication is
returned, and session establishment processing stops.
3) Once the secure session is established and both sides have been
authenticated, certificate validation and identity expectations
are performed.
a) The (D)TLS server side of the connection identifies the
authenticated identity from the (D)TLS client's principal
certificate using appropriate certificate path validation
procedures (e.g. [RFC5280]) using configuration information
from the tlstmCertToSNTable mapping table. The resulting
derived securityName is recorded in the tmStateReference
cache as tmSecurityName. The details of the lookup process
are fully described in the DESCRIPTION clause of the
tlstmCertToSNTable MIB object. If this verification fails in
any way (for example because of failures in cryptographic
verification or the lack of an appropriate row in the
tlstmCertToSNTable) then the session establishment MUST fail,
the tlstmSessionInvalidClientCertificates object is
incremented and processing is stopped.
b) The (D)TLS client side of the connection SHOULD verify that
authenticated identity of the (D)TLS server's certificate is
the certificate expected. This can be done using the
configuration found in the tlstmAddrTable if the client is
establishing the connection based on SNMP-TARGET-MIB
configuration. The client MUST always perform appropriate
certificate path validation procedures (e.g. [RFC5280]) to
ensure the certificate is cryptographically valid.
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If strong authentication is desired then the (D)TLS server
address or naming mechanism MUST always be verified against
the certificate's contents. Methods for doing this are
described in [I-D.saintandre-tls-server-id-check]. Matching
the server's naming against SubjectAltName extension values
is the preferred mechanism for comparison, but matching the
CommonName MAY be used.
(D)TLS provides assurance that the authenticated identity has
been signed by a trusted configured certificate authority.
If verification of the server's certificate fails in any way
(for example because of failures in cryptographic
verification or the presented identity was not the expected
identity) then the session establishment MUST fail, the
tlstmSessionInvalidServerCertificates object is incremented
and processing is stopped.
4) The (D)TLS-specific session identifier is passed to the TLS
Transport Model and associated with the tmStateReference cache
entry to indicate that the session has been established
successfully and to point to a specific (D)TLS session for future
use.
5.4. Closing a Session
The TLS Transport Model provides the following primitive to close a
session:
statusInformation =
closeSession(
IN tmStateReference -- transport info
)
The following describes the procedure to follow to close a session
between a client and server. This process is followed by any SNMP
engine closing the corresponding SNMP session.
1) Look up the session in the cache and the LCD using the
tmStateReference.
2) If there is no session open associated with the tmStateReference,
then closeSession processing is completed.
3) Delete the entry from the cache and any other implementation-
dependent information in the LCD.
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4) Have (D)TLS close the specified session. This SHOULD include
sending a close_notify TLS Alert to inform the other side that
session cleanup may be performed.
6. MIB Module Overview
This MIB module provides management of the TLS Transport Model. It
defines needed textual conventions, statistical counters and
configuration infrastructure necessary for session establishment.
Example usage of the configuration tables can be found in Appendix C.
6.1. Structure of the MIB Module
Objects in this MIB module are arranged into subtrees. Each subtree
is organized as a set of related objects. The overall structure and
assignment of objects to their subtrees, and the intended purpose of
each subtree, is shown below.
6.2. Textual Conventions
Generic and Common Textual Conventions used in this module can be
found summarized at http://www.ops.ietf.org/mib-common-tcs.html
This module defines the following new Textual Conventions:
o A new TransportDomain and TransportAddress format for describing
(D)TLS connection addressing requirements.
o Public certificate fingerprint Hashing Types and Values. These
textual conventions allow for MIB module objects to refer
generically to a stored X.509 certificate using a simple hash
value as a reference pointer.
6.3. Statistical Counters
The TLSTM-MIB defines some statical counters that can provide network
managers with feedback about (D)TLS session usage and potential
errors that a MIB-instrumented device may be experiencing.
6.4. Configuration Tables
The TLSTM-MIB defines configuration tables that a manager can use for
help in configuring a MIB-instrumented device for sending and
receiving SNMP messages over (D)TLS. In particular, there is a MIB
table that extends the SNMP-TARGET-MIB for configuring certificates
to be used and a MIB table for mapping incoming (D)TLS client
certificates to securityNames.
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6.5. Relationship to Other MIB Modules
Some management objects defined in other MIB modules are applicable
to an entity implementing the TLS Transport Model. In particular, it
is assumed that an entity implementing the TLSTM-MIB will implement
the SNMPv2-MIB [RFC3418], the SNMP-FRAMEWORK-MIB [RFC3411], the SNMP-
TARGET-MIB [RFC3413], the SNMP-NOTIFICATION-MIB [RFC3413] and the
SNMP-VIEW-BASED-ACM-MIB [RFC3415].
The TLSTM-MIB module contained in this document is for managing TLS
Transport Model information.
6.5.1. MIB Modules Required for IMPORTS
The TLSTM-MIB module imports items from SNMPV2-SMI [RFC2578],
SNMPV2-TC [RFC2579], SNMP-FRAMEWORK-MIB [RFC3411], SNMP-TARGET-MIB
[RFC3413] and SNMP-CONF [RFC2580].
7. MIB Module Definition
TLSTM-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE,
OBJECT-IDENTITY, snmpModules, snmpDomains,
Counter32, Unsigned32
FROM SNMPv2-SMI
TEXTUAL-CONVENTION, TimeStamp, RowStatus, StorageType
FROM SNMPv2-TC
MODULE-COMPLIANCE, OBJECT-GROUP
FROM SNMPv2-CONF
SnmpAdminString
FROM SNMP-FRAMEWORK-MIB
snmpTargetParamsName, snmpTargetAddrName
FROM SNMP-TARGET-MIB
;
tlstmMIB MODULE-IDENTITY
LAST-UPDATED "200807070000Z"
ORGANIZATION " "
CONTACT-INFO "WG-EMail:
Subscribe:
Chairs:
Co-editors:
"
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DESCRIPTION "The TLS Transport Model MIB
Copyright (C) The IETF Trust (2008). This
version of this MIB module is part of RFC XXXX;
see the RFC itself for full legal notices."
-- NOTE to RFC editor: replace XXXX with actual RFC number
-- for this document and remove this note
REVISION "200807070000Z"
DESCRIPTION "The initial version, published in RFC XXXX."
-- NOTE to RFC editor: replace XXXX with actual RFC number
-- for this document and remove this note
::= { snmpModules xxxx }
-- RFC Ed.: replace xxxx with IANA-assigned number and
-- remove this note
-- ************************************************
-- subtrees of the SNMP-DTLS-TM-MIB
-- ************************************************
tlstmNotifications OBJECT IDENTIFIER ::= { tlstmMIB 0 }
tlstmObjects OBJECT IDENTIFIER ::= { tlstmMIB 1 }
tlstmConformance OBJECT IDENTIFIER ::= { tlstmMIB 2 }
-- ************************************************
-- Objects
-- ************************************************
snmpTLSDomain OBJECT-IDENTITY
STATUS current
DESCRIPTION
"The SNMP over TLS transport domain. The corresponding
transport address is of type SnmpTLSAddress.
The securityName prefix to be associated with the
snmpTLSDomain is 'tls'. This prefix may be used by
security models or other components to identify what secure
transport infrastructure authenticated a securityName."
::= { snmpDomains xx }
-- RFC Ed.: replace xx with IANA-assigned number and
-- remove this note
-- RFC Ed.: replace 'tls' with the actual IANA assigned prefix string
-- if 'tls' is not assigned to this document.
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snmpDTLSUDPDomain OBJECT-IDENTITY
STATUS current
DESCRIPTION
"The SNMP over DTLS/UDP transport domain. The corresponding
transport address is of type SnmpDTLSUDPAddress.
When an SNMP entity uses the snmpDTLSUDPDomain transport
model, it must be capable of accepting messages up to
the maximum MTU size for an interface it supports, minus the
needed IP, UDP, DTLS and other protocol overheads.
