Re: The fixed-point project

[Ludovic Courtès]

Mark H Weaver <address@hidden> skribis:

> Hi Ludovic,
>
> address@hidden (Ludovic Courtès) writes:
>
>> However, in theory, that doesn’t save us from trusting-trust
>> attacks [1]: the bootstrap GCC could contain a trap, such that the trap
>> is always preserved across recompilations of GCC, even if it’s absent
>> From the GCC source being compiled.
>>
>> David A. Wheeler’s thesis [2] addresses this topic.  Roughly, it shows
>> that a compiler can be tested for traps by relying on a “trusted”
>> compiler [3].
>
> I don't think this is an adequate summary of David's technique for
> defeating Thompson viruses.  Under his method, one needn't trust any
> single compiler.  Instead, one uses several different compilers to
> bootstrap a single compiler, and checking that the results of all of
> those bootstraps yield the same result.

Right.

> One need only trust that the first-stage compilers aren't _all_
> compromised with the same Thompson virus.  This is much more
> reasonable than expecting everyone to trust the Guix bootstrap
> tarballs.  In order to defeat this method, a Thompson virus would have
> to be sophisticated enough to hide itself in all of the compilers, and
> be able to jump from one compiler to another.

Yes, you’re right (I may have been fooled by the wording in
<http://www.dwheeler.com/trusting-trust/dissertation/html/wheeler-trusting-trust-ddc.html#4.2.Informal%20description%20of%20DDC>.)

In Guix we can use different variants of the bootstrap compiler to build
the tarballs, but in practice I suspect these would have to remain
variants of the same thing (GCC), not completely different compilers.

Ludo’.