[Docs] [txt|pdf] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 draft-ietf-isms-dtls-tm

ISMS                                                         W. Hardaker
Internet-Draft                                              Sparta, Inc.
Intended status: Standards Track                           June 24, 2009
Expires: December 26, 2009


           Transport Layer Security Transport Model for SNMP
                   draft-hardaker-isms-dtls-tm-05.txt

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.  This document may contain material
   from IETF Documents or IETF Contributions published or made publicly
   available before November 10, 2008.  The person(s) controlling the
   copyright in some of this material may not have granted the IETF
   Trust the right to allow modifications of such material outside the
   IETF Standards Process.  Without obtaining an adequate license from
   the person(s) controlling the copyright in such materials, this
   document may not be modified outside the IETF Standards Process, and
   derivative works of it may not be created outside the IETF Standards
   Process, except to format it for publication as an RFC or to
   translate it into languages other than English.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on December 26, 2009.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal



Hardaker                Expires December 26, 2009               [Page 1]

Internet-Draft               SNMP over DTLS                    June 2009


   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

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 monitoring and managing the TLS Transport Model for
   SNMP.

























Hardaker                Expires December 26, 2009               [Page 2]

Internet-Draft               SNMP over DTLS                    June 2009


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1.  Conventions  . . . . . . . . . . . . . . . . . . . . . . .  7
   2.  The Datagram Transport Layer Security Protocol . . . . . . . .  8
     2.1.  The (D)TLS Record Protocol . . . . . . . . . . . . . . . .  8
     2.2.  The (D)TLS Handshake Protocol  . . . . . . . . . . . . . .  9
     2.3.  SNMP requirements of (D)TLS  . . . . . . . . . . . . . . . 10
   3.  How the TLSTM fits into the Transport Subsystem  . . . . . . . 10
     3.1.  Security Capabilities of this Model  . . . . . . . . . . . 12
       3.1.1.  Threats  . . . . . . . . . . . . . . . . . . . . . . . 12
       3.1.2.  Message Protection . . . . . . . . . . . . . . . . . . 13
       3.1.3.  (D)TLS Sessions  . . . . . . . . . . . . . . . . . . . 14
     3.2.  Security Parameter Passing . . . . . . . . . . . . . . . . 15
     3.3.  Notifications and Proxy  . . . . . . . . . . . . . . . . . 15
   4.  Elements of the Model  . . . . . . . . . . . . . . . . . . . . 16
     4.1.  Certificates . . . . . . . . . . . . . . . . . . . . . . . 16
       4.1.1.  The Certificate Infrastructure . . . . . . . . . . . . 16
       4.1.2.  Provisioning for the Certificate . . . . . . . . . . . 17
     4.2.  Messages . . . . . . . . . . . . . . . . . . . . . . . . . 18
     4.3.  SNMP Services  . . . . . . . . . . . . . . . . . . . . . . 19
       4.3.1.  SNMP Services for an Outgoing Message  . . . . . . . . 19
       4.3.2.  SNMP Services for an Incoming Message  . . . . . . . . 20
     4.4.  (D)TLS Services  . . . . . . . . . . . . . . . . . . . . . 21
       4.4.1.  Services for Establishing a Session  . . . . . . . . . 21
       4.4.2.  (D)TLS Services for an Incoming Message  . . . . . . . 22
       4.4.3.  (D)TLS Services for an Outgoing Message  . . . . . . . 23
     4.5.  Cached Information and References  . . . . . . . . . . . . 24
       4.5.1.  TLS Transport Model Cached Information . . . . . . . . 24
   5.  Elements of Procedure  . . . . . . . . . . . . . . . . . . . . 24
     5.1.  Procedures for an Incoming Message . . . . . . . . . . . . 25
       5.1.1.  DTLS Processing for Incoming Messages  . . . . . . . . 25
       5.1.2.  Transport Processing for Incoming Messages . . . . . . 26
     5.2.  Procedures for an Outgoing Message . . . . . . . . . . . . 27
     5.3.  Establishing a Session . . . . . . . . . . . . . . . . . . 29
     5.4.  Closing a Session  . . . . . . . . . . . . . . . . . . . . 31
   6.  MIB Module Overview  . . . . . . . . . . . . . . . . . . . . . 31
     6.1.  Structure of the MIB Module  . . . . . . . . . . . . . . . 32
     6.2.  Textual Conventions  . . . . . . . . . . . . . . . . . . . 32
     6.3.  Statistical Counters . . . . . . . . . . . . . . . . . . . 32
     6.4.  Configuration Tables . . . . . . . . . . . . . . . . . . . 32
     6.5.  Relationship to Other MIB Modules  . . . . . . . . . . . . 32
       6.5.1.  MIB Modules Required for IMPORTS . . . . . . . . . . . 33
   7.  MIB Module Definition  . . . . . . . . . . . . . . . . . . . . 33
   8.  Operational Considerations . . . . . . . . . . . . . . . . . . 49
     8.1.  Sessions . . . . . . . . . . . . . . . . . . . . . . . . . 49
     8.2.  Notification Receiver Credential Selection . . . . . . . . 50
     8.3.  contextEngineID Discovery  . . . . . . . . . . . . . . . . 50



Hardaker                Expires December 26, 2009               [Page 3]

Internet-Draft               SNMP over DTLS                    June 2009


   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 50
     9.1.  Certificates, Authentication, and Authorization  . . . . . 51
     9.2.  Use with SNMPv1/SNMPv2c Messages . . . . . . . . . . . . . 52
     9.3.  MIB Module Security  . . . . . . . . . . . . . . . . . . . 52
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 52
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 54
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 54
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 54
     12.2. Informative References . . . . . . . . . . . . . . . . . . 55
   Appendix A.  Target and Notificaton Configuration Example  . . . . 56
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 58








































Hardaker                Expires December 26, 2009               [Page 4]

Internet-Draft               SNMP over DTLS                    June 2009


1.  Introduction

   It is important to understand the modular SNMPv3 architecture as
   defined by [RFC3411] and enhanced by the Transport Subsystem
   [I-D.ietf-isms-tmsm].  It is also important to understand the
   terminology of the SNMPv3 architecture in order to understand where
   the Transport Model described in this document fits into the
   architecture and how it interacts with the other architecture
   subsystems.  For a detailed overview of the documents that describe
   the current Internet-Standard Management Framework, please refer to
   Section 7 of [RFC3410].

   This document describes a Transport Model that makes use of the
   Transport Layer Security (TLS) [RFC5246] and the Datagram Transport
   Layer Security (DTLS) Protocol [RFC4347], within a transport
   subsystem [I-D.ietf-isms-tmsm].  DTLS is the datagram variant of the
   Transport Layer Security (TLS) protocol [RFC5246].  The Transport
   Model in this document is referred to as the Transport Layer Security
   Transport Model (TLSTM).  TLS and DTLS take advantage of the X.509
   public keying infrastructure [X509].  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 specifies a portion of the Management Information
   Base (MIB) to define objects for monitoring and managing the TLS
   Transport Model for SNMP.

   Managed objects are accessed via a virtual information store, termed
   the Management Information Base or MIB.  MIB objects are generally
   accessed through the Simple Network Management Protocol (SNMP).
   Objects in the MIB are defined using the mechanisms defined in the
   Structure of Management Information (SMI).  This memo specifies a MIB
   module that is compliant to the SMIv2, which is described in STD 58,
   RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580
   [RFC2580].

   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
   equally as legitimate.




Hardaker                Expires December 26, 2009               [Page 5]

Internet-Draft               SNMP over DTLS                    June 2009


 +----------------------------------------------------------------+
 |                              Network                           |
 +----------------------------------------------------------------+
     ^                     ^             ^               ^
     |Notifications        |Commands     |Commands       |Notifications
 +---|---------------------|--------+ +--|---------------|-------------+
 |   V                     V        | |  V               V             |
 | +------------+  +------------+   | | +-----------+   +----------+   |
 | |  (D)TLS    |  |  (D)TLS    |   | | | (D)TLS    |   | (D)TLS   |   |
 | |   Service  |  |   Service  |   | | |  Service  |   |  Service |   |
 | |   (Client) |  |   (Server) |   | | |  (Client) |   |  (Server)|   |
 | +------------+  +------------+   | | +-----------+   +----------+   |
 |          ^          ^            | |       ^              ^         |
 |          |          |            | |       |              |         |
 |       +--+----------+            | |     +-+--------------+         |
 | +-----|---------+----+           | | +---|--------+----+            |
 | |     V         |LCD | +-------+ | | |   V        |LCD | +--------+ |
 | | +------+      +----+ |       | | | | +------+   +----+ |        | |
 | | | DTLS | <---------->| Cache | | | | | DTLS |    <---->| Cache  | |
 | | |  TM  |           | |       | | | | |  TM  |        | |        | |
 | | +------+           | +-------+ | | | +------+        | +--------+ |
 | |Transport Subsystem |    ^      | | |Transport Sub.   |      ^     |
 | +--------------------+    |      | | +-----------------+      |     |
 |    ^                      +----+ | |    ^                     |     |
 |    |                           | | |    |                     |     |
 |    v                           | | |    V                     |     |
 | +-------+ +----------+ +-----+ | | | +-----+ +------+ +-----+ |     |
 | |       | |Message   | |Sec. | | | | |     | |  MP  | |Sec. | |     |
 | | Disp. | |Processing| |Sub- | | | | |Disp.| | Sub- | |Sub- | |     |
 | |       | |Subsystem | |sys. | | | | |     | |system| |sys. | |     |
 | |       | |          | |     | | | | |     | |      | |     | |     |
 | |       | |          | |+---+| | | | |     | |      | |+---+| |     |
 | |       | | +-----+  | ||   || | | | |     | |+----+| ||   || |     |
 | |      <--->|v3MP |<-->||TSM|<-+ | | |    <-->|v3MP|<->|TSM|<-+     |
 | |       | | +-----+  | ||   ||   | | |     | |+----+| ||   ||       |
 | +-------+ |          | |+---+|   | | +-----+ |      | |+---+|       |
 |    ^      |          | |     |   | |    ^    |      | |     |       |
 |    |      +----------+ +-----+   | |    |    +------+ +-----+       |
 |    +-+------------+              | |  +-+------------+              |
 |      ^            ^              | |  ^              ^              |
 |      |            |              | |  |              |              |
 |      v            v              | |  V              V              |
 | +-------------+ +--------------+ | | +-----------+ +--------------+ |
 | |   COMMAND   | | NOTIFICATION | | | |  COMMAND  | | NOTIFICATION | |
 | |  RESPONDER  | |  ORIGINATOR  | | | | GENERATOR | |  RESPONDER   | |
 | | application | | applications | | | |application| | application  | |
 | +-------------+ +--------------+ | | +-----------+ +--------------+ |
 |                      SNMP entity | |                    SNMP entity |



Hardaker                Expires December 26, 2009               [Page 6]

Internet-Draft               SNMP over DTLS                    June 2009


 +----------------------------------+ +--------------------------------+

1.1.  Conventions

   For consistency with SNMP-related specifications, this document
   favors terminology as defined in STD62 rather than favoring
   terminology that is consistent with non-SNMP specifications.  This is
   consistent with the IESG decision to not require the SNMPv3
   terminology be modified to match the usage of other non-SNMP
   specifications when SNMPv3 was advanced to Full Standard.

   Authentication in this document typically refers to the English
   meaning of "serving to prove the authenticity of" the message, not
   data source authentication or peer identity authentication.

   Large portions of this document simultaneously refer to both TLS and
   DTLS when discussing TLSTM components that function equally with
   either protocol.  "(D)TLS" is used in these places to indicate that
   the statement applies to either or both protocols as appropriate.
   When a distinction between the protocols is needed they are referred
   to independently through the use of "TLS" or "DTLS".  The Transport
   Model, however, is named "TLS Transport Model" and refers not to the
   TLS or DTLS protocol but to the standard defined in this document,
   which includes support for both TLS and DTLS.

