Network Working Group J. Salowey
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track T. Petch
Expires: November 5, 2010 Engineering Networks Ltd
R. Gerhards
Adiscon GmbH
H. Feng
Huaweisymantec Technologies
May 4, 2010
Datagram Transport Layer Security (DTLS) Transport Mapping for Syslog
draft-ietf-syslog-dtls-05.txt
Abstract
This document describes the transport of syslog messages over DTLS
(Datagram Transport Level Security). It provides a secure transport
for syslog messages in cases where a connection-less transport is
desired.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Security Requirements for Syslog . . . . . . . . . . . . . . . 6
4. Using DTLS to Secure Syslog . . . . . . . . . . . . . . . . . 7
5. Protocol Elements . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Transport . . . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Port and Service Code Assignment . . . . . . . . . . . . . 8
5.3. Initiation . . . . . . . . . . . . . . . . . . . . . . . . 8
5.3.1. Certificate-Based Authentication . . . . . . . . . . . 9
5.4. Sending data . . . . . . . . . . . . . . . . . . . . . . . 9
5.4.1. Message Size . . . . . . . . . . . . . . . . . . . . . 10
5.5. Closure . . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Congestion Control . . . . . . . . . . . . . . . . . . . . . . 11
7. Security Policies . . . . . . . . . . . . . . . . . . . . . . 12
8. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
9.1. DTLS Renegotiation . . . . . . . . . . . . . . . . . . . . 14
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
11.1. Normative References . . . . . . . . . . . . . . . . . . . 16
11.2. Informative References . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
The syslog protocol [RFC5424] is designed to run over different
transports for different environments. This document defines the
transport of syslog messages over the datagram transport layer
security protocol (DTLS) [RFC4347].
The datagram transport layer security protocol (DTLS) [RFC4347] is
designed to meet the requirements of applications that need secure
datagram transport. DTLS has been mapped onto different transports,
including UDP [RFC0768] and DCCP [RFC4340]. This memo defines both
options, namely syslog over DTLS over UDP and syslog over DTLS over
DCCP.
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2. Terminology
The following definitions from [RFC5424] are used in this document:
o An "originator" generates syslog content to be carried in a
message.
o A "collector" gathers syslog content for further analysis.
o A "relay" forwards messages, accepting messages from originators
or other relays, and sending them to collectors or other relays.
o A "transport sender" passes syslog messages to a specific
transport protocol.
o A "transport receiver" takes syslog messages from a specific
transport protocol.
This document adds the following definitions:
o A "DTLS client" is an application that can initiate a DTLS Client
Hello to a server.
o A "DTLS server" is an application that can receive a DTLS Client
Hello from a client 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 [RFC2119].
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3. Security Requirements for Syslog
The security requirements for the transport of syslog messages are
discussed in Section 2 of [RFC5425]. These also apply to this
specification.
The following secondary threat is also considered in this document:
o Denial of service is discussed in [RFC5424], which states that an
attacker may send more messages to a transport receiver than the
transport receiver could handle. When using a secure transport
protocol handshake, an attacker may use a spoofed IP source to
engage the server in a cryptographic handshake to deliberately
consume the server's resources.
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4. Using DTLS to Secure Syslog
DTLS can be used as a secure transport to counter all the primary
threats to syslog described in [RFC5425]:
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.
In addition DTLS also provides:
o A cookie exchange mechanism during handshake to counter Denial of
Service attacks.
o A sequence number in the header to counter replay attacks.
Note: This secure transport (i.e., DTLS) only secures syslog
transport in a hop-by-hop manner, and is not concerned with the
contents of syslog messages. In particular, the authenticated
identity of the transport sender (e.g., subject name in the
certificate) is not necessarily related to the HOSTNAME field of the
syslog message. When authentication of syslog message origin is
required, [I-D.ietf-syslog-sign] can be used.
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5. Protocol Elements
5.1. Transport
DTLS can run over multiple transports. Implementations of this
specification MUST support DTLS over UDP and SHOULD support DTLS over
DCCP [RFC5238]. Transports, such as UDP or DCCP do not provide
session multiplexing and session-demultiplexing. In such cases, the
application implementer provides this functionality by mapping a
unique combination of the remote address, remote port number, local
address and local port number to a session.
Each syslog message is delivered by the DTLS record protocol, which
assigns a sequence number to each DTLS record. Although the DTLS
implementer may adopt a queue mechanism to resolve reordering, it may
not assure that all the messages are delivered in order when mapping
on the UDP transport.
