COMMUNICATION TERMINALS AND PROGRAMS

• Main Authors: KOBAYASHI, Tetsutaro, OKANO, Yuki, NISHIMAKI, Ryo, YOSHIDA, Reo
• Format: Patent
• Language: English; French; German
• Published: 07.09.2022
• Subjects: ELECTRIC COMMUNICATION TECHNIQUE; ELECTRICITY; TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHICCOMMUNICATION

The present invention provides a communication terminal that can update data that was previously saved in a server device to data that can be decrypted on the communication terminal side using an updated session key, without the data being decrypted on the server device side. A communication terminal that shares a session key with another communication terminal and sends cipher text to the other communication terminal via a server device, includes: a common key cipher text obtaining unit that encrypts a message based on a common key to obtain common key cipher text; a function computation result obtaining unit that computes the common key and the session key based on a predetermined first function to obtain a function computation result; a public key cipher text obtaining unit that encrypts the function computation result based on a public key to obtain public key cipher text; and a cipher text sending unit that sends the common key cipher text and the public key cipher text to the server device.