Public Key Pinning Extension for HTTP
draft-ietf-websec-key-pinning-01

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Document Type Active Internet-Draft (websec WG)
Last updated 2011-12-09 (latest revision 2011-11-30)
Replaces draft-evans-palmer-key-pinning
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Web Security                                                    C. Evans
Internet-Draft                                                 C. Palmer
Intended status: Standards Track                            Google, Inc.
Expires: June 11, 2012                                  December 9, 2011

                 Public Key Pinning Extension for HTTP
                    draft-ietf-websec-key-pinning-01

Abstract

   This memo describes an extension to the HTTP protocol allowing web
   host operators to instruct user agents (UAs) to remember ("pin") the
   hosts' cryptographic identities for a given period of time.  During
   that time, UAs will require that the host present a certificate chain
   including at least one Subject Public Key Info structure whose
   fingerprint matches one or more of the pinned fingerprints for that
   host.  By effectively reducing the scope of 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 and other authentication errors and
   attacks.

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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on June 11, 2012.

Copyright Notice

   Copyright (c) 2011 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

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   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.

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1.  Introduction

   We propose a new HTTP header to enable a web host to express to user
   agents (UAs) which Subject Public Key Info (SPKI) structure(s) UAs
   MUST expect to be present in the host's certificate chain in future
   connections using TLS (see [rfc-5246]).  We call this "public key
   pinning".  At least one user agent (Google Chrome) has experimented
   with shipping with a user-extensible embeded set of pins.  Although
   effective, this does not scale.  This proposal addresses the scale
   problem.

   Deploying public key pinning safely will require operational and
   organizational maturity due to the risk that hosts may make
   themselves unavailable by pinning to a SPKI that becomes invalid.
   (See Section 3.)  We believe that, with care, host operators can
   greatly reduce the risk of MITM attacks and other false-
   authentication problems for their users without incurring undue risk.

   We intend for hosts to use public key pinning together with HSTS (as
   defined in [hsts-draft], but is possible to pin keys without
   requiring HSTS.

   This draft is being discussed on the WebSec Working Group mailing
   list, websec@ietf.org.

1.1.  Requirements Language

   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 [rfc-2119].

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2.  Server and Client Behavior

2.1.  Response Header Field Syntax

   To set a pin, hosts use a new HTTP header field, Public-Key-Pins, in
   their HTTP responses.  Figure 1 describes the syntax of the header
   field.

   Public-Key-Pins = "Public-Key-Pins" ":" LWS directives

   directives      = max-age LWS ";" LWS pins
                     / pins LWS ";" LWS max-age

   max-age         = "max-age" LWS "=" LWS delta-seconds

   pins            = pin
                     / pin LWS ";" LWS pins

   pin             = "pin-" token LWS "=" LWS quoted-string
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