The securityName prefix to be associated with the
snmpDTLSUDPDomain is 'dudp'. This prefix may be used by
security models or other components to identify what secure
transport infrastructure authenticated a securityName."
::= { snmpDomains yy }
-- RFC Ed.: replace yy with IANA-assigned number and
-- remove this note
-- RFC Ed.: replace 'dudp' with the actual IANA assigned prefix string
-- if 'dtls' is not assigned to this document.
snmpDTLSSCTPDomain OBJECT-IDENTITY
STATUS current
DESCRIPTION
"The SNMP over DTLS/SCTP transport domain. The corresponding
transport address is of type SnmpDTLSSCTPAddress.
When an SNMP entity uses the snmpDTLSSCTPDomain transport
model, it must be capable of accepting messages up to
the maximum MTU size for an interface it supports, minus the
needed IP, SCTP, DTLS and other protocol overheads.
The securityName prefix to be associated with the
snmpDTLSSCTPDomain is 'dsct'. This prefix may be used by
security models or other components to identify what secure
transport infrastructure authenticated a securityName."
::= { snmpDomains zz }
-- RFC Ed.: replace zz with IANA-assigned number and
-- remove this note
-- RFC Ed.: replace 'dsct' with the actual IANA assigned prefix string
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-- if 'dtls' is not assigned to this document.
SnmpTLSAddress ::= TEXTUAL-CONVENTION
DISPLAY-HINT "1a"
STATUS current
DESCRIPTION
"Represents a TCP connection address for an IPv4 address, an
IPv6 address or an ASCII encoded host name and port number.
The hostname must be encoded in ASCII, as specified in RFC3490
(Internationalizing Domain Names in Applications) followed by
a colon ':' (ASCII character 0x3A) and a decimal port number
in ASCII. The name SHOULD be fully qualified whenever
possible.
An IPv4 address must be a dotted decimal format followed by a
colon ':' (ASCII character 0x3A) and a decimal port number in
ASCII.
An IPv6 address must be a colon separated format, surrounded
by square brackets (ASCII characters 0x5B and 0x5D), followed
by a colon ':' (ASCII character 0x3A) and a decimal port
number in ASCII.
Values of this textual convention may not be directly usable
as transport-layer addressing information, and may require
run-time resolution. As such, applications that write them
must be prepared for handling errors if such values are not
supported, or cannot be resolved (if resolution occurs at the
time of the management operation).
The DESCRIPTION clause of TransportAddress objects that may
have snmpTLSAddress values must fully describe how (and
when) such names are to be resolved to IP addresses and vice
versa.
This textual convention SHOULD NOT be used directly in object
definitions since it restricts addresses to a specific
format. However, if it is used, it MAY be used either on its
own or in conjunction with TransportAddressType or
TransportDomain as a pair.
When this textual convention is used as a syntax of an index
object, there may be issues with the limit of 128
sub-identifiers specified in SMIv2, STD 58. It is RECOMMENDED
that all MIB documents using this textual convention make
explicit any limitations on index component lengths that
management software must observe. This may be done either by
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including SIZE constraints on the index components or by
specifying applicable constraints in the conceptual row
DESCRIPTION clause or in the surrounding documentation."
SYNTAX OCTET STRING (SIZE (1..255))
SnmpDTLSUDPAddress ::= TEXTUAL-CONVENTION
DISPLAY-HINT "1a"
STATUS current
DESCRIPTION
"Represents a UDP connection address for an IPv4 address, an
IPv6 address or an ASCII encoded host name and port number.
The hostname must be encoded in ASCII, as specified in RFC3490
(Internationalizing Domain Names in Applications) followed by
a colon ':' (ASCII character 0x3A) and a decimal port number
in ASCII. The name SHOULD be fully qualified whenever
possible.
An IPv4 address must be a dotted decimal format followed by a
colon ':' (ASCII character 0x3A) and a decimal port number in
ASCII.
An IPv6 address must be a colon separated format, surrounded
by square brackets (ASCII characters 0x5B and 0x5D), followed
by a colon ':' (ASCII character 0x3A) and a decimal port
number in ASCII.
Values of this textual convention may not be directly usable
as transport-layer addressing information, and may require
run-time resolution. As such, applications that write them
must be prepared for handling errors if such values are not
supported, or cannot be resolved (if resolution occurs at the
time of the management operation).
The DESCRIPTION clause of TransportAddress objects that may
have snmpDTLSUDPAddress values must fully describe how (and
when) such names are to be resolved to IP addresses and vice
versa.
This textual convention SHOULD NOT be used directly in object
definitions since it restricts addresses to a specific
format. However, if it is used, it MAY be used either on its
own or in conjunction with TransportAddressType or
TransportDomain as a pair.
When this textual convention is used as a syntax of an index
object, there may be issues with the limit of 128
sub-identifiers specified in SMIv2, STD 58. It is RECOMMENDED
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that all MIB documents using this textual convention make
explicit any limitations on index component lengths that
management software must observe. This may be done either by
including SIZE constraints on the index components or by
specifying applicable constraints in the conceptual row
DESCRIPTION clause or in the surrounding documentation."
SYNTAX OCTET STRING (SIZE (1..255))
SnmpDTLSSCTPAddress ::= TEXTUAL-CONVENTION
DISPLAY-HINT "1a"
STATUS current
DESCRIPTION
"Represents a SCTP connection address for an IPv4 address, an
IPv6 address or an ASCII encoded host name and port number.
The hostname must be encoded in ASCII, as specified in RFC3490
(Internationalizing Domain Names in Applications) followed by
a colon ':' (ASCII character 0x3A) and a decimal port number
in ASCII. The name SHOULD be fully qualified whenever
possible.
An IPv4 address must be a dotted decimal format followed by a
colon ':' (ASCII character 0x3A) and a decimal port number in
ASCII.
An IPv6 address must be a colon separated format, surrounded
by square brackets (ASCII characters 0x5B and 0x5D), followed
by a colon ':' (ASCII character 0x3A) and a decimal port
number in ASCII.
Values of this textual convention may not be directly usable
as transport-layer addressing information, and may require
run-time resolution. As such, applications that write them
must be prepared for handling errors if such values are not
supported, or cannot be resolved (if resolution occurs at the
time of the management operation).
The DESCRIPTION clause of TransportAddress objects that may
have snmpDTLSSCTPAddress values must fully describe how (and
when) such names are to be resolved to IP addresses and vice
versa.
This textual convention SHOULD NOT be used directly in object
definitions since it restricts addresses to a specific
format. However, if it is used, it MAY be used either on its
own or in conjunction with TransportAddressType or
TransportDomain as a pair.
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When this textual convention is used as a syntax of an index
object, there may be issues with the limit of 128
sub-identifiers specified in SMIv2, STD 58. It is RECOMMENDED
that all MIB documents using this textual convention make
explicit any limitations on index component lengths that
management software must observe. This may be done either by
including SIZE constraints on the index components or by
specifying applicable constraints in the conceptual row
DESCRIPTION clause or in the surrounding documentation."
SYNTAX OCTET STRING (SIZE (1..255))
FingerprintType ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION
"Identifies an algorithm type that can be used to uniquely
reference other data of a potentially arbitrary length. If a
hashing algorithm is used, then the algorithm should be
sufficiently robust enough and it's output long enough that
hash-collisions should not occur. Other mechanisms of defining
fingerprints include other forms of unique identification such
as serial numbers or concatenated combinations of data such
that the result is sufficiently unique.
Objects making use of this TEXTUAL-CONVENTION SHOULD be
accompanied by another object or objects of type
FingerprintValue.
This TEXTUAL-CONVENTION SHOULD NOT be used as a form of
cryptographic verification. Two matching sets of
FingerprintType/FingerprintValue should not be considered
authenticated. These TEXTUAL-CONVENTIONs are only intended for
use as a reference to a stored copy of a longer data source and
the full data sources need to be compared to assure collisions
have not resulted."
