Electronic Music Distribution (EMD) is undergoing two fundamental shifts. The delivery over wired broadband
networks to personal computers is being replaced by delivery over heterogeneous wired and wireless networks,
e.g. 3G and Wi-Fi, to a range of devices such as mobile phones, game consoles and in-car players. Moreover,
restrictive DRM models bound to a limited set of devices are being replaced by flexible standards-based DRM
schemes and increasingly forensic tracking technologies based on watermarking. Success of these EMD services
will partially depend on scalable, low-complexity and bandwidth eficient content protection systems.
In this context, we propose a new partial encryption scheme for Advanced Audio Coding (AAC) compressed
audio which is particularly suitable for emerging EMD applications. The scheme encrypts only the scale-factor
information in the AAC bitstream with an additive one-time-pad. This allows intermediate network nodes to
transcode the bitstream to lower data rates without accessing the decryption keys, by increasing the scale-factor
values and re-quantizing the corresponding spectral coeficients. Furthermore, the decryption key for each user
is customized such that the decryption process imprints the audio with a unique forensic tracking watermark.
This constitutes a secure, low-complexity watermark embedding process at the destination node, i.e. the player.
As opposed to server-side embedding methods, the proposed scheme lowers the computational burden on servers
and allows for network level bandwidth saving measures such as multi-casting and caching.