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영어

Revocation of a private key is an indispensable factor if user-operation aspects, such as an information management system in a cloud computing environment, are considered. Although there is a public key infrastructure (PKI)-based certificate revocation list in the private key revocation function, the revocation function of a PKI cannot be applied to functional encryption as it is. The cloud environment has limitations, such as no smooth access privilege change, and re-allocation that uses the existing proxy re-encryption. To solve the problem, functional encryption that is suitable for the cloud used as external storage, and for which revocation is possible, was proposed. This study proposes medical data management based on functional encryption that can restrict access privileges to the users concerned, if data access privileges stored within a health cloud are terminated. If many users exist in the health cloud environment, communications volume and computation requirements are expected to increase enormously due to the packet processing load of a trusted third party. Therefore, a revocation function is executed by postponing the revocation function for a certain period of time (D) for efficient retention and management of a revocation list, and by increasing key numbers when a specific time arrives. A system and protocol must be configured in which the first ciphertext is converted into a secondary ciphertext so that the revocation of access privileges to data stored in the health cloud server can be made, and a user whose access privileges were revoked cannot conduct secondary decryption.