SYNTAX OBJECT IDENTIFIER
FingerprintValue ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION
"A Fingerprint value that can be used to uniquely reference
other data of potentially arbitrary length.
Objects making use of this TEXTUAL-CONVENTION SHOULD always be
accompanied by a FingerprintType object that dictates the
format of values stored in objects of type FingerprintValue.
This TEXTUAL-CONVENTION SHOULD NOT be used as a form of
cryptographic verification. Two matching sets of
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FingerprintType/FingerprintValue should not be considered
authenticated. These TEXTUAL-CONVENTIONs are only intended for
use as a reference to a stored copy of a longer data source and
the full data sources need to be compared to assure collisions
have not resulted."
SYNTAX OCTET STRING
-- The Fingerprint Identifiers Objects
tlstmFingerprintTypes OBJECT IDENTIFIER ::= { tlstmObjects 1 }
tlstmMD5 OBJECT-IDENTITY
STATUS current
DESCRIPTION
"An identifier for the MD5 hashing algorithm to be used with
FingerprintType objects. The resulting value to be placed into
the corresponding FingerprintValue object should be a
full-length MD5 hash (16 octets)."
::= { tlstmFingerprintTypes 1 }
tlstmSHA1 OBJECT-IDENTITY
STATUS current
DESCRIPTION
"An identifier for the SHA1 hashing algorithm to be used with
FingerprintType objects. The resulting value to be placed into
the corresponding FingerprintValue object should be a
full-length SHA1 hash (20 octets)."
::= { tlstmFingerprintTypes 2 }
tlstmSHA256 OBJECT-IDENTITY
STATUS current
DESCRIPTION
"An identifier for the SHA256 hashing algorithm to be used with
FingerprintType objects. The resulting value to be placed into
the corresponding FingerprintValue object should be a
full-length SHA256 hash (32 octets)."
::= { tlstmFingerprintTypes 3 }
-- The tlstmSession Group
tlstmSession OBJECT IDENTIFIER ::= { tlstmObjects 2 }
tlstmSessionOpens OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an openSession() request has been
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executed as an (D)TLS client, whether it succeeded or failed."
::= { tlstmSession 1 }
tlstmSessionCloses OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times a closeSession() request has been
executed as an (D)TLS client, whether it succeeded or failed."
::= { tlstmSession 2 }
tlstmSessionOpenErrors OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an openSession() request failed to open a
session as a (D)TLS client, for any reason."
::= { tlstmSession 3 }
tlstmSessionNoAvailableSessions OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an outgoing message was dropped because
the session associated with the passed tmStateReference was no
longer (or was never) available."
::= { tlstmSession 4 }
tlstmSessionInvalidClientCertificates OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an incoming session was not established
on an (D)TLS server because the presented client certificate was
invalid. Reasons for invalidation includes, but is not
limited to, cryptographic validation failures and lack of a
suitable mapping row in the tlstmCertToSNTable."
::= { tlstmSession 5 }
tlstmSessionInvalidServerCertificates OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
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DESCRIPTION
"The number of times an outgoing session was not established
on an (D)TLS client because the presented server certificate was
invalid. Reasons for invalidation includes, but is not
limited to, cryptographic validation failures and an unexpected
presented certificate identity."
::= { tlstmSession 6 }
tlstmTLSProtectionErrors OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times (D)TLS processing resulted in a message
being discarded because it failed its integrity test,
decryption processing or other (D)TLS processing."
::= { tlstmSession 7 }
-- Configuration Objects
tlstmConfig OBJECT IDENTIFIER ::= { tlstmObjects 3 }
-- Certificate mapping
tlstmCertificateMapping OBJECT IDENTIFIER ::= { tlstmConfig 1 }
tlstmCertToSNCount OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A count of the number of entries in the
tlstmCertToSNTable"
::= { tlstmCertificateMapping 1 }
tlstmCertToSNTableLastChanged OBJECT-TYPE
SYNTAX TimeStamp
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The value of sysUpTime.0 when the tlstmCertToSNTable
was last modified through any means, or 0 if it has not been
modified since the command responder was started."
::= { tlstmCertificateMapping 2 }
tlstmCertToSNTable OBJECT-TYPE
SYNTAX SEQUENCE OF TlstmCertToSNEntry
MAX-ACCESS not-accessible
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STATUS current
DESCRIPTION
"A table listing the X.509 certificates known to the entity
and the associated method for determining the SNMPv3 security
name from a certificate.
On an incoming (D)TLS/SNMP connection the client's presented
certificate must be examined and validated based on an
established trusted path from a CA certificate or self-signed
public certificate (e.g. RFC5280). This table provides a
mapping from a validated certificate to a SNMPv3 securityName.
This table does not provide any mechanisms for uploading
trusted certificates and the transfer of any needed trusted
certificates for path validation is expected to occur through
an out-of-band transfer.
Once the authenticity of a certificate has been verified, this
table is consulted to determine the appropriate securityName
to identify with the remote connection. This is done by
considering each active row from this table in prioritized
order according to its tlstmCertToSNID value. Each row's
tlstmCertToSNHashType and tlstmCertToSNHashValue values
determine whether the row is a match for the incoming
connection:
1) If the row's tlstmCertToSNHashType and
tlstmCertToSNHashValue values identify the presented
certificate and the contents of the presented
certificate match a locally cached copy of the
certificate then consider the row as a successful
match.
2) If the row's tlstmCertToSNHashType and
tlstmCertToSNHashValue values identify a locally held
copy of a trusted CA certificate and that CA
certificated was used to validate the presented
certificate then consider the row as a successful
match.
Once a matching row has been found, the tlstmCertToSNMapType
value can be used to determine how the securityName to
associate with the session should be determined. See the
tlstmCertToSNMapType column's DESCRIPTION for details on
determining the securityName value. If it is impossible to
determine the resulting securityName from the row's data
combined with the data presented in the certificate then
additional rows MUST be searched looking for another potential
match. If a resulting securityName mapped from a given row is
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not compatible with the needed requirements of a legal
securityName (i.e., VACM imposes a 32-octet-maximum length)
then it must be considered an invalid match and additional
rows MUST be searched looking for another potential match.
Missing values of tlstmCertToSNID are acceptable and
implementations should continue to the next highest numbered
row. E.G., the table may legally contain only two rows with
tlstmCertToSNID values of 10 and 20.
Users are encouraged to make use of certificates with
subjectAltName fields that can be used as securityNames so
that a single root CA certificate can allow all child
certificate's subjectAltName to map directly to a securityName
via a 1:1 transformation. However, this table is flexible to
allow for situations where existing deployed certificate
infrastructures do not provide adequate subjectAltName values
for use as SNMPv3 securityNames. Certificates may also be
mapped to securityNames using the CommonName portion of the
Subject field but usage of the CommonName field is deprecated.
Direct mapping from each individual certificate fingerprint to
a securityName is also possible but requires one entry in the
table per securityName and requires more management operations
to completely configure a device."
::= { tlstmCertificateMapping 3 }
tlstmCertToSNEntry OBJECT-TYPE
SYNTAX TlstmCertToSNEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A row in the tlstmCertToSNTable that specifies a
mapping for an incoming (D)TLS certificate to a securityName
to use for a connection."
INDEX { tlstmCertToSNID }
::= { tlstmCertToSNTable 1 }
TlstmCertToSNEntry ::= SEQUENCE {
tlstmCertToSNID Unsigned32,
tlstmCertToSNHashType FingerprintType,
tlstmCertToSNHashValue FingerprintValue,
tlstmCertToSNMapType INTEGER,
tlstmCertToSNSecurityName SnmpAdminString,
tlstmCertToSNSANType INTEGER,
tlstmCertToSNStorageType StorageType,
tlstmCertToSNRowStatus RowStatus
}
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tlstmCertToSNID OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A unique, prioritized index for a given certificate entry."
