Internet Engineering Task Force (IETF) J. Salowey
Request for Comments: 6012 Cisco Systems, Inc.
Category: Standards Track T. Petch
ISSN: 2070-1721 Engineering Networks Ltd
R. Gerhards
Adiscon GmbH
H. Feng
Huaweisymantec Technologies
October 2010
Datagram Transport Layer Security (DTLS) Transport Mapping for Syslog
Abstract
This document describes the transport of syslog messages over the
Datagram Transport Layer Security (DTLS) protocol. It provides a
secure transport for syslog messages in cases where a connectionless
transport is desired.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6012.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Salowey, et al. Standards Track [Page 1]
RFC 6012 DTLS Transport Mapping for Syslog October 2010
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Security Requirements for Syslog . . . . . . . . . . . . . . . 4
4. Using DTLS to Secure Syslog . . . . . . . . . . . . . . . . . 4
5. Protocol Elements . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Transport . . . . . . . . . . . . . . . . . . . . . . . . 5
5.2. Port and Service Code Assignment . . . . . . . . . . . . . 5
5.3. Initiation . . . . . . . . . . . . . . . . . . . . . . . . 5
5.3.1. Certificate-Based Authentication . . . . . . . . . . . 6
5.4. Sending Data . . . . . . . . . . . . . . . . . . . . . . . 6
5.4.1. Message Size . . . . . . . . . . . . . . . . . . . . . 7
5.5. Closure . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Congestion Control . . . . . . . . . . . . . . . . . . . . . . 8
7. Security Policies . . . . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9.1. DTLS Renegotiation . . . . . . . . . . . . . . . . . . . . 9
9.2. Message Loss . . . . . . . . . . . . . . . . . . . . . . . 9
9.3. Private Key Generation . . . . . . . . . . . . . . . . . . 9
9.4. Trust Anchor Installation and Storage . . . . . . . . . . 9
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative References . . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . . 11
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RFC 6012 DTLS Transport Mapping for Syslog October 2010
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 (DTLS) protocol [RFC4347].
The Datagram Transport Layer Security (DTLS) protocol [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 the Datagram Congestion Control Protocol
(DCCP) [RFC4340]. This memo defines both options, namely syslog over
DTLS over UDP, and syslog over DTLS over DCCP.
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.
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, [RFC5848] 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 Transport Layer Security (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 6514 has been allocated as the default port for
syslog over DTLS as defined in this document. The service code SYLG
(1398361159) 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 used, 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. The transport sender MUST NOT
send any syslog messages before the DTLS handshake has successfully
completed.
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RFC 6012 DTLS Transport Mapping for Syslog October 2010
Implementations MUST support DTLS 1.0 [RFC4347] and MUST support the
mandatory to implement cipher suite, which is
TLS_RSA_WITH_AES_128_CBC_SHA as specified in [RFC5246]. If
additional cipher suites are supported, then implementations MUST NOT
negotiate a cipher suite that employs NULL integrity or
authentication algorithms.
Where privacy is REQUIRED, then implementations must either negotiate
a cipher suite that employs a non-NULL encryption algorithm or else
achieve privacy by other means, such as a physically secured network.
However, as [RFC5424], Section 8, points out, "In most cases, passing
clear-text messages is a benefit to the operations staff if they are
sniffing the packets from the wire", and so where privacy is not a
requirement, then it is advantageous to use a NULL encryption
algorithm.
5.3.1. Certificate-Based Authentication
The mandatory to implement cipher suites for DTLS use certificates
[RFC5280] to authenticate peers. Both the syslog transport sender
(DTLS client) and the 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:
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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 the syslog [RFC5424] protocol.
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], a DTLS record MUST NOT span
multiple datagrams. When mapping onto different transports, DTLS has
different record size limitations. For UDP, see Section 3.2 of
[RFC5426]. For DCCP, the application implementer SHOULD determine
the maximum record size allowed by the DTLS protocol running over
DCCP, as specified in [RFC4340]. The message size SHOULD NOT exceed
the DTLS maximum record size limitation of 2^14 bytes. To be
consistent with [RFC5425], 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.
