Syslog Working Group                                             F. Miao
Internet-Draft                                                  M. Yuzhi
Intended status: Standards Track                     Huawei Technologies
Expires: November 13, 2007                                  May 12, 2007

                    TLS Transport Mapping for Syslog

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   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-

   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

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on November 13, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2007).


   This document describes the use of Transport Layer Security (TLS) to
   provide a secure connection for the transport of syslog messages.
   This document describes the security threats to syslog and how TLS
   can be used to counter such threats.

Miao & Yuzhi            Expires November 13, 2007               [Page 1]

Internet-Draft      TLS Transport Mapping for Syslog            May 2007

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Security Requirements for Syslog . . . . . . . . . . . . . . .  3
   3.  TLS to Secure Syslog . . . . . . . . . . . . . . . . . . . . .  4
   4.  Protocol Elements  . . . . . . . . . . . . . . . . . . . . . .  5
     4.1.  Port Assignment  . . . . . . . . . . . . . . . . . . . . .  5
     4.2.  Initiation . . . . . . . . . . . . . . . . . . . . . . . .  5
       4.2.1.  Server Identity  . . . . . . . . . . . . . . . . . . .  5
       4.2.2.  Client Identity  . . . . . . . . . . . . . . . . . . .  6
       4.2.3.  Cryptographic Level  . . . . . . . . . . . . . . . . .  7
     4.3.  Sending data . . . . . . . . . . . . . . . . . . . . . . .  7
       4.3.1.  Message Length . . . . . . . . . . . . . . . . . . . .  7
     4.4.  Closure  . . . . . . . . . . . . . . . . . . . . . . . . .  8
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
     5.1.  Authentication . . . . . . . . . . . . . . . . . . . . . .  8
     5.2.  Cipher Suites  . . . . . . . . . . . . . . . . . . . . . .  9
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
     6.1.  Port Number  . . . . . . . . . . . . . . . . . . . . . . .  9
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  9
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
   Intellectual Property and Copyright Statements . . . . . . . . . . 12

Miao & Yuzhi            Expires November 13, 2007               [Page 2]

Internet-Draft      TLS Transport Mapping for Syslog            May 2007

1.  Introduction

   This document describes the use of Transport Layer Security (TLS [6])
   to provide a secure connection for the transport of syslog [2]
   messages.  This document describes the security threats to syslog and
   how TLS can be used to counter such threats.

1.1.  Terminology

   The following definitions are used in this document:

   o  A "sender" passes syslog messages to a specific transport

   o  A "receiver" takes syslog messages from a specific transport

   o  A "relay" forwards messages, accepting messages from originators
      or other relays, and sending them to collectors or other relays.

   o  A "collector" gathers syslog content for further analysis.

   o  A "TLS client" is an application that can initiate a TLS
      connection by sending a Client Hello to a peer.

   o  A "TLS server" is an application that can receive a Client Hello
      from a peer and reply with a Server Hello.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [1].

2.  Security Requirements for Syslog

   syslog messages may pass several hops to arrive at the intended
   receiver.  Some intermediary networks may not be trusted by the
   sender/relay, receiver, or all because the network is in a different
   security domain or at a different security level from the receiver,
   relay, or sender.  Another security concern is that the sender/relay,
   or receiver itself is in an insecure network.

   There are several threats to be addressed for syslog security.  The
   primary threats are:

   o  Masquerade.  An unauthorized sender/relay may send messages to a
      legitimate receiver, or an unauthorized receiver tries to deceive
      a legitimate sender/relay into sending syslog messages to it.

Miao & Yuzhi            Expires November 13, 2007               [Page 3]

Internet-Draft      TLS Transport Mapping for Syslog            May 2007

   o  Modification.  An attacker between the sender/relay and the
      receiver may modify an in-transit syslog message from the sender/
      relay and then forward the message to the receiver.  Such
      modification may make the receiver misunderstand the message or
      cause the receiver to behave in undesirable ways.

   o  Disclosure.  An unauthorized entity may examine the contents of
      the syslog messages, gaining unauthorized access to the
      information.  Some data in syslog messages is sensitive and may be
      useful to an attacker, such as the password of an authorized
      administrator or user.

