A cryptographic hash function is a well-defined procedure that accepts a block of data and generates a fixed-length bit string known as the hash value or digest. A hash function is one-way, meaning the hash function procedure is irreversible. There is no function to derive the plain source data from the hash value. The hash algorithms available through SQL Server 2008 are: SHA-1 (Secure Hash Algorithm), MD5, MD4, MD2 (MD: Message Digest). CHECKSUM computes a hash value, called the checksum, over its list of arguments.