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Comments

1. For those who are interested, this is what has happened. SHA-0 is a cryptographic hash function; a function that when given an input of arbitrary size will produce an output of some fixed size.

   A cryptographic hash function should satisfy 3 properties: given the value of a hash, it should be infeasible to find the input that produced the hash; given any input x, it should be infeasible to find another input x' such that the hashes of x and x' match; it should be infeasible to find two different inputs that have the same hash value.

   The last property is what has been broken. The researchers have found what people call a collision. They have done this without trying all possibilities.

   by ramanan on August 17 2004, 4:23 am   #

2. Moreover, once you find a collision, finding a “significant collision” only takes twice as long (expected time) as if took you to find the original collision…I thought SHA-0 was not one of the premier hashing functions anyways though. (i.e. the hash values are too small or something like that)...Do you know if the problems with SHA-0 extend to the other SHA’s (e.g. SHA-256?)

   by Ryan on August 17 2004, 2:47 pm   #

3. SHA-0 isn’t used at all I think. There was a weakness found in SHA that allowed for an attack in 2⁶¹ steps, so it was replaced by SHA-1. This attack is a variation of the attack originally described. You can read more about SHA if you are so inclined.

   by ramanan on August 17 2004, 8:57 pm   #

4. I see…it is 160-bits…I mistakenly thought it was 80-bits, which is way too short. But the 160-bits give you the brute-force-and-ignorance collision finding algorithm in about 2⁸⁰ steps (i.e. birthday paradox). So that is probably where I saw the 80 in a description and just didn’t read it well enough. And of course if had 80-bit hash values (instead of 160-bits) then that is obviously way too small. (~ 2⁴⁰ steps to find a collision).

   by Ryan on August 17 2004, 9:20 pm   #

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