Perceptual cryptography on MPEG Layer III bit-streams

Whereas conventional cryptography is suitable for any kind of data, it does not allow for perceptual degradation of encrypted data in multimedia-compressed formats. We present perceptual cryptography applied to MPEG Layer III compressed audio (MP3). The inputs of the cipher are the plaintext MP3 bit-stream, encryption key and encryption percentage. The cipher outputs a MPEG Layer III compliant bit-stream (ciphertext) that is perceptually less valuable than the original bit-stream. The original MP3 bit-stream can be recovered using the ciphertext bit-stream and the same decryption key and percentage used on encryption. An introduction to MP3 audio compression is given followed by a description of the perceptual cipher and its applications. The paper addresses the relationship between the encryption percentage and the subjective quality.