When DTLS runs over an unreliable transport, such as UDP, reliability
is not provided. With DTLS, an originator or relay may not realize
that a collector has gone down or lost its DTLS connection state so
messages may be lost.
Syslog over DTLS over TCP MUST NOT be used. If a secure transport is
required with TCP then the appropriate security mechanism is syslog
over TLS as described in [RFC5425].
5.2. Port and Service Code Assignment
A syslog transport sender is always a DTLS client and a transport
receiver is always a DTLS server.
The UDP and DCCP port [TBD] has been allocated as the default port
for syslog over DTLS as defined in this document. The service code
[TBD] has been assigned to syslog.
5.3. Initiation
The transport sender initiates a DTLS connection by sending a DTLS
Client Hello to the transport receiver. Implementations MUST support
the denial of service countermeasures defined by DTLS. When these
countermeasures are enabled, the transport receiver responds with a
DTLS Hello Verify Request containing a cookie. The transport sender
responds with a DTLS Client Hello containing the received cookie
which initiates the DTLS handshake. When the DTLS handshake has
finished, the transport sender MAY then send the first syslog
message.
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Implementations MUST support DTLS 1.1 [RFC4347] and MUST support the
mandatory to implement cipher suite, which is
TLS_RSA_WITH_AES_128_CBC_SHA.
5.3.1. Certificate-Based Authentication
The mandatory to implement ciphersuites for DTLS use certificates
[RFC5280] to authenticate peers. Both syslog transport sender (DTLS
client) and syslog transport receiver (DTLS server) MUST implement
certificate-based authentication. This consists of validating the
certificate and verifying that the peer has the corresponding private
key. The latter part is performed by DTLS. To ensure
interoperability between clients and servers, the methods for
certificate validation defined in sections 4.2.1 and 4.2.2 of
[RFC5425] SHALL be implemented.
Both transport receiver and transport sender implementations MUST
provide means to generate a key pair and self-signed certificate in
case a key pair and certificate are not available through another
mechanism.
The transport receiver and transport sender SHOULD provide mechanisms
to record the certificate or certificate fingerprint used by the
remote endpoint for the purpose of correlating an identity with the
sent or received data.
5.4. Sending data
All syslog messages MUST be sent as DTLS "application data". It is
possible that multiple syslog messages be contained in one DTLS
record, or that a syslog message be transferred in multiple DTLS
records. The application data is defined with the following ABNF
[RFC5234] expression:
APPLICATION-DATA = 1*SYSLOG-FRAME
SYSLOG-FRAME = MSG-LEN SP SYSLOG-MSG
MSG-LEN = NONZERO-DIGIT *DIGIT
SP = %d32
NONZERO-DIGIT = %d49-57
DIGIT = %d48 / NONZERO-DIGIT
SYSLOG-MSG is defined in syslog [RFC5424] protocol.
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5.4.1. Message Size
The message length is the octet count of the SYSLOG-MSG in the
SYSLOG-FRAME. A transport receiver MUST use the message length to
delimit a syslog message. There is no upper limit for a message
length per se. As stated in [RFC4347], each DTLS record MUST fit
within a single DTLS datagram. When mapping onto different
transports, DTLS has different record size limitations. The
application implementer SHOULD determine the maximum record size
allowed by DTLS protocol running over the transport in use. The
message size SHOULD NOT exceed the DTLS maximum record size
limitation of 2^14 bytes. To be consistent with RFC 5425, in
establishing a baseline for interoperability, this specification
requires that a transport receiver MUST be able to process messages
with a length up to and including 2048 octets. Transport receivers
SHOULD be able to process messages with lengths up to and including
8192 octets.
5.5. Closure
A transport sender MUST close the associated DTLS connection if the
connection is not expected to deliver any syslog messages later. It
MUST send a DTLS close_notify alert before closing the connection. A
transport sender (DTLS client) MAY choose to not wait for the
transport receiver's close_notify alert and simply close the DTLS
connection. Once the transport receiver gets a close_notify from the
transport sender, it MUST reply with a close_notify.
When no data is received from a DTLS connection for a long time
(where the application decides what "long" means), a transport
receiver MAY close the connection. The transport receiver (DTLS
server) MUST attempt to initiate an exchange of close_notify alerts
with the transport sender before closing the connection. Transport
receivers that are unprepared to receive any more data MAY close the
connection after sending the close_notify alert.
