# Decrypting SHA-256 with SHA-256 as input?

Is there a way to somewhat decrypt a SHA-256 hash, provided that the initial string was also a SHA-256 hash?

If not, could anyone link me to a rainbow table containing some of the $16^{64}$ possible hashes?

• Firstly, SHA-256 isn't an encryption scheme so the verb 'decrypt' isn't appropriate here. I think you mean finding the plaintext which gives the hash value. Secondly, a hash value computed with SHA-256 is composed of 256bits so all the possible values are all the 256-bit words (note that $16^{64} = 2 ^{4\times64} = 2^{256}$). – Raoul722 Feb 28 '16 at 16:23

A rainbow table could cover only a tiny portion of the $2^{256}$ possible inputs. Something like $2^{80}$ hashes would be on the upper end, if not beyond, a feasible amount of work if someone really wanted to be able to crack such hashes. A random 256-bit value would have only abut a $2^{-176}$ chance of being in it, meaning no hash you encountered in practice would be found.