::= { tlstmCertToSNEntry 1 }
tlstmCertToSNHashType OBJECT-TYPE
SYNTAX FingerprintType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The hash algorithm to use when applying a hash to a X.509
certificate for purposes of referring to it from the
tlstmCertToSNHashValue column."
DEFVAL { tlstmSHA256 }
::= { tlstmCertToSNEntry 2 }
tlstmCertToSNHashValue OBJECT-TYPE
SYNTAX FingerprintValue
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"A cryptographic hash of a X.509 certificate. The results of
a successful matching fingerprint is dictated by the
tlstmCertToSNMapType column. A match of the fingerprint MUST
only be considered successful if both the fingerprint type
(tlstmCertToSNMapType) and fingerprint value
(tlstmCertToSNHashValue) columns have been found equal to the
type and value of the certificate being checked."
::= { tlstmCertToSNEntry 3 }
tlstmCertToSNMapType OBJECT-TYPE
SYNTAX INTEGER { specified(1), bySubjectAltName(2), byCN(3) }
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The mapping type used to obtain the securityName from the
certificate. The possible values of use and their usage
methods are defined as follows:
specified(1): The securityName that should be used to
associate with the session is directly
specified in the tlstmCertToSNecurityName column
from this table.
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bySubjectAltName(2):
The securityName that should be used to
associate with the session should be taken from
the subjectAltName(s) portion of the client's
X.509 certificate. The subjectAltName used MUST
be the first encountered subjectAltName type
indicated by the tlstmCertToSNSANType column.
If no subjectAltName of the given type is found
within the certificate then additional rows in
the tlstmCertToSNTable must be searched.
byCN(3): The securityName that should be used to
associate with the session should be taken from
the CommonName portion of the Subject field from
the client's presented X.509 certificate.
If the resulting mapped value from the subjectAltName
component is not compatible with the needed requirements of a
legal securityName (i.e., VACM imposes a 32-octet-maximum
length) then the next appropriate subjectAltName of the
correct type should be used if available.
If this object is of type bySubjectAltName(2) and no
subjectAltName value can be found that meets the requirements
of this object then any additional rows in the
tlstmCertToSNTable must be searched.
If this object is of type byCN(3) and the CommonName value
does not meet the requirements of this object then any
additional rows in the tlstmCertToSNTable must be searched."
DEFVAL { specified }
::= { tlstmCertToSNEntry 4 }
tlstmCertToSNSecurityName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(0..32))
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The securityName that the session should use if the
tlstmCertToSNMapType is set to specified(1), otherwise the
value in this column should be ignored. If
tlstmCertToSNMapType is set to specifed(1) and this column
contains a zero-length string (which is not a legal
securityName value) this row is effectively disabled and the
match will not be considered successful and other rows in the
table will need to be searched."
DEFVAL { "" }
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::= { tlstmCertToSNEntry 5 }
tlstmCertToSNSANType OBJECT-TYPE
SYNTAX INTEGER { any(1), rfc822Name(2), dNSName(3),
ipAddress(4), otherName(5) }
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"Specifies the subjectAltName type that may be used to extract
the securityName from.
The any(1) value indicates the (D)TLS server should use the
first value found for any of the following subjectAltName
value types for the securityName: rfc822Name, dNSName, and
ipAddress.
When multiple types for a given subjectAltName type are
encountered within a certificate the first legally usable
value is the one selected.
Values for type ipAddress(4) are converted to a valid
securityName by:
1) for IPv4 the value is converted into a decimal dotted
quad address (e.g. '192.0.2.1')
2) for IPv6 addresses the value is converted into a
32-character hexadecimal string without any colon
separators.
Values for type otherName(5) are converted to a valid
securityName by using only the decoded value portion of the
OthenName sequence. i.e. the OBJECT IDENTIFIER portion of the
OtherName sequence is not included as part of the resulting
securityName."
DEFVAL { any }
::= { tlstmCertToSNEntry 6 }
tlstmCertToSNStorageType OBJECT-TYPE
SYNTAX StorageType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The storage type for this conceptual row. Conceptual rows
having the value 'permanent' need not allow write-access to
any columnar objects in the row."
DEFVAL { nonVolatile }
::= { tlstmCertToSNEntry 7 }
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tlstmCertToSNRowStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status of this conceptual row. This object may be used
to create or remove rows from this table.
To create a row in this table, a manager must set this object
to either createAndGo(4) or createAndWait(5).
Until instances of all corresponding columns are appropriately
configured, the value of the corresponding instance of the
tlstmParamsRowStatus column is 'notReady'.
In particular, a newly created row cannot be made active until
the corresponding tlstmCertToSNHashType,
tlstmCertToSNHashValue, tlstmCertToSNMapType,
tlstmCertToSNSecurityName, and tlstmCertToSNSANType columns
have been set.
The following objects may not be modified while the
value of this object is active(1):
- tlstmCertToSNHashType
- tlstmCertToSNHashValue
- tlstmCertToSNMapType
- tlstmCertToSNSecurityName
- tlstmCertToSNSANType
An attempt to set these objects while the value of
tlstmParamsRowStatus is active(1) will result in
an inconsistentValue error."
::= { tlstmCertToSNEntry 8 }
-- Maps securityNames to certificates for use by the SNMP-TARGET-MIB
tlstmParamsCount OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A count of the number of entries in the tlstmParamsTable"
::= { tlstmCertificateMapping 4 }
tlstmParamsTableLastChanged OBJECT-TYPE
SYNTAX TimeStamp
MAX-ACCESS read-only
STATUS current
DESCRIPTION
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"The value of sysUpTime.0 when the tlstmParamsTable
was last modified through any means, or 0 if it has not been
modified since the command responder was started."
::= { tlstmCertificateMapping 5 }
tlstmParamsTable OBJECT-TYPE
SYNTAX SEQUENCE OF TlstmParamsEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"This table extends the SNMP-TARGET-MIB's
snmpTargetParamsTable with an additional (D)TLS client-side
certificate fingerprint identifier to use when establishing
new (D)TLS connections."
::= { tlstmCertificateMapping 6 }
tlstmParamsEntry OBJECT-TYPE
SYNTAX TlstmParamsEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A conceptual row containing a locally held certificate's hash
type and hash value for a given snmpTargetParamsEntry. The
values in this row should be ignored if the connection that
needs to be established, as indicated by the SNMP-TARGET-MIB
infrastructure, is not a certificate and (D)TLS based
connection. The connection SHOULD NOT be established if the
certificate fingerprint stored in this entry does not point to
a valid locally held certificate or if it points to an usable
certificate (such as might happen when the certificate's
expiration date has been reached)."
INDEX { IMPLIED snmpTargetParamsName }
::= { tlstmParamsTable 1 }
TlstmParamsEntry ::= SEQUENCE {
tlstmParamsClientHashType FingerprintType,
tlstmParamsClientHashValue FingerprintValue,
tlstmParamsStorageType StorageType,
tlstmParamsRowStatus RowStatus
}
tlstmParamsClientHashType OBJECT-TYPE
SYNTAX FingerprintType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The hash algorithm type for the hash stored in the
tlstmParamsClientHash column to identify a locally-held X.509
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certificate that should be used when initiating a (D)TLS
connection as a (D)TLS client."
DEFVAL { tlstmSHA256 }
::= { tlstmParamsEntry 1 }
tlstmParamsClientHashValue OBJECT-TYPE
SYNTAX FingerprintValue
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"A cryptographic hash of a X.509 certificate. This object
should store the hash of a locally held X.509 certificate that
should be used when initiating a (D)TLS connection as a (D)TLS
client."
::= { tlstmParamsEntry 2 }
tlstmParamsStorageType OBJECT-TYPE
SYNTAX StorageType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The storage type for this conceptual row. Conceptual rows
having the value 'permanent' need not allow write-access to
any columnar objects in the row."