   The secondary threat is:

   o  Message stream modification.  An attacker may delete one or more
      syslog message from a series of messages, replay a message, or
      alter the delivery sequence.  The syslog protocol itself is not
      based on message order, but an event in a syslog message may
      relate semantically to events in other messages, so message
      ordering may be important to understanding a sequence of events.

   The following threats are deemed to be of lesser importance for
   syslog, and are not addressed in this document:

   o  Denial of Service

   o  Traffic Analysis

3.  TLS to Secure Syslog

   TLS can be used as a secure transport to counter all the primary
   threats to syslog described in section 2:

   o  Confidentiality to counter disclosure of the message contents;

   o  Integrity checking to counter modifications to a message on a hop-
      by-hop basis;

   o  Server or mutual authentication to counter masquerade.

   Note: This secure transport (i.e.  TLS) only secures syslog in a hop-
   by-hop manner, the threat of end-to-end message stream modification
   is not addressed in this document.

Miao & Yuzhi            Expires November 13, 2007               [Page 4]

Internet-Draft      TLS Transport Mapping for Syslog            May 2007

4.  Protocol Elements

4.1.  Port Assignment

   A syslog sender/relay is always a TLS client and a syslog receiver is
   always a TLS server.

   The TCP port NNN has been allocated as the default port for syslog
   over TLS, as defined in this document.

   Note to RFC Editor: please replace NNN with the IANA-assigned value,
   and remove this note.

4.2.  Initiation

   The sender/relay should initiate a connection to the receiver and
   then send the TLS Client Hello to begin the TLS handshake.  When the
   TLS handshake has finished the sender/relay MAY then send the first
   syslog message.

   TLS uses certificates [3] to authenticate peers.  If a client
   authenticates a server it MUST validate the certificate.
   Authentication in this specification means that the recipient of a
   certificate must actually check the certificate rather than just
   accept a certificate.

4.2.1.  Server Identity

   A procedure similar to RFC2818 [7] is used to check the server's
   identity in the certificate.

   In general, the client is configured with the hostname or IP address
   of the TLS server.  As a consequence, the hostname or IP address for
   the server is known to the client.  If the hostname (or IP address)
   is available, the client MUST check it against the server's identity
   as presented in the server's certificate message, in order to prevent
   man-in-the-middle attacks.

   If the client has external information as to the expected identity of
   the server, the hostname (or IP address) check MAY be omitted.  (For
   instance, a client may be connecting to a machine whose address and
   hostname are dynamic but the client knows the certificate that the
   server will present.)  In such cases, it is important to narrow the
   scope of acceptable certificates as much as possible in order to
   prevent man-in-the-middle attacks.  In special cases, it may be
   appropriate for the client to simply ignore the server's identity,
   but it must be understood that this leaves the connection open to
   active attack.

Miao & Yuzhi            Expires November 13, 2007               [Page 5]

Internet-Draft      TLS Transport Mapping for Syslog            May 2007

   If a subjectAltName extension of type dNSName is present, that MUST
   be used as the identity.  Otherwise, the (most specific) Common Name
   field in the Subject field of the certificate MUST be used.  Although
   the use of the Common Name is current practice, it is deprecated and
   Certification Authorities are encouraged to use the dNSName instead.

   Matching is performed using the matching rules specified by RFC3280
   [3].  Names may contain the wildcard character * which is considered
   to match any single domain name component or component fragment.
   E.g., * matches but not f*.com matches but not  If the client is configured with IP address
   of the server, the hostname should be got first through a trusted
   mechanism such as a preconfigured hosts table or DNSSEC [8].

   If the iPAddress subjectAltName is present in the certificate, it
   must exactly match the IP address configured or resolved from the
   configured hostname through a trusted mechanism such as a
   preconfigured hosts table or DNSSEC.

   It is recommended to use dNSName in the certificate rather than any
   other type subjectAltName for certificate verification, such as
   ipAddress.  If more than one identity of a given type is presented in
   the certificate (e.g., more than one dNSName name), a match in any
   one of the set is considered acceptable.

