| 摘要 |
PROBLEM TO BE SOLVED: To provide a security system capable of improving safety of cloud-key management type encryption.SOLUTION: A security system 1 comprises an encryption device 11, a processing device 12 and a decryption service providing device 13. The decryption service providing device 13 stores in a storage unit 131 a secret key based on the ElGamal encryption method on a group G, an encrypted text based on the ElGamal encryption method is inputted in an input unit 132, and a decryption unit 133 decrypts the encrypted text according to the ElGamal encryption method using the secret key s and outputs the obtained decryption result. However, it is difficult to obtain (xof G) for any (x of G) from (xof G) and (xof G) for i=1,...,t where t is a positive integer. In other words, the group G is a group which is difficult for the Delayed Target One More Diffie-Hellman problem. |
