Client computer for protecting confidential file, server computer therefor, method therefor, and computer program

A client computer includes an encryption/decryption unit for encrypting a confidential file in which an encryption key ID is embedded using an encryption key corresponding to the encryption key ID and decrypting the confidential file using a decryption key corresponding to the encryption key ID, an encryption key storage unit for storing the encryption key, a decryption key storage unit for storing the decryption key, a compliance requirement storage unit for storing security compliance requirements for the client computer transmitted from a server computer, and a security requirement monitoring unit for determining, according to a read command or a write command for the confidential file issued by application software, whether the client computer complies with the security compliance requirements, and, when the requirements are complied with, passing the encryption key and the encryption key ID corresponding to the encryption key from the encryption key storage unit to the encryption/decryption unit in respo