Re: [websec] Pete Resnick's No Objection on draft-ietf-websec-key-pinning-19: (with COMMENT)

[Ryan Sleevi <[e-mail]>]

On Mon, Aug 4, 2014 at 5:49 PM, Pete Resnick <[e-mail]>
wrote:

> Pete Resnick has entered the following ballot position for
> draft-ietf-websec-key-pinning-19: No Objection
>
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> The document, along with other ballot positions, can be found here:
> http://datatracker.ietf.org/doc/draft-ietf-websec-key-pinning/
>
>
>
> ----------------------------------------------------------------------
> COMMENT:
> ----------------------------------------------------------------------
>
> 1: The first sentence is quite confusing. Might I suggest instead:
>
>    This document defines a new HTTP header that enables user agents
>    (UAs) to determine which Subject Public Key Info (SPKI) structures
>    will be present in the web host's certificate chain in future TLS
>    [RFC5246] connections.
>
> 2.1:
>
>    Public-Key-Directives = [ directive ] *( OWS ";" OWS [ directive ] )
>
> Are you sure that's correct? First of all, it may be completely empty.
> That seems like something you wouldn't want. Second of all, it allows for
> semicolons without directives between them, which may or may not be what
> you want. It's not clear to me why you made this semicolon-delimited
> instead of comma-delimited, which would be much more in line with the
> rest of HTTP. Then you'd simply get:
>
>    Public-Key-Directives = 1#directive
>

Correct. Supporting the #rule directive is NOT desired, because
intermediaries are allowed to perform coalescing of such headers, per RFC
7230 3.2.2

That is, as noted in
http://tools.ietf.org/html/draft-ietf-websec-key-pinning-19#section-2.3.1 ,
third paragraph, only the first PKP header field or PKP-RO header field
MUST be processed.

The concern here is header injection (from hostile script on a host), and
to provide a consistent declaration of directive processing. For example,
if multiple instances of the Public-Key-Directives headers were processed,
a hostile script (such as through obtaining code exploitation on the
server) would be able to set additional pins to a certificate/set of
certificates under the attacker's control.


>
> But if you insist on semicolons, you want either:
>
>    Public-Key-Directives = directive *( OWS ";" OWS directive )
>
> or if you want to allow for empty elements:
>
>    Public-Key-Directives = *( ";" OWS ) directive *( OWS ";" [ OWS
>     directive ] )
>
> If the following is acceptable:
>
>    Public-Key-Directives: ;;;;;
>
> then your original is fine.
>

Correct. The ABNF here is the functionally same as Section 6.1 of RFC 6797.
However, 6797 predates the HTTPBis work, in particular, the work in Section
7 of RFC 7230 to specify better semantics for #rule.

Compared to 2616 (which allowed ",,," #rule combinations), 7230 Section 7
adopts language similar to what you've proposed.

This would be a breaking change to existing implementations (in that
headers previously declared valid would not be), but I think it would be
good (for consistency with 7230). Before making this change, I think it
would be good to get some feedback from the WG members to see if they also
agree.


>
> s/hahs/hash
>
> 10.1:
>
> Update 4627 to 7159
>
> I think W3C.REC-html401-19991224 is informative. This document says that
> you MUST NOT do what's in that document.
>
>
>