ISMS W. Hardaker
Internet-Draft Sparta, Inc.
Intended status: Standards Track October 22, 2009
Expires: April 25, 2010
Transport Layer Security Transport Model for SNMP
draft-ietf-isms-dtls-tm-01.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 . . . . . . . . . . . . . . . . . . . . 14
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 . . . . . . . 19
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
6.4.1. Notifications . . . . . . . . . . . . . . . . . . . . 30
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 . . . . . . . . 54
8.3. contextEngineID Discovery . . . . . . . . . . . . . . . . 54
9. Security Considerations . . . . . . . . . . . . . . . . . . . 55
9.1. Certificates, Authentication, and Authorization . . . . . 55
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9.2. Use with SNMPv1/SNMPv2c Messages . . . . . . . . . . . . . 56
9.3. MIB Module Security . . . . . . . . . . . . . . . . . . . 56
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 57
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 59
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 59
12.1. Normative References . . . . . . . . . . . . . . . . . . . 59
12.2. Informative References . . . . . . . . . . . . . . . . . . 61
Appendix A. (D)TLS Overview . . . . . . . . . . . . . . . . . . . 62
A.1. The (D)TLS Record Protocol . . . . . . . . . . . . . . . . 62
A.2. The (D)TLS Handshake Protocol . . . . . . . . . . . . . . 62
Appendix B. PKIX Certificate Infrastructure . . . . . . . . . . . 63
Appendix C. Target and Notificaton Configuration Example . . . . 64
C.1. Configuring the Notification Generator . . . . . . . . . . 65
C.2. Configuring the Command Responder . . . . . . . . . . . . 65
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
[RFC5590]. 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 [RFC5590]. 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], [RFC2579] and [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
application types is an example only and other combinations are
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equally as legitimate.
+----------------------------------------------------------------+
| Network |
+----------------------------------------------------------------+
^ | ^ |
|Notifications |Commands |Commands |Notifications
+---|---------------------|--------+ +--|---------------|-------------+
| | 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 | |
| | RESPONDER | | ORIGINATOR | | | | GENERATOR | | RESPONDER | |
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| | 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.
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 and in this
memo is "principal". A principal is the "who" on whose behalf
services are provided or processing takes place. A principal can be,
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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 [RFC5246] and [RFC4347] for
complete descriptions of the protocols.
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, Notification Originator and Proxy
Forwarder 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].
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]).
4. Disclosure - The disclosure threat is the danger of eavesdropping
on the exchanges between SNMP engines.
Symmetric cryptography (e.g., [AES], [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).
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 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
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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.
See Section 9 for more detail on the security considerations
associated with the DTLSTM and these security threats.
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. 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
security level dependent algorithms (for example a security level to
cipher_suites mapping table) then different security levels may be
utilized by the application.
The authentication, integrity and privacy algorithms used by the
(D)TLS Protocols 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
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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 tlsSessionID 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 pairing 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
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.
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3.3. Notifications and Proxy
(D)TLS sessions may be initiated by (D)TLS clients on behalf of
command generators, notification originators or proxy forwarders.
Command generators are frequently operated by a human, but
notification originators and proxy forwarders 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 tlstmParamsClientFingerprint parameter of
the tlstmParamsTable should be set a value that refers to a locally
held certificate to be used. The tlstmAddrServerFingerprint 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 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.
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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. A brief 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 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.
Having received a certificate, the authenticated tmSecurityName of
the principal is looked up using the tlstmCertToSNTable. This table
either:
o Maps a certificate's fingerprint type and value to a directly
specified tmSecurityName, or
o Identifies a certificate issuer's fingerprint and allows a child
certificate's subjectAltName or CommonName to be mapped to the
tmSecurityNome.
Implementations MAY 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.
The typical enterprise configuration will map a "subjectAltName"
component of the tbsCertificate to the TLSTM specific tmSecurityName.
The authenticated identity can be obtained by the TLS Transport Model
by extracting the subjectAltName(s) from the peer's certificate. The
receiving application will then have an appropriate tmSecurityName
for use by other SNMPv3 components like an access control model.
An example of this type of mapping setup can be found in Appendix C
This tmSecurityName may be later translated from a TLSTM specific
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tmSecurityName to a SNMP engine securityName by the security model.
