Can I use neural network to identify a hash function like sha256? I mean, generate a bunch of hash codes by different hash functions and also labels. Then, feed these codes into a neural network. Will it work?
No. The output of a cryptographic hash function (like SHA256) is indistinguishable from random data. The only feature that'd be useful to a neural network would be the length of the hash -- and you don't need a neural network to tell you that a 256-bit value could be SHA256.