I'll start with my question and then give it a little bit of explanation:

Why can't an encryption function be inverted easily such that

if enc(a) = a', enc'(a') = a

So, i understand that there is a lot of complexity to encryptions making them hard to crack - it's kind of the point.

BUT (by my logic) they can't contain randomness since enc(a) will always equal a' so it must be a fixed encryption function.

Much in the same way that you can integrate a derivative to obtain the original (including a constant, granted, but these are relatively easy to find), surely there's a way to do this with encryption? Someone created the encryption function to run through a series of statements and operations to get to the hash, why can't they work backwards to obtain the original?

This post has been edited by **macosxnerd101**: 01 July 2013 - 09:11 AM

Reason for edit:: Renamed topic for better discussion