A security model, like the TSM security model [RFC5591], 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
)
The abstract data elements returned from or passed as parameters into
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.
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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 outgoingMessage field.
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 returned from or passed as parameters into
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.
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.
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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 after being processed by
(D)TLS and removed of the (D)TLS transport layer data.
incomingMessageLength: The length of the incomingMessage field.
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 returned from or passed as parameters into
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.
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
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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.
tlsSessionID: An implementation-dependent session identifier to
reference the specific (D)TLS session.
Neither DTLS or UDP provides 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 given 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 tlsSessionID for
the session. Other implementation-dependent data from (D)TLS may
also be returned. The tlsSessionID is formatted and stored in an
implementation-dependent manner. It is tied to the tmSecurityData
for future use of this session and must remain constant and unique
while the session is open.
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:
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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 returned from or passed as parameters into
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
might 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 wholeDtlsMsg field.
incomingMessage: The whole SNMP message after being processed by
(D)TLS and removed of the (D)TLS transport layer data.
incomingMessageLength: The length of the incomingMessage field.
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.
statusInformation = -- errorIndication or success
tlsWrite(
IN tlsSessionID -- Session identifier for (D)TLS
IN outgoingMessage -- the message to send
IN outgoingMessageLength -- its length
)
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The abstract data elements returned from or passed as parameters into
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 outgoingMessage field.
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" [RFC5590] 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" [RFC5590]
5. Elements of Procedure
Abstract service interfaces have been defined by [RFC3411] and
further augmented by [RFC5590] 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.
To simplify the elements of procedure, the release of state
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.
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An error indication in statusInformation will typically include the
Object Identifier (OID) and value for an incremented error counter.
This may be accompanied by the requested securityLevel and the
tmStateReference. Per-message context information is not accessible
to Transport Models, so for the returned counter OID and value,
contextEngine would be set to the local value of snmpEngineID and
contextName to the default context for error counters.
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. It is assumed that
TLS and DTLS/SCP protocol implementations already provide appropriate
message demultiplexing and only the processing steps in Section 5.1.2
are needed.
5.1.1. DTLS Processing for Incoming Messages
DTLS is significantly different in terms of session handling than
when TLS or DTLS is run over session based streaming protocols like
TCP or SCTP. Specifically, the DTLS protocol, when run over UDP,
does not have a session identifier 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 session demultiplexing
process.
A process for demultiplexing multiple DTLS sessions arriving over UDP
must be incorporated into the procedures for processing an incoming
message. The steps in this section describe one possible method to
accomplish this, 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
an 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 (such as a session initialization
or session modification message) then the message should be
processed by the underlying DTLS framework 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 increment the tlstmDTLSProtectionErrors counter,
discard and stop processing the message.
7) The output of the tlsRead ASI 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.
Create a tmStateReference cache for the subsequent reference and
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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 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 -- 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 -- 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 the tmSessionID, tmTransportAddress, tmSecurityName,
tmRequestedSecurityLevel, and tmSameSecurity values from the
tmStateReference. Note: The tmSessionID value may be undefined
if no session exists yet over which the message can be sent.
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 (described in greater
detail in step 4b). An implementation MAY choose to return an
error to the calling module and stop processing of the message.
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, return an error indication to the
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calling module and stop processing of the message.
5) Using either the session indicated by the tmSessionID if there
was one or the session resulting from a previous step (3 or 4),
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 when establishing a
SNMP over (D)TLS session between SNMP engines for exchanging 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.
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
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 is reported in the
tmStateReference cache as tmSecurityLevel. For (D)TLS to provide
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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 processing stops.
3) Once a (D)TLS secured session is established and both sides have
performed any appropriate certificate authentication verification
(e.g. [RFC5280]) then each side will determine and/or check the
identity of the remote entity using the procedures described
below.
a) The (D)TLS server side of the connection identifies the
authenticated identity from the (D)TLS client's principal
certificate 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 any verification fails in any way (for
example because of failures in cryptographic verification or
because of the lack of an appropriate row in the
tlstmCertToSNTable) then the session establishment MUST fail,
the tlstmSessionInvalidClientCertificates object is
incremented and processing stops.
b) The (D)TLS client side of the connection MUST verify that
authenticated identity of the (D)TLS server's certificate is
the certificate expected. This can be done using the
configuration fingerprints found in the tlstmAddrTable if the
client is establishing the connection based on SNMP-TARGET-
MIB configuration or based on external certificate path
validation processes (e.g. [RFC5280]).