DEFVAL { nonVolatile }
::= { tlstmParamsEntry 3 }
tlstmParamsRowStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status of this conceptual row. This object may be used
to create or remove rows from this table.
To create a row in this table, a manager must set this object
to either createAndGo(4) or createAndWait(5).
Until instances of all corresponding columns are appropriately
configured, the value of the corresponding instance of the
tlstmParamsRowStatus column is 'notReady'.
In particular, a newly created row cannot be made active until
the corresponding tlstmParamsClientHashType and
tlstmParamsClientHashValue columns have been set.
The following objects may not be modified while the
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value of this object is active(1):
- tlstmParamsClientHashType
- tlstmParamsClientHashValue
An attempt to set these objects while the value of
tlstmParamsRowStatus is active(1) will result in
an inconsistentValue error.
If this row is deleted it has no effect on the corresponding
row in the targetParamsTable.
If the corresponding row in the targetParamsTable is deleted
then this row must be automatically removed."
::= { tlstmParamsEntry 4 }
-- Lists expected certificate fingerprints to be presented by a DTLS
-- server
tlstmAddrCount OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A count of the number of entries in the tlstmAddrTable"
::= { tlstmCertificateMapping 7 }
tlstmAddrTableLastChanged OBJECT-TYPE
SYNTAX TimeStamp
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The value of sysUpTime.0 when the tlstmAddrTable
was last modified through any means, or 0 if it has not been
modified since the command responder was started."
::= { tlstmCertificateMapping 8 }
tlstmAddrTable OBJECT-TYPE
SYNTAX SEQUENCE OF TlstmAddrEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"This table extends the SNMP-TARGET-MIB's snmpTargetAddrTable
with an expected (D)TLS server-side certificate identifier to
expect when establishing a new (D)TLS connections. If a
matching row in this table exists and the row is active then a
local copy of the certificate matching the fingerprint
identifier should be compared against the certificate being
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presented by the server. If the certificate presented by the
server does not match the locally held copy then the
connection MUST NOT be established. If no matching row exists
in this table then the connection SHOULD still proceed if
another certificate validation path algorithm (e.g. RFC5280)
can be followed to a configured trust anchor. "
::= { tlstmCertificateMapping 9 }
tlstmAddrEntry OBJECT-TYPE
SYNTAX TlstmAddrEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A conceptual row containing a copy of a locally held
certificate's hash type and hash value for a given
snmpTargetAddrEntry. The values in this row should be ignored
if the connection that needs to be established, as indicated
by the SNMP-TARGET-MIB infrastructure, is not a (D)TLS based
connection. If an tlstmAddrEntry exists for a given
snmpTargetAddrEntry then the presented server certificate MUST
match or the connection MUST NOT be established. If a row in
this table does not exist to match a snmpTargetAddrEntry row
then the connection SHOULD still proceed if some other
certificate validation path algorithm (e.g. RFC5280) can be
followed to a configured trust anchor."
INDEX { IMPLIED snmpTargetAddrName }
::= { tlstmAddrTable 1 }
TlstmAddrEntry ::= SEQUENCE {
tlstmAddrServerHashType FingerprintType,
tlstmAddrServerHashValue FingerprintValue,
tlstmAddrStorageType StorageType,
tlstmAddrRowStatus RowStatus
}
tlstmAddrServerHashType OBJECT-TYPE
SYNTAX FingerprintType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The hash algorithm type for the hash stored in the
tlstmAddrServerHash column to identify a local copy of the
public X.509 certificate presented by the TLS server."
DEFVAL { tlstmSHA256 }
::= { tlstmAddrEntry 1 }
tlstmAddrServerHashValue OBJECT-TYPE
SYNTAX FingerprintValue
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MAX-ACCESS read-create
STATUS current
DESCRIPTION
"A cryptographic hash of a public X.509 certificate. This
object should store the hash of a local copy of the public
X.509 certificate that the remote server should present during
the (D)TLS connection setup. The presented certificate and
the locally held copy, referred to by this hash value, MUST
match exactly or the connection MUST NOT be established."
::= { tlstmAddrEntry 2 }
tlstmAddrStorageType OBJECT-TYPE
SYNTAX StorageType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The storage type for this conceptual row. Conceptual rows
having the value 'permanent' need not allow write-access to
any columnar objects in the row."
DEFVAL { nonVolatile }
::= { tlstmAddrEntry 3 }
tlstmAddrRowStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status of this conceptual row. This object may be used
to create or remove rows from this table.
To create a row in this table, a manager must
set this object to either createAndGo(4) or
createAndWait(5).
Until instances of all corresponding columns are
appropriately configured, the value of the
corresponding instance of the tlstmAddrRowStatus
column is 'notReady'.
In particular, a newly created row cannot be made active until
the corresponding tlstmAddrServerHashType, and
tlstmAddrServerHashValue columns have been set.
The following objects may not be modified while the
value of this object is active(1):
- tlstmAddrServerHashType
- tlstmAddrServerHashValue
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An attempt to set these objects while the value of
tlstmAddrRowStatus is active(1) will result in
an inconsistentValue error.
If this row is deleted it has no effect on the corresponding
row in the targetAddrTable.
If the corresponding row in the targetAddrTable is deleted
then this row must be automatically removed."
::= { tlstmAddrEntry 4 }
-- ************************************************
-- tlstmMIB - Conformance Information
-- ************************************************
tlstmCompliances OBJECT IDENTIFIER ::= { tlstmConformance 1 }
tlstmGroups OBJECT IDENTIFIER ::= { tlstmConformance 2 }
-- ************************************************
-- Compliance statements
-- ************************************************
tlstmCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP engines that support the
TLSTM-MIB"
MODULE
MANDATORY-GROUPS { tlstmStatsGroup,
tlstmIncomingGroup, tlstmOutgoingGroup }
::= { tlstmCompliances 1 }
-- ************************************************
-- Units of conformance
-- ************************************************
tlstmStatsGroup OBJECT-GROUP
OBJECTS {
tlstmSessionOpens,
tlstmSessionCloses,
tlstmSessionOpenErrors,
tlstmSessionNoAvailableSessions,
tlstmSessionInvalidClientCertificates,
tlstmSessionInvalidServerCertificates,
tlstmTLSProtectionErrors
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}
STATUS current
DESCRIPTION
"A collection of objects for maintaining
statistical information of an SNMP engine which
implements the SNMP TLS Transport Model."
::= { tlstmGroups 1 }
tlstmIncomingGroup OBJECT-GROUP
OBJECTS {
tlstmCertToSNCount,
tlstmCertToSNTableLastChanged,
tlstmCertToSNHashType,
tlstmCertToSNHashValue,
tlstmCertToSNMapType,
tlstmCertToSNSecurityName,
tlstmCertToSNSANType,
tlstmCertToSNStorageType,
tlstmCertToSNRowStatus
}
STATUS current
DESCRIPTION
"A collection of objects for maintaining
incoming connection certificate mappings to
securityNames of an SNMP engine which implements the
SNMP TLS Transport Model."
::= { tlstmGroups 2 }
tlstmOutgoingGroup OBJECT-GROUP
OBJECTS {
tlstmParamsCount,
tlstmParamsTableLastChanged,
tlstmParamsClientHashType,
tlstmParamsClientHashValue,
tlstmParamsStorageType,
tlstmParamsRowStatus,
tlstmAddrCount,
tlstmAddrTableLastChanged,
tlstmAddrServerHashType,
tlstmAddrServerHashValue,
tlstmAddrStorageType,
tlstmAddrRowStatus
}
STATUS current
DESCRIPTION
"A collection of objects for maintaining
outgoing connection certificates to use when opening
connections as a result of SNMP-TARGET-MIB settings."
