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Computer Science

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  • $\begingroup$ The answer below seems correct, but far too advanced for anybody with these questions. A random function should give a different value every time you execute it. ie: h(5)=20, h(5)=12, h(5)=1032, ... If you guarantee that your 'random' function at least gives the same value for the same input then it's a hash, like: h(5)=20, h(5)=20, h(6)=7354, h(6)=7354, h(7)=89, ... $\endgroup$ Commented Apr 29, 2015 at 17:34
  • $\begingroup$ haha yeah I think you addressed one of my big questions (if the main goal of a hash function is to construct a repeatable uniform distribution then why not use an RNG with a set seed) but understanding the security concerns also helps explain why an actual implementation is more complicated. Thanks for the explanation! $\endgroup$ Commented Apr 29, 2015 at 17:40
  • $\begingroup$ The security concerns are about the ability to find collisions. You don't want a hash of "Rob Fielding is allowed to use the bazooka" to hash to the same value as "Mohammad Atta is allowed to use the bazooka". $\endgroup$ Commented Apr 29, 2015 at 17:42
  • $\begingroup$ hmm why not? (as opposed to two more random strings?) $\endgroup$ Commented Apr 29, 2015 at 17:44
  • $\begingroup$ As an example of how exactly that scenario could happen... say that your function works on the string from left to right, and the end hash is effectively the sum of the chars "llowed to use the bazooka". Everybody is now allowed to use the bazooka. If I try to change the input message, it should resolve to completely random garbage. It should be too hard to come up with a valid message that hashes with the original. $\endgroup$ Commented Apr 29, 2015 at 17:48