Methods for verifying that the proper destination was reached
based on the presented certificate are described in
[I-D.saintandre-tls-server-id-check]. Matching the server's
naming against SubjectAltName extension values SHOULD be 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.
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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 stops.
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.
(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, an implementation that wishes to support
multiple identities MAY use separate TCP, UDP or SCTP port numbers to
indicate the desired principal or some other implementation-dependent
solution.
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 and its contents.
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,
notifications 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 New TransportDomain and TransportAddress formats for describing
(D)TLS connection addressing requirements.
o Public certificate fingerprint allowing MIB module objects to
generically refer to a stored X.509 certificate using a
cryptographic hash 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
configuring a MIB-instrumented device for sending and receiving SNMP
messages over (D)TLS. In particular, there is are MIB tables that
extend the SNMP-TARGET-MIB for configuring (D)TLS certificate usage
and a MIB table for mapping incoming (D)TLS client certificates to
SNMPv3 securityNames.
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6.4.1. Notifications
The TLSTM-MIB defines notifications to alert management stations when
a (D)TLS connection fails because the server's presented certificate
did not meet an expected value, according to the tlstmAddrTable.
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 likely 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 SNMPv2-CONF [RFC2580].
7. MIB Module Definition
TLSTM-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE,
OBJECT-IDENTITY, snmpModules, snmpDomains,
Counter32, Unsigned32, NOTIFICATION-TYPE
FROM SNMPv2-SMI
TEXTUAL-CONVENTION, TimeStamp, RowStatus, StorageType
FROM SNMPv2-TC
MODULE-COMPLIANCE, OBJECT-GROUP, NOTIFICATION-GROUP
FROM SNMPv2-CONF
SnmpAdminString
FROM SNMP-FRAMEWORK-MIB
snmpTargetParamsName, snmpTargetAddrName
FROM SNMP-TARGET-MIB
;
tlstmMIB MODULE-IDENTITY
LAST-UPDATED "200807070000Z"
ORGANIZATION "ISMS Working Group"
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CONTACT-INFO "WG-EMail: isms@lists.ietf.org
Subscribe: isms-request@lists.ietf.org
Chairs:
Juergen Schoenwaelder
Jacobs University Bremen
Campus Ring 1
28725 Bremen
Germany
+49 421 200-3587
j.schoenwaelder@jacobs-university.de
Russ Mundy
SPARTA, Inc.
7110 Samuel Morse Drive
Columbia, MD 21046
USA
Co-editors:
Wes Hardaker
Sparta, Inc.
P.O. Box 382
Davis, CA 95617
USA
ietf@hardakers.net
"
DESCRIPTION "
The TLS Transport Model MIB
Copyright (c) 2009 IETF Trust and the persons
identified as authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, are permitted provided that the
following conditions are met:
- Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the following
disclaimer in the documentation and/or other materials
provided with the distribution.
- Neither the name of Internet Society, IETF or IETF Trust,
nor the names of specific contributors, may be used to endorse
or promote products derived from this software without
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specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
CONTRIBUTORS 'AS IS' AND ANY EXPRESS OR IMPLIED WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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 TLSTM-MIB
-- ************************************************
tlstmNotifications OBJECT IDENTIFIER ::= { tlstmMIB 0 }
tlstmObjects OBJECT IDENTIFIER ::= { tlstmMIB 1 }
tlstmConformance OBJECT IDENTIFIER ::= { tlstmMIB 2 }
-- ************************************************
-- tlstmObjects - Objects
-- ************************************************
snmpTLSDomain OBJECT-IDENTITY
STATUS current
DESCRIPTION
"The SNMP over TLS transport domain. The corresponding
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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 which 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.
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 which 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.
The securityName prefix to be associated with the
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snmpDTLSSCTPDomain is 'dsct'. This prefix may be used by
security models or other components to identify which 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
-- 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 US-US-ASCII encoded hostname and port number.
An IPv4 address must be in dotted decimal format followed by a
colon ':' (US-ASCII character 0x3A) and a decimal port number
in US-ASCII.