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::= { tlstmGroups 3 }
END
8. Operational Considerations
This section discusses various operational aspects of the solution
8.1. Sessions
A session is discussed throughout this document as meaning a security
association between the (D)TLS client and the (D)TLS server. State
information for the sessions are maintained in each TLSTM and this
information is created and destroyed as sessions are opened and
closed. Because of the connectionless nature of UDP, a "broken"
session, one side up one side down, could result if one side of a
session is brought down abruptly (i.e., reboot, power outage, etc.).
Whenever possible, implementations SHOULD provide graceful session
termination through the use of disconnect messages. Implementations
SHOULD also have a system in place for dealing with "broken"
sessions. Implementations SHOULD support the session resumption
feature of TLS.
To simplify session management it is RECOMMENDED that implementations
utilize two separate ports, one for Notification sessions and one for
Command sessions. If this implementation recommendation is followed,
(D)TLS clients will always send REQUEST messages and (D)TLS servers
will always send RESPONSE messages. With this assertion,
implementations may be able to simplify "broken" session handling,
session resumption, and other aspects of session management such as
guaranteeing that Request- Response pairs use the same session.
Implementations SHOULD limit the lifetime of established sessions
depending on the algorithms used for generation of the master session
secret, the privacy and integrity algorithms used to protect
messages, the environment of the session, the amount of data
transferred, and the sensitivity of the data.
8.2. Notification Receiver Credential Selection
When an SNMP engine needs to establish an outgoing session for
notifications, the snmpTargetParamsTable includes an entry for the
snmpTargetParamsSecurityName of the target. However, the receiving
SNMP engine (Server) does not know which (D)TLS certificate to offer
to the Client so that the tmSecurityName identity-authentication will
be successful. The best solution would be to maintain a one-to-one
mapping between certificates and incoming ports for notification
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receivers, although other implementation dependent mechanisms may be
used instead. This can be handled at the Notification Originator by
configuring the snmpTargetAddrTable (snmpTargetAddrTDomain and
snmpTargetAddrTAddress) and then requiring the receiving SNMP engine
to monitor multiple incoming static ports based on which principals
are capable of receiving notifications. Implementations MAY also
choose to designate a single Notification Receiver Principal to
receive all incoming TRAPS and INFORMS.
8.3. contextEngineID Discovery
Because most Command Responders have contextEngineIDs that are
identical to the USM securityEngineID, the USM provides Command
Generators with the ability to discover a default contextEngineID to
use. Because the TLS Transport Model does not make use of a
discoverable securityEngineID like the USM does, it may be difficult
for Command Generators to discover a suitable default
contextEngineID. Implementations should consider offering another
engineID discovery mechanism to continue providing Command Generators
with a contextEngineID discovery mechanism. A recommended discovery
solution is documented in [RFC5343].
9. Security Considerations
This document describes a transport model that permits SNMP to
utilize (D)TLS security services. The security threats and how the
(D)TLS transport model mitigates these threats are covered in detail
throughout this document. Security considerations for DTLS are
covered in [RFC4347] and security considerations for TLS are
described in Section 11 and Appendices D, E, and F of TLS 1.2
[RFC5246]. DTLS adds to the security considerations of TLS only
because it is more vulnerable to denial of service attacks. A random
cookie exchange was added to the handshake to prevent anonymous
denial of service attacks. RFC 4347 recommends that the cookie
exchange is utilized for all handshakes and therefore it is
RECOMMENDED that implementers also support this cookie exchange.
9.1. Certificates, Authentication, and Authorization
Implementations are responsible for providing a security certificate
configuration installation . Implementations SHOULD support
certificate revocation lists and expiration of certificates or other
access control mechanisms.
(D)TLS provides for both authentication of the identity of the (D)TLS
server and authentication of the identity of the (D)TLS client.
Access to MIB objects for the authenticated principal MUST be
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enforced by an access control subsystem (e.g. the VACM).
Authentication of the Command Generator principal's identity is
important for use with the SNMP access control subsystem to ensure
that only authorized principals have access to potentially sensitive
data. The authenticated identity of the Command Generator
principal's certificate is mapped to an SNMP model-independent
securityName for use with SNMP access control.
Furthermore, the (D)TLS handshake only provides assurance that the
certificate of the authenticated identity has been signed by an
configured accepted Certificate Authority. (D)TLS has no way to
further authorize or reject access based on the authenticated
identity. An Access Control Model (such as the VACM) provides access
control and authorization of a Command Generator's requests to a
Command Responder and a Notification Responder's authorization to
receive Notifications from a Notification Originator. However to
avoid man-in-the-middle attacks both ends of the (D)TLS based
connection MUST check the certificate presented by the other side
against what was expected. For example, Command Generators must
check that the Command Responder presented and authenticated itself
with a X.509 certificate that was expected. Not doing so would allow
an impostor, at a minimum, to present false data, receive sensitive
information and/or provide a false-positive belief that configuration
was actually received and acted upon. Authenticating and verifying
the identity of the (D)TLS server and the (D)TLS client for all
operations ensures the authenticity of the SNMP engine that provides
MIB data.
The instructions found in the DESCRIPTION clause of the
tlstmCertToSNTable object must be followed exactly. Specifically, it
is important that if a row matching a certificate or a certificate's
issuer is found but the translation to a securityName using the row
fails that the lookup process stops and no further rows are
consulted. It is also important that the rows of the table be search
in order starting with the row containing the lowest numbered
tlstmCertToSNID value.
9.2. Use with SNMPv1/SNMPv2c Messages
The SNMPv1 and SNMPv2c message processing described in RFC3484 (BCP
74) [RFC3584] always selects the SNMPv1(1) Security Model for an
SNMPv1 message, or the SNMPv2c(2) Security Model for an SNMPv2c
message. When running SNMPv1/SNMPv2c over a secure transport like
the TLS Transport Model, the securityName and securityLevel used for
access control decisions are then derived from the community string,
not the authenticated identity and securityLevel provided by the TLS
Transport Model.
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9.3. MIB Module Security
There are a number of management objects defined in this MIB module
with a MAX-ACCESS clause of read-write and/or read-create. Such
objects may be considered sensitive or vulnerable in some network
environments. The support for SET operations in a non-secure
environment without proper protection can have a negative effect on
network operations. These are the tables and objects and their
sensitivity/vulnerability:
o The tlstmParamsTable can be used to change the outgoing X.509
certificate used to establish a (D)TLS connection. Modification
to objects in this table need to be adequately authenticated since
modification to values in this table will have profound impacts to
the security of outbound connections from the device. Since
knowledge of authorization rules and certificate usage mechanisms
may be considered sensitive, protection from disclosure of the
SNMP traffic via encryption is also highly recommended.
o The tlstmAddrTable can be used to change the expectations of the
certificates presented by a remote (D)TLS server. Modification to
objects in this table need to be adequately authenticated since
modification to values in this table will have profound impacts to
the security of outbound connections from the device. Since
knowledge of authorization rules and certificate usage mechanisms
may be considered sensitive, protection from disclosure of the
SNMP traffic via encryption is also highly recommended.
o The tlstmCertToSNTable is used to specify the mapping of incoming
X.509 certificates to SNMPv3 securityNames. Modification to
objects in this table need to be adequately authenticated since
modification to values in this table will have profound impacts to
the security of incoming connections to the device. Since
knowledge of authorization rules and certificate usage mechanisms
may be considered sensitive, protection from disclosure of the
SNMP traffic via encryption is also highly recommended.
Some of the readable objects in this MIB module (i.e., objects with a
MAX-ACCESS other than not-accessible) may be considered sensitive or
vulnerable in some network environments. It is thus important to
control even GET and/or NOTIFY access to these objects and possibly
to even encrypt the values of these objects when sending them over
the network via SNMP. These are the tables and objects and their
sensitivity/vulnerability:
o This MIB contains a collection of counters that monitor the (D)TLS
connections being established with a device. Since knowledge of
connection and certificate usage mechanisms may be considered
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sensitive, protection from disclosure of the SNMP traffic via
encryption is also highly recommended.
