Calculate SHA-1 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 algorithms.
"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 1 is a cryptographic "one way" hash function. Produces keys expressed as 160 bit hex number.
SHA1 was developed by the NSA.
SHA1 is considered to be more secure from MD5. More info can be found at Wikipedia