ENCRYPTION DEVICE, DECRYPTION DEVICE, ENCRYPTION METHOD, AND ENCRYPTION PROGRAM

摘要

PROBLEM TO BE SOLVED: To provide an encryption device which, when a plurality of users encrypt data using a key generated independently for each user, can eliminate data duplication even though a key generated by a user is not known on the storage side in which encrypted data is stored.SOLUTION: First hash value calculation means 82 calculates a hash value for a left block. Encryption-use pseudo-random number generation means 83 generates, using an exclusive-OR of the hash value and a right-end block as an input block, a pseudo-random number equal in length to the left block. Common key block encryption means 84 generates, for an input block, a block ciphertext using a secrete key. Ciphertext generation means 85 generates ciphertext by combining an exclusive-OR of the pseudo-random number and the left block and the block ciphertext. Duplication elimination means 86 compares the hash value or real value of the left block in two pieces of ciphertext and, when the compared values match, deletes the left block in one of the two pieces of ciphertext.