SNMP versions prior to SNMPv3 did not include adequate security.
Even if the network itself is secure (for example by using IPsec),
even then, there is no control as to who on the secure network is
allowed to access and GET/SET (read/change/create/delete) the objects
in this MIB module.
It is RECOMMENDED that implementers consider the security features as
provided by the SNMPv3 framework (see [RFC3410], section 8),
including full support for the SNMPv3 cryptographic mechanisms (for
authentication and privacy).
Further, deployment of SNMP versions prior to SNMPv3 is NOT
RECOMMENDED. Instead, it is RECOMMENDED to deploy SNMPv3 and to
enable cryptographic security. It is then a customer/operator
responsibility to ensure that the SNMP entity giving access to an
instance of this MIB module is properly configured to give access to
the objects only to those principals (users) that have legitimate
rights to indeed GET or SET (change/create/delete) them.
10. IANA Considerations
IANA is requested to assign:
1. a TCP port number in the range 1..1023 in the
http://www.iana.org/assignments/port-numbers registry which will
be the default port for SNMP command messages over a TLS
Transport Model as defined in this document,
2. a TCP port number in the range 1..1023 in the
http://www.iana.org/assignments/port-numbers registry which will
be the default port for SNMP notification messages over a TLS
Transport Model as defined in this document,
3. a UDP port number in the range 1..1023 in the
http://www.iana.org/assignments/port-numbers registry which will
be the default port for SNMP command messages over a DTLS/UDP
connection as defined in this document,
4. a UDP port number in the range 1..1023 in the
http://www.iana.org/assignments/port-numbers registry which will
be the default port for SNMP notification messages over a DTLS/
UDP connection as defined in this document,
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5. a SCTP port number in the range 1..1023 in the
http://www.iana.org/assignments/port-numbers registry which will
be the default port for SNMP command messages over a DTLS/SCTP
connection as defined in this document,
6. a SCTP port number in the range 1..1023 in the
http://www.iana.org/assignments/port-numbers registry which will
be the default port for SNMP notification messages over a DTLS/
SCTP connection as defined in this document,
7. an SMI number under snmpDomains for the snmpTLSDomain object
identifier,
8. an SMI number under snmpDomains for the snmpDTLSUDPDomain object
identifier,
9. an SMI number under snmpDomains for the snmpDTLSSCTPDomain
object identifier,
10. a SMI number under snmpModules, for the MIB module in this
document,
11. "tls" as the corresponding prefix for the snmpTLSDomain in the
SNMP Transport Model registry,
12. "dudp" as the corresponding prefix for the snmpDTLSUDPDomain in
the SNMP Transport Model registry,
13. "dsct" as the corresponding prefix for the snmpDTLSSCTPDomain in
the SNMP Transport Model registry;
14. Editor's note: this section should be replaced with appropriate
descriptive assignment text after IANA assignments are made and
prior to publication.
11. Acknowledgements
This document closely follows and copies the Secure Shell Transport
Model for SNMP defined by David Harrington and Joseph Salowey in
[I-D.ietf-isms-secshell].
This document was reviewed by the following people who helped provide
useful comments: David Harrington, Alan Luchuk, Ray Purvis.
This work was supported in part by the United States Department of
Defense. Large portions of this document are based on work by
General Dynamics C4 Systems and the following individuals: Brian
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Baril, Kim Bryant, Dana Deluca, Dan Hanson, Tim Huemiller, John
Holzhauer, Colin Hoogeboom, Dave Kornbau, Chris Knaian, Dan Knaul,
Charles Limoges, Steve Moccaldi, Gerardo Orlando, and Brandon Yip.
12. References
12.1. Normative References
[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.
[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.
[RFC3413] Levi, D., Meyer, P., and B. Stewart, "Simple Network
Management Protocol (SNMP) Applications", STD 62,
RFC 3413, December 2002.
[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.
[RFC3415] Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based
Access Control Model (VACM) for the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3415,
December 2002.
[RFC3418] Presuhn, R., "Management Information Base (MIB) for the
Simple Network Management Protocol (SNMP)", STD 62,
RFC 3418, December 2002.
[RFC3584] Frye, R., Levi, D., Routhier, S., and B. Wijnen,
"Coexistence between Version 1, Version 2, and Version 3
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of the Internet-standard Network Management Framework",
BCP 74, RFC 3584, August 2003.
[RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[I-D.ietf-isms-transport-security-model]
Harington, D., "Transport Security Model for SNMP".
[I-D.ietf-isms-tmsm]
Harington, D. and J. Schoenwaelder, "Transport Subsystem
for the Simple Network Management Protocol (SNMP)".
12.2. Informative References
[RFC2522] Karn, P. and W. Simpson, "Photuris: Session-Key Management
Protocol", RFC 2522, March 1999.
[RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[I-D.ietf-isms-secshell]
Harington, D. and J. Salowey, "Secure Shell Transport
Model for SNMP".
[RFC5343] Schoenwaelder, J., "Simple Network Management Protocol
(SNMP) Context EngineID Discovery".
[I-D.saintandre-tls-server-id-check]
Saint-Andre, P., Zeilenga, K., Hodges, J., and B. Morgan,
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"Best Practices for Checking of Server Identities in the
Context of Transport Layer Security (TLS)".
[AES] National Institute of Standards, "Specification for the
Advanced Encryption Standard (AES)".
[DES] National Institute of Standards, "American National
Standard for Information Systems-Data Link Encryption".
[DSS] National Institute of Standards, "Digital Signature
Standard".
[RSA] Rivest, R., Shamir, A., and L. Adleman, "A Method for
Obtaining Digital Signatures and Public-Key
Cryptosystems".
[x509] Rivest, R., Shamir, A., and L. M. Adleman, "A Method for
Obtaining Digital Signatures and Public-Key
Cryptosystems".
Appendix A. (D)TLS Overview
The (D)TLS protocol is composed of two layers: the (D)TLS Record
Protocol and the (D)TLS Handshake Protocol. The following
subsections provide an overview of these two layers. Please refer to
[RFC4347] for a complete description of the protocol.
A.1. The (D)TLS Record Protocol
At the lowest layer, layered on top of the transport control protocol
or a datagram transport protocol (e.g. UDP or SCTP) is the (D)TLS
Record Protocol.
The (D)TLS Record Protocol provides security that has three basic
properties:
o The session can be confidential. Symmetric cryptography is used
for data encryption (e.g., AES [AES], DES [DES] etc.). The keys
for this symmetric encryption are generated uniquely for each
session and are based on a secret negotiated by another protocol
(such as the (D)TLS Handshake Protocol). The Record Protocol can
also be used without encryption.
o Messages can have data integrity. Message transport includes a
message integrity check using a keyed MAC. Secure hash functions
(e.g., SHA, MD5, etc.) are used for MAC computations. The Record
Protocol can operate without a MAC, but is generally only used in
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this mode while another protocol is using the Record Protocol as a
transport for negotiating security parameters.
o Messages are protected against replay. (D)TLS uses explicit
sequence numbers and integrity checks. DTLS uses a sliding window
to protect against replay of messages within a session.
(D)TLS also provides protection against replay of entire sessions.
In a properly-implemented keying material exchange, both sides will
generate new random numbers for each exchange. This results in
different encryption and integrity keys for every session.
A.2. The (D)TLS Handshake Protocol
The (D)TLS Record Protocol is used for encapsulation of various
higher-level protocols. One such encapsulated protocol, the (D)TLS
Handshake Protocol, allows the server and client to authenticate each
other and to negotiate an integrity algorithm, an encryption
algorithm and cryptographic keys before the application protocol
transmits or receives its first octet of data. Only the (D)TLS
client can initiate the handshake protocol. The (D)TLS Handshake
Protocol provides security that has three basic properties:
o The peer's identity can be authenticated using asymmetric (public
key) cryptography (e.g., RSA [RSA], DSS [DSS], etc.). This
authentication can be made optional, but is generally required by
at least one of the peers.
