[cabfpub] AIA chasing

Ryan Sleevi sleevi at google.com
Mon Apr 3 09:08:11 MST 2017

That is most unfortunate.

It doesn't look like the code in
https://gist.github.com/mozkeeler/29754494dcdb3b169483595283f29923 fully
accounts for the value of AIA with respect to finding alternative paths on
such connections. That is, it seems like it undercounts for situations such

Leaf -> Intermediate 1 -> Intermediate 2 -> Old CA
        -> Intermediate 1 -> Intermediate 2' -> New CA
        -> Intermediate 1' -> New CA

The analysis Mozilla performed only appeared to examine the end-entity
certificate, as noted in
https://bugzilla.mozilla.org/show_bug.cgi?id=399324#c80 . However, Chrome's
experience with AIA is that it is most useful for covering the root key
rollover and intermediate rollover scenarios. I can think of a number of CA
members who have exercised this code path, but such data was excluded from
your analysis.

I appreciate you looking into this matter, though, and for ensuring the
data and tools were publicly available in order to perform such an analysis.

An alternative methodology to examine would be to examine the supplied
chains from the subset of servers (or user error reports) for which you're
interested in, and determine whether there exists a path to a known Mozilla
trust anchor. For example, you could use the CCADB disclosures, crt.sh
dataset (which handedly already groups by ca_id), or directly from
Certificate Transparency log servers. For such situations where the server
did not supply a path that immediately resolved, but one or more paths was
known to Mozilla, you could examine whether or not the AIA identity
provided by the common elements in that path (even if the only common
element was the leaf) would have provided one or more intermediates known
to be valid.

I do hope you reconsider, because it does appear that the testing
methodology was flawed.

On Mon, Apr 3, 2017 at 10:51 AM, Gervase Markham via Public <
public at cabforum.org> wrote:

> Participants may be interested in some recent research we did on AIA
> chasing:
> https://bugzilla.mozilla.org/show_bug.cgi?id=399324#c80
> The upshot is that Firefox has no plans to implement this feature.
> Gerv
> _______________________________________________
> Public mailing list
> Public at cabforum.org
> https://cabforum.org/mailman/listinfo/public
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