Although closure alerts form part of DTLS, they, like all alerts, are
not retransmitted by DTLS and so may be lost over an unreliable
network.
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6. Congestion Control
Because syslog can generate unlimited amounts of data, transferring
this data over UDP is generally problematic, because UDP lacks
congestion control mechanisms. Congestion control mechanisms that
respond to congestion by reducing traffic rates and establish a
degree of fairness between flows that share the same path are vital
to the stable operation of the Internet (see [RFC2914] and
[RFC5405]).
DCCP has congestion control. For this reason the syslog over DTLS
over DCCP option is recommended in preference to the syslog over the
DTLS over UDP option. Implementations of syslog over DTLS over DCCP
MUST support CCID 3 and SHOULD support CCID 2 to ensure
interoperability.
The congestion control considerations from section 4.3 of [RFC5426]
also apply to syslog over DTLS over udp.
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7. Security Policies
Syslog transport over DTLS has been designed to minimize the security
and operational differences for environments where both [RFC5425] and
syslog over DTLS are supported. The security policies for syslog
over DTLS are the same as those described in [RFC5425].
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8. IANA Consideration
IANA is requested to assign a registered UDP and DCCP port number for
syslog over DTLS. The same value as for syslog over TLS (6514) is
requested.
IANA is requested to assign the service code SYLG to syslog for use
with DCCP. The allocation in the service code registry should be as
follows:
1398361159 SYLG Syslog Protocol [RFCTBD]
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9. Security Considerations
The security considerations in [RFC5425], [RFC5246] and [RFC4347]
apply to this document.
9.1. DTLS Renegotiation
TLS and DTLS renegotiation may be vulnerable to attacks described in
[RFC5746]. Although RFC 5746 provides a fix for some of the issues,
renegotiation can still cause problems for applications since
connection security parameters can change without the application
knowing it. Therefore it is RECOMMENDED that renegotiation be
disabled for syslog over DTLS. If renegotiation is allowed then the
specification in RFC 5746 MUST be followed and the implementation
MUST make sure that the connection still has adequate security and
that any identities extracted from client and server certificates do
not change during renegotiation.
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10. Acknowledgements
The authors would like to thank Wes Hardaker for his review on this
proposal and contributing his valuable suggestions on the use of
DTLS. Thanks also to Pasi Eronen, David Harrington, Chris Lonvick,
Eliot Lear, Anton Okmyanskiy, Juergen Schoenwaelder, Richard Graveman
and members of the syslog working group for their comments,
suggestions and review.
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11. References
11.1. Normative References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram
Congestion Control Protocol (DCCP)", RFC 4340, March 2006.
[RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5238] Phelan, T., "Datagram Transport Layer Security (DTLS) over
the Datagram Congestion Control Protocol (DCCP)",
RFC 5238, May 2008.
[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.
[RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009.
[RFC5425] Miao, F., Ma, Y., and J. Salowey, "Transport Layer
Security (TLS) Transport Mapping for Syslog", RFC 5425,
March 2009.
[RFC5426] Okmianski, A., "Transmission of Syslog Messages over UDP",
RFC 5426, March 2009.
[RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,
"Transport Layer Security (TLS) Renegotiation Indication
Extension", RFC 5746, February 2010.
11.2. Informative References
[I-D.ietf-syslog-sign]
Kelsey, J., Callas, J., and A. Clemm, "Signed syslog
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Messages", draft-ietf-syslog-sign-29 (work in progress),
December 2009.
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41,
RFC 2914, September 2000.
[RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines
for Application Designers", BCP 145, RFC 5405,
November 2008.
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Authors' Addresses
Joseph Salowey
Cisco Systems, Inc.
2901 3rd. Ave
Seattle, WA 98121
USA
Email: jsalowey@cisco.com
Tom Petch
Engineering Networks Ltd
18 Parkwood Close
Lymm, Cheshire WA13 0NQ
UK
Email: tomSecurity@network-engineer.co.uk
Rainer Gerhards
Adiscon GmbH
Mozartstrasse 21
Grossrinderfeld, BW 97950
Germany
Email: rgerhards@adiscon.com
Hongyan. Feng
Huaweisymantec Technologies
20245 Steven Creek Blvd
Cupertino, CA 95014
Email: fhyfeng@gmail.com
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