Secret calculation device, secret calculation system, secret calculation method, and computer program product

A secret calculation method implemented in a secret calculation device, the method comprising:

• performing a first secret calculation operation on a first ciphertext obtained by encrypting input data according to a first homomorphic encryption method by using first homomorphic computation based on a first homomorphic encryption method to calculate a second ciphertext;
• converting, by using a ciphertext conversion method defined between the first homomorphic encryption method and a second homomorphic encryption method, the second ciphertext into a third ciphertext encrypted by the second homomorphic encryption method without decrypting the second ciphertext;
• and
• performing a second secret calculation operation on the third ciphertext by using second homomorphic computation based on the second homomorphic encryption method to calculate a fourth ciphertext.

A computer program product comprising a computer-readable medium including programmed instructions, the instructions causing a computer to execute:

• performing a first secret calculation operation on a first ciphertext obtained by encrypting input data according to a first homomorphic encryption method by using first homomorphic computation based on a first homomorphic encryption method to calculate a second ciphertext;
• converting, by using a ciphertext conversion method defined between the first homomorphic encryption method and a second homomorphic encryption method, the second ciphertext into a third ciphertext encrypted by the second homomorphic encryption method without decrypting the second ciphertext;
• and
• performing a second secret calculation operation on the third ciphertext by using second homomorphic computation based on the second homomorphic encryption method to calculate a fourth ciphertext.