   SHA1(str)
   SHA(str)
Calculates an SHA1 160-bit checksum for the string, as described in
RFC 3174 (Secure Hash Algorithm). The value is returned as a string of 40 hex
digits, or NULL if the argument was NULL.
One of the possible uses for this function is as a hash key. You can
also use it as a cryptographically safe function for storing passwords.
