Abstract: In this study we propose an I-frame encryption scheme for encryption of moving image video data and a licensing agent which provides automatic user authentication and data decoding when multimedia data encrypted in the system server is executed in the client system by the user. The licensing agent performs user authentication based on Public Key Infrastructure (PKI) using a shared key pool and encryption/decryption of multimedia data. In addition, a private key distribution system based on a secret key is used to prevent leakage of the key and trace the paths of leakage if a key has leaked. In experiment analysis, we verified that the proposed system significantly reduces delay time, including decryption time, when playing back video data files in the client system compared with existing systems.