[110464] in cryptography@c2.net mail archive
Re: PlayStation 3 predicts next US president
daemon@ATHENA.MIT.EDU (Allen)
Tue Dec 11 13:37:54 2007
Date: Mon, 10 Dec 2007 21:37:14 -0800
From: Allen <netsecurity@sound-by-design.com>
CC: cryptography@metzdowd.com
In-Reply-To: <5e01c29a0712101602i8d3fe0eof12662f466247a1d@mail.gmail.com>
silky wrote:
> On Dec 11, 2007 5:06 AM, Allen <netsecurity@sound-by-design.com> wrote:
>> What puzzles me in all this long and rather arcane discussion is
>> why isn't the solution of using a double hash - MD5 *and* SHA
>> whatever. The odds of find a double collision go way up.
>>
>> Some open source software people are already doing this. I've
>> played around with the sample files that are out there and find
>> an easy way to do this but I don't have either the horsepower or
>> skill to be at all definitive.
>>
>> My gut tells me that using two processes that use different
>> algorithms, even though compromised, will raise the bar so high
>> that it would be secure for a long time.
>>
>> At my skill level and horsepower I can't find even a single way
>> to do this with CRC32 and MD5. Granted, that certainly doesn't
>> mean a whole lot.
>
> Work has actually been done on this exact topic.
>
> One link is here: http://cryptography.hyperlink.cz/2004/otherformats.html
>
> I think there may be more; I'm not sure.
Thanks for the pointer. Very interesting and it proves that I
don't have the horsepower at this point. (Just wait until I build
that Microwulf! With the new quad core chips I should hit about
50 GigaFLOPS. And cheeep - less than 4K)
But my real point is that CRC32 while has only 2^16
possibilities, even SHA 1 with its degraded state has (IIRC) 2^55
and if we go to SHA 256 it has 2^256 possibilities.
Since MD5 and SHA 256 use two different algorithms the odds of
creating a double collision are tiny at this point.
So take your enhanced Tripwire like program and have it compute
two different hashes. Yes, you can create a collision in the MD5,
but can you also create a simultaneous collision in the SHA 256?
This is my point.
Best,
Allen
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