Patent ID: 10419213

Abstract:
A random number generating unit generates random numbers s1, s2, s′1, and s′2. A public keys randomizing unit generates first randomized public keys information obtained by randomizing public keys using the random number s1 and second randomized public keys information obtained by randomizing the public keys using the random number s2. A proxy calculation unit calculates a first commission result by using a secret key and calculates a second commission result by using the secret key. A verification unit calculates a first verification value by using the random number s2, calculates a second verification value by using the random number s1, and verifies whether or not the first verification value and the second verification value coincide with each other. A common key calculation unit calculates a common key by using the random numbers s′1 and s′2 if the first verification value and the second verification value coincide with each other.