Patent EP-3817323-A1 (EP)
Inventor: SHIMIZU TOSHIYA
IPC: G06F21/62
Filed: 2020-10-15
Abstract: An encryption processing system includes: an encrypted data generation device that encrypts secret information; party devices of a first number, the party devices each including a key pair of a public key and a private key; and a fragment combining device that collects and combines pieces of fragment information shared by the party devices of the first number, wherein the encrypted data generation device includes: a first generation unit that generates synthesis keys of a third number by performing, a third number of times, a process for selecting public keys of a second number to be used for key restoration from public keys of the first number to generate the synthesis key, the third number being a number of combinations of selecting the public keys of the second number from the public keys of the first number; a second generation unit that generates an intermediate text from confidential texts of a fourth number generated by encrypting each piece of the secret information by using the public keys of the party devices of the fourth number having decryption authority for the secret information among the party devices of the first number, and generates secret information ciphertexts of the third number by further encrypting the intermediate text using each of the synthesis keys; and a first public unit that makes public encrypted data including the secret information ciphertexts of the third number and a first signature relating to the secret information ciphertexts of the third number, each of the party devices includes: a first verification unit that verifies validity of the encrypted data by using the first signature; a third generation unit that generates, when the validity has been verified, by using a private key included in an own party device, decryption key fragments of a fifth number, and generates second signatures of the fifth number respectively corresponding to the decryption key fragments of the fifth number, the fifth number being a number of combinations of selecting the party devices of a number obtained by subtracting one from the second number from among the party devices of a number obtained by subtracting one from the first number; and a second public unit that makes public the decryption key fragments of the fifth number and the corresponding second signatures, the fragment combining device includes: a second verification unit that verifies validity of the decryption key fragments of the fifth number by using the decryption key fragments of the fifth number and the corresponding second signatures; a fourth generation unit that generates a decryption key by combining decryption key fragments of the second number corresponding to any one of the secret information ciphertexts of the third number among the decryption key fragments of the fifth number that are made public by each of the party devices of the first number, and generates the intermediate text by decrypting the secret information ciphertext corresponding to the generated decryption key with the generated decryption key; and a third public unit that makes public the intermediate text generated by the fourth generation unit, and each of the party devices further includes: a decryption unit that decrypts, when the own party device has the decryption authority, the intermediate text that is made public by the third public unit using the private key included in the own party device, and restores the secret information.