Re: $10,000 CertainKey Challange Awarded

From: WinTerMiNator (me_at_privacy.net)
Date: 02/19/05 

Date: Sat, 19 Feb 2005 13:26:40 +0100

"Gregory G Rose" <ggr@qualcomm.com> a écrit dans le message de news:
cv62bl$15q@qualcomm.com...
> In article <37n34aF5fgc69U1@individual.net>,
> WinTerMiNator <me@privacy.net> wrote:
>>- Use both, concatenate MD5+SHA1 of same file. Works also with SHA1+TIGER
>>or
>>SHA256+GOST... Unlikely that a collision for a given hash also collides
>>for
>>the second one!
>
> Intuitively obvious, and completely incorrect.
>
> Greg.
Hello Greg,

- First, the fact to concatenate two hashes increase the difficulty of
"birthday attack": for example, with SHA1+TIGER one would need to generate
~2^((160+192)/2) = 2^176 documents to have a ~0.5 probability to find a
collision.
- Secondly, the best choices here are to concatenate hashes algorithms
coming from different origins: MD5+SHA1 is the "bad" choice, since both are
"descendents" of MD4 and might suffer of the same kind of defect. SHA1+TIGER
or SHA256+GOST (the hash Russian standard, not the cipher one) are of
different origins and are probably not sensitive to the same attack.

Now that I have developed my thoughts, could you develop your "completely
incorrect"?

Regards, 

-- 
Michel Nallino aka WinTerMiNator
http://www.winterminator.fr.st (Internet et sécurité)
http://www.gnupgwin.fr.st (GnuPG pour Windows)
Adresse e-mail invalide; pour me contacter:
http://www.cerbermail.com/?vdU5HHs5WG

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