Key exchange system, terminal, server, key exchange method, and program

A terminal connected to another terminal that performs key exchange and a server that performs authentication of each terminal and mediation of the key exchange via a communication network, the terminal comprising:

• a processor;
• and
• a memory storing program instructions that cause the processor to:
• generate a ciphertext obtained by encrypting predetermined data, using a public key of token control encryption and generated by the server, and a token generated from a nonce used when the authentication is performed between the terminal and the server by federation using OpenID Connect;
• and
• transmit the ciphertext to the server.

A key exchange method used in a key exchange system including a plurality of terminals that perform key exchange and a server that performs authentication of each of the terminals and mediation of the key exchange,

• the key exchange method comprising steps performed by the server, the steps including:
• generating a nonce used when the authentication is performed between the server and the terminal by federation using OpenID Connect;
• generating a public key and a secret key of token control encryption;
• transmitting the nonce and the public key to the terminal;
• and
• decrypting a ciphertext received from the terminal by using the secret key and a token received from the terminal,
• the key exchange method further comprising steps performed by the terminal, the steps including:
• generating a ciphertext obtained by encrypting predetermined data by using the public key and a token generated from the nonce;
• and
• transmitting the ciphertext to the server.