   The terms "manager" and "agent" are not used in this document,
   because in the RFC 3411 architecture [RFC3411], all SNMP entities
   have the capability of acting in either manager or agent or in both
   roles depending on the SNMP application types supported in the
   implementation.  Where distinction is required, the application names
   of Command Generator, Command Responder, Notification Originator,
   Notification Receiver, and Proxy Forwarder are used.  See "SNMP
   Applications" [RFC3413] for further information.

   Throughout this document, the terms "client" and "server" are used to
   refer to the two ends of the (D)TLS transport connection.  The client
   actively opens the (D)TLS connection, and the server passively
   listens for the incoming (D)TLS connection.  Either SNMP entity may
   act as client or as server, as discussed further below.

   The User-Based Security Model (USM) [RFC3414] is a mandatory-to-
   implement Security Model in STD 62.  While (D)TLS and USM frequently
   refer to a user, the terminology preferred in RFC3411 [RFC3411] and
   in this memo is "principal".  A principal is the "who" on whose
   behalf services are provided or processing takes place.  A principal
   can be, among other things, an individual acting in a particular
   role; a set of individuals, with each acting in a particular role; an
   application or a set of applications, or a combination of these



Hardaker                Expires December 26, 2009               [Page 7]

Internet-Draft               SNMP over DTLS                    June 2009


   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 Datagram 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 (D)TLS protocol is composed of two layers: the
   (D)TLS Record Protocol and the (D)TLS Handshake Protocol.  The
   following sections provide an overview of these two layers.  Please
   refer to [RFC4347] for a complete description of the protocol.
   Readers familiar with (D)TLS can skip Section 2 except for section
   Section 2.3.

2.1.  The (D)TLS Record Protocol

   At the lowest layer, layered on top of the transport control protocol
   or a datagram transport protocol (e.g.  UDP or SCTP) is the (D)TLS
   Record Protocol.

   The (D)TLS Record Protocol provides security that has three basic
   properties:

   o  The session can be confidential.  Symmetric cryptography is used
      for data encryption (e.g., AES [AES], DES [DES] etc.).  The keys
      for this symmetric encryption are generated uniquely for each
      session and are based on a secret negotiated by another protocol
      (such as the (D)TLS Handshake Protocol).  The Record Protocol can
      also be used without encryption.

   o  Messages can have data integrity.  Message transport includes a
      message integrity check using a keyed MAC.  Secure hash functions
      (e.g., SHA, MD5, etc.) are used for MAC computations.  The Record
      Protocol can operate without a MAC, but is generally only used in
      this mode while another protocol is using the Record Protocol as a
      transport for negotiating security parameters.



Hardaker                Expires December 26, 2009               [Page 8]

Internet-Draft               SNMP over DTLS                    June 2009


   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.

2.2.  The (D)TLS Handshake Protocol

   The (D)TLS Record Protocol is used for encapsulation of various
   higher-level protocols.  One such encapsulated protocol, the (D)TLS
   Handshake Protocol, allows the server and client to authenticate each
   other and to negotiate an integrity algorithm, an encryption
   algorithm and cryptographic keys before the application protocol
   transmits or receives its first octet of data.  Only the (D)TLS
   client can initiate the handshake protocol.  The (D)TLS Handshake
   Protocol provides security that has three basic properties:

   o  The peer's identity can be authenticated using asymmetric (public
      key) cryptography (e.g., RSA [RSA], DSS [DSS], etc.).  This
      authentication can be made optional, but is generally required by
      at least one of the peers.

      (D)TLS supports three authentication modes: authentication of both
      the server and the client, server authentication with an
      unauthenticated client, and total anonymity.  For authentication
      of both entities, each entity provides a valid certificate chain
      leading to an acceptable certificate authority.  Each entity is
      responsible for verifying that the other's certificate is valid
      and has not expired or been revoked.  See
      [I-D.saintandre-tls-server-id-check] for further details on
      standardized processing when checking Server certificate
      identities.

   o  The negotiation of a shared secret is secure: the negotiated
      secret is unavailable to eavesdroppers, and for any authenticated
      handshake the secret cannot be obtained, even by an attacker who
      can place himself in the middle of the session.

   o  The negotiation is not vulnerable to malicious modification: it is
      infeasible for an attacker to modify negotiation communication
      without being detected by the parties to the communication.

   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



Hardaker                Expires December 26, 2009               [Page 9]

Internet-Draft               SNMP over DTLS                    June 2009


      fragmentation.

2.3.  SNMP requirements of (D)TLS

   To properly support the SNMP over TLS Transport Model, the (D)TLS
   implementation requires the following:

   o  The TLS Transport Model SHOULD always use authentication of both
      the server and the client.

   o  At a minimum the TLS Transport Model MUST support authentication
      of the Command Generator principals to guarantee the authenticity
      of the securityName.

   o  The TLS Transport Model SHOULD support the message encryption to
      protect sensitive data from eavesdropping attacks.


3.  How the TLSTM fits into the Transport Subsystem

   A transport model is a component of the Transport Subsystem.  The TLS
   Transport Model thus fits between the underlying (D)TLS transport
   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:


   +------------------------------+



Hardaker                Expires December 26, 2009              [Page 10]

Internet-Draft               SNMP over DTLS                    June 2009


   |    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        | | |    |
   | |              | |  |  +------------+  |  | +------------+ | |    |
   | |              | |  |  +------------+  |  | +------------+ | |    |
   | |              | |  +->| 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 |
   +-------------------------------------------------------------------+



Hardaker                Expires December 26, 2009              [Page 11]

Internet-Draft               SNMP over DTLS                    June 2009


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.

   2.  Masquerade - The masquerade threat is the danger that management
       operations unauthorized for a given principal may be attempted by
       assuming the identity of another principal that has the
       appropriate authorizations.

       The TLSTM provides for authentication of the Command Generator,
       Command Responder, Notification Generator, Notification Responder
       and Proxy Forwarder through the use of X.509 certificates.

       The masquerade threat can be mitigated against by using an
       appropriate Access Control Model (ACM) such as the View-based
       Access Control Module (VACM) [RFC3415].  In addition, it is
       important to authenticate and verify both the authenticated
       identity of the (D)TLS client and the (D)TLS server to protect
       against this threat.  (See Section 9 for more detail.)

   3.  Message stream modification - The re-ordering, delay or replay of
       messages can and does occur through the natural operation of many
       connectionless transport services.  The message stream
       modification threat is the danger that messages may be
       maliciously re-ordered, delayed or replayed to an extent which is
       greater than can occur through the natural operation of
       connectionless transport services, in order to effect
       unauthorized management operations.

       (D)TLS provides replay protection with a MAC that includes a
       sequence number.  Since UDP provides no sequencing ability DTLS
       uses a sliding window protocol with the sequence number for
       replay protection, see [RFC4347].  The technique used is similar



Hardaker                Expires December 26, 2009              [Page 12]

Internet-Draft               SNMP over DTLS                    June 2009


       to that as in IPsec AH/ESP [RFC4302] [RFC4303], by maintaining a
       bitmap window of received records.  Records that are too old to
       fit in the window and records that have previously been received
       are silently discarded.  The replay detection feature is
       optional, since packet duplication can also occur naturally due
       to routing errors and does not necessarily indicate an active
       attack.  Applications may conceivably detect duplicate packets
       and accordingly modify their data transmission strategy.

   4.  Disclosure - The disclosure threat is the danger of eavesdropping
       on the exchanges between SNMP engines.  Protecting against this
       threat may be required by local policy at the deployment site.

       Symmetric cryptography (e.g., AES [AES], DES [DES] etc.) can be
       used by (D)TLS for data privacy.  The keys for this symmetric
       encryption are generated uniquely for each session and are based
       on a secret negotiated by another protocol (such as the (D)TLS
       Handshake Protocol).

   5.  Denial of Service - the RFC 3411 architecture [RFC3411] states
       that denial of service (DoS) attacks need not be addressed by an
       SNMP security protocol.  However, datagram-based security
       protocols like DTLS are susceptible to a variety of denial of
       service attacks because it is more vulnerable to spoofed
       messages.

       In order to counter both of these attacks, DTLS borrows the
       stateless cookie technique used by Photuris [RFC2522] and IKEv2
       [RFC4306] and is described fully in section 4.2.1 of [RFC4347].
       This mechanism, though, does not provide any defense against
       denial of service attacks mounted from valid IP addresses.  DTLS
       Transport Model server implementations MUST support DTLS cookies.

       Implementations are not required to perform the stateless cookie
       exchange for every DTLS handshakes but in environments where
       amplification could be an issue or has been detected it is
       RECOMMENDED that the cookie exchange is utilized.

3.1.2.  Message Protection

   The RFC 3411 architecture recognizes three levels of security:

   o  without authentication and without privacy (noAuthNoPriv)

   o  with authentication but without privacy (authNoPriv)

   o  with authentication and with privacy (authPriv)




Hardaker                Expires December 26, 2009              [Page 13]

Internet-Draft               SNMP over DTLS                    June 2009


   The TLS Transport Model determines from (D)TLS the identity of the
   authenticated principal, and the type and address associated with an
   incoming message, and the TLS Transport Model provides this
   information to (D)TLS for an outgoing message.

   When an application requests a session for a message, through the
   cache, the application requests a security level for that session.
   The TLS Transport Model MUST ensure that the (D)TLS session provides
   security at least as high as the requested level of security.  How
   the security level is translated into the algorithms used to provide
   data integrity and privacy is implementation-dependent.  However, the
   NULL integrity and encryption algorithms MUST NOT be used to fulfill
   security level requests for authentication or privacy.
   Implementations MAY choose to force (D)TLS to only allow
   cipher_suites that provide both authentication and privacy to
   guarantee this assertion.

   If a suitable interface between the TLS Transport Model and the
   (D)TLS Handshake Protocol is implemented to allow the selection of
   security level dependent algorithms, for example a security level to
   cipher_suites mapping table, then different security levels may be
   utilized by the application.  However, different port numbers will
   need to be used by at least one side of the connection to
   differentiate between the (D)TLS sessions.  This is the only way to
   ensured proper selection of a session ID for an incoming (D)TLS
   message.

   The authentication, integrity and privacy algorithms used by the
   (D)TLS Protocol [RFC4347] may vary over time as the science of
   cryptography continues to evolve and the development of (D)TLS
   continues over time.  Implementers are encouraged to plan for changes
   in operator trust of particular algorithms and implementations should
   offer configuration settings for mapping algorithms to SNMPv3
   security levels.

3.1.3.  (D)TLS Sessions

   (D)TLS sessions are opened by the TLS Transport Model during the
   elements of procedure for an outgoing SNMP message.  Since the sender
   of a message initiates the creation of a (D)TLS session if needed,
   the (D)TLS session will already exist for an incoming message.

   Implementations MAY choose to instantiate (D)TLS sessions in
   anticipation of outgoing messages.  This approach might be useful to
   ensure that a (D)TLS session to a given target can be established
   before it becomes important to send a message over the (D)TLS
   session.  Of course, there is no guarantee that a pre-established
   session will still be valid when needed.



Hardaker                Expires December 26, 2009              [Page 14]

Internet-Draft               SNMP over DTLS                    June 2009


   DTLS sessions, when used over UDP, are uniquely identified within the
   TLS Transport Model by the combination of transportDomain,
   transportAddress, securityName, and requestedSecurityLevel associated
   with each session.  Each unique combination of these parameters MUST
   have a locally-chosen unique dtlsSessionID associated for active
   sessions.  For further information see Section 4.4 and Section 5.
   TLS and DTLS over SCTP sessions, on the other hand, do not require a
   unique paring of attributes since their lower layer protocols (TCP
   and SCTP) already provide adequate session framing.

