An efficient implementation of a low-complexity MP3 algorithm with a stream cipher

For portable devices with MP3 codec, the demands of digital right management arise recently. To provide a secure scheme to the most portable devices with MP3 codec, this work efficiently implements a secure MP3 algorithm on a dual-core system with one DSP and one RISC. The secure MP3 algorithm is a combination of a proposed low-complexity MP3 algorithm and a stream cipher. The low-complexity MP3 algorithm is executed on DSP and the stream cipher is on RISC. This separated design can dynamically update the type of stream ciphers in various applications. However, some of the main data, rather than an entire MP3 file, is encrypted in the MP3 frame. The partially encrypted data have variable size, determined by the specified security level. The security scheme offers two advantages. The first is that the encrypting and decrypting structures are identical. The second is that the scheme easily determines the quality of the encrypted MP3. For saving the computational power to obtain long playing time for a portable device, a low-complexity MP3 encoder and decoder are implemented using ADSP-2181 with 16-bit fixed-point data precision. MP3 encoding requires only 27.2 KB/16.8 KB (data RAM/program RAM), and decoding requires 23.6 KB/20.7 KB for decoder. The peak MIPS of the encoder and decoder are 21.05 and 17.67, respectively. This work can be applied to a Digital Rights Management (DRM) system for limiting the access of the music.