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Re: On showing the weakness in the MD5 digest function and getting bitten by scalar contextby tachyon (Chancellor) |
on Aug 27, 2004 at 08:14 UTC ( [id://386281]=note: print w/replies, xml ) | Need Help?? |
To find another string that maps to the same digest (i.e. a collision in the MD5-space) should theoretically take 2^128 steps. Actually that is right and wrong. Hash collisions conform to the Birthday Paradox which says that if you have 23 people in a room there is a 50% probability that 2 people will share a birthday (have a collision). This 'paradox' applies to hashes as well. For example you have a 50% probability of a collision in a 32 bit hash after a mere 77163 tries (roughly 2^16 ie nothing like 2^32) UpdateCorrected technical inexactitude. The birthday paradox is the correct answer if you simply want a collision. To get a specific collision with a given digest it is not. cheers tachyon
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