3.2.  Security Parameter Passing

   For the (D)TLS server-side, (D)TLS-specific security parameters
   (i.e., cipher_suites, X.509 certificate fields, IP address and port)
   are translated by the TLS Transport Model into security parameters
   for the TLS Transport Model and security model (i.e., securityLevel,
   securityName, transportDomain, transportAddress).  The transport-
   related and (D)TLS-security-related information, including the
   authenticated identity, are stored in a cache referenced by
   tmStateReference.

   For the (D)TLS client-side, the TLS Transport Model takes input
   provided by the dispatcher in the sendMessage() Abstract Service
   Interface (ASI) and input from the tmStateReference cache.  The
   (D)TLS Transport Model converts that information into suitable
   security parameters for (D)TLS and establishes sessions as needed.

   The elements of procedure in Section 5 discuss these concepts in much
   greater detail.

3.3.  Notifications and Proxy

   (D)TLS sessions may be initiated by (D)TLS clients on behalf of
   command generators or notification originators.  Command generators
   are frequently operated by a human, but notification originators are
   usually unmanned automated processes.  The targets to whom
   notifications should be sent is typically determined and configured
   by a network administrator.

   The SNMP-TARGET-MIB module [RFC3413] contains objects for defining
   management targets, including transportDomain, transportAddress,
   securityName, securityModel, and securityLevel parameters, for
   Notification Generator, Proxy Forwarder, and SNMP-controllable
   Command Generator applications.  Transport domains and transport
   addresses are configured in the snmpTargetAddrTable, and the
   securityModel, securityName, and securityLevel parameters are
   configured in the snmpTargetParamsTable.  This document defines a MIB
   module that extends the SNMP-TARGET-MIB's snmpTargetParamsTable to



Hardaker                Expires December 26, 2009              [Page 15]

Internet-Draft               SNMP over DTLS                    June 2009


   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 tlstmParamsHashType and
   tlstmParamsHashValue parameters of the tlstmParamsTable should be set
   to values that refer to a locally held certificate to be used.  Other
   parameters, for example cryptographic configuration such as cipher
   suites to use, must come from configuration mechanisms not defined in
   this document.  The other needed configuration may be configured
   using SNMP or other implementation-dependent mechanisms (for example,
   via a CLI).  This securityName defined in the
   snmpTargetParamsSecurityName column will be used by the access
   control model to authorize any notifications that need to be sent.


4.  Elements of the Model

   This section contains definitions required to realize the (D)TLS
   Transport Model defined by this document.  Readers familiar with
   X.509 certificates can skip this section until Section 4.1.2.

4.1.  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 (D)TLS and the its effects on SNMP over (D)TLS.

4.1.1.  The Certificate Infrastructure

   Users of a public key SHALL 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



Hardaker                Expires December 26, 2009              [Page 16]

Internet-Draft               SNMP over DTLS                    June 2009


   certificate-using client, certificates can be distributed via
   untrusted communications and server systems, and can be cached in
   unsecured storage in certificate-using systems.

   ITU-T X.509 (formerly CCITT X.509) or ISO/IEC/ITU 9594-8, which was
   first published in 1988 as part of the X.500 Directory
   recommendations, defines a standard certificate format [X509] which
   is a certificate which binds a subject (principal) to a public key
   value.  This was later further documented in [RFC5280].

   A X.509 certificate is a sequence of three required fields:

   tbsCertificate:  The field contains the names of the subject and
      issuer, a public key associated with the subject, a validity
      period, and other associated information.  This field may also
      contain extension components.

   signatureAlgorithm:  The signatureAlgorithm field contains the
      identifier for the cryptographic algorithm used by the certificate
      authority (CA) to sign this certificate.

   signatureValue:  The signatureValue field contains a digital
      signature computed upon the ASN.1 DER encoded tbsCertificate
      field.  The ASN.1 DER encoded tbsCertificate is used as the input
      to the signature function.  This signature value is then ASN.1 DER
      encoded as a BIT STRING and included in the Certificate's
      signature field.  By generating this signature, a CA certifies the
      validity of the information in the tbsCertificate field.  In
      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.

4.1.2.  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



Hardaker                Expires December 26, 2009              [Page 17]

Internet-Draft               SNMP over DTLS                    June 2009


   entity can use for certificate verification.  SNMP entities MAY also
   be provisioned with a X.509 certificate revocation mechanism which
   can be used to verify that a certificate has not been revoked.

   The authenticated tmSecurityName of the principal is looked up using
   the tlstmCertificateToSNTable.  This table either:

   o  Maps a certificate's fingerprint hash type and value to a directly
      specified tmSecurityName.

   o  Identifies a certificate issuer's fingerprint hash type and value
      and allows child certificate's subjectAltName or CommonName to
      directly used as the tmSecurityNome.

   The certificate trust anchors, being either CA certificates or public
   keys for use by self-signed certificates, must be installed through
   an out of band trusted mechanism into the server and its authenticity
   MUST be verified before access is granted.  Implementations SHOULD
   choose to discard any connections for which no potential
   tlstmCertificateToSNTable mapping exists before performing
   certificate verification to avoid expending computational resources
   associated with certificate verification.

   The typical enterprise configuration will map the "subjectAltName"
   component of the tbsCertificate to the TLSTM specific tmSecurityName.
   Thus, the authenticated identity can be obtained by the TLS Transport
   Model by extracting the subjectAltName from the peer's certificate
   and the receiving application will have an appropriate tmSecurityName
   for use by components like an access control model.  This setup
   requires very little configuration: a single row in the
   tlstmCertificateToSNTable referencing a certificate authority.

   An example mapping setup can be found in Appendix A

   This tmSecurityName may be later translated from a TLSTM specific
   tmSecurityName to a SNMP engine securityName by the security model.
   A security model, like the TSM security model, may perform an
   identity mapping or a more complex mapping to derive the securityName
   from the tmSecurityName offered by the TLS Transport Model.

4.2.  Messages

   As stated in Section 4.1.1 of [RFC4347], each DTLS record must fit
   within a single DTLS datagram.  The TLSTM SHOULD prohibit SNMP
   messages from being sent that exceeds the maximum DTLS message size.
   The TLSTM implementation SHOULD return an error when the DTLS message
   size would be exceeded and the message won't be sent.




Hardaker                Expires December 26, 2009              [Page 18]

Internet-Draft               SNMP over DTLS                    June 2009


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 passed as parameters in the abstract
   service primitives are as follows:

   statusInformation:  An indication of whether the passing of the
      message was successful.  If not it is an indication of the
      problem.

   destTransportDomain:  The transport domain for the associated
      destTransportAddress.  The Transport Model uses this parameter to
      determine the transport type of the associated
      destTransportAddress.  This parameter may also be used by the
      transport subsystem to route the message to the appropriate
      Transport Model.  This document specifies three TLS and DTLS based
      Transport Domains for use: the snmpTLSDomain, the
      snmpDTLSUDPDomain and the snmpDTLSSCTPDomain.

   destTransportAddress:  The transport address of the destination TLS
      Transport Model in a format specified by the SnmpTLSAddress, the
      SnmpDTLSUDPAddress or the SnmpDTLSSCTPAddress TEXTUAL-CONVENTIONs.







Hardaker                Expires December 26, 2009              [Page 19]

Internet-Draft               SNMP over DTLS                    June 2009


   outgoingMessage:  The outgoing message to send to (D)TLS for
      encapsulation.

   outgoingMessageLength:  The length of the outgoing message.

   tmStateReference:  A handle/reference to tmSecurityData to be used
      when securing outgoing messages.

4.3.2.  SNMP Services for an Incoming Message

   The TLS Transport Model processes the received message from the
   network using the (D)TLS service and then passes it to the dispatcher
   using the following ASI:


      statusInformation =
      receiveMessage(
      IN   transportDomain               -- origin transport domain
      IN   transportAddress              -- origin transport address
      IN   incomingMessage               -- the message received
      IN   incomingMessageLength         -- its length
      IN   tmStateReference              -- reference to transport state
       )

   The abstract data elements passed as parameters in the abstract
   service primitives are as follows:

   statusInformation:  An indication of whether the passing of the
      message was successful.  If not it is an indication of the
      problem.

   transportDomain:  The transport domain for the associated
      transportAddress.  This document specifies three TLS and DTLS
      based Transport Domains for use: the snmpTLSDomain, the
      snmpDTLSUDPDomain and the snmpDTLSSCTPDomain.

   transportAddress:  The transport address of the source of the
      received message in a format specified by the SnmpTLSAddress, the
      SnmpDTLSUDPAddress or the SnmpDTLSSCTPAddress TEXTUAL-CONVENTION.

   incomingMessage:  The whole SNMP message stripped of all (D)TLS
      protection data.

   incomingMessageLength:  The length of the SNMP message after being
      processed by (D)TLS.






Hardaker                Expires December 26, 2009              [Page 20]

Internet-Draft               SNMP over DTLS                    June 2009


   tmStateReference:  A handle/reference to tmSecurityData to be used by
      the security model.

4.4.  (D)TLS Services

   This section describes the services provided by the (D)TLS Transport
   Model with their inputs and outputs.  These services are between the
   TLS Transport Model and the (D)TLS transport layer.  The following
   sections describe services for establishing and closing a session and
   for passing messages between the (D)TLS transport layer and the TLS
   Transport Model.

4.4.1.  Services for Establishing a Session

   The TLS Transport Model provides the following ASI to describe the
   data passed between the Transport Model and the (D)TLS transport
   layer for session establishment.


   statusInformation =           -- errorIndication or success
   openSession(
   IN   destTransportDomain      -- transport domain to be used
   IN   destTransportAddress     -- transport address to be used
   IN   securityName             -- on behalf of this principal
   IN   securityLevel            -- Level of Security requested
   OUT  tlsSessionID             -- Session identifier for (D)TLS
   )

   The abstract data elements passed as parameters in the abstract
   service primitives are as follows:

   statusInformation:  An indication of whether the process was
      successful or not.  If not, then the status information will
      include the error indication provided by (D)TLS.

   destTransportDomain:  The transport domain for the associated
      destTransportAddress.  The TLS Transport Model uses this parameter
      to determine the transport type of the associated
      destTransportAddress.  This document specifies three TLS and DTLS
      based Transport Domains for use: the snmpTLSDomain, the
      snmpDTLSUDPDomain, and the snmpDTLSSCTPDomain.

   destTransportAddress:  The transport address of the destination TLS
      Transport Model in a format specified by the SnmpTLSAddress, the
      SnmpDTLSUDPAddress or the SnmpDTLSSCTPAddress TEXTUAL-CONVENTION.






Hardaker                Expires December 26, 2009              [Page 21]

Internet-Draft               SNMP over DTLS                    June 2009


   securityName:  The security name representing the principal on whose
      behalf the message will be sent.

   securityLevel:  The level of security requested by the application.

   dtlsSessionID:  An implementation-dependent session identifier to
      reference the specific (D)TLS session.

   DTLS and UDP do not provide a session de-multiplexing mechanism and
   it is possible that implementations will only be able to identify a
   unique session based on a unique combination of source address,
   destination address, source UDP port number and destination UDP port
   number.  Because of this, when establishing a new sessions
   implementations MUST use a different UDP source port number for each
   connection to a remote destination IP-address/port-number combination
   to ensure the remote entity can properly disambiguate between
   multiple sessions from a host to the same port on a server.  TLS and
   DTLS over SCTP provide session de-multiplexing so this restriction is
   not needed for TLS or DTLS over SCTP implementations.

   The procedural details for establishing a session are further
   described in Section 5.3.

   Upon completion of the process the TLS Transport Model returns status
   information and, if the process was successful the dtlsSessionID.
   Other implementation-dependent data from (D)TLS are also returned.
   The dtlsSessionID is stored in an implementation- dependent manner
   and tied to the tmSecurityData for future use of this session.

