[cabfpub] Issuance of certificates for keys reported as compromised

Ryan Sleevi sleevi at google.com
Tue Aug 21 12:34:06 MST 2018


I seem to recall we've discussed this before. There are a number of
practical challenges with this, and that any reasonable proposal would need
to provide interoperable guidance for. In short, it was substantial work,
for questionable gain, and while it sounds sensible, the devil is in the
details.

We need to define what a compromised key is, how it was reported, and how
it was determined. Without these basic things, you have the potential for
malicious DoS. For example, we know of some CAs that revoke certificates as
compromised even with faulty demonstration of proof, or insufficient proof.
We've had substantial discussions about what counts as reasonable proof
versus not - e.g. the signing of nonces or the like.

You then have to have CAs consistently reporting (e.g. through CRLs and
OCSP) the reason for revocation. All CAs would need to check all other CAs,
or there would need to be some meta-service to aggregate. If there is an
aggregated metaservice, you have to determine how to authenticate that
metaservice and its information - it becomes a single point of attack for
DoS.

Once you've built a system that allows revoking an entire key off the
Internet, you then have to deal with the policy ramifications of such a
centralized risk, such as giving a single avenue for political or external
attacks, such as revoking keys as 'compromised' if, for example, they are
used to host 'objectionable' content.

As you can see, these are just a few of the issues that present themselves.

On Tue, Aug 21, 2018 at 2:42 PM Tim Hollebeek via Public <
public at cabforum.org> wrote:

>
>
> Should we update the BRs to disallow issuance of certificates for key
> pairs that have been previously reported as compromised?
>
>
>
> I’m not aware of any CAs that currently do that check today, but it’s not
> that difficult to do.  It might be a sensible thing to add in the future.
> However it only works if all CAs do it, otherwise subscribers will just get
> their compromised key signed by a different CA.
>
>
>
> -Tim
> _______________________________________________
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> Public at cabforum.org
> https://cabforum.org/mailman/listinfo/public
>
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