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Re: Chinese Professor Cracks Fifth Data Security Algorithm (SHA-1)
From: Blue Boar <BlueBoar () thievco com>
Date: Wed, 21 Mar 2007 14:24:03 -0700

My understanding that the kind of birthday attack under discussion would
start at 80-bits if SHA-1 (at 160-bits) were 100% secure. The attack
under discussion is reported to reduce that to the neighborhood of
60-something bits.

I am not a mathematician though, so I would be perfectly willing to
believe I was wrong about that.


3APA3A wrote:
Dear Blue Boar,

It's  not  clear  if  this 'crack' cam be applied to birthday attack. My
in-mind 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
in-mind 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
challenge-response   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 160-bit 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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