In this paper, the 128bit AES block cipher algorithm OCB (Offset Code Book) mode for privacy and authenticity of high speed packet data was efficiently designed in C language level and was optimized to support the required capacity of contents server using high performance DSP. It is known that OCB mode is about two times faster than CBC-MAC mode. As an experimental result, the encryption / decryption speed of the implemented block cipher was 308Mbps, 311 Mbps respectively at 1GHz clock speed, which is 50% faster than a general design with 3.5% more memory usage.