4.4.2.  (D)TLS Services for an Incoming Message

   When the TLS Transport Model invokes the (D)TLS record layer to
   verify proper security for the incoming message, it must use the
   following ASI:


   statusInformation =           -- errorIndication or success
   tlsRead(
   IN   tlsSessionID             -- Session identifier for (D)TLS
   IN   wholeTlsMsg              -- as received on the wire
   IN   wholeTlsMsgLength        -- length as received on the wire
   OUT  incomingMessage          -- the whole SNMP message from (D)TLS
   OUT  incomingMessageLength    -- the length of the SNMP message
   )

   The abstract data elements passed as parameters in the abstract
   service primitives are as follows:




Hardaker                Expires December 26, 2009              [Page 22]

Internet-Draft               SNMP over DTLS                    June 2009


   statusInformation:  An indication of whether the process was
      successful or not.  If not, then the status information will
      include the error indication provided by (D)TLS.

   tlsSessionID:  An implementation-dependent session identifier to
      reference the specific (D)TLS session.  How the (D)TLS session ID
      is obtained for each message is implementation-dependent.  As an
      implementation hint, for dtls over udp the TLS Transport Model can
      examine incoming messages to determine the source IP address,
      source port number, destination IP address, and destination port
      number and use these values to look up the local tlsSessionID in
      the list of active sessions.

   wholeDtlsMsg:  The whole message as received on the wire.

   wholeDtlsMsgLength:  The length of the message as it was received on
      the wire.

   incomingMessage:  The whole SNMP message stripped of all (D)TLS
      privacy and integrity data.

   incomingMessageLength:  The length of the SNMP message stripped of
      all (D)TLS privacy and integrity data.

4.4.3.  (D)TLS Services for an Outgoing Message

   When the TLS Transport Model invokes the (D)TLS record layer to
   encapsulate and transmit a SNMP message, it must use the following
   ASI.


   statusInformation =           -- errorIndication or success
   tlsWrite(
   IN   tlsSessionID             -- Session identifier for (D)TLS
   IN   outgoingMessage          -- the message to send
   IN   outgoingMessageLength    -- its length
   )

   The abstract data elements passed as parameters in the abstract
   service primitives are as follows:

   statusInformation:  An indication of whether the process was
      successful or not.  If not, then the status information will
      include the error indication provided by (D)TLS.







Hardaker                Expires December 26, 2009              [Page 23]

Internet-Draft               SNMP over DTLS                    June 2009


   tlsSessionID:  An implementation-dependent session identifier to
      reference the specific (D)TLS session that the message should be
      sent using.

   outgoingMessage:  The outgoing message to send to (D)TLS for
      encapsulation.

   outgoingMessageLength:  The length of the outgoing message.

4.5.  Cached Information and References

   When performing SNMP processing, there are two levels of state
   information that may need to be retained: the immediate state linking
   a request-response pair, and potentially longer-term state relating
   to transport and security.  "Transport Subsystem for the Simple
   Network Management Protocol" [I-D.ietf-isms-tmsm] defines general
   requirements for caches and references.

4.5.1.  TLS Transport Model Cached Information

   The TLSTM has no specific responsibilities regarding the cached
   information beyond those discussed in "Transport Subsystem for the
   Simple Network Management Protocol" [I-D.ietf-isms-tmsm]


5.  Elements of Procedure

   Abstract service interfaces have been defined by RFC 3411 to describe
   the conceptual data flows between the various subsystems within an
   SNMP entity.  The TLSTM uses some of these conceptual data flows when
   communicating between subsystems.  These RFC 3411-defined data flows
   are referred to here as public interfaces.

   To simplify the elements of procedure, the release of state
   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 with zero value or random
   value data prior to being released.

   An error indication may return an OID and value for an incremented
   counter if the information is available at the point where the error
   is detected.






Hardaker                Expires December 26, 2009              [Page 24]

Internet-Draft               SNMP over DTLS                    June 2009


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.  The first section
   describes the needed steps for de-multiplexing multiple DTLS sessions
   (which is needed for DTLS over UDP) and the second section describes
   the steps which are specific to transport processing once the (D)TLS
   processing has been completed.

5.1.1.  DTLS Processing for Incoming Messages

   DTLS is significantly different in terms of session handling than
   SSH, TLS or other TCP-based session streams.  The DTLS protocol,
   which is datagram-based, does not have a session identifier when run
   over UDP that allows implementations to determine through which
   session a packet is arriving.  DTLS over SCTP and TLS over TCP
   streams have built in session demultiplexing and these steps are not
   necessary, although it is still critical that implementations be able
   to derive a tlsSessionID from any demultiplexing regardless of how it
   is done.

   For DTLS over UDP a process for de-multiplexing sessions when used
   over UDP must be incorporated into the procedures for an incoming
   message.  The steps in this section describe how this can be
   accomplished, although any implementation dependent method for doing
   so should be suitable as long as the results are consistently
   deterministic.  The important results from the steps in this section
   are the transportDomain, the transportAddress, the wholeMessage, the
   wholeMessageLength, and a unique implementation-dependent session
   identifier.

   This procedure assumes that upon session establishment, an entry in a
   local transport mapping table is created in the Transport Model's
   LCD.  This transport mapping table entry should be able to map a
   unique combination of the remote address, remote port number, local
   address and local port number to a implementation-dependent
   tlsSessionID.

   1)  The TLS Transport Model examines the raw UDP message, in an
       implementation-dependent manner.  If the message is not a DTLS
       message then it should be discarded.  If the message is not a
       (D)TLS Application Data message then the message should be
       processed by the underlying DTLS framework as it is (for example)
       a session initialization or session modification message and no
       further steps below should be taken by the DTLS Transport.





Hardaker                Expires December 26, 2009              [Page 25]

Internet-Draft               SNMP over DTLS                    June 2009


   2)  The TLS Transport Model queries the LCD using the transport
       parameters to determine if a session already exists and its
       tlsSessionID.  As noted previously, the source and destination
       addresses and ports of the message should uniquely assign the
       message to a specific session identifier.  However, another
       implementation-dependent method may be used if so desired.

   3)  If a matching entry in the LCD does not exist then the message is
       discarded.  Increment the tlstmSessionNoAvailableSessions counter
       and stop processing the message.

       Note that an entry would already exist if the client and server's
       session establishment procedures had been successfully completed
       (as described both above and in Section 5.3) even if no message
       had yet been sent through the newly established session.  An
       entry may not exist, however, if a "rogue" message was routed to
       the SNMP entity by mistake.  An entry might also be missing
       because of a "broken" session (see operational considerations).

   4)  Retrieve the tlsSessionID from the LCD.

   5)  The tlsWholeMsg, and the tlsSessionID are passed to DTLS for
       integrity checking and decryption using the tlsRead() ASI.

   6)  If the message fails integrity checks or other (D)TLS security
       processing then the tlstmDTLSProtectionErrors counter is
       incremented, the message is discarded and processing of the
       message is stopped.

   7)  The output of the tlsRead results in an incomingMessage and an
       incomingMessageLength.  These results and the tlsSessionID are
       used below in the Section 5.1.2 to complete the processing of the
       incoming message.

5.1.2.  Transport Processing for Incoming Messages

   The procedures in this section describe how the TLS Transport Model
   should process messages that have already been properly extracted
   from the (D)TLS stream, such as described in Section 5.1.1.

   1)  Create a tmStateReference cache for the subsequent reference and
       assign the following values within it:

       tmTransportDomain  = snmpTLSDomain, snmpDTLSUDPDomain or
          snmpDTLSSCTPDomain as appropriate.






Hardaker                Expires December 26, 2009              [Page 26]

Internet-Draft               SNMP over DTLS                    June 2009


       tmTransportAddress  = The address the message originated from,
          determined in an implementation dependent way.

       tmSecurityLevel  = The derived tmSecurityLevel for the session,
          as discussed in Section 3.1.2 and Section 5.3.

       tmSecurityName  = The derived tmSecurityName for the session as
          discussed in and Section 5.3.  This value MUST be constant
          during the lifetime of the (D)TLS session.

       tmSessionID  = The tlsSessionID, which MUST be A unique session
          identifier for this (D)TLS session.  The contents and format
          of this identifier are implementation dependent as long as it
          is unique to the session.  A session identifier MUST NOT be
          reused until all references to it are no longer in use.  The
          tmSessionID is equal to the tlsSessionID discussed in
          Section 5.1.1. tmSessionID refers to the session identifier
          when stored in the tmStateReference and tlsSessionID refers to
          the session identifier when stored in the LCD.  They MUST
          always be equal when processing a given session's traffic.

   2)  The wholeMessage and the wholeMessageLength are assigned values
       from the incomingMessage and incomingMessageLength values from
       the (D)TLS processing.

   3)  The TLS Transport Model passes the transportDomain,
       transportAddress, wholeMessage, and wholeMessageLength to the
       dispatcher using the receiveMessage ASI:


       statusInformation =
       receiveMessage(
       IN   transportDomain     -- snmpTLSDomain, snmpDTLSUDPDomain,
                                -- or snmpDTLSSCTPDomain
       IN   transportAddress    -- address for the received message
       IN   wholeMessage        -- the whole SNMP message from (D)TLS
       IN   wholeMessageLength  -- the length of the SNMP message
       IN   tmStateReference    -- (NEW) transport info
        )

5.2.  Procedures for an Outgoing Message

   The dispatcher sends a message to the TLS Transport Model using the
   following ASI:







Hardaker                Expires December 26, 2009              [Page 27]

Internet-Draft               SNMP over DTLS                    June 2009


      statusInformation =
      sendMessage(
      IN   destTransportDomain           -- transport domain to be used
      IN   destTransportAddress          -- transport address to be used
      IN   outgoingMessage               -- the message to send
      IN   outgoingMessageLength         -- its length
      IN   tmStateReference              -- (NEW) transport info
      )

   This section describes the procedure followed by the TLS Transport
   Model whenever it is requested through this ASI to send a message.

   1)  Extract tmSessionID, tmTransportAddress, tmSecurityName,
       tmRequestedSecurityLevel. and tmSameSecurity from the
       tmStateReference.  Note: The tmSessionID value may be undefined
       if session exists yet.

   2)  If tmSameSecurity is true and either tmSessionID is undefined or
       refers to a session that is no longer open then increment the
       tlstmSessionNoAvailableSessions counter, discard the message and
       return the error indication in the statusInformation.  Processing
       of this message stops.

   3)  If tmSameSecurity is false and tmSessionID refers to a session
       that is no longer available then an implementation SHOULD open a
       new session using the openSession() ASI as described below in
       step 4b.  An implementation MAY choose to return an error to the
       calling module.

   4)  If tmSessionID is undefined, then use tmTransportAddress,
       tmSecurityName and tmRequestedSecurityLevel to see if there is a
       corresponding entry in the LCD suitable to send the message over.

       4a)  If there is a corresponding LCD entry, then this session
            will be used to send the message.

       4b)  If there is not a corresponding LCD entry, then open a
            session using the openSession() ASI (discussed further in
            Section 4.4.1).  Implementations MAY wish to offer message
            buffering to prevent redundant openSession() calls for the
            same cache entry.  If an error is returned from
            OpenSession(), then discard the message, increment the
            tlstmSessionOpenErrors, and return an error indication to
            the calling module.







Hardaker                Expires December 26, 2009              [Page 28]

Internet-Draft               SNMP over DTLS                    June 2009


   5)  Using either the session indicated by the tmSessionID if there
       was one or the session resulting in the previous step, pass the
       outgoingMessage to (D)TLS for encapsulation and transmission.