(D)TLS supports three authentication modes: authentication of both
the server and the client, server authentication with an
unauthenticated client, and total anonymity. For authentication
of both entities, each entity provides a valid certificate chain
leading to an acceptable certificate authority. Each entity is
responsible for verifying that the other's certificate is valid
and has not expired or been revoked. See
[I-D.saintandre-tls-server-id-check] for further details on
standardized processing when checking Server certificate
identities.
o The negotiation of a shared secret is secure: the negotiated
secret is unavailable to eavesdroppers, and for any authenticated
handshake the secret cannot be obtained, even by an attacker who
can place himself in the middle of the session.
o The negotiation is not vulnerable to malicious modification: it is
infeasible for an attacker to modify negotiation communication
without being detected by the parties to the communication.
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o DTLS uses a stateless cookie exchange to protect against anonymous
denial of service attacks and has retransmission timers, sequence
numbers, and counters to handle message loss, reordering, and
fragmentation.
Appendix B. PKIX Certificate Infrastructure
Users of a public key from a PKIX / X.509 certificate can be be
confident that the associated private key is owned by the correct
remote subject (person or system) with which an encryption or digital
signature mechanism will be used. This confidence is obtained
through the use of public key certificates, which are data structures
that bind public key values to subjects. The binding is asserted by
having a trusted CA digitally sign each certificate. The CA may base
this assertion upon technical means (i.e., proof of possession
through a challenge- response protocol), presentation of the private
key, or on an assertion by the subject. A certificate has a limited
valid lifetime which is indicated in its signed contents. Because a
certificate's signature and timeliness can be independently checked
by a certificate-using client, certificates can be distributed via
untrusted communications and server systems, and can be cached in
unsecured storage in certificate-using systems.
ITU-T X.509 (formerly CCITT X.509) or ISO/IEC/ITU 9594-8, which was
first published in 1988 as part of the X.500 Directory
recommendations, defines a standard certificate format [x509] which
is a certificate which binds a subject (principal) to a public key
value. This was later further documented in [RFC5280].
A X.509 certificate is a sequence of three required fields:
tbsCertificate: The field contains the names of the subject and
issuer, a public key associated with the subject, a validity
period, and other associated information. This field may also
contain extension components.
signatureAlgorithm: The signatureAlgorithm field contains the
identifier for the cryptographic algorithm used by the certificate
authority (CA) to sign this certificate.
signatureValue: The signatureValue field contains a digital
signature computed upon the ASN.1 DER encoded tbsCertificate
field. The ASN.1 DER encoded tbsCertificate is used as the input
to the signature function. This signature value is then ASN.1 DER
encoded as a BIT STRING and included in the Certificate's
signature field. By generating this signature, a CA certifies the
validity of the information in the tbsCertificate field. In
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particular, the CA certifies the binding between the public key
material and the subject of the certificate.
The basic X.509 authentication procedure is as follows: A system is
initialized with a number of root certificates that contain the
public keys of a number of trusted CAs. When a system receives a
X.509 certificate, signed by one of those CAs, the certificate has to
be verified. It first checks the signatureValue field by using the
public key of the corresponding trusted CA. Then it compares the
decrypted information with a digest of the tbsCertificate field. If
they match, then the subject in the tbsCertificate field is
authenticated.
Appendix C. Target and Notificaton Configuration Example
Configuring the SNMP-TARGET-MIB and NOTIFICATION-MIB along with
access control settings for the SNMP-VIEW-BASED-ACM-MIB can be a
daunting task without an example to follow. The following section
describes an example of what pieces must be in place to accomplish
this configuration.
The isAccessAllowed() ASI requires configuration to exist in the
following SNMP-VIEW-BASED-ACM-MIB tables:
vacmSecurityToGroupTable
vacmAccessTable
vacmViewTreeFamilyTable
The only table that needs to be discussed as particularly different
here is the vacmSecurityToGroupTable. This table is indexed by both
the SNMPv3 security model and the security name. The security model,
when TLSTM is in use, should be set to the value of XXX corresponding
to the TSM [I-D.ietf-isms-transport-security-model]. An example
vacmSecurityToGroupTable row might be filled out as follows (using a
single SNMP SET request):
Note to RFC editor: replace XXX in the previous paragraph above with
the actual IANA-assigned number for the TSM security model and remove
this note.
vacmSecurityModel = XXX (TSM)
vacmSecurityName = "blueberry"
vacmGroupaName = "administrators"
vacmSecurityToGroupStorageType = 3 (nonVolatile)
vacmSecurityToGroupStatus = 4 (createAndGo)
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Note to RFC editor: replace XXX in the vacmSecurityModel line above
with the actual IANA-assigned number for the TSM security model and
remove this note.
This example will assume that the "administrators" group has been
given proper permissions via rows in the vacmAccessTable and
vacmViewTreeFamilyTable.
Depending on whether this VACM configuration is for a Command
Responder or a Command Generator the security name "blueberry" will
come from a few different locations.
For Notification Generator's performing authorization checks, the
server's certificate must be verified against the expected
certificate before proceeding to send the notification. The
securityName be set by the SNMP-TARGET-MIB's
snmpTargetParamsSecurityName column or other configuration mechanism
and the certificate to use would be taken from the appropriate entry
in the tlstmParamsTable. The tlstmParamsTable augments the SNMP-
TARGET-MIB's snmpTargetParamsTable with client-side certificate
information.
For Command Responder applications, the vacmSecurityName "blueberry"
value is a value that needs to come from an incoming (D)TLS session.
The mapping from a recevied (D)TLS client certificate to a
securityName is done with the tlstmCertToSNTable. The certificates
must be loaded into the device so that a tlstmCertToSNEntry may refer
to it. As an example, consider the following entry which will
provide a mapping from a X.509's hash fingerprint directly to the
"blueberry" securityName:
tlstmCertToSNID = 1 (chosen by ordering preference)
tlstmCertToSNHashType = tlstmSHA256
tlstmCertToSNHashValue = (appropriate sha256 fingerprint)
tlstmCertToSNMapType = specified(1)
tlstmCertToSNSecurityName = "blueberry"
tlstmCertToSNStorageType = 3 (nonVolatile)
tlstmCertToSNRowStatus = 4 (createAndGo)
The above is an example of how to map a particular certificate to a
particular securityName. It is recommended that users make use of
direct subjectAltName or CommonName mappings where possible since it
will provide a more scalable approach to certificate management.
This entry provides an example of using a subjectAltName mapping:
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tlstmCertToSNID = 1 (chosen by ordering preference)
tlstmCertToSNHashType = tlstmSHA256
tlstmCertToSNHashValue = (appropriate sha256 fingerprint)
tlstmCertToSNMapType = bySubjectAltName(2)
tlstmCertToSNSANType = 1 (any)
tlstmCertToSNStorageType = 3 (nonVolatile)
tlstmCertToSNRowStatus = 4 (createAndGo)
The above entry indicates the subjectAltName field for certificates
created by an Issuing certificate with a corresponding hash type and
value will be trusted to always produce common names that are
directly 1 to 1 mappable into SNMPv3 securityNames. This type of
configuration should only be used when the certificate authorities
naming conventions are carefully controlled.
For the example, if the incoming (D)TLS client provided certificate
contained a subjectAltName where the first listed subjectAltName in
the extension is the rfc822Name of "blueberry" and the certificate
was signed by a certificate matching the tlstmCertToSNHashType and
tlstmCertToSNHashValue values above and the CA's certificate was
properly installed on the device then the string "blueberry" would be
used as the securityName for the session.
Author's Address
Wes Hardaker
Sparta, Inc.
P.O. Box 382
Davis, CA 95617
US
Phone: +1 530 792 1913
Email: ietf@hardakers.net
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