Public Key Pinning Extension for HTTP
RFC 7469

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Internet Engineering Task Force (IETF)                          C. Evans
Request for Comments: 7469                                     C. Palmer
Category: Standards Track                                      R. Sleevi
ISSN: 2070-1721                                             Google, Inc.
                                                              April 2015

                 Public Key Pinning Extension for HTTP

Abstract

   This document defines a new HTTP header that allows web host
   operators to instruct user agents to remember ("pin") the hosts'
   cryptographic identities over a period of time.  During that time,
   user agents (UAs) will require that the host presents a certificate
   chain including at least one Subject Public Key Info structure whose
   fingerprint matches one of the pinned fingerprints for that host.  By
   effectively reducing the number of trusted authorities who can
   authenticate the domain during the lifetime of the pin, pinning may
   reduce the incidence of man-in-the-middle attacks due to compromised
   Certification Authorities.

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/rfc7469.

Evans, et al.                Standards Track                    [Page 1]
RFC 7469          Public Key Pinning Extension for HTTP       April 2015

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.

Evans, et al.                Standards Track                    [Page 2]
RFC 7469          Public Key Pinning Extension for HTTP       April 2015

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   5
   2.  Server and Client Behavior  . . . . . . . . . . . . . . . . .   5
     2.1.  Response Header Field Syntax  . . . . . . . . . . . . . .   5
       2.1.1.  The Pin Directive . . . . . . . . . . . . . . . . . .   6
       2.1.2.  The max-age Directive . . . . . . . . . . . . . . . .   7
       2.1.3.  The includeSubDomains Directive . . . . . . . . . . .   7
       2.1.4.  The report-uri Directive  . . . . . . . . . . . . . .   7
       2.1.5.  Examples  . . . . . . . . . . . . . . . . . . . . . .   8
     2.2.  Server Processing Model . . . . . . . . . . . . . . . . .   9
       2.2.1.  HTTP-over-Secure-Transport Request Type . . . . . . .   9
       2.2.2.  HTTP Request Type . . . . . . . . . . . . . . . . . .   9
     2.3.  User Agent Processing Model . . . . . . . . . . . . . . .  10
       2.3.1.  Public-Key-Pins Response Header Field Processing  . .  10
       2.3.2.  Interaction of Public-Key-Pins and Public-Key-Pins-
               Report-Only . . . . . . . . . . . . . . . . . . . . .  11
       2.3.3.  Noting a Pinned Host - Storage Model  . . . . . . . .  11
       2.3.4.  HTTP-Equiv <Meta> Element Attribute . . . . . . . . .  13
     2.4.  Semantics of Pins . . . . . . . . . . . . . . . . . . . .  13
     2.5.  Noting Pins . . . . . . . . . . . . . . . . . . . . . . .  14
     2.6.  Validating Pinned Connections . . . . . . . . . . . . . .  15
     2.7.  Interactions with Preloaded Pin Lists . . . . . . . . . .  16
     2.8.  Pinning Self-Signed End Entities  . . . . . . . . . . . .  16
   3.  Reporting Pin Validation Failure  . . . . . . . . . . . . . .  16
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
     4.1.  Maximum max-age . . . . . . . . . . . . . . . . . . . . .  19
     4.2.  Using includeSubDomains Safely  . . . . . . . . . . . . .  20
     4.3.  Backup Pins . . . . . . . . . . . . . . . . . . . . . . .  21
     4.4.  Interactions With Cookie Scoping  . . . . . . . . . . . .  21
     4.5.  Hostile Pinning . . . . . . . . . . . . . . . . . . . . .  21
   5.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  22