Abstract
In this paper, we introