Ciphertext decryption delegation system, ciphertext decryption authority delegated way, ciphertext conversion device, the decryption authority holder for the device and the ciphertext conversion program

摘要

PPROBLEM TO BE SOLVED: To decrypt a cipher generated by an attribute-based encryption system using a secret key by an ID-based encryption system. PSOLUTION: A system for transferring cipher decryption authority is provided with: a device for decryption authority transfer candidates, which performs encryption processing based on an IBE secret key, and a public parameter corresponding to the IBE secret key; a device for decryption authority holder, which performs encryption processing based on an ABE secret key, and an ABE public key corresponding to the ABE secret key; and a cipher conversion device which converts an ABE cipher into an IBE cipher, wherein the device for decryption authority holder stores auxiliary information which is a part of the IBE secret key, and generates a conversion key which is used when the cipher conversion device converts the ABE cipher based on a part of the public parameter, the auxiliary information, the ABE secret key, and a value which attributes show, and the cipher conversion device stores the ABE cipher and the conversion key, and converts the ABE cipher into the IBE cipher based on the conversion key. PCOPYRIGHT: (C)2011,JPO&INPIT