Re-encryption key generation method, re-encryption method, re-encryption key generation system and re-encryption system

摘要

PROBLEM TO BE SOLVED: To enable a message receiver to register a re-encryption key alone when a new message sender is added according to the addition of a new field, without cooperation of the message receiver and a proxy, and to enable the execution of re-encryption key generation processing, re-encryption processing, decryption processing etc. at a high speed.SOLUTION: With the cooperation of a message reception terminal and a proxy terminal which receives a message, a temporary conversion key for converting a message, which is destined from an unfixed message transmission terminal to a message reception terminal, into a message destined to the proxy terminal is generated, using temporary information which does not include the information of the message transmission terminal. When the message transmission terminal is fixed, the message reception terminal associates the temporary information of the temporary conversion key with the information of the fixed message transmission terminal, to generate a connection key to fix the unfixed message transmission terminal to a fixed message transmission terminal.