[Trans] White out (was Re: Reviving Redaction)

[Rob Stradling <[e-mail]>]

I think the "white out" proposal that was discussed at the CT Policy 
Days is likely to be far more controversial than the various redaction 
proposals.

"White out" proposes a mechanism for removing or omitting entire 
certificates from logs whilst still "proving" that those certificates 
are "included".  Relying parties have to trust the log to only "white 
out" certs for good reasons.  ISTM that this defeats most of the purpose 
of CT!

 From https://tools.ietf.org/html/rfc6962#section-1...
   "Certificate transparency aims to mitigate the problem of misissued
    certificates by providing publicly auditable, append-only, untrusted
    logs of all issued certificates."

ISTM that supporting "white out" would turn that sentence into this...
   "Certificate transparency aims to mitigate the problem of misissued
    certificates by providing publicly auditable, modifiable, trusted
    logs of some issued certificates."

That sounds not too dissimilar to the WebPKI minus CT!

On 06/03/17 22:26, Jeremy Rowley wrote:
> On the CT days, there was an emphasis on a distinction between white washing
> a cert (removing it from CT) and redaction. Is the white washing in scope
> for the Trans list and this discussion or should it be separate?
>
> I ask because two of the main arguments cited for redaction tend to be:
> 1) Network/New project mapping reveals
> 2) Inclusion if PII in logged certs
>
> If white washing address the second concern, a specification around that
> process could eliminate a good deal of the push for redaction.
>
>
> -----Original Message-----
> From: Trans [mailto:[e-mail]] On Behalf Of Rob Stradling
> Sent: Monday, March 6, 2017 2:39 PM
> To: Ben Laurie <[e-mail]>
> Cc: [e-mail]; Peter Bowen <[e-mail]>
> Subject: Re: [Trans] Reviving Redaction
>
> On 06/03/17 21:22, Ben Laurie wrote:
>> I think you can waste a lot of brainpower on redaction, but really the
>> answer is: if you don't want to publish your names, then don't use a
>> mechanism that requires you to.
>
> I agree that that's the ideal answer, but as we've seen, there is resistance
> to that answer from various participants in the CT ecosystem.
>
>> There are alternatives: name-constrained sub-CAs.
>
> We removed that option from 6962-bis.  It's now in
> draft-strad-trans-redaction, but IIRC the Chrome team hinted that they're
> unlikely to ever support it (at least in its current form).
>
>> Private CAs. You can even have private CT to go along with them.
>
> Private CAs don't suit every use case, AFAIK.
>
>> Why mess up a protocol whose intent is to show everything?
>
> Because Security and Useability aren't always in perfect harmony?
>
> Much as I'd love to stop wasting brainpower on redaction, I think it's a
> conversation that needs to continue for now (although not indefinitely!)
>
>> On 6 March 2017 at 21:16, Rob Stradling wrote:
>>
>>     On 06/03/17 06:06, Peter Bowen wrote:
>>     <snip>
>>
>>         8) The only way to get the content of a full certificate is to
>>         have a
>>         full certificate.
>>
>>         Rationale: An alternative option is to have some sort of escrow
> key
>>         that can "unlock" a precertificate.
>>
>>
>>     In previous iterations of 6962-bis, we proposed a redaction
>>     mechanism that envisaged replacing domains labels with ?s in
>>     precertificates. That mechanism was deemed problematic by the Chrome
>>     team precisely because "The only way to get the content of a full
>>     certificate is to have a full certificate".
>>     What recourse does a domain owner have when they discover a
>>     precertificate for their domain space that they don't recognize?
>>     How do they figure out whether the (pre)cert was misissued or
>>     whether it was legitimately requested by a different team within
>>     their organization?
>>
>>     The redaction mechanism that's documented in
>>     https://tools.ietf.org/html/draft-strad-trans-redaction-01#section-3.3
>>
> <https://tools.ietf.org/html/draft-strad-trans-redaction-01#section-3.3>
>>     attempted to find a solution to this problem of recourse by swapping
>>     ?s for a hash of the unredacted domain.  However, this mechanism has
>>     also been deemed problematic, because it could be trivial to
>>     determine unredacted labels via dictionary attacks.
>>
>>     I think a "sort of escrow key" may be the only viable way to
>>     construct a redaction mechanism that is deemed non-problematic by
>>     everyone.
>>
>>         This quickly turns into 'where do we keep the escrow key?' and
>>         'who gets
>>         to access the escrow key?'.  If there is no such thing, then these
>>         questions don't exist.
>>
>>
>>     I think these questions will need to be both asked and answered,
>>     although I'd be delighted to be proved wrong.
>>
>>         Do others agree that these are true and can be used as givens for
>>         reviewing any proposed designs?
>>
>>
>>     Your other points all LGTM.

-- 
Rob Stradling
Senior Research & Development Scientist
COMODO - Creating Trust Online