Re: [Acme] HPKP in ACME

I would definitely support removing ", and servers SHOULD emit pinning
headers", especially because of the footgun risk you indicated, but I think
there *is* some merit in continuing to recommend support for HPKP on the
client side.

On Mon, Feb 13, 2017 at 12:33 PM Jacob Hoffman-Andrews <jsha@eff.org> wrote:

> Martin brought up a section I've been considering removing:
>
> > Clients SHOULD support HTTP public key pinning [RFC7469], and servers
> SHOULD emit pinning headers.
>
> Here's my reasoning:
>
> - Public key pinning isn't implemented in most HTTPS libraries outside
> of browsers, so this is a considerable burden on implementers.
> - Public key pinning carries a fairly high risk of footgunning. The
> consequence of a failed pin for a CA that serves many ACME clients would
> be that some of those clients would fail to renew their certs, causing
> cascading breakage.
> - There is relatively little confidential information conveyed in ACME,
> and there are other defenses built into ACME (like including the account
> key as part of the challenge data), so HPKP is not strongly necessary.
>
> Any objections?
>
> PR to remove: https://github.com/ietf-wg-acme/acme/pull/244
>
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