Calculate SHA-256 hash of an input string.
Hashing in general is defined as a transformation of a string of characters into a fixed-length key that represents the original string.
Special importance have the so called "one way" hashing logarithms.
"One way" hashing algorithms offer the feature that from a string we can get a hash key but from the hash key we can not find the original string.
So "one way" hashing algorithms can be used as digital signature for files or emails,
since the original file (string of characters) can be hashed (signed) into a key but from the known key we can not reproduce the original content.
Secure Hash Algorithm 256 is a cryptographic "one way" hash function. Produces keys expressed as 256 bit hex number.
It is designed by the National Security Agency (NSA).
SHA256 is considered to be more secure from SHA-1. More info can be found at Wikipedia