A data processing apparatus with software protecting functions capable of enhancing the level of encryption security independently of the memory management method of the system comprising the apparatus. Upon receiving target data to be encrypted, an encryption key generation unit generates an encryption key in accordance with an attribute of the target data. Using the encryption key, an encryption unit encrypts the target data. The encrypted data is placed into a storage unit. When a request is made to process the encrypted data, a decryption key generation unit generates a decryption key in accordance with the attribute of the encrypted data. A decryption unit decrypts the encrypted data using the decryption key. The decrypted data is processed by a processing unit. A control unit supplies the encryption unit with the data processed by the processing unit as data to be encrypted.