4 ms·

You are. One of the defining properties of a cryptographic hash is that you cannot easily deduce the input given the output, nor can you easily construct an inp

by orib 18y ago

You are. One of the defining properties of a cryptographic hash is that you cannot easily deduce the input given the output, nor can you easily construct an input to produce a given output. (see the overview at http://en.wikipedia.org/wiki/Cryptographic_hash http://en.wikipedia.org/wiki/Cryptographic_hash) However, it's still possible to do a dictionary attack on the database of hashes ("is the hash of "password" the same as the user's password hash? yes? Bingo!")

rw 18y ago
Provided, of course, that P != NP.
- tptacek 18y ago
  Message digest functions are not, generally, number-theoretic.
  - cperciva 18y ago
    How is this relevant? The question of P ?= NP isn't limited to number-theoretic functions -- if P = NP then it is possible to find a preimage to any (polynomial time) hash function in polynomial time.
    - tptacek 18y ago
      You're right.
eru 18y ago
You should use individual salting for each password to make this at least a bit more difficult.