Syslog Working Group F. Miao
Internet-Draft M. Yuzhi
Expires: December 9, 2006 Huawei Technologies
June 7, 2006
TLS Transport Mapping for SYSLOG
draft-ietf-syslog-transport-tls-02.txt
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Copyright (C) The Internet Society (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 Fundamentals . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. How TLS works . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Security Properties . . . . . . . . . . . . . . . . . . . 5
4. TLS to secure Syslog . . . . . . . . . . . . . . . . . . . . . 5
5. Protocol Elements . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Port Assignment . . . . . . . . . . . . . . . . . . . . . 6
5.2. Initiation . . . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Sending data . . . . . . . . . . . . . . . . . . . . . . . 7
5.3.1. Frame Length . . . . . . . . . . . . . . . . . . . . . 7
5.4. Closure . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Consideration . . . . . . . . . . . . . . . . . . . . 8
6.1. Authentication . . . . . . . . . . . . . . . . . . . . . . 8
6.2. Generic Certificate . . . . . . . . . . . . . . . . . . . 8
6.3. TLS Session Resumption . . . . . . . . . . . . . . . . . . 8
7. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 10
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1. Introduction
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.
1.1. Terminology
The following definitions are used in this document:
o A sender is an application that can generate and send or forward a
Syslog [2] message from an application to another application.
Note: the definition of sender is different from syslog-protocol.
o A receiver is an application that can receive a Syslog message.
o An originator is an application that can generate a Syslog
message.
o A relay is an application that can receive Syslog messages and
forward them to another receiver. A relay will be both a sender
and 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 or the receiver or both because the network is in a different
security domain or at a different security level from the receiver or
sender. Another security concern is that the sender or receiver
itself is in an insecure network.
There are several threats to be addressed for Syslog security. The
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primary threats are:
o Masquerade. An unauthorized sender may send messages to a
legitimate receiver, or an unauthorized receiver tries to deceive
a legitimate sender into sending Syslog messages to it.
o Modification. An attacker between the sender and receiver may
modify an in-transit Syslog message from the sender and then
forward the message to receiver. Such modification may make the
receiver misunderstands the message or causes 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 Fundamentals
3.1. How TLS works
TLS [4] establishes a private end-to-end connection, optionally
including strong mutual authentication, using a variety of
cryptosystems. Initially, a handshake phase uses three subprotocols
to set up a record layer, authenticate endpoints, set parameters, and
report errors. Then, there is an ongoing layered record protocol
that handles encryption, compression, and reassembly for the
remainder of the connection. An application data protocol, such as
Syslog, is layered on the record protocol.
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3.2. Security Properties
The TLS record protocol is used to encapsulate various higher level
protocols. It provides connection security with confidentiality,
integrity, authentication, and replay prevention.
Confidentiality is provided using symmetric cryptography for data
encryption. TLS supports both stream cipher and block cipher. The
key for encryption is derived from a secret established by the
handshake protocol. The secret is kept private even if there is an
eavesdropper in the middle.
Integrity is provided by using HMAC [6] (computed with a secure hash
function) to check the integrity of a message. Modification without
the appropriate key is detectable.
Authentication is provided by a handshake protocol. The peer's
identity is authenticated using a certificate and signature, based on
asymmetric cryptography.
Replay prevention is provided by using a Sequence Number in each TLS
record that is used to detect a missing record, the replay of a
record, or alteration of the delivery sequence.
4. 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
The security service is also applicable to BSD Syslog defined in
RFC3164 [7]. But, it is not ensured that the protocol specification
defined in this document applicable to BSD Syslog.
5. Protocol Elements
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5.1. Port Assignment
A Syslog sender 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.
5.2. Initiation
The sender 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 may then send the first Syslog
message.
TLS uses certificate [5] to authenticate the peers. When a sender
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 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, the receiver MUST validate
the certificate. A sender's certificate may be:
o A 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 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 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.
TLS permits the resumption of an earlier TLS session or the use of
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another active session when a new session is requested, in order to
save the expense of another TLS handshake. The security parameters
of the resumed session are reused for the requested session. The
certificate MUST be checked when resuming a session. If the resumed
session and current session use different certificates, resumption
MUST not happen. The security parameters SHOULD be checked against
security requirement of requested session to make sure the resumed
session provides proper security.
5.3. Sending data
All Syslog messages MUST be sent as TLS "application data". There
MAY be multiple Syslog message in the same TLS record. The
application data is defined with the following ABNF [3] expression:
APPLICATION-DATA = 1*SYSLOG-FRAME
SYSLOG-FRAME = FRAME-LEN SP SYSLOG-MSG
FRAME-LEN = NONZERO-DIGIT 0*DIGIT
SP = %d32
DIGIT = %d48 / NONZERO-DIGIT
NONZERO-DIGIT = %d49-57
SYSLOG-MSG is defined in Syslog [2] protocol.
5.3.1. Frame Length
The frame length is the octet count of a SYSLOG frame including the
FRAME-LEN and SP parts. A receiver MUST use the frame length field
to delimit a Syslog message.
5.4. Closure
A Syslog sender MUST close the associated TLS connection if the
connection is not expected to deliver Syslog message later. It MUST
send a TLS closure_notify alert before closing the connection. A
sender MAY choose not to wait for the receiver's closure_notify alert
and simply close the connection, thus generating an incomplete close
on the receiver side. Once the receiver gets closure_notify from the
sender, it MUST reply with a closure_notify unless it becomes aware
that the connection has already been closed by the sender (e.g., the
closure was indicated by TCP).
When no data is received from a connection for a long time (where the
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application decides what "long" means), a receiver MAY close a
connection. The receiver MUST attempt to initiate an exchange of
closure_notify alerts with the sender before closing the connection.
Receivers that are unprepared to receive any more data MAY close the
connection after sending the closure_notify alert, thus generating an
incomplete close on the sender side. When the sender has received
the closure_notify alert from the receiver and still has pending data
to send, the sender SHOULD send the pending data before sending the
closure_notify alert.
6. Security Consideration
6.1. 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 UDP 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 to ensure that
information received is authentic.
When confidentiality is a concern, a sender MUST authenticate the
receiver to make sure it is talking to the right peer.
6.2. 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. Any communication that is bound to the
certificate is at risk.
6.3. TLS Session Resumption
Different applications in the same host may have different security
levels (e.g., the kernel may have higher a security level than a
document editor application). If a requested session resumes an
existing session, then the requesting application can decrypt the
Syslog messages of the resumed session using same cipher parameters
as defined for the resumed session. When a session is being resumed
from an application with a different security level, care must be
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taken to avoid disclosing sensitive data to an unauthorized
application. A sensitive session must not be resumable.
7. IANA Consideration
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.
8. Acknowledgments
Authors appreciate Anton Okmianski, Rainer Gerhards, Balazs Scheidler
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
author would like to acknowledge David Harrington for his detailed
reviews of the content and grammar of the document.
9. References
9.1. 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-16 (work in progress), January 2006.
[3] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[4] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[5] 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.
[6] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication", RFC 2104, February 1997.
9.2. Informative References
[7] Lonvick, C., "The BSD Syslog Protocol", RFC 3164, August 2001.
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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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