Cryptography problem: make an invertible, easy-in-both-directions function from [0...2^256 - 1] to [0...2^256 - 2] (or more generally, -k for small k) where the exceptions to the invertibility are computationally infeasible to find.
Has there been any work on this?
密码学问题：在[0…2^256-1]到[0…2^256-2]（或者更一般地说，-k代表小k）的两个方向上制作一个可逆的、简单的函数，其中可逆性的异常在计算上是不可能找到的。
这方面有什么进展吗？