An IPv6 address must be a colon separated format, surrounded
by square brackets ('[', US-ASCII character 0x5B, and ']',
US-ASCII character 0x5D), followed by a colon ':' (US-ASCII
character 0x3A) and a decimal port number in US-ASCII.
A hostname is always in US-US-ASCII (as per RFC1033);
internationalized hostnames are encoded in US-US-ASCII as
specified in RFC 3490. The hostname is followed by a colon
':' (US-US-ASCII character 0x3A) and a decimal port number in
US-US-ASCII. The name SHOULD be fully qualified whenever
possible.
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.
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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
including SIZE constraints on the index components or by
specifying applicable constraints in the conceptual row
DESCRIPTION clause or in the surrounding documentation."
REFERENCE
"RFC 1033: DOMAIN ADMINISTRATORS OPERATIONS GUIDE
RFC 3490: Internationalizing Domain Names in Applications
RFC 3986: Uniform Resource Identifier (URI): Generic Syntax
RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2
"
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 US-ASCII encoded hostname and port number.
An IPv4 address must be a dotted decimal format followed by a
colon ':' (US-ASCII character 0x3A) and a decimal port number in
US-ASCII.
An IPv6 address must be a colon separated format, surrounded
by square brackets ('[', US-ASCII character 0x5B, and ']',
US-ASCII character 0x5D), followed by a colon ':' (US-ASCII
character 0x3A) and a decimal port number in US-ASCII.
A hostname is always in US-US-ASCII (as per RFC1033);
internationalized hostnames are encoded in US-US-ASCII as
specified in RFC 3490. The hostname is followed by a colon
':' (US-US-ASCII character 0x3A) and a decimal port number in
US-US-ASCII. The name SHOULD be fully qualified whenever
possible.
Values of this textual convention may not be directly usable
as transport-layer addressing information, and may require
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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
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."
REFERENCE
"RFC 1033: DOMAIN ADMINISTRATORS OPERATIONS GUIDE
RFC 3490: Internationalizing Domain Names in Applications
RFC 3986: Uniform Resource Identifier (URI): Generic Syntax
RFC 4347: Datagram Transport Layer Security
RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2
"
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 US-ASCII encoded hostname and port number.
An IPv4 address must be a dotted decimal format followed by a
colon ':' (US-ASCII character 0x3A) and a decimal port number in
US-ASCII.
An IPv6 address must be a colon separated format, surrounded
by square brackets ('[', US-ASCII character 0x5B, and ']',
US-ASCII character 0x5D), followed by a colon ':' (US-ASCII
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character 0x3A) and a decimal port number in US-ASCII.
A hostname is always in US-US-ASCII (as per RFC1033);
internationalized hostnames are encoded in US-US-ASCII as
specified in RFC 3490. The hostname is followed by a colon
':' (US-US-ASCII character 0x3A) and a decimal port number in
US-US-ASCII. The name SHOULD be fully qualified whenever
possible.
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.
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))
Fingerprint ::= TEXTUAL-CONVENTION
DISPLAY-HINT "1x:254x"
STATUS current
DESCRIPTION
"A Fingerprint value that can be used to uniquely reference
other data of potentially arbitrary length.
A Fingerprint value is composed of a 1-octet hashing algorithm
type. The octet value encoded is taken from the IANA TLS
HashAlgorithm Registry (RFC5246). The remaining octets are
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filled using the results of the hashing algorithm.
This TEXTUAL-CONVENTION SHOULD NOT be used as a form of
cryptographic verification and a data source with a matching
fingerprint should not be considered authenticated because the
value matches. This TEXTUAL-CONVENTION is only intended for
use as a reference to a stored copy of a longer data source.
The contents of full data source referenced by this fingerprint
needs to be compared against to assure collisions have not
resulted."
REFERENCE
"RFC 1033: DOMAIN ADMINISTRATORS OPERATIONS GUIDE
RFC 3490: Internationalizing Domain Names in Applications
RFC 3986: Uniform Resource Identifier (URI): Generic Syntax
RFC 4347: Datagram Transport Layer Security
RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2
"
SYNTAX OCTET STRING (SIZE (1..255))
-- The tlstmSession Group
tlstmSession OBJECT IDENTIFIER ::= { tlstmObjects 1 }
tlstmSessionOpens OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an openSession() request has been
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."
