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Re: Chinese Professor Cracks Fifth Data Security Algorithm (SHA1)
From: 3APA3A <3APA3A () SECURITY NNOV RU>
Date: Thu, 22 Mar 2007 00:48:09 +0300
Dear Blue Boar,
To be more precise, theoretically, if compare bruteforce with birthday,
160 bit birthday is equivalent to 81bit bruteforce by calculation
complexity (number of arithmetic operations).
I do not compare birthday vs bruteforce, I compare bruteforce vs
bruteforce and birthday vs birthday.
Practically, if you define some real values instead of mathematical
symbols, software algorithm implementation and physical limitations must
be also considered. Software implementation may be impossible or require
more CPU cycles to implement algorithm with less arithmetic operations
because, e.g. it requires more physical memory than you can address with
64bit integer :)
Thursday, March 22, 2007, 12:24:03 AM, you wrote to 3APA3A () SECURITY NNOV RU:
BB> My understanding that the kind of birthday attack under discussion would
BB> start at 80bits if SHA1 (at 160bits) were 100% secure. The attack
BB> under discussion is reported to reduce that to the neighborhood of
BB> 60something bits.
BB> I am not a mathematician though, so I would be perfectly willing to
BB> believe I was wrong about that.
BB> BB
BB> 3APA3A wrote:
Dear Blue Boar,
It's not clear if this 'crack' cam be applied to birthday attack. My
inmind computations were: because birthday attack requires ~square root
of N computations where bruteforce requires ~N/2, impact of 2000 times N
decrease for birthday is ~64 times faster. 64 = 2^6. Because complexity
is ~square root of possible combinations, it's equivalent of traditional
birthday attack, with 160(2*6)=148 bits hash (150 is my mistake in
inmind computations).
Of cause, since I completely wasted 10 years after obtaining Master
degree in Mathematics and 3 years after loosing last pencil I may be
completely wrong in computations :)
Wednesday, March 21, 2007, 9:48:55 PM, you wrote to 3APA3A () SECURITY NNOV RU:
BB> 3APA3A wrote:
I know meaning of 'hash function' term, I wrote few articles on
challengeresponse authentication and I did few hash functions
implementations for hashtables and authentication in FreeRADIUS and
3proxy. Can I claim my right for sarcasm after calling ability to
bruteforce 160bit hash 2000 times faster 'a crack'?
BB> Fair enough, your sarcasm tags didn't render properly in my MUA. I was
BB> fooled by you stating that the birthday attack would be 150 bits.
BB> BB

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 Re: Chinese Professor Cracks Fifth Data Security Algorithm (SHA1), (continued)