   If the hostname does not match the identity in the certificate,
   clients SHOULD log the error in some form or another (see next
   paragraph), and SHOULD terminate the connection with a bad
   certificate error.  Clients MAY provide a configuration setting that
   disables this check but MUST enable it by default.

   The application developer must take some care to consider the case
   when, for whatever reason, there is a problem with authenticating the
   other end of the connection.  Since this problem will prevent log
   messages from being transmitted, each device having this problem
   should use whatever means are available to inform the administrator
   of the problem.  This may include producing an error code on a
   console, returning an error to a user (if there is one), or writing a
   file to disk, being mindful that such writes should be rate limited
   in the case of attacks.

4.2.2.  Client Identity

   If a server authenticates a client and the client presents a
   certificate to the server, the server MUST validate the certificate.
   The subjectAltName may be the host name, IP address, MAC, device ID,
   etc.  SubjectAltName is not necessarily unique for different
   certificates.  For example, certificates for some types of printer

Miao & Yuzhi            Expires November 13, 2007               [Page 6]

Internet-Draft      TLS Transport Mapping for Syslog            May 2007

   might use the same subjectAltName.

   A client certificate may be issued by an operator when a device/
   application is being provisioned, or by a vendor when the device/
   application is manufactured.  This document does not define how the
   client certificate is issued.

4.2.3.  Cryptographic Level

   Syslog applications SHOULD be implemented in a manner that permits
   administrators, as a matter of local policy, to select the
   cryptographic level and authentication options they desire.

   TLS permits the resumption of an earlier TLS session or the use of
   another active session when a new session is requested, in order to
   save the expense of another full TLS handshake.  The security
   parameters of the resumed session are reused for the requested
   session.  The security parameters SHOULD be checked against the
   security requirement of the requested session to make sure that the
   resumed session provides proper security.

4.3.  Sending data

   All syslog messages MUST be sent as TLS "application data".  It is
   possible that multiple syslog messages be contained in one TLS
   record, or that a syslog message be transferred in multiple TLS
   records.  The application data is defined with the following ABNF [5]




   SP = %d32

   NONZERO-DIGIT = %d49-57


   SYSLOG-MSG is defined in syslog [2] protocol.

4.3.1.  Message Length

   The message length is the octet count of the SYSLOG-MSG in the
   SYSLOG-FRAME.  A receiver MUST use the message length to delimit a
   syslog message.  There is no upper limit for a message length per se.

Miao & Yuzhi            Expires November 13, 2007               [Page 7]

Internet-Draft      TLS Transport Mapping for Syslog            May 2007

   However, in order to establish a baseline for interoperability, this
   specification requires that a receiver MUST be able to process
   messages with a length up to and including 2048 octets.  Receiver
   SHOULD be able to process messages with lengths up to and including
   8192 octets.

4.4.  Closure

   A TLS client MUST close the associated TLS connection if the
   connection is not expected to deliver any syslog messages later.  It
   MUST send a TLS close_notify alert before closing the connection.  A
   client MAY choose to not wait for the server's close_notify alert and
   simply close the connection, thus generating an incomplete close on
   the server side.  Once the server gets a close_notify from the
   client, it MUST reply with a close_notify unless it becomes aware
   that the connection has already been closed by the client (e.g., the
   closure was indicated by TCP).

   When no data is received from a connection for a long time (where the
   application decides what "long" means), a server MAY close the
   connection.  The server MUST attempt to initiate an exchange of
   close_notify alerts with the client before closing the connection.
   Servers that are unprepared to receive any more data MAY close the
   connection after sending the close_notify alert, thus generating an
   incomplete close on the client side.  When the client has received
   the close_notify alert from the server and still has pending data to
   send, it SHOULD send the pending data before sending the close_notify

5.  Security Considerations

5.1.  Authentication

   TLS supports three authentication modes: authentication of both
   parties, server authentication with an unauthenticated client, and
   total anonymity.  An implementation compliant with this specification
   MUST support all three authentication modes for interoperability.

