[websec] Certificate Pinning via HSTS

[Chris Palmer <[e-mail]>]

Hi all,

Chris Evans and I work at Google on the Chrome security team. We have
devised this specification for a new extension to Strict Transport
Security to allow site operators to "pin" certificates: UAs will
require that TLS connections be validated with at least one of the
public keys identified in the new "pins" directive in the HSTS header.
(Sites can pin to one or more public keys in end entity, subordinate
CA, and/or root CA certificates, for flexibility and disaster
recovery.)

We hope that this mechanism opens up the benefits of certificate
pinning to more sites. Currently, Chrome can "pre-load" HSTS behavior
and certificate pins for sites, but the mechanism for doing this
(email us!) does not scale.

We eagerly anticipate your comments, questions, concerns, et c. As you
can see from the Ideas section, there are some unanswered questions
about the behavior of UAs and hosts, and possible extensions to the
policy.