SHA-256 generates an almost-unique 256-bit (32-byte) signature for a text.
SHA-256 is one of the successor hash functions to SHA-1
(collectively referred to as SHA-2), and is one of the strongest hash functions available.
SHA-256 is not much more complex to code than SHA-1,
and has not yet been compromised in any way. The 256-bit key makes it a good partner-function for AES.