See Appendix A.2 of [RFC5424] for implementation guidance on message
length, including fragmentation.
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
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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 are a component of TLS and so of DTLS, they,
like all alerts, are not retransmitted by DTLS and so may be lost
over an unreliable network.
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 establishing 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. If DCCP is available, syslog over DTLS
over DCCP is RECOMMENDED in preference to syslog over DTLS over UDP.
Implementations of syslog over DTLS over DCCP MUST support Congestion
Control Identifier (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.
7. Security Policies
Syslog transport over DTLS has been designed to minimize the security
and operational differences for environments where both syslog over
TLS [RFC5425] and syslog over DTLS are supported. The security
policies for syslog over DTLS are the same as those described in
[RFC5425], and all the normative requirements of Section 5 of
[RFC5425] apply.
8. IANA Considerations
IANA has assigned a registered UDP and DCCP port number for syslog
over DTLS. The values are the same as for syslog over TLS. That is,
the registry has been updated as follows:
syslog-tls 6514/udp syslog over DTLS [RFC6012]
syslog-tls 6514/dccp syslog over DTLS [RFC6012]
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IANA has assigned the service code SYLG to syslog for use with DCCP.
The allocation in the Service Code subregistry of the Datagram
Congestion Control Protocol (DCCP) Parameters registry is as follows:
1398361159 SYLG Syslog Protocol [RFC6012]
9. Security Considerations
The security considerations in [RFC4347], [RFC5246], [RFC5425], and
[RFC5280] 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.
9.2. Message Loss
The transports described in this document are unreliable. It is
possible for messages to be lost or removed by an attacker without
the knowledge of the receiver. [RFC5424] notes that implementers who
wish a lossless stream should be using tls/tcp as their transport.
In addition, the use of signed syslog messages [RFC5848] can also
provide an indication of message loss.
9.3. Private Key Generation
Transport receiver and transport sender implementations often
generate their own key pairs. An inadequate random number generator
(RNG) or an inadequate pseudo-random number generator (PRNG) to
generate these keys can result in little or no security. See
[RFC4086] for random number generation guidance.
9.4. Trust Anchor Installation and Storage
Trust anchor installation and storage is critical. Transmission of a
trust anchor, especially self-signed certificates used as trust
anchors, from transport receiver to transport sender for installation
requires one or more out-of-band steps. Care must be taken to ensure
the installed trust anchor is in fact the correct trust anchor. The
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RFC 6012 DTLS Transport Mapping for Syslog October 2010
fingerprint mechanism mentioned in Section 5.3.1 can be used by the
transport sender to ensure the transport receiver's self-signed
certificate is properly installed. Trust anchor information must be
securely stored. Changes to trust anchor information can cause
acceptance of certificates that should be rejected.
10. Acknowledgements
The authors would like to thank Wes Hardaker for his review of this
proposal and for 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, the members of the syslog working group, and the members of
the IESG for their review, comments, and suggestions.
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.
Salowey, et al. Standards Track [Page 10]
RFC 6012 DTLS Transport Mapping for Syslog October 2010
[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
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41,
RFC 2914, September 2000.
[RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness
Requirements for Security", BCP 106, RFC 4086, June 2005.
[RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines
for Application Designers", BCP 145, RFC 5405,
November 2008.
[RFC5848] Kelsey, J., Callas, J., and A. Clemm, "Signed Syslog
Messages", RFC 5848, May 2010.
Salowey, et al. Standards Track [Page 11]
RFC 6012 DTLS Transport Mapping for Syslog October 2010
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 Stevens Creek Blvd.
Cupertino, CA 95014
EMail: fhyfeng@gmail.com
Salowey, et al. Standards Track [Page 12]
RFC, FYI, BCP