Patent ID: 9276734
Filing Date: 2016-03-01
CPC Classification: G06F,H04L

Claim Text:
1. A confidential computation system which is a computer system comprising: a client configured to execute data encryption by a homomorphic encryption method using a secret key and send the encrypted data to a server; and the server configured to execute homomorphic computation processing on the encrypted data received from the client and return a result of the computation to the client, the confidential computation system characterized in that the client executes processing for executing the data encryption by adding an error vector to plaintext, the error vector being not larger than a predetermined criterion, and processing for sending limitation information to the server, the limitation information being formed from a sublattice basis of a lattice generated by the secret key, and the server executes processing for receiving the limitation information from the client and storing the limitation information in a storage device, and in the homomorphic computation processing on the encrypted data received from the client, processing for, when a bit length of ciphertext which is under the homomorphic computation processing or is a result of the homomorphic computation processing is equal to or larger than a predetermined value, reducing the bit length of the ciphertext to a value not larger than a predetermined threshold by translating a vector of the ciphertext to an inside of a region formed from the sublattice basis corresponding to the stored limitation information.