5.3.  Establishing a Session

   The TLS Transport Model provides the following primitive to establish
   a new (D)TLS session (previously discussed in Section 4.4.1):


   statusInformation =           -- errorIndication or success
   openSession(
   IN   destTransportDomain      -- transport domain to be used
   IN   destTransportAddress     -- transport address to be used
   IN   securityName             -- on behalf of this principal
   IN   securityLevel            -- Level of Security requested
   OUT  tlsSessionID             -- Session identifier for (D)TLS
   )

   The following sections describe the procedures followed by a TLS
   Transport Model when establishing a session as a Command Generator, a
   Notification Originator or as part of a Proxy Forwarder.

   The following describes the procedure to follow to establish a
   session between SNMP engines to exchange SNMP messages.  This process
   is followed by any SNMP engine establishing a session for subsequent
   use.

   This MAY be done automatically for SNMP messages which are not
   Response or Report messages.

   (D)TLS provides no explicit manner for transmitting an identity the
   client wishes to connect to during or prior to key exchange to
   facilitate certificate selection at the server (e.g. at a
   Notification Receiver).  I.E., there is no available mechanism for
   sending notifications to a specific principal at a given TCP, UDP or
   SCTP port.  Therefore, implementations MAY support responding with
   multiple identities using separate TCP, UDP or SCTP port numbers to
   indicate the desired principal or some other implementation-dependent
   solution.

   1)  The client selects the appropriate certificate and cipher_suites
       for the key agreement based on the tmSecurityName and the
       tmRequestedSecurityLevel for the session.  For sessions being
       established as a result of a SNMP-TARGET-MIB based operation, the
       certificate will potentially have been identified via the
       tlstmParamsTable mapping and the cipher_suites will have to be
       taken from system-wide or implementation-specific configuration.



Hardaker                Expires December 26, 2009              [Page 29]

Internet-Draft               SNMP over DTLS                    June 2009


       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 should be reported in
       the tmStateReference cache as tmSecurityLevel.  For (D)TLS to
       provide strong authentication, each principal acting as a Command
       Generator SHOULD have its own certificate.

   2)  Using the destTransportDomain and destTransportAddress values,
       the client will initiate the (D)TLS handshake protocol to
       establish session keys for message integrity and encryption.

       If the attempt to establish a session is unsuccessful, then
       tlstmSessionOpenErrors is incremented, an error indication is
       returned, and session establishment processing stops.

   3)  Once the secure session is established and both sides have been
       authenticated, certificate validation and identity expectations
       are performed.

       a)  The (D)TLS server side of the connection identifies the
           authenticated identity from the (D)TLS client's principal
           certificate using the tlstmCertificateToSNTable mapping table
           and records this in the tmStateReference cache as
           tmSecurityName.  The details of the lookup process are fully
           described in the DESCRIPTION clause of the
           tlstmCertificateToSNTable MIB object.  If this verification
           fails in any way (for example because of failures in
           cryptographic verification or the lack of an appropriate row
           in the tlstmCertificateToSNTable) then the session
           establishment MUST fail, the
           tlstmSessionInvalidClientCertificates object is incremented
           and processing is stopped.

       b)  The (D)TLS client side of the connection SHOULD verify that
           authenticated identity of the (D)TLS server's certificate is
           the expected identity and MUST do so if the client
           application is a Notification Generator.  If strong
           authentication is desired then the (D)TLS server certificate
           MUST always be verified and checked against the expected
           identity.  Methods for doing this are described in
           [I-D.saintandre-tls-server-id-check].  (D)TLS provides



Hardaker                Expires December 26, 2009              [Page 30]

Internet-Draft               SNMP over DTLS                    June 2009


           assurance that the authenticated identity has been signed by
           a trusted configured certificate authority.  If verification
           of the server's certificate fails in any way (for example
           because of failures in cryptographic verification or the
           presented identity was not the expected identity) then the
           session establishment MUST fail, the
           tlstmSessionInvalidServerCertificates object is incremented
           and processing is stopped.

   4)  The (D)TLS-specific session identifier is passed to the TLS
       Transport Model and associated with the tmStateReference cache
       entry to indicate that the session has been established
       successfully and to point to a specific (D)TLS session for future
       use.

5.4.  Closing a Session

   The TLS Transport Model provides the following primitive to close a
   session:


   statusInformation =
   closeSession(
   IN  tmStateReference        -- transport info
   )

   The following describes the procedure to follow to close a session
   between a client and server.  This process is followed by any SNMP
   engine closing the corresponding SNMP session.

   1)  Look up the session in the cache and the LCD using the
       tmStateReference.

   2)  If there is no session open associated with the tmStateReference,
       then closeSession processing is completed.

   3)  Delete the entry from the cache and any other implementation-
       dependent information in the LCD.

   4)  Have (D)TLS close the specified session.  This SHOULD include
       sending a close_notify TLS Alert to inform the other side that
       session cleanup may be performed.


6.  MIB Module Overview

   This MIB module provides management of the TLS Transport Model.  It
   defines needed textual conventions, statistical counters and



Hardaker                Expires December 26, 2009              [Page 31]

Internet-Draft               SNMP over DTLS                    June 2009


   configuration infrastructure necessary for session establishment.
   Example usage of the configuration tables can be found in Appendix A.

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 two new Textual Conventions: a new
   TransportDomain and TransportAddress format for describing (D)TLS
   connection addressing requirements.

6.3.  Statistical Counters

   The TLSTM-MIB defines some statical counters that can provide network
   managers with feedback about (D)TLS session usage and potential
   errors that a MIB-instrumented device may be experiencing.

6.4.  Configuration Tables

   The TLSTM-MIB defines configuration tables that a manager can use for
   help in configuring a MIB-instrumented device for sending and
   receiving SNMP messages over (D)TLS.  In particular, there is a MIB
   table that extends the SNMP-TARGET-MIB for configuring certificates
   to be used and a MIB table for mapping incoming (D)TLS client
   certificates to securityNames.

6.5.  Relationship to Other MIB Modules

   Some management objects defined in other MIB modules are applicable
   to an entity implementing the TLS Transport Model.  In particular, it
   is assumed that an entity implementing the TLSTM-MIB will implement
   the SNMPv2-MIB [RFC3418], the SNMP-FRAMEWORK-MIB [RFC3411], the SNMP-
   TARGET-MIB [RFC3413], the SNMP-NOTIFICATION-MIB [RFC3413] and the
   SNMP-VIEW-BASED-ACM-MIB [RFC3415].

   This MIB module is for managing TLS Transport Model information.







Hardaker                Expires December 26, 2009              [Page 32]

Internet-Draft               SNMP over DTLS                    June 2009


6.5.1.  MIB Modules Required for IMPORTS

   The following MIB module imports items from SNMPV2-SMI [RFC2578],
   SNMPV2-TC [RFC2579], SNMP-FRAMEWORK-MIB [RFC3411], SNMP-TARGET-MIB
   [RFC3413] and SNMP-CONF [RFC2580].


7.  MIB Module Definition


TLSTM-MIB DEFINITIONS ::= BEGIN

IMPORTS
    MODULE-IDENTITY, OBJECT-TYPE,
    OBJECT-IDENTITY, snmpModules, snmpDomains,
    Counter32, Unsigned32
      FROM SNMPv2-SMI
    TEXTUAL-CONVENTION, TimeStamp, RowStatus, StorageType
      FROM SNMPv2-TC
    MODULE-COMPLIANCE, OBJECT-GROUP
      FROM SNMPv2-CONF
    SnmpAdminString
      FROM SNMP-FRAMEWORK-MIB
    snmpTargetParamsEntry
      FROM SNMP-TARGET-MIB
    ;

tlstmMIB MODULE-IDENTITY
    LAST-UPDATED "200807070000Z"
    ORGANIZATION " "
    CONTACT-INFO "WG-EMail:
                  Subscribe:

                  Chairs:
                  Co-editors:
                                "

    DESCRIPTION  "The TLS Transport Model MIB

                  Copyright (C) The IETF Trust (2008). This
                  version of this MIB module is part of RFC XXXX;
                  see the RFC itself for full legal notices."
-- NOTE to RFC editor: replace XXXX with actual RFC number
--                     for this document and remove this note

       REVISION     "200807070000Z"
       DESCRIPTION  "The initial version, published in RFC XXXX."
-- NOTE to RFC editor: replace XXXX with actual RFC number



Hardaker                Expires December 26, 2009              [Page 33]

Internet-Draft               SNMP over DTLS                    June 2009


--                     for this document and remove this note

    ::= { snmpModules xxxx }
-- RFC Ed.: replace xxxx with IANA-assigned number and
--          remove this note

-- ************************************************
-- subtrees of the SNMP-DTLS-TM-MIB
-- ************************************************

tlstmNotifications OBJECT IDENTIFIER ::= { tlstmMIB 0 }
tlstmObjects       OBJECT IDENTIFIER ::= { tlstmMIB 1 }
tlstmConformance   OBJECT IDENTIFIER ::= { tlstmMIB 2 }

-- ************************************************
-- Objects
-- ************************************************

snmpTLSDomain OBJECT-IDENTITY
    STATUS      current
    DESCRIPTION
        "The SNMP over TLS transport domain. The corresponding
        transport address is of type SnmpTLSAddress.

        The securityName prefix to be associated with the
        snmpTLSDomain is 'tls'.  This prefix may be used by
        security models or other components to identify what secure
        transport infrastructure authenticated a securityName."

    ::= { snmpDomains xx }


-- RFC Ed.: replace xx with IANA-assigned number and
--          remove this note

-- RFC Ed.: replace 'tls' with the actual IANA assigned prefix string
--          if 'tls' is not assigned to this document.

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.



Hardaker                Expires December 26, 2009              [Page 34]

Internet-Draft               SNMP over DTLS                    June 2009


        The securityName prefix to be associated with the
        snmpDTLSUDPDomain is 'dudp'.  This prefix may be used by
        security models or other components to identify what secure
        transport infrastructure authenticated a securityName."

    ::= { snmpDomains yy }


-- RFC Ed.: replace yy with IANA-assigned number and
--          remove this note

-- RFC Ed.: replace 'dudp' with the actual IANA assigned prefix string
--          if 'dtls' is not assigned to this document.

snmpDTLSSCTPDomain OBJECT-IDENTITY
    STATUS      current
    DESCRIPTION
        "The SNMP over DTLS/SCTP transport domain. The corresponding
        transport address is of type SnmpDTLSSCTPAddress.

        When an SNMP entity uses the snmpDTLSSCTPDomain transport
        model, it must be capable of accepting messages up to
        the maximum MTU size for an interface it supports, minus the
        needed IP, SCTP, DTLS and other protocol overheads.

        The securityName prefix to be associated with the
        snmpDTLSSCTPDomain is 'dsct'.  This prefix may be used by
        security models or other components to identify what secure
        transport infrastructure authenticated a securityName."

    ::= { snmpDomains zz }


-- RFC Ed.: replace zz with IANA-assigned number and
--          remove this note

-- RFC Ed.: replace 'dsct' with the actual IANA assigned prefix string
--          if 'dtls' is not assigned to this document.

SnmpTLSAddress ::= TEXTUAL-CONVENTION
    DISPLAY-HINT "1a"
    STATUS       current
    DESCRIPTION
        "Represents a TCP connection address for an IPv4 address, an
        IPv6 address or an ASCII encoded host name and port number.

        The hostname must be encoded in ASCII, as specified in RFC3490
        (Internationalizing Domain Names in Applications) followed by



Hardaker                Expires December 26, 2009              [Page 35]

Internet-Draft               SNMP over DTLS                    June 2009


        a colon ':' (ASCII character 0x3A) and a decimal port number
        in ASCII. The name SHOULD be fully qualified whenever
        possible.

        An IPv4 address must be a dotted decimal format followed by a
        colon ':' (ASCII character 0x3A) and a decimal port number in
        ASCII.

