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Historically hashes have been from a large set (say 256 characters) to a smaller set (256 bits).

Also, hash functions that are P-complete have no known parallel algorithm; they must be computed serially which ensures a certain amount of temporal cost in computing them.

Three questions:

  1. What is the technical term for hashes that map to a larger set than the domain?

  2. Are there any good P-complete hashes?

  3. Are there any good P-complete hashes that map to a larger set?

otus
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Chad Brewbaker
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    Encoding the string into a Game of Life grid and playing K rounds is an example of a P-complete hash. There must be a better one out there. –  Dec 19 '12 at 17:43
  • Combining a hash with an iterated stream cipher should do the trick. – CodesInChaos Dec 23 '12 at 23:10
  • http://crypto.stackexchange.com/questions/5061/are-there-secure-stream-ciphers-that-cannot-be-parallelized – Chad Brewbaker Dec 26 '12 at 17:32

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