Expect-CT Extension for HTTP
draft-ietf-httpbis-expect-ct-04

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HTTP                                                            E. Stark
Internet-Draft                                                    Google
Intended status: Experimental                               May 19, 2018
Expires: November 20, 2018

                      Expect-CT Extension for HTTP
                    draft-ietf-httpbis-expect-ct-04

Abstract

   This document defines a new HTTP header field, named Expect-CT, that
   allows web host operators to instruct user agents to expect valid
   Signed Certificate Timestamps (SCTs) to be served on connections to
   these hosts.  When configured in enforcement mode, user agents (UAs)
   will remember that hosts expect SCTs and will refuse connections that
   do not conform to the UA's Certificate Transparency policy.  When
   configured in report-only mode, UAs will report the lack of valid
   SCTs to a URI configured by the host, but will allow the connection.
   By turning on Expect-CT, web host operators can discover
   misconfigurations in their Certificate Transparency deployments and
   ensure that misissued certificates accepted by UAs are discoverable
   in Certificate Transparency logs.

Note to Readers

   Discussion of this draft takes place on the HTTP working group
   mailing list (ietf-http-wg@w3.org), which is archived at
   https://lists.w3.org/Archives/Public/ietf-http-wg/ [1].

   Working Group information can be found at http://httpwg.github.io/
   [2]; source code and issues list for this draft can be found at
   https://github.com/httpwg/http-extensions/labels/expect-ct [3].

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 https://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."

Stark                   Expires November 20, 2018               [Page 1]
Internet-Draft                  Expect-CT                       May 2018

   This Internet-Draft will expire on November 20, 2018.

Copyright Notice

   Copyright (c) 2018 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Server and Client Behavior  . . . . . . . . . . . . . . . . .   5
     2.1.  Response Header Field Syntax  . . . . . . . . . . . . . .   5
       2.1.1.  The report-uri Directive  . . . . . . . . . . . . . .   6
       2.1.2.  The enforce Directive . . . . . . . . . . . . . . . .   6
       2.1.3.  The max-age Directive . . . . . . . . . . . . . . . .   7
       2.1.4.  Examples  . . . . . . . . . . . . . . . . . . . . . .   7
     2.2.  Server Processing Model . . . . . . . . . . . . . . . . .   7
       2.2.1.  HTTP-over-Secure-Transport Request Type . . . . . . .   8
       2.2.2.  HTTP Request Type . . . . . . . . . . . . . . . . . .   8
     2.3.  User Agent Processing Model . . . . . . . . . . . . . . .   8
       2.3.1.  Expect-CT Header Field Processing . . . . . . . . . .   8
       2.3.2.  HTTP-Equiv <meta> Element Attribute . . . . . . . . .   9
       2.3.3.  Noting Expect-CT  . . . . . . . . . . . . . . . . . .   9
       2.3.4.  Storage Model . . . . . . . . . . . . . . . . . . . .   9
     2.4.  Evaluating Expect-CT Connections for CT Compliance  . . .  10
   3.  Reporting Expect-CT Failure . . . . . . . . . . . . . . . . .  11
     3.1.  Generating a violation report . . . . . . . . . . . . . .  11
     3.2.  Sending a violation report  . . . . . . . . . . . . . . .  13
     3.3.  Receiving a violation report  . . . . . . . . . . . . . .  14
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
     4.1.  Maximum max-age . . . . . . . . . . . . . . . . . . . . .  15
     4.2.  Avoiding amplification attacks  . . . . . . . . . . . . .  15
   5.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  15