Network Working Group J. Salowey Internet-Draft Cisco Systems, Inc. Intended status: Standards Track T. Petch Expires: August 8, 2010 Engineering Networks Ltd R. Gerhards Adiscon GmbH H. Feng February 4, 2010 Datagram Transport Layer Security (DTLS) Transport Mapping for Syslog draft-ietf-syslog-dtls-01.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 to IETF in full conformance with the provisions of BCP 78 and 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- Drafts. 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. 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Expires August 8, 2010 [Page 2] Internet-Draft DTLS Transport Mapping for Syslog February 2010 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 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. Security Policies . . . . . . . . . . . . . . . . . . . . . . 11 7. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 12 8. Security Considerations . . . . . . . . . . . . . . . . . . . 13 8.1. Cryptographic Level . . . . . . . . . . . . . . . . . . . 13 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 10.1. Normative References . . . . . . . . . . . . . . . . . . . 15 10.2. Informative References . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 Salowey, et al. Expires August 8, 2010 [Page 3] Internet-Draft DTLS Transport Mapping for Syslog February 2010 1. Introduction The Syslog protocol [RFC5424] is designed to run over different transports for different environments. Syslog over TLS [RFC5425] provides a combination of TCP transport reliability with TLS security [RFC5246]. However, TCP performance can be a problem when a network has a high rate of lost packets. In these circumstances, an operator might prefer using UDP to TCP as transport. Transmission of Syslog Messages over UDP [RFC5426] defines how to provide unreliable, non- secure datagram transport for SYSLOG. The datagram transport layer security protocol (DTLS) [RFC4347] is designed to meet the requirements of applications that need secure datagram transport, by combining UDP transport with TLS security. DTLS has been mapped onto different transports (i.e. UDP [RFC0768] and DCCP [RFC4340] ), to secure syslog in more situations. As the Internet best runs on the basis of appropriate resource sharing, SYSLOG over DTLS over DCCP [RFC5238] is defined in this document. For systems where DCCP is either not available or not usable (such as the aforementioned situation), DTLS over UDP is also defined. In those circumstances where reliability or ordering is important, SYSLOG over TLS is appropriate. Syslog over TLS does not provide application layer acknowledgements and therefore is not a fully reliable solution. Salowey, et al. Expires August 8, 2010 [Page 4] Internet-Draft DTLS Transport Mapping for Syslog February 2010 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: A "DTLS client" is an application that can initiate a DTLS Client Hello to a server. A "DTLS server" is an application that can receive a Client Hello from a client and reply with a Server Hello. The term "connection" used in this document is used to refer to a secure association between transport sender and transport receiver that permits the transmission of one or more SYSLOG messages within the lifetime of the connection. 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]. Salowey, et al. Expires August 8, 2010 [Page 5] Internet-Draft DTLS Transport Mapping for Syslog February 2010 3. Security Requirements for Syslog Syslog messages are secured in a hop-by-hop manner. The security requirements for Syslog are discussed in [RFC5425]. The following secondary threat is also considered in this document: o Denial of Service. 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. Salowey, et al. Expires August 8, 2010 [Page 6] Internet-Draft DTLS Transport Mapping for Syslog February 2010 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. Salowey, et al. Expires August 8, 2010 [Page 7] Internet-Draft DTLS Transport Mapping for Syslog February 2010 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 delivered in order when mapping on 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 connection state so messages may be lost. When TCP is used syslog over DTLS MUST NOT be used. If a secure transport is required with TCP then the appropriate mechanism is syslog over TLS. 5.2. Port 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. 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. TLS typically uses certificates [RFC5280] to authenticate peers. Salowey, et al. Expires August 8, 2010 [Page 8] Internet-Draft DTLS Transport Mapping for Syslog February 2010 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 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 [RFC5425] SHALL be implemented. Both transport receiver and transport sender implementations MUST provide means to generate a key pair and self-signed certificate in the case that a key pair and certificate are not available through another mechanism. The transport receiver and transport sender SHOULD provide mechanisms to record the end-entity certificate for the purpose of correlating it 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. Salowey, et al. Expires August 8, 2010 [Page 9] Internet-Draft DTLS Transport Mapping for Syslog February 2010 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. 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 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 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. Salowey, et al. Expires August 8, 2010 [Page 10] Internet-Draft DTLS Transport Mapping for Syslog February 2010 6. 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]. Salowey, et al. Expires August 8, 2010 [Page 11] Internet-Draft DTLS Transport Mapping for Syslog February 2010 7. 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. Salowey, et al. Expires August 8, 2010 [Page 12] Internet-Draft DTLS Transport Mapping for Syslog February 2010 8. Security Considerations The security considerations in [RFC5425], [RFC5246] and [RFC4347] apply to this document. 8.1. 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. An exiting DTLS session MUST NOT be reused if its protection does not match the minimum policy requirements of the new SYSLOG over DTLS session request. Salowey, et al. Expires August 8, 2010 [Page 13] Internet-Draft DTLS Transport Mapping for Syslog February 2010 9. 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 and Eliot Lear and members of the Syslog working group for their comments, suggestions and review. Salowey, et al. Expires August 8, 2010 [Page 14] Internet-Draft DTLS Transport Mapping for Syslog February 2010 10. References 10.1. 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. 10.2. Informative References [I-D.ietf-syslog-sign] Kelsey, J., Callas, J., and A. Clemm, "Signed syslog Messages", draft-ietf-syslog-sign-29 (work in progress), December 2009. [RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, Salowey, et al. Expires August 8, 2010 [Page 15] Internet-Draft DTLS Transport Mapping for Syslog February 2010 RFC 2914, September 2000. [RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines for Application Designers", BCP 145, RFC 5405, November 2008. Salowey, et al. Expires August 8, 2010 [Page 16] Internet-Draft DTLS Transport Mapping for Syslog February 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 Email: fhyfeng@gmail.com Salowey, et al. Expires August 8, 2010 [Page 17]