Progressive audio scrambling via complete binary tree's traversal and wavelet transform

In this paper, we firstly propose an effective audio scrambling method based on the pre-order traversal of a complete binary tree in time domain. The proposed method is fast, simple and has good scrambling effect. Then, with the aim of strengthening the anti-decryption capability, we present a wavelet-domain based scheme by considering not only the pre-order but also the in-/post-order based scrambling methods. First, an audio signal is wavelet-decomposed and retrieves the layers of wavelet coefficients. Then, the coefficients in each layer are scrambled by randomly chosen one out of the three methods. Anyone without knowledge of the correct wavelet decomposition parameters and the scrambling method used for each layer will never be able to descramble the signal successfully. Moreover, the new scheme also achieves progressive scrambling that enables to generate the audio outputs with different quality levels by controlling the scrambling degree as required.