sha is a simple program that hashes files. It uses the National Institute of Standards and Technology's Secure Hash Algorithm. It can use SHA-1, SHA-256, SHA-384, or SHA-512, which generate respectively, hashes of 160, 256, 384, or 512 bits. sha can be used in scripts to do, for example, file integrity checking.
For more information on SHA (the algorithms), visit: http://csrc.nist.gov/encryption/tkhash.html