ENCRYPTION DEVICE, DECRYPTION DEVICE, AUTHENTICATION DEVICE, VERIFICATION DEVICE, ENCRYPTION METHOD, DECRYPTION METHOD, AUTHENTICATION METHOD, VERIFICATION METHOD, ENCRYPTION PROGRAM, DECRYPTION PROGRAM, AUTHENTICATION PROGRAM, AND VERIFICATION PROGRAM

摘要

PROBLEM TO BE SOLVED: To provide an encryption system and a signature method that reduce sizes of an encrypted message,a signature, and other encryption information.

SOLUTION: After a plane text is encoded, a mapping step (610) is executed to map the encoded message H(M) to an intermediate number b of a predetermined set B, and the result is encrypted (220) to generate and transmit a short ciphertext (230). The mapping is reversible at least on condition that the message H(M) (encoded upon occasion) is within a limit set such as a set [0, h"] of short messages. Further, a signature is mapped to a short signature for providing the short signature. The mapping is reversible at least on condition that a source message (H(M)) used to generate the signature is short. Output of signcryption, group signature, and ring signature is reduced.

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