Network Working Group A. Langley Internet-Draft Google Inc Expires: May 5, 2014 Nov 2013 A TLS padding extension draft-agl-tls-padding-01 Abstract This memo describes the a TLS extension that can be used to pad ClientHello messages to a desired size. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on May 5, 2014. Copyright Notice Copyright (c) 2013 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 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 Simplified BSD License. Langley Expires May 5, 2014 [Page 1] Internet-Draft TLS Padding Extension Nov 2013 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . . 4 3. Padding Extension . . . . . . . . . . . . . . . . . . . . . . . 5 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 5. Normative References . . . . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 Langley Expires May 5, 2014 [Page 2] Internet-Draft TLS Padding Extension Nov 2013 1. Introduction Successive TLS [RFC5246] versions have added support for more cipher suites and, over time, more TLS extensions have been defined. This has caused the size of the TLS ClientHello to grow and the additional size has caused some implementation bugs to come to light. At least some of these implementation bugs can be ameliorated by making the ClientHello even larger. This memo describes a TLS extension that can be used to pad a ClientHello to a desired size in order to avoid implementation bugs caused by certain ClientHello sizes. Langley Expires May 5, 2014 [Page 3] Internet-Draft TLS Padding Extension Nov 2013 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 May 5, 2014 [Page 4] Internet-Draft TLS Padding Extension Nov 2013 3. Padding Extension A new extension type (""padding(TBD)"") is defined and MAY be included by the client in its ClientHello message. enum { padding(TBD), (65535) } ExtensionType The client MUST fill the padding extension completely with zero bytes, although the padding extension may be empty. The server SHOULD verify that the extension is either empty or contains only zero bytes, in order to avoid allowing the padding extension contents to be used as a side-channel. (Although the length of the extension can still be used as such.) The server MUST NOT echo the extension. Langley Expires May 5, 2014 [Page 5] Internet-Draft TLS Padding Extension Nov 2013 4. IANA Considerations IANA is requested to assign an extension value for the padding extension from its ExtensionType registry. Langley Expires May 5, 2014 [Page 6] Internet-Draft TLS Padding Extension Nov 2013 5. 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. Langley Expires May 5, 2014 [Page 7] Internet-Draft TLS Padding Extension Nov 2013 Author's Address Adam Langley Google Inc Email: agl@google.com Langley Expires May 5, 2014 [Page 8]