        An IPv6 address must be a colon separated format, surrounded
        by square brackets (ASCII characters 0x5B and 0x5D), followed
        by a colon ':' (ASCII character 0x3A) and a decimal port
        number in ASCII.

        Values of this textual convention may not be directly usable
        as transport-layer addressing information, and may require
        run-time resolution. As such, applications that write them
        must be prepared for handling errors if such values are not
        supported, or cannot be resolved (if resolution occurs at the
        time of the management operation).

        The DESCRIPTION clause of TransportAddress objects that may
        have snmpTLSAddress values must fully describe how (and
        when) such names are to be resolved to IP addresses and vice
        versa.

        This textual convention SHOULD NOT be used directly in object
        definitions since it restricts addresses to a specific
        format. However, if it is used, it MAY be used either on its
        own or in conjunction with TransportAddressType or
        TransportDomain as a pair.

        When this textual convention is used as a syntax of an index
        object, there may be issues with the limit of 128
        sub-identifiers specified in SMIv2, STD 58. It is RECOMMENDED
        that all MIB documents using this textual convention make
        explicit any limitations on index component lengths that
        management software must observe.  This may be done either by
        including SIZE constraints on the index components or by
        specifying applicable constraints in the conceptual row
        DESCRIPTION clause or in the surrounding documentation."
    SYNTAX       OCTET STRING (SIZE (1..255))

SnmpDTLSUDPAddress ::= TEXTUAL-CONVENTION
    DISPLAY-HINT "1a"
    STATUS       current
    DESCRIPTION
        "Represents a UDP connection address for an IPv4 address, an
        IPv6 address or an ASCII encoded host name and port number.



Hardaker                Expires December 26, 2009              [Page 36]

Internet-Draft               SNMP over DTLS                    June 2009


        The hostname must be encoded in ASCII, as specified in RFC3490
        (Internationalizing Domain Names in Applications) followed by
        a colon ':' (ASCII character 0x3A) and a decimal port number
        in ASCII. The name SHOULD be fully qualified whenever
        possible.

        An IPv4 address must be a dotted decimal format followed by a
        colon ':' (ASCII character 0x3A) and a decimal port number in
        ASCII.

        An IPv6 address must be a colon separated format, surrounded
        by square brackets (ASCII characters 0x5B and 0x5D), followed
        by a colon ':' (ASCII character 0x3A) and a decimal port
        number in ASCII.

        Values of this textual convention may not be directly usable
        as transport-layer addressing information, and may require
        run-time resolution. As such, applications that write them
        must be prepared for handling errors if such values are not
        supported, or cannot be resolved (if resolution occurs at the
        time of the management operation).

        The DESCRIPTION clause of TransportAddress objects that may
        have snmpDTLSUDPAddress values must fully describe how (and
        when) such names are to be resolved to IP addresses and vice
        versa.

        This textual convention SHOULD NOT be used directly in object
        definitions since it restricts addresses to a specific
        format. However, if it is used, it MAY be used either on its
        own or in conjunction with TransportAddressType or
        TransportDomain as a pair.

        When this textual convention is used as a syntax of an index
        object, there may be issues with the limit of 128
        sub-identifiers specified in SMIv2, STD 58. It is RECOMMENDED
        that all MIB documents using this textual convention make
        explicit any limitations on index component lengths that
        management software must observe.  This may be done either by
        including SIZE constraints on the index components or by
        specifying applicable constraints in the conceptual row
        DESCRIPTION clause or in the surrounding documentation."
    SYNTAX       OCTET STRING (SIZE (1..255))

SnmpDTLSSCTPAddress ::= TEXTUAL-CONVENTION
    DISPLAY-HINT "1a"
    STATUS       current
    DESCRIPTION



Hardaker                Expires December 26, 2009              [Page 37]

Internet-Draft               SNMP over DTLS                    June 2009


        "Represents a SCTP connection address for an IPv4 address, an
        IPv6 address or an ASCII encoded host name and port number.

        The hostname must be encoded in ASCII, as specified in RFC3490
        (Internationalizing Domain Names in Applications) followed by
        a colon ':' (ASCII character 0x3A) and a decimal port number
        in ASCII. The name SHOULD be fully qualified whenever
        possible.

        An IPv4 address must be a dotted decimal format followed by a
        colon ':' (ASCII character 0x3A) and a decimal port number in
        ASCII.

        An IPv6 address must be a colon separated format, surrounded
        by square brackets (ASCII characters 0x5B and 0x5D), followed
        by a colon ':' (ASCII character 0x3A) and a decimal port
        number in ASCII.

        Values of this textual convention may not be directly usable
        as transport-layer addressing information, and may require
        run-time resolution. As such, applications that write them
        must be prepared for handling errors if such values are not
        supported, or cannot be resolved (if resolution occurs at the
        time of the management operation).

        The DESCRIPTION clause of TransportAddress objects that may
        have snmpDTLSSCTPAddress values must fully describe how (and
        when) such names are to be resolved to IP addresses and vice
        versa.

        This textual convention SHOULD NOT be used directly in object
        definitions since it restricts addresses to a specific
        format. However, if it is used, it MAY be used either on its
        own or in conjunction with TransportAddressType or
        TransportDomain as a pair.

        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))

X509IdentifierHashType ::= TEXTUAL-CONVENTION



Hardaker                Expires December 26, 2009              [Page 38]

Internet-Draft               SNMP over DTLS                    June 2009


    STATUS       current
    DESCRIPTION
       "Identifies a hashing algorithm type that will be used for
       identifying an X.509 certificate.

       The md5(1) value SHOULD NOT be used."
    SYNTAX       INTEGER  { md5(1), sha1(2), sha256(3) }

X509IdentifierHash ::= TEXTUAL-CONVENTION
    STATUS       current
    DESCRIPTION
       "A hash value that uniquely identifies a certificate within a
       systems local certificate store.  The length of the value
       stored in an object of type X509IdentifierHash is dependent on
       the hashing algorithm that produced the hash.

       MIB structures making use of this textual convention should
       have an accompanying object of type X509IdentifierHashType.
       "
    SYNTAX       OCTET STRING

-- 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



Hardaker                Expires December 26, 2009              [Page 39]

Internet-Draft               SNMP over DTLS                    June 2009


        "The number of times an openSession() request failed to open a
        session as a (D)TLS client, for any reason."
    ::= { tlstmSession 3 }


tlstmSessionNoAvailableSessions  OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
        "The number of times an outgoing message was dropped because
        the session associated with the passed tmStateReference was no
        longer (or was never) available."
    ::= { tlstmSession 4 }

tlstmSessionInvalidClientCertificates OBJECT-TYPE
    SYNTAX       Counter32
    MAX-ACCESS   read-only
    STATUS       current
    DESCRIPTION
        "The number of times an incoming session was not established
        on an (D)TLS server because the presented client certificate was
        invalid.  Reasons for invalidation includes, but is not
        limited to, cryptographic validation failures and lack of a
        suitable mapping row in the tlstmCertificateToSNTable."
    ::= { 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 }



Hardaker                Expires December 26, 2009              [Page 40]

Internet-Draft               SNMP over DTLS                    June 2009


-- Configuration Objects

tlstmConfig          OBJECT IDENTIFIER ::= { tlstmObjects 2 }

-- Certificate mapping

tlstmCertificateMapping    OBJECT IDENTIFIER ::= { tlstmConfig 1 }

tlstmCertificateToSNCount OBJECT-TYPE
    SYNTAX      Unsigned32
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        "A count of the number of entries in the
        tlstmCertificateToSNTable"
    ::= { tlstmCertificateMapping 1 }

tlstmCertificateToSNTableLastChanged OBJECT-TYPE
    SYNTAX      TimeStamp
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
        "The value of sysUpTime.0 when the tlstmCertificateToSNTable
        was last modified through any means, or 0 if it has not been
        modified since the command responder was started."
    ::= { tlstmCertificateMapping 2 }

tlstmCertificateToSNTable OBJECT-TYPE
    SYNTAX      SEQUENCE OF TlstmCertificateToSNEntry
    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 should be examined and validated based on an
        established trusted CA certificate or self-signed public
        certificate.  This table does not provide a mechanism for
        uploading the certificates as that is expected to occur
        through an out-of-band transfer.

        Once the authenticity of the certificate has been verified,
        this table can be consulted to determine the appropriate
        securityName to identify the remote connection.  This is done
        by comparing the issuer's fingerprint hash type and value and
        the certificate's fingerprint hash type and value against the



Hardaker                Expires December 26, 2009              [Page 41]

Internet-Draft               SNMP over DTLS                    June 2009


        tlstmCertHashType and tlstmCertHashValue values in each
        entry of this table.  If a matching entry is found then the
        securityName is selected based on the tlstmCertMapType,
        tlstmCertHashType, tlstmCertHashValue and
        tlstmCertSecurityName fields and the resulting securityName
        is used to identify the other side of the (D)TLS connection.

        This table should be treated as an ordered list of mapping
        rules to check.  The first mapping rule appropriately matching
        a certificate in the local certificate store with a
        corresponding hash type (tlstmCertHashType) and hash value
        (tlstmCertHashValue) will be used to perform the mapping from
        X.509 certificate values to a securityName.  If, after a
        matching row is found but the mapping can not succeed for some
        other reason then further attempts to perform the mapping MUST
        NOT be taken.  For example, if the entry being checked
        contains a tlstmCertMapType of bySubjectAltName(2) and an
        incoming connection uses a certificate with an issuer
        certificate matching the tlstmCertHashType and
        tlstmCertHashValue fields but the connecting certificate does
        not contain a subjectAltName field then the lookup operation
        must be treated as a failure. No further rows are examined for
        other potential mappings.

        Missing values of tlstmCertID are acceptable and
        implementations should treat missing entries as a failed match
        and should continue to the next highest numbered row.  E.G.,
        the table may legally contain only two rows with tlstmCertID
        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
        enough 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 which is also a
        scalable method of mapping certificate components to
        securityNames.  Finally, direct mapping from each individual
        certificate fingerprint to a securityName is possible but
        requires one entry in the table per securityName."
    ::= { tlstmCertificateMapping 3 }

tlstmCertificateToSNEntry OBJECT-TYPE
    SYNTAX      TlstmCertificateToSNEntry



Hardaker                Expires December 26, 2009              [Page 42]

Internet-Draft               SNMP over DTLS                    June 2009


    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "A row in the tlstmCertificateToSNTable that specifies a
        mapping for an incoming (D)TLS certificate to a securityName
        to use for the connection."
    INDEX   { tlstmCertID }
    ::= { tlstmCertificateToSNTable 1 }

TlstmCertificateToSNEntry ::= SEQUENCE {
    tlstmCertID           Unsigned32,
    tlstmCertHashType     X509IdentifierHashType,
    tlstmCertHashValue    X509IdentifierHash,
    tlstmCertMapType      INTEGER,
    tlstmCertSecurityName SnmpAdminString,
    tlstmCertStorageType  StorageType,
    tlstmCertRowStatus    RowStatus
}

tlstmCertID OBJECT-TYPE
    SYNTAX      Unsigned32
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "A unique arbitrary number index for a given certificate
        entry."
    ::= { tlstmCertificateToSNEntry 1 }

tlstmCertHashType  OBJECT-TYPE
    SYNTAX      X509IdentifierHashType
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
       "The hash algorithm to use when applying a hash to a X.509
       certificate for purposes of referring to it from the
       tlstmCertHashValue column.

