If the hash algorithm is properly designed and distributes the hashes uniformly over the output space, "finding a hash collision" by random guessing is.

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Presentation transcript:

If the hash algorithm is properly designed and distributes the hashes uniformly over the output space, "finding a hash collision" by random guessing is exceedingly unlikely (it's more likely that a million people will correctly guess all the California Lottery numbers every day for a billion trillion years). This astonishing fact is due to the astonishingly large number of possible hashes available: a 128-bit hash can have 3.4 x 10^38 possible values, which is: 340,282,366,920,938,463,463,374,607,431,768,211,456 possible hashes

atoms in the universe = 1078 to just under 1081 = 1 gig numbers / sec 1 gig = 10^9 = 2^30 128 bit will take 2^98 secs = 2^73 years = 10^20 years 100,000,000,000,000,000,000 years (1 year = 2^25 secs) atoms in the universe = 1078 to just under 1081 = i.e. 2246 to 2256

Hash collisions Thought to be impossible Only one known so far for a “good” algorithm MD5 hash collision

SHA-1: 160 bit hash Start with 512 bit blocks of input, pad it if needed. Expand to 80 32-bit subkeys (Wt) Initialize some hash blocks (A, B, …E) Use input to generate Wt, Kt is a constant. F is a changeable functions, constructed from shifts, and XORs. Do 80 rounds. Then use more input. Can be made to be fast.