A Transport Layer Security (TLS) ClientHello Padding Extension
RFC 7685
| Document | Type |
RFC - Proposed Standard
(October 2015; No errata)
Updates RFC 5246
Was draft-ietf-tls-padding (tls WG)
|
|
|---|---|---|---|
| Last updated | 2015-10-21 | ||
| Replaces | draft-agl-tls-padding | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Joseph Salowey | ||
| Shepherd write-up | Show (last changed 2015-08-05) | ||
| IESG | IESG state | RFC 7685 (Proposed Standard) | |
| Consensus Boilerplate | Yes | ||
| Telechat date | |||
| Responsible AD | Stephen Farrell | ||
| Send notices to | (None) | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA action state | RFC-Ed-Ack | ||
Internet Engineering Task Force (IETF) A. Langley
Request for Comments: 7685 Google Inc
Updates: 5246 October 2015
Category: Standards Track
ISSN: 2070-1721
A Transport Layer Security (TLS) ClientHello Padding Extension
Abstract
This memo describes a Transport Layer Security (TLS) extension that
can be used to pad ClientHello messages to a desired size.
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/rfc7685.
Copyright Notice
Copyright (c) 2015 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 Standards Track [Page 1]
RFC 7685 TLS ClientHello Padding Extension October 2015
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 2
3. Padding Extension . . . . . . . . . . . . . . . . . . . . . . 2
4. Example Usage . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 3
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. Normative References . . . . . . . . . . . . . . . . . . . . 4
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4
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 one of these implementation bugs can be ameliorated by
making the ClientHello even larger. This is desirable given that
fully comprehensive patching of affected implementations is difficult
to achieve.
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.
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].
3. Padding Extension
A new extension type ("padding(21)") is defined and MAY be included
by the client in its ClientHello message.
enum {
padding(21), (65535)
} ExtensionType;
Langley Standards Track [Page 2]
RFC 7685 TLS ClientHello Padding Extension October 2015
The "extension_data" for the extension consists of an arbitrary
number of zero bytes. For example, the smallest "padding" extension
is four bytes long and is encoded as 0x00 0x15 0x00 0x00. A ten-byte
extension would include six bytes of "extension_data" and would be
encoded as:
00 15 00 06 00 00 00 00 00 00
|---| |---| |---------------|
| | |
| | \- extension_data: 6 zero bytes
| |
| \------------- 16-bit, extension_data length
|
\------------------- extension_type for padding extension
The client MUST fill the padding extension completely with zero
bytes, although the padding extension_data field may be empty.
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