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::= { 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
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
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tlstmConfig OBJECT IDENTIFIER ::= { tlstmObjects 2 }
-- 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
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; 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
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tlstmCertToSNFingerprint value determines whether the row is a
match for the incoming connection:
1) If the row's tlstmCertToSNFingerprint value identifies
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 tlstmCertToSNFingerprint value identifies
a locally held copy of a trusted CA certificate and
that CA certificated was used to validate the path to
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 a 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 not compatible with
the needed requirements of a securityName (e.g., VACM imposes
a 32-octet-maximum length and the certificate derived
securityName could be longer) 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
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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,
tlstmCertToSNFingerprint Fingerprint,
tlstmCertToSNMapType INTEGER,
tlstmCertToSNSecurityName SnmpAdminString,
tlstmCertToSNSANType INTEGER,
tlstmCertToSNStorageType StorageType,
tlstmCertToSNRowStatus RowStatus
}
tlstmCertToSNID OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A unique, prioritized index for the given entry."
::= { tlstmCertToSNEntry 1 }
tlstmCertToSNFingerprint OBJECT-TYPE
SYNTAX Fingerprint
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"A cryptographic hash of a X.509 certificate. The results of
a successful matching fingerprint to either the trusted CA in
the certificate validation path or to the certificate itself
is dictated by the tlstmCertToSNMapType column."
::= { tlstmCertToSNEntry 2 }
tlstmCertToSNMapType OBJECT-TYPE
SYNTAX INTEGER { specified(1), bySubjectAltName(2), byCN(3) }
MAX-ACCESS read-create
STATUS current
DESCRIPTION
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"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. Note: The tlstmCertToSNSecurityName
column's value is ignored for all other
tlstmCertToSNMapType values.
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 the resulting mapped value from the
subjectAltName component is not compatible with
the needed requirements of a securityName (e.g.,
VACM imposes a 32-octet-maximum length and the
certificate derived securityName could be
longer) then the next appropriate subjectAltName
of the correct type should be used if available.
If no appropriate subjectAltName of the given
type is found within the certificate then
additional rows in the tlstmCertToSNTable must
be searched for additional
tlstmCertToSNFingerprint matches.
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 value of the CommonName component is not
compatible with the needed requirements of a
securityName (e.g., VACM imposes a
32-octet-maximum length and the certificate
derived securityName could be longer) then
additional rows in the tlstmCertToSNTable must
be searched for additional
tlstmCertToSNFingerprint matches."
DEFVAL { specified }
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::= { tlstmCertToSNEntry 3 }
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 for a proper match."
DEFVAL { "" }
::= { tlstmCertToSNEntry 4 }
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.
Note that the resulting length is the maximum length
supported by the View-Based Access Control Model
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(VACM). Note that using both the Transport Security
Model's support for transport prefixes (see the
SNMP-TSM-MIB::snmpTsmConfigurationUsePrefix object for
details) will result in securityName lengths that
exceed what VACM can handle.
Values for type otherName(5) are converted to a valid
securityName by using only the decoded value portion of the
OtherName sequence. I.E. the OBJECT IDENTIFIER portion of the
OtherName sequence is not included as part of the resulting
securityName."
DEFVAL { any }
::= { tlstmCertToSNEntry 5 }
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 6 }
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 tlstmCertToSNFingerprint,
tlstmCertToSNMapType, tlstmCertToSNSecurityName, and
tlstmCertToSNSANType columns have been set.
The following objects may not be modified while the
value of this object is active(1):
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- tlstmCertToSNFingerprint
- tlstmCertToSNMapType
- tlstmCertToSNSecurityName
- tlstmCertToSNSANType
An attempt to set these objects while the value of
tlstmParamsRowStatus is active(1) will result in
an inconsistentValue error."
::= { tlstmCertToSNEntry 7 }
-- 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
"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 fingerprint hash of a locally
held certificate for a given snmpTargetParamsEntry. The
values in this row should be ignored if the connection that
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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 {
tlstmParamsClientFingerprint Fingerprint,
tlstmParamsStorageType StorageType,
tlstmParamsRowStatus RowStatus
}
tlstmParamsClientFingerprint OBJECT-TYPE
SYNTAX Fingerprint
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 1 }
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 2 }
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
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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 tlstmParamsClientFingerprint column has
been set.
