Syslog Working Group F. Miao
Internet-Draft M. Yuzhi
Intended status: Standards Track Huawei Technologies
Expires: June 4, 2007 December 01, 2006
TLS Transport Mapping for Syslog
draft-ietf-syslog-transport-tls-06.txt
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Copyright (C) The IETF Trust (2006).
Abstract
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.
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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 . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Port Assignment . . . . . . . . . . . . . . . . . . . . . 5
4.2. Initiation . . . . . . . . . . . . . . . . . . . . . . . . 5
4.3. Sending data . . . . . . . . . . . . . . . . . . . . . . . 6
4.3.1. Frame Length . . . . . . . . . . . . . . . . . . . . . 6
4.4. Closure . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5.1. Authentication . . . . . . . . . . . . . . . . . . . . . . 7
5.2. Generic Certificate . . . . . . . . . . . . . . . . . . . 7
5.3. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
8. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . . . 10
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1. Introduction
This document describes the use of Transport Layer Security (TLS [6])
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.
1.1. Terminology
The following definitions are used in this document:
o A sender is an application that can generate and send a Syslog [2]
message to another application.
o A receiver is an application that can receive a Syslog message.
o A relay is an application that can receive Syslog messages and
forward them to another receiver.
o A collector is an application that can receive messages but does
not relay them to any other receiver.
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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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.
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o Modification. An attacker between the sender/relay and receiver
may modify an in-transit Syslog message from the sender/relay and
then forward the message to 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 content 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 a Syslog
message from a series of messages, replay a message or alter the
delivery sequence. 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 and
secondary threats to Syslog described in section 2:
o Confidentiality to counter disclosure of the message contents
o Integrity check to counter modifications to a message
o Peer authentication to counter masquerade
o Sequence number along with integrity check to counter message
stream modification
4. Protocol Elements
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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 certificate [4] to authenticate the peers. When a sender/
relay authenticates a receiver it MUST validate the certificate. It
SHOULD check the common name (CN) of the certificate against the host
name of the receiver if it has knowledge of a common name/host name
mapping. If the common name does not match the host name, the
sender/relay SHOULD send an "access_denied" error alert using the TLS
alert protocol to terminate the handshake, and then it SHOULD close
the connection.
When a receiver authenticates a sender/relay, the receiver MUST
validate the certificate. A sender's (or relay's) certificate may
be:
o An unique certificate, which is issued to a host and whose Common
Name may be host name, IP address, MAC, or device ID.
o A generic certificate, which is issued to a class of application
or device. For example, all cable modems from a vendor may be
issued the same generic certificate.
A sender/relay 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 sender/relay certificate is issued.
Syslog applications SHOULD be implemented in a manner that permits
administrators to select the cryptographic level they desire. It
SHOULD be an administrator decision, as a matter of local policy,
what security level (e.g. cryptographic algorithms and length of
keys) is required.
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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 security
requirement of requested session to make sure the resumed session
provides proper security.
4.3. Sending data
All Syslog messages MUST be sent as TLS "application data". It is
possible that there are multiple Syslog messages in one TLS record,
or a Syslog message is transferred in multiple TLS records. The
application data is defined with the following ABNF [5] expression:
APPLICATION-DATA = 1*SYSLOG-FRAME
SYSLOG-FRAME = FRAME-LEN SP SYSLOG-MSG
FRAME-LEN = NONZERO-DIGIT *DIGIT
SP = %d32
NONZERO-DIGIT = %d49-57
DIGIT = %d48 / NONZERO-DIGIT
SYSLOG-MSG is defined in Syslog [2] protocol.
4.3.1. Frame Length
The frame length is the octet count of a Syslog frame including the
FRAME-HEADER and SP parts. A receiver MUST use the frame length
field to delimit a Syslog message. There is no upper limit for a
frame length per se. However, in order to establish a baseline for
interoperability, the specification requires that a receiver MUST be
able to process frame with size up to and including 2048 octets. It
SHOULD be able to receive frame with size up to and including 8192
octets.
4.4. Closure
A Syslog sender/relay MUST close the associated TLS connection if the
connection is not expected to deliver Syslog message later. It MUST
send a TLS close_notify alert before closing the connection. A
sender/relay MAY choose not to wait for the receiver's close_notify
alert and simply close the connection, thus generating an incomplete
close on the receiver side. Once the receiver gets close_notify from
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the sender/relay, it MUST reply with a close_notify unless it becomes
aware that the connection has already been closed by the sender/relay
(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 receiver MAY close a
connection. The receiver MUST attempt to initiate an exchange of
close_notify alerts with the sender/relay before closing the
connection. Receivers those are unprepared to receive any more data
MAY close the connection after sending the close_notify alert, thus
generating an incomplete close on the sender/relay side. When the
sender/relay has received the close_notify alert from the receiver
and still has pending data to send, it SHOULD send the pending data
before sending the close_notify alert.
5. Security Considerations
5.1. Authentication
TLS supports three authentication modes: authentication of both
parties, server authentication with an unauthenticated client, and
total anonymity.
TLS authentication and the establishment of secrets is based on
certificates and asymmetric cryptography. This makes TLS transport
much 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, the receiver SHOULD authenticate the sender/relay to ensure that
information received is authentic.
For the deployment where confidentiality is a concern, receiver
authentication is required for sender/relay to make sure it is
talking to the right peer. It is up to the operator to decide
whether confidentiality is a concern for a specific deployment.
5.2. Generic Certificate
When a certificate is issued to a class of device or application, the
certificate may be shared by multiple hosts. Multiple hosts know the
private key of the certificate. When the certificate in one host is
compromised, then the certificate for all hosts that share the
certificate is compromised. An attacker may impersonate a legitimate
sender to send Syslog message to a receiver.
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5.3. Cipher Suites
TLS [6] specifies a mandatory cipher suite to enable minimum
interoperability for TLS implementation. This specification does not
specify a mandatory cipher suite other than the one in TLS
specification, and the one for TLS applies to this specification for
minimum interoperability purpose.
If there is update to TLS specification in the future, the latest
mandatory cipher suite in the update will apply to this
specification, too. The implementors 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 [3]. The
implementors 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 http://www.iana.org/assignments/port-numbers 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. 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] Orman, H. and P. Hoffman, "Determining Strengths For Public Keys
Used For Exchanging Symmetric Keys", BCP 86, RFC 3766,
April 2004.
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[4] 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.
[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.
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
Email: miaofy@huawei.com
URI: www.huawei.com
Ma Yuzhi
Huawei Technologies
No. 3, Xinxi Rd
Shangdi Information Industry Base
Haidian District, Beijing 100085
P. R. China
Phone: +86 10 8288 2008
Email: myz@huawei.com
URI: www.huawei.com
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