       The md5(1) value SHOULD NOT be used."
    DEFVAL { sha256 }
    ::= { tlstmCertificateToSNEntry 2 }


tlstmCertHashValue OBJECT-TYPE
    SYNTAX      X509IdentifierHash
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "A cryptographic hash of a X.509 certificate.  The use of this



Hardaker                Expires December 26, 2009              [Page 43]

Internet-Draft               SNMP over DTLS                    June 2009


        hash is dictated by the tlstmCertMapType column.
        "
    ::= { tlstmCertificateToSNEntry 3 }

tlstmCertMapType OBJECT-TYPE
    SYNTAX      INTEGER { specified(1), bySubjectAltName(2), byCN(3) }
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "The mapping type used to obtain the securityName from the
        certificate.  The possible values of use and their usage
        methods are defined as follows:

        specified(1): The securityName that should be used locally to
                      identify the remote entity is directly specified
                      in the tlstmCertSecurityName column from this
                      table.  The tlstmCertHashValue MUST refer to a
                      X.509 client certificate that will be mapped
                      directly to the securityName specified in the
                      tlstmCertSecurityName column.

        bySubjectAltName(2):
                      The securityName that should be used locally to
                      identify the remote entity should be taken from
                      the subjectAltName portion of the X.509
                      certificate.  The tlstmCertHashValue MUST refer
                      to a trust anchor certificate that is
                      responsible for issuing certificates with
                      carefully controlled subjectAltName fields.

        byCN(3):      The securityName that should be used locally to
                      identify the remote entity should be taken from
                      the CommonName portion of the Subject field from
                      the X.509 certificate.  The tlstmCertHashValue
                      MUST refer to a trust anchor certificate that is
                      responsible for issuing certificates with
                      carefully controlled CommonName fields."
    DEFVAL { specified }
    ::= { tlstmCertificateToSNEntry 4 }

tlstmCertSecurityName OBJECT-TYPE
    SYNTAX      SnmpAdminString (SIZE(0..32))
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "The securityName that the session should use if the
        tlstmCertMapType is set to specified(1), otherwise the value
        in this column should be ignored.  If tlstmCertMapType is set



Hardaker                Expires December 26, 2009              [Page 44]

Internet-Draft               SNMP over DTLS                    June 2009


        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."
    DEFVAL { "" }
    ::= { tlstmCertificateToSNEntry 5 }

tlstmCertStorageType 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 }
    ::= { tlstmCertificateToSNEntry 6 }


tlstmCertRowStatus 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.

        The value of this object has no effect on whether
        other objects in this conceptual row can be modified."
    ::= { tlstmCertificateToSNEntry 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



Hardaker                Expires December 26, 2009              [Page 45]

Internet-Draft               SNMP over DTLS                    June 2009


        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 augments the SNMP-TARGET-MIB's
        snmpTargetParamsTable with an additional (D)TLS client-side
        certificate certificate identifier to use when establishing
        new (D)TLS connections."
    ::= { tlstmCertificateMapping 6 }

tlstmParamsEntry OBJECT-TYPE
    SYNTAX      TlstmParamsEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
        "A conceptual row containing a locally held certificate's hash
        type and hash value for a given snmpTargetParamsEntry.  The
        values in this row should be ignored if the connection
        that needs to be established, as indicated by the
        SNMP-TARGET-MIB infrastructure, is not a (D)TLS based
        connection."
    AUGMENTS    { snmpTargetParamsEntry }
    ::= { tlstmParamsTable 1 }

TlstmParamsEntry ::= SEQUENCE {
    tlstmParamsHashType        X509IdentifierHashType,
    tlstmParamsHashValue       X509IdentifierHash,
    tlstmParamsStorageType     StorageType,
    tlstmParamsRowStatus       RowStatus
}

tlstmParamsHashType  OBJECT-TYPE
    SYNTAX      X509IdentifierHashType
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
       "The hash algorithm type for the hash stored in the
       tlstmParamsHash column to identify a locally-held X.509
       certificate that should be used when initiating a (D)TLS
       connection as a (D)TLS client."
    DEFVAL { sha256 }
    ::= { tlstmParamsEntry 1 }




Hardaker                Expires December 26, 2009              [Page 46]

Internet-Draft               SNMP over DTLS                    June 2009


tlstmParamsHashValue OBJECT-TYPE
    SYNTAX      X509IdentifierHash
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "A cryptographic hash of a X.509 certificate.  This object
        should store the hash of a locally held X.509 certificate that
        should be used when initiating a (D)TLS connection as a (D)TLS
        client."
    ::= { tlstmParamsEntry 2 }

tlstmParamsStorageType OBJECT-TYPE
    SYNTAX       StorageType
    MAX-ACCESS   read-create
    STATUS       current
    DESCRIPTION
        "The storage type for this conceptual row. Conceptual rows
        having the value 'permanent' need not allow write-access to
        any columnar objects in the row."
    DEFVAL      { nonVolatile }
    ::= { tlstmParamsEntry 3 }


tlstmParamsRowStatus OBJECT-TYPE
    SYNTAX      RowStatus
    MAX-ACCESS  read-create
    STATUS      current
    DESCRIPTION
        "The status of this conceptual row.  This object may be used
        to create or remove rows from this table.

        The value of this object has no effect on whether
        other objects in this conceptual row can be modified."
    ::= { tlstmParamsEntry 4 }

-- ************************************************
-- tlstmMIB - Conformance Information
-- ************************************************

tlstmCompliances OBJECT IDENTIFIER ::= { tlstmConformance 1 }

tlstmGroups OBJECT IDENTIFIER ::= { tlstmConformance 2 }



-- ************************************************
-- Compliance statements
-- ************************************************



Hardaker                Expires December 26, 2009              [Page 47]

Internet-Draft               SNMP over DTLS                    June 2009


tlstmCompliance MODULE-COMPLIANCE
    STATUS      current
    DESCRIPTION
        "The compliance statement for SNMP engines that support the
        TLSTM-MIB"
    MODULE
        MANDATORY-GROUPS { tlstmStatsGroup,
                           tlstmIncomingGroup, tlstmOutgoingGroup }
    ::= { tlstmCompliances 1 }

-- ************************************************
-- Units of conformance
-- ************************************************
tlstmStatsGroup OBJECT-GROUP
    OBJECTS {
        tlstmSessionOpens,
        tlstmSessionCloses,
        tlstmSessionOpenErrors,
        tlstmSessionNoAvailableSessions,
        tlstmSessionInvalidClientCertificates,
        tlstmSessionInvalidServerCertificates,
        tlstmTLSProtectionErrors
    }
    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 {
        tlstmCertificateToSNCount,
        tlstmCertificateToSNTableLastChanged,
        tlstmCertHashType,
        tlstmCertHashValue,
        tlstmCertMapType,
        tlstmCertSecurityName,
        tlstmCertStorageType,
        tlstmCertRowStatus
    }
    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 }



Hardaker                Expires December 26, 2009              [Page 48]

Internet-Draft               SNMP over DTLS                    June 2009


tlstmOutgoingGroup OBJECT-GROUP
    OBJECTS {
        tlstmParamsCount,
        tlstmParamsTableLastChanged,
        tlstmParamsHashType,
        tlstmParamsHashValue,
        tlstmParamsStorageType,
        tlstmParamsRowStatus
    }
    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 }

END


8.  Operational Considerations

   This section discusses various operational aspects of the solution

8.1.  Sessions

   A session is discussed throughout this document as meaning a security
   association between the (D)TLS client and the (D)TLS server.  State
   information for the sessions are maintained in each TLSTM and this
   information is created and destroyed as sessions are opened and
   closed.  Because of the connectionless nature of UDP, a "broken"
   session, one side up one side down, could result if one side of a
   session is brought down abruptly (i.e., reboot, power outage, etc.).
   Whenever possible, implementations SHOULD provide graceful session
   termination through the use of disconnect messages.  Implementations
   SHOULD also have a system in place for dealing with "broken"
   sessions.  Implementations SHOULD support the session resumption
   feature of TLS.

   To simplify session management it is RECOMMENDED that implementations
   utilize two separate ports, one for Notification sessions and one for
   Command sessions.  If this implementation recommendation is followed,
   (D)TLS clients will always send REQUEST messages and (D)TLS servers
   will always send RESPONSE messages.  With this assertion,
   implementations may be able to simplify "broken" session handling,
   session resumption, and other aspects of session management such as
   guaranteeing that Request- Response pairs use the same session.

   Implementations SHOULD limit the lifetime of established sessions



Hardaker                Expires December 26, 2009              [Page 49]

Internet-Draft               SNMP over DTLS                    June 2009


   depending on the algorithms used for generation of the master session
   secret, the privacy and integrity algorithms used to protect
   messages, the environment of the session, the amount of data
   transferred, and the sensitivity of the data.

8.2.  Notification Receiver Credential Selection

   When an SNMP engine needs to establish an outgoing session for
   notifications, the snmpTargetParamsTable includes an entry for the
   snmpTargetParamsSecurityName of the target.  However, the receiving
   SNMP engine (Server) does not know which (D)TLS certificate to offer
   to the Client so that the tmSecurityName identity-authentication will
   be successful.  The best solution would be to maintain a one-to-one
   mapping between certificates and incoming ports for notification
   receivers, although other implementation dependent mechanisms may be
   used instead.  This can be handled at the Notification Originator by
   configuring the snmpTargetAddrTable (snmpTargetAddrTDomain and
   snmpTargetAddrTAddress) and then requiring the receiving SNMP engine
   to monitor multiple incoming static ports based on which principals
   are capable of receiving notifications.  Implementations MAY also
   choose to designate a single Notification Receiver Principal to
   receive all incoming TRAPS and INFORMS.

8.3.  contextEngineID Discovery

   Because most Command Responders have contextEngineIDs that are
   identical to the USM securityEngineID, the USM provides Command
   Generators with the ability to discover a default contextEngineID to
   use.  Because the TLS Transport Model does not make use of a
   discoverable securityEngineID like the USM does, it may be difficult
   for Command Generators to discover a suitable default
   contextEngineID.  Implementations should consider offering another
   engineID discovery mechanism to continue providing Command Generators
   with a contextEngineID discovery mechanism.  A recommended discovery
   solution is documented in [RFC5343].


9.  Security Considerations

   This document describes a transport model that permits SNMP to
   utilize (D)TLS security services.  The security threats and how the
   (D)TLS transport model mitigates these threats are covered in detail
   throughout this document.  Security considerations for DTLS are
   covered in [RFC4347] and security considerations for TLS are
   described in Section 11 and Appendices D, E, and F of TLS 1.2
   [RFC5246].  DTLS adds to the security considerations of TLS only
   because it is more vulnerable to denial of service attacks.  A random
   cookie exchange was added to the handshake to prevent anonymous



Hardaker                Expires December 26, 2009              [Page 50]

Internet-Draft               SNMP over DTLS                    June 2009


   denial of service attacks.  RFC 4347 recommends that the cookie
   exchange is utilized for all handshakes and therefore it is
   RECOMMENDED that implementers also support this cookie exchange.

9.1.  Certificates, Authentication, and Authorization

   Implementations are responsible for providing a security certificate
   configuration installation .  Implementations SHOULD support
   certificate revocation lists and expiration of certificates or other
   access control mechanisms.

   (D)TLS provides for both authentication of the identity of the (D)TLS
   server and authentication of the identity of the (D)TLS client.
   Access to MIB objects for the authenticated principal MUST be
   enforced by an access control subsystem (e.g. the VACM).

   Authentication of the Command Generator principal's identity is
   important for use with the SNMP access control subsystem to ensure
   that only authorized principals have access to potentially sensitive
   data.  The authenticated identity of the Command Generator
   principal's certificate is mapped to an SNMP model-independent
   securityName for use with SNMP access control.