   It is RECOMMENDED that mutual authentication be deployed in all cases
   as that will prevent masquerade attacks, modification of the
   messages, and disclosure of the contents of the messages.  Server
   authentication does not prevent masquerade attacks but does prevent
   modification and disclosure.  Unauthenticated TLS sessions do not
   address any of the threats as an unauthenticated TLS session is
   susceptible to a man-in-the-middle attack.  Deploying syslog over TLS
   with total anonymity is NOT RECOMMENDED.

Miao & Yuzhi            Expires November 13, 2007               [Page 8]

Internet-Draft      TLS Transport Mapping for Syslog            May 2007

   TLS authentication and the distribution of keys is based on
   certificates and asymmetric cryptography.  This makes TLS transport
   more expensive than non-TLS plain transport.  An attacker may
   initialize many TLS connections to a receiver as a denial of service
   attack.  Since a receiver may act upon received data, for syslog over
   TLS, it is recommended that the receiver authenticate the sender/
   relay to ensure that information received is authentic.

5.2.  Cipher Suites

   TLS [6] specifies a mandatory cipher suite to enable minimum
   interoperability for TLS implementation.  This specification does not
   specify any mandatory cipher suite other than the one in the TLS
   specification, and the cipher suite for TLS applies to this
   specification for minimum interoperability purposes.

   If there is an update to the TLS specification in the future, the
   latest mandatory cipher suite in the update will apply to this
   specification, too.  The implementers and deployers should be aware
   of the strengths of the public keys algorithm in the suite for
   exchanging symmetric keys, which is elaborated in BCP86 [4].  The
   implementers and deployers should also be aware of the latest TLS and
   other IETF cryptography standards including BCP86.

6.  IANA Considerations

6.1.  Port Number

   IANA is requested to assign a TCP port number in the range 1..1023 in
   the registry which will
   be the default port for syslog over TLS, as defined in this document.

7.  Acknowledgments

   Authors appreciate Eric Rescorla, Rainer Gerhards, Tom Petch, Anton
   Okmianski, Balazs Scheidler, Bert Wijnen, and Chris Lonvick for their
   effort on issues resolving discussion.  Authors would also like to
   appreciate Balazs Scheidler, Tom Petch and other persons for their
   input on security threats of syslog.  The authors would like to
   acknowledge David Harrington for his detailed reviews of the content
   and grammar of the document.

8.  References

Miao & Yuzhi            Expires November 13, 2007               [Page 9]

Internet-Draft      TLS Transport Mapping for Syslog            May 2007

8.1.  Normative References

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

   [2]  Gerhards, R., "The syslog Protocol",
        draft-ietf-syslog-protocol-19 (work in progress), November 2006.

   [3]  Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509
        Public Key Infrastructure Certificate and Certificate Revocation
        List (CRL) Profile", RFC 3280, April 2002.

   [4]  Orman, H. and P. Hoffman, "Determining Strengths For Public Keys
        Used For Exchanging Symmetric Keys", BCP 86, RFC 3766,
        April 2004.

   [5]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
        Specifications: ABNF", RFC 4234, October 2005.

   [6]  Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
        Protocol Version 1.1", RFC 4346, April 2006.

8.2.  Informative References

   [7]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [8]  Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
        "DNS Security Introduction and Requirements", RFC 4033,
        March 2005.

Authors' Addresses

   Miao Fuyou
   Huawei Technologies
   No. 3, Xinxi Rd
   Shangdi Information Industry Base
   Haidian District, Beijing  100085
   P. R. China

   Phone: +86 10 8288 2008

Miao & Yuzhi            Expires November 13, 2007              [Page 10]

Internet-Draft      TLS Transport Mapping for Syslog            May 2007

   Ma Yuzhi
   Huawei Technologies
   No. 3, Xinxi Rd
   Shangdi Information Industry Base
   Haidian District, Beijing  100085
   P. R. China

   Phone: +86 10 8288 2008

Miao & Yuzhi            Expires November 13, 2007              [Page 11]

Internet-Draft      TLS Transport Mapping for Syslog            May 2007

Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at


   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).

Miao & Yuzhi            Expires November 13, 2007              [Page 12]