The tlstmParamsClientFingerprint object may not be modified
while the value of this object is active(1).
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 3 }
-- 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
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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
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 fingerprint 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 {
tlstmAddrServerFingerprint Fingerprint,
tlstmAddrStorageType StorageType,
tlstmAddrRowStatus RowStatus
}
tlstmAddrServerFingerprint OBJECT-TYPE
SYNTAX Fingerprint
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"A cryptographic hash of a public X.509 certificate. This
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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 1 }
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 2 }
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 tlstmAddrServerFingerprint column has been
set.
The tlstmAddrServerFingerprint object may not be modified
while the value of this object is active(1).
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
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row in the targetAddrTable.
If the corresponding row in the targetAddrTable is deleted
then this row must be automatically removed."
::= { tlstmAddrEntry 3 }
-- ************************************************
-- tlstmNotifications - Notifications Information
-- ************************************************
tlstmServerCertNotFound NOTIFICATION-TYPE
STATUS current
DESCRIPTION
"Notification that the server certificate presented by a SNMP
over (D)TLS server could not be found in the tlstmAddrTable."
::= { tlstmNotifications 1 }
tlstmServerAuthFailure NOTIFICATION-TYPE
OBJECTS { tlstmAddrServerFingerprint }
STATUS current
DESCRIPTION
"Notification that the server certificate presented by an SNMP
over (D)TLS server was found, but the connection could not be
established because of a cryptographic validation failure."
::= { tlstmNotifications 2 }
-- ************************************************
-- tlstmCompliances - 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,
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tlstmIncomingGroup,
tlstmOutgoingGroup,
tlstmNotificationGroup }
::= { tlstmCompliances 1 }
-- ************************************************
-- Units of conformance
-- ************************************************
tlstmStatsGroup OBJECT-GROUP
OBJECTS {
tlstmSessionOpens,
tlstmSessionCloses,
tlstmSessionOpenErrors,
tlstmSessionNoAvailableSessions,
tlstmSessionInvalidClientCertificates,
tlstmSessionInvalidServerCertificates,
tlstmTLSProtectionErrors
}
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,
tlstmCertToSNFingerprint,
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,
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tlstmParamsClientFingerprint,
tlstmParamsStorageType,
tlstmParamsRowStatus,
tlstmAddrCount,
tlstmAddrTableLastChanged,
tlstmAddrServerFingerprint,
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."
::= { tlstmGroups 3 }
tlstmNotificationGroup NOTIFICATION-GROUP
NOTIFICATIONS {
tlstmServerCertNotFound,
tlstmServerAuthFailure
}
STATUS current
DESCRIPTION
"Notifications"
::= { tlstmGroups 4 }
END
8. Operational Considerations
This section discusses various operational aspects of deploying
TLSTM.
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
implementation and this information is created and destroyed as
sessions are opened and closed. A "broken" session (one side up and
one side down) can 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.
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To simplify session management it is RECOMMENDED that implementations
use separate ports for Notification sessions and 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.
One solution is to maintain a one-to-one mapping between certificates
and incoming ports for notification receivers. This can be handled
at the Notification Originator by configuring the snmpTargetAddrTable
(snmpTargetAddrTDomain and snmpTargetAddrTAddress) and 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 or
select an implementation specific method of selecting a server
certificate to present to clients.
8.3. contextEngineID Discovery
Most Command Responders have contextEngineIDs that are identical to
the USM securityEngineID. USM provides a discovery service that
allows Command Generators to determine a securityEngineID and thus a
default contextEngineID to use. Because the TLS Transport Model does
not make use of a securityEngineID, 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 suitable
contextEngineID mechanism. A recommended discovery solution is
documented in [RFC5343].
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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 this
specification also RECOMMENDEDs that implementers also support this
cookie exchange.
9.1. Certificates, Authentication, and Authorization
Implementations are responsible for providing a security certificate
installation and configuration mechanism. Implementations SHOULD
support certificate revocation lists.
(D)TLS provides for authentication of the identity of both the (D)TLS
server and the (D)TLS client. Access to MIB objects for the
authenticated principal MUST be 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.
