Network Working Group A. Langley Internet-Draft Google Inc Intended status: Standards Track January 20, 2010 Expires: July 24, 2010 Transport Layer Security (TLS) Next Protocol Negotiation Extension draft-agl-tls-nextprotoneg-00 Abstract This document describes a Transport Layer Security (TLS) extension for application layer protocol negotiation. This allows the application layer to negotiate which protocol should be performed over the secure connection in a manner which avoids additional round trips and which is independent of the application layer protocols. 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. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on July 24, 2010. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of Langley Expires July 24, 2010 [Page 1] Internet-Draft TLS Next Protocol Negotiation January 2010 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4 3. Next Protocol Negotiation Extension . . . . . . . . . . . . . 5 4. Security considerations . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.1. Normative References . . . . . . . . . . . . . . . . . . . 9 7.2. Informative References . . . . . . . . . . . . . . . . . . 9 Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . . 10 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11 Langley Expires July 24, 2010 [Page 2] Internet-Draft TLS Next Protocol Negotiation January 2010 1. Introduction The use of TLS [RFC5246] over TCP [RFC0793] unavoidably adds at least a round trip to the time taken to establish a connection. By allowing the application layer to perform negotiation during that round trip one gains several advantages: Firstly, for various reasons, different application layer protocols are increasingly being carried over TLS using a small set of TCP port numbers, most often port 443. Rather than forcing systems administrators to use different IP addresses for every service, negotiation allows multiple services to exist with the same IP address. Secondly, newer versions of the same application layer protocol can perform discovery and avoid additional round trips after the TLS handshake. To illustrate the second point, consider HTTP [RFC2616] pipelining. Although it has seen little adoption because of interference from middleware, there is no reason not to use it over TLS where the transport is known to be pristine. However, even over TLS, the client cannot make pipelined requests until the first reply indicates that the remote peer supports the feature. If the client could negotiate HTTP/1.1 support before the first request, it could start sending pipelined requests immediately. Langley Expires July 24, 2010 [Page 3] Internet-Draft TLS Next Protocol Negotiation January 2010 2. Requirements Notation 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 [RFC2119]. Langley Expires July 24, 2010 [Page 4] Internet-Draft TLS Next Protocol Negotiation January 2010 3. Next Protocol Negotiation Extension A new extension type ("next_protocol_negotiation(TBD)") is defined and MAY be included by the client in its "ClientHello" message. If, and only if, the server sees this extension in the "ClientHello", it MAY choose to include the extension in its "ServerHello". enum { next_protocol_negotiation(TBD), (65535) } ExtensionType; A new handshake message type ("next_protocol(TBD)") is defined. If, and only if, the server included a "next_protocol_negotiation" extension in its ServerHello message, the client MUST send a "NextProtocol" message after its "ChangeCipherSpec" and before its "Finished" message. struct { opaque selected_protocol<0..255>; opaque padding<0..255>; } NextProtocol; The "extension_data" field of a "next_protocol_negotiation" in a "ClientHello" MUST be empty. The "extension_data" field in a "ServerHello" and the "NextProtocol" message contain opaque bytes to be used by the application layer to negotiate the application layer protocol. The format of this data is not specified in this draft. Unlike many other TLS extensions, this extension does not establish properties of the session, only of the connection. When session resumption or session tickets [RFC5077] are used, the previous contents of this extension are irrelevant and only the values in the new handshake messages are considered. For the same reasons, after a handshake has been performed for a given connection, renegotiations on the same connection MUST NOT include the "next_protocol_negotiation" extension. Langley Expires July 24, 2010 [Page 5] Internet-Draft TLS Next Protocol Negotiation January 2010 4. Security considerations The server's list of supported protocols is still advertised in the clear with this extension. This may be undesirable for certain protocols (such as Tor [tor]) where one could imagine that hostile networks would terminate any TLS connection with a server that advertised such a capability. In this case, clients may wish to opportunistically select a protocol that wasn't advertised by the server. However, the workings of such a scheme are outside the scope of this document. Langley Expires July 24, 2010 [Page 6] Internet-Draft TLS Next Protocol Negotiation January 2010 5. IANA Considerations This document requires IANA to update its registry of TLS extensions to assign an entry, referred herein as "next_protocol_negotiation". This document also requires IANA to update its registry of TLS handshake types to assign an entry, referred herein as "next_protocol". Langley Expires July 24, 2010 [Page 7] Internet-Draft TLS Next Protocol Negotiation January 2010 6. Acknowledgements This document benefited specifically from discussions with Wan-Teh Chang and Nagendra Modadugu. Langley Expires July 24, 2010 [Page 8] Internet-Draft TLS Next Protocol Negotiation January 2010 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008. 7.2. Informative References [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, "Transport Layer Security (TLS) Session Resumption without Server-Side State", RFC 5077, January 2008. [tor] Dingledine, R., Matthewson, N., and P. Syverson, "Tor: The Second-Generation Onion Router", August 2004. Langley Expires July 24, 2010 [Page 9] Internet-Draft TLS Next Protocol Negotiation January 2010 Appendix A. Changes To be removed by RFC Editor before publication Langley Expires July 24, 2010 [Page 10] Internet-Draft TLS Next Protocol Negotiation January 2010 Author's Address Adam Langley Google Inc Email: agl@google.com Langley Expires July 24, 2010 [Page 11]