   Furthermore, the (D)TLS handshake only provides assurance that the
   certificate of the authenticated identity has been signed by an
   configured accepted Certificate Authority.  (D)TLS has no way to
   further authorize or reject access based on the authenticated
   identity.  An Access Control Model (such as the VACM) provides access
   control and authorization of a Command Generator's requests to a
   Command Responder and a Notification Responder's authorization to
   receive Notifications from a Notification Originator.  However to
   avoid man-in-the-middle attacks both ends of the (D)TLS based
   connection MUST check the certificate presented by the other side
   against what was expected.  For example, Command Generators must
   check that the Command Responder presented and authenticated itself
   with a X.509 certificate that was expected.  Not doing so would allow
   an impostor, at a minimum, to present false data, receive sensitive
   information and/or provide a false-positive belief that configuration
   was actually received and acted upon.  Authenticating and verifying
   the identity of the (D)TLS server and the (D)TLS client for all
   operations ensures the authenticity of the SNMP engine that provides
   MIB data.

   The instructions found in the DESCRIPTION clause of the
   tlstmCertificateToSNTable object must be followed exactly.
   Specifically, it is important that if a row matching a certificate or
   a certificate's issuer is found but the translation to a securityName
   using the row fails that the lookup process stops and no further rows



Hardaker                Expires December 26, 2009              [Page 51]

Internet-Draft               SNMP over DTLS                    June 2009


   are consulted.  It is also important that the rows of the table be
   search in order starting with the row containing the lowest numbered
   tlstmCertID 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

   The MIB objects in this document must be protected with an adequate
   level of at least integrity protection, especially those objects
   which are writable.  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.

   SNMP versions prior to SNMPv3 did not include adequate security.
   Even if the network itself is secure (for example by using IPSec or
   (D)TLS) 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 section 8 of [RFC3410]),
   including full support for the USM (see [RFC3414]) and the TLS
   Transport Model cryptographic mechanisms (for authentication and
   privacy).


10.  IANA Considerations

   IANA is requested to assign:

   1.   a TCP port number in the range 1..1023 in the
        http://www.iana.org/assignments/port-numbers registry which will
        be the default port for SNMP command messages over a TLS
        Transport Model as defined in this document,

   2.   a TCP port number in the range 1..1023 in the
        http://www.iana.org/assignments/port-numbers registry which will



Hardaker                Expires December 26, 2009              [Page 52]

Internet-Draft               SNMP over DTLS                    June 2009


        be the default port for SNMP notification messages over a TLS
        Transport Model as defined in this document,

   3.   a UDP port number in the range 1..1023 in the
        http://www.iana.org/assignments/port-numbers registry which will
        be the default port for SNMP command messages over a DTLS/UDP
        connection as defined in this document,

   4.   a UDP port number in the range 1..1023 in the
        http://www.iana.org/assignments/port-numbers registry which will
        be the default port for SNMP notification messages over a DTLS/
        UDP connection as defined in this document,

   5.   a SCTP port number in the range 1..1023 in the
        http://www.iana.org/assignments/port-numbers registry which will
        be the default port for SNMP command messages over a DTLS/SCTP
        connection as defined in this document,

   6.   a SCTP port number in the range 1..1023 in the
        http://www.iana.org/assignments/port-numbers registry which will
        be the default port for SNMP notification messages over a DTLS/
        SCTP connection as defined in this document,

   7.   an SMI number under snmpDomains for the snmpTLSDomain object
        identifier,

   8.   an SMI number under snmpDomains for the snmpDTLSUDPDomain object
        identifier,

   9.   an SMI number under snmpDomains for the snmpDTLSSCTPDomain
        object identifier,

   10.  a SMI number under snmpModules, for the MIB module in this
        document,

   11.  "tls" as the corresponding prefix for the snmpTLSDomain in the
        SNMP Transport Model registry,

   12.  "dudp" as the corresponding prefix for the snmpDTLSUDPDomain in
        the SNMP Transport Model registry,

   13.  "dsct" as the corresponding prefix for the snmpDTLSSCTPDomain in
        the SNMP Transport Model registry;








Hardaker                Expires December 26, 2009              [Page 53]

Internet-Draft               SNMP over DTLS                    June 2009


11.  Acknowledgements

   This document closely follows and copies the Secure Shell Transport
   Model for SNMP defined by David Harrington and Joseph Salowey in
   [I-D.ietf-isms-secshell].

   This document was reviewed by the following people who helped provide
   useful comments: David Harrington, Alan Luchuk, Ray Purvis.

   This work was supported in part by the United States Department of
   Defense.  Large portions of this document are based on work by
   General Dynamics C4 Systems and the following individuals: Brian
   Baril, Kim Bryant, Dana Deluca, Dan Hanson, Tim Huemiller, John
   Holzhauer, Colin Hoogeboom, Dave Kornbau, Chris Knaian, Dan Knaul,
   Charles Limoges, Steve Moccaldi, Gerardo Orlando, and Brandon Yip.


12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2578]  McCloghrie, K., Ed., Perkins, D., Ed., and J.
              Schoenwaelder, Ed., "Structure of Management Information
              Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.

   [RFC2579]  McCloghrie, K., Ed., Perkins, D., Ed., and J.
              Schoenwaelder, Ed., "Textual Conventions for SMIv2",
              STD 58, RFC 2579, April 1999.

   [RFC2580]  McCloghrie, K., Perkins, D., and J. Schoenwaelder,
              "Conformance Statements for SMIv2", STD 58, RFC 2580,
              April 1999.

   [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
              Architecture for Describing Simple Network Management
              Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
              December 2002.

   [RFC3413]  Levi, D., Meyer, P., and B. Stewart, "Simple Network
              Management Protocol (SNMP) Applications", STD 62,
              RFC 3413, December 2002.

   [RFC3414]  Blumenthal, U. and B. Wijnen, "User-based Security Model
              (USM) for version 3 of the Simple Network Management
              Protocol (SNMPv3)", STD 62, RFC 3414, December 2002.



Hardaker                Expires December 26, 2009              [Page 54]

Internet-Draft               SNMP over DTLS                    June 2009


   [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.

   [I-D.ietf-isms-transport-security-model]
              Harington, D., "Transport Security Model for SNMP".

   [I-D.ietf-isms-tmsm]
              Harington, D. and J. Schoenwaelder, "Transport Subsystem
              for the Simple Network Management Protocol (SNMP)".

   [X509]     Rivest, R., Shamir, A., and L. M. Adleman, "A Method for
              Obtaining Digital Signatures and Public-Key
              Cryptosystems".

12.2.  Informative References

   [RFC2522]  Karn, P. and W. Simpson, "Photuris: Session-Key Management
              Protocol", RFC 2522, March 1999.

   [RFC3410]  Case, J., Mundy, R., Partain, D., and B. Stewart,
              "Introduction and Applicability Statements for Internet-
              Standard Management Framework", RFC 3410, December 2002.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              December 2005.




Hardaker                Expires December 26, 2009              [Page 55]

Internet-Draft               SNMP over DTLS                    June 2009


   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, December 2005.

   [RFC4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              RFC 4306, December 2005.

   [I-D.ietf-isms-secshell]
              Harington, D. and J. Salowey, "Secure Shell Transport
              Model for SNMP".

   [RFC5343]  Schoenwaelder, J., "Simple Network Management Protocol
              (SNMP) Context EngineID Discovery".

   [I-D.saintandre-tls-server-id-check]
              Saint-Andre, P., Zeilenga, K., Hodges, J., and B. Morgan,
              "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".


Appendix A.  Target and Notificaton Configuration Example

   Configuring the SNMP-TARGET-MIB and NOTIFICATION-MIB along with
   access control settings for the SNMP-VIEW-BASED-ACM-MIB can be a
   daunting task without an example to follow.  The following section
   describes an example of what pieces must be in place to accomplish
   this configuration.

   The isAccessAllowed() ASI requires configuration to exist in the
   following SNMP-VIEW-BASED-ACM-MIB tables:

      vacmSecurityToGroupTable
      vacmAccessTable
      vacmViewTreeFamilyTable

   The only table that needs to be discussed as particularly different



Hardaker                Expires December 26, 2009              [Page 56]

Internet-Draft               SNMP over DTLS                    June 2009


   here is the vacmSecurityToGroupTable.  This table is indexed by both
   the SNMPv3 security model and the security name.  The security model,
   when TLSTM is in use, should be set to the value of XXX corresponding
   to the TSM [I-D.ietf-isms-transport-security-model].  An example
   vacmSecurityToGroupTable row might be filled out as follows (using a
   single SNMP SET request):

   Note to RFC editor: replace XXX in the previous paragraph above with
   the actual IANA-assigned number for the TSM security model and remove
   this note.


      vacmSecurityModel              = XXX (TSM)
      vacmSecurityName               = "blueberry"
      vacmGroupaName                 = "administrators"
      vacmSecurityToGroupStorageType = 3 (nonVolatile)
      vacmSecurityToGroupStatus      = 4 (createAndGo)

   Note to RFC editor: replace XXX in the vacmSecurityModel line above
   with the actual IANA-assigned number for the TSM security model and
   remove this note.

   This example will assume that the "administrators" group has been
   given proper permissions via rows in the vacmAccessTable and
   vacmViewTreeFamilyTable.

   Depending on whether this VACM configuration is for a Command
   Responder or a Command Generator the security name "blueberry" will
   come from a few different locations.

   For Notification Generator's performing authorization checks, the
   server's certificate must be verified against the expected
   certificate before proceeding to send the notification.  The
   securityName be set by the SNMP-TARGET-MIB's
   snmpTargetParamsSecurityName column or other configuration mechanism
   and the certificate to use would be taken from the appropriate entry
   in the tlstmParamsTable.  The tlstmParamsTable augments the SNMP-
   TARGET-MIB's snmpTargetParamsTable with client-side certificate
   information.

   For Command Responder applications, the vacmSecurityName "blueberry"
   value is a value that needs to come from an incoming (D)TLS session.
   The mapping from a recevied (D)TLS client certificate to a
   securityName is done with the tlstmCertificateToSNTable.  The
   certificates must be loaded into the device so that a
   tlstmCertificateToSNEntry may refer to it.  As an example, consider
   the following entry which will provide a mapping from a X.509's hash
   fingerprint directly to the "blueberry" securityName:



Hardaker                Expires December 26, 2009              [Page 57]

Internet-Draft               SNMP over DTLS                    June 2009


     tlstmCertID           = 1         (chosen by ordering preference)
     tlstmCertHashType     = sha256
     tlstmCertHashValue    = (appropriate sha256 fingerprint)
     tlstmCertMapType      = specified(1)
     tlstmCertSecurityName = "blueberry"
     tlstmCertStorageType  = 3 (nonVolatile)
     tlstmCertRowStatus    = 4 (createAndGo)

   The above is an example of how to map a particular certificate to a
   particular securityName.  It is recommended that users make use of
   direct subjectAltName or CommonName mappings where possible since it
   will provide a more scalable approach to certificate management.
   This entry provides an example of using a subjectAltName mapping:

     tlstmCertID          = 1         (chosen by ordering preference)
     tlstmCertHashType    = sha256
     tlstmCertHashValue   = (appropriate sha256 fingerprint)
     tlstmCertMapType     = bySubjectAltName(2)
     tlstmCertStorageType = 3 (nonVolatile)
     tlstmCertRowStatus   = 4 (createAndGo)

   The above entry indicates the subjectAltName field for certificates
   created by an Issuing certificate with a corresponding hash type and
   value will be trusted to always produce common names that are
   directly 1 to 1 mappable into SNMPv3 securityNames.  This type of
   configuration should only be used when the certificate authorities
   naming conventions are carefully controlled.

   For the example, if the incoming (D)TLS client provided certificate
   contained a subjectAltName of "blueberry" and the certificate was
   signed by a certificate matching the tlstmCertHashType and
   tlstmCertHashValue values above and the CA's certificate was properly
   installed on the device then the CommonName of "blueberry" would be
   used as the securityName for the session.


Author's Address

   Wes Hardaker
   Sparta, Inc.
   P.O. Box 382
   Davis, CA  95617
   US

   Phone: +1 530 792 1913
   Email: ietf@hardakers.net





Hardaker                Expires December 26, 2009              [Page 58]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/