Build a MAC (keyed hash function) from the given block cipher. The block cipher is run in CBC mode, and the MAC value is the final value of the initialization vector. Thus, the hash size of the resulting hash is the block size of the block cipher. The optional argument iv specifies the first initialization vector, with a default of all zeroes. The optional argument pad specifies a padding scheme to be applied to the input data; if not provided, no padding is performed.
add_substring b pos len adds len characters from byte array b, starting at character number pos, to the running hash computation.
add_string str adds all characters of string str to the running hash computation.
add_byte b adds the character having code b to the running hash computation. b must be between 0 and 255 inclusive.
Terminate the hash computation and return the hash value for the input data provided via the add_* methods. The hash value is a string of length hash_size characters. After calling result, the hash can no longer accept additional data. Hence, do not call any of the add_* methods after result.