In data security technologies, generally, fully encrypted data (such as video data and audio data) is stored in a server, a personal computer (PC) client sends, to a server, a download request of downloading the data, and the server performs identity authentication on the client. If the authentication succeeds, the server returns, to the client, a decryption key of the data requested to be downloaded; the client downloads the encrypted data from the server, and decrypts the data by using the previously received decryption key while playing the data.