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
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false 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. It is also
important that the rows of the table be searched in prioritized 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.
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
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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
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:
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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 receipt of 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 receipt of 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 receipt of 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 receipt of SNMP notification messages
over a DTLS/UDP connection as defined in this document,
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 receipt of 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 receipt of 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,
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13. "dsct" as the corresponding prefix for the snmpDTLSSCTPDomain in
the SNMP Transport Model registry;
If possible, IANA is requested to use matching port numbers for all
assignments for SNMP Commands being sent over TLS, DTLS/UDP, DTLS/
SCTP.
If possible, IANA is requested to use matching port numbers for all
assignments for SNMP Notifications being sent over TLS, DTLS/UDP,
DTLS/SCTP.
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
[RFC5292].
This document was reviewed by the following people who helped provide
useful comments (in alphabetical order): Andy Donati, Pasi Eronen,
David Harrington, Jeffrey Hutzelman, Alan Luchuk, Randy Presuhn, Ray
Purvis, Joseph Salowey, Jurgen Schonwalder, Dave Shield.
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
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",
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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
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.
[RFC5590] Harrington, D. and J. Schoenwaelder, "Transport Subsystem
for the Simple Network Management Protocol (SNMP)",
RFC 5590, June 2009.
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[RFC5591] Harrington, D. and W. Hardaker, "Transport Security Model
for the Simple Network Management Protocol (SNMP)",
RFC 5591, June 2009.
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.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[RFC5292] Chen, E. and S. Sangli, "Address-Prefix-Based Outbound
Route Filter for BGP-4", RFC 5292, August 2008.
[RFC5343] Schoenwaelder, J., "Simple Network Management Protocol
(SNMP) Context EngineID Discovery", RFC 5343,
September 2008.
[I-D.saintandre-tls-server-id-check]
Saint-Andre, P., Zeilenga, K., Hodges, J., and B. Morgan,
"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".
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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], [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
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
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Protocol provides security that has four 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.
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
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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 tbsCertificate 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 by the CA 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, the
CA certifies the validity of the information in the tbsCertificate
field. In 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.
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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 4, corresponding
to the TSM [RFC5591]. An example vacmSecurityToGroupTable row might
be filled out as follows (using a single SNMP SET request):
vacmSecurityModel = 4 (TSM)
vacmSecurityName = "blueberry"
vacmGroupName = "administrators"
vacmSecurityToGroupStorageType = 3 (nonVolatile)
vacmSecurityToGroupStatus = 4 (createAndGo)
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.
C.1. Configuring the Notification Generator
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 expected
certificate from the server may be listed in the tlstmAddrTable or
may be determined through other X.509 path validation mechanisms.
The securityName to use for VACM authorization checks is set by the
SNMP-TARGET-MIB's snmpTargetParamsSecurityName column.
The certificate that the notification generator should present to the
server is taken from the tlstmParamsClientFingerprint column from the
appropriate entry in the tlstmParamsTable table.
C.2. Configuring the Command Responder
For Command Responder applications, the vacmSecurityName "blueberry"
value is a value that needs derive from an incoming (D)TLS session.
The mapping from a recevied (D)TLS client certificate to a
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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 client's public X.509's hash fingerprint
directly to the "blueberry" securityName:
tlstmCertToSNID = 1 (chosen by ordering preference)
tlstmCertToSNFingerprint = HASH (appropriate fingerprint)
tlstmCertToSNMapType = 1 (specified)
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, however, that users make
use of direct subjectAltName or CommonName mappings where possible as
it provides a more scalable approach to certificate management. This
entry provides an example of using a subjectAltName mapping:
tlstmCertToSNID = 1 (chosen by ordering preference)
tlstmCertToSNFingerprint = HASH (appropriate fingerprint)
tlstmCertToSNMapType = 2 (bySubjectAltName)
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 fingerprint
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.
In 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", the certificate was
signed by a certificate matching the tlstmCertToSNFingerprint value
and the CA's certificate was properly installed on the device then
the string "blueberry" would be used as the securityName for the
session.
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Author's Address
Wes Hardaker
Sparta, Inc.
P.O. Box 382
Davis, CA 95617
USA
Phone: +1 530 792 1913
Email: ietf@hardakers.net
Hardaker Expires April 25, 2010 [Page 67]
