Re: [CFRG] Threshold Sig required - Random bit flip hits Cert Transparency Log

Phillip Hallam-Baker <phill@hallambaker.com> Thu, 08 July 2021 16:37 UTC

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From: Phillip Hallam-Baker <phill@hallambaker.com>
Date: Thu, 08 Jul 2021 12:36:59 -0400
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To: Tim Dierks <tim@dierks.org>
Cc: IRTF CFRG <cfrg@irtf.org>
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Subject: Re: [CFRG] Threshold Sig required - Random bit flip hits Cert Transparency Log
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On Thu, Jul 8, 2021 at 11:21 AM Tim Dierks <tim@dierks.org> wrote:

> On Thu, Jul 8, 2021 at 12:54 AM Phillip Hallam-Baker <
> phill@hallambaker.com> wrote:
>
>> If you have a single CPU, you will always have the possibility of an
>> error. Not all faults are transient. If the data was corrupted in
>> the cache, it is going to be corrupted both times it is hashed. And
>> optimizing compilers can screw you in really imaginative ways.
>>
>
> We will always have errors, that's the reason we have to take care. But I
> believe that errors like this can be detected and prevented from being
> committed/released using relatively straightforward redundant checks as
> illustrated. If you can identify in the flow described where a bit error
> could occur without detection, I'd be interested to know; we're protecting
> a lot of data using similar designs. The failure of a reproducible log is
> one thing; I'm very interested in avoiding errors when wrapping keys that
> might lead to large quantities of data being unrecoverable if not detected
> prior to commit.
>

The potential for loss of static data is something that has been of
great concern to me throughout. Data at Rest is a much harder problem than
data in transit precisely because of the fact that loss of data is usually
more serious than disclosure.

Ransomware works because nobody can take new pictures of the kids.


When encrypting data to a threshold group that the encryptor is a member
of, I perform a trial decryption using the threshold shares. But that does
not work for cases where the encryptor is not permitted to decrypt.