A common key block encryption device includes a first hash unit applying locked key permutation to a variable-length s-bit plaintext, and outputting a fixed-length n-bit first block and a second (s-n)-bit block; a first encryption processing unit outputting a third block encrypted by element of n-bit block tweakable block cipher using tweak, inputting the first block; a second encryption processing unit generating a random number (s-n)-bit block with a result of group computation of the third block and the first block as input by using an arbitrary cipher having theoretical security at least against a known-plaintext attack; and a second hash unit applying the locked key permutation to the result of the group computation of the random number block and the second block, and to the third block to output a fifth n-bit block and a sixth (s-n)-bit block. The fifth and sixth blocks are concatenated into an s-bit encryption.