Public Key Pinning Extension for HTTP

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Document Type Active Internet-Draft (websec WG)
Last updated 2012-10-16
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: April 19, 2013                                 October 16, 2012

                 Public Key Pinning Extension for HTTP


   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

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
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   This Internet-Draft will expire on April 19, 2013.

Copyright Notice

   Copyright (c) 2012 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
   ( in effect on the date of

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   publication of this document.  Please review these documents
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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 embedded set of pins.  Although
   effective, this does not scale.  This proposal addresses the scale

   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

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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

   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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