| 摘要 |
PROBLEM TO BE SOLVED: To update an encryption key without providing an encryption key.SOLUTION: Ciphertext stored in a memory and encrypted by an encryption key is updated into encryption key updated ciphertext which is encrypted by a new encryption key from a terminal. The terminal includes: an encryption processing part which uses a homomorphic pseudo random number generator to generate ciphertext of data from a pseudo random number defining an encryption key as a seed and a pseudo random number defining data as a seed and transmits the generated ciphertext; and an encryption key processing part which generates data for key update from an inverse element of the encryption key and the new encryption key and transmits the generated data for key update to a storage device. The storage device includes: a memory for storing received ciphertext; and a key update processing part which generates the encryption key updated ciphertext from a pseudo random number defining received data for key update as a seed and a pseudo random number defining ciphertext as a seed and stores the encryption key updated ciphertext in the memory in place of the ciphertext. |
