ciphertext group of blocks 305 is output from the hash keys and includes hashed ciphertext values c 1 u2032 through cm u2032 and c u2032 m 1 the hashed ciphertext group of blocks 305 is passed to an exclusive or block 303 which exclusive or 39 s the hashed ciphertext with the checksum produced by the checksum generator 301 the output of the exclusive or block is the hash value 304 thus the simple universal hash function 300 is a function of the plaintext blocks as well as the ciphertext blocks and the hash key k 3 the final hash value 304 is not necessarily the size of one block of the block cipher but may be smaller in general as an example if the block cipher block size is 128 bits as in aes and if the hash value is only supposed to be 16 bits then the hash key k 3 will be of size 48 bits 48 128 8 log 8 in general the key size k 3 will be 128 t log t where 128 t is the size of the hash value 304 in case the hash value is only 16 bits a checksum 301 of 16 bits is computed from the plaintext blocks p 1 p 2 to pm in one embodiment the checksum can be computed by taking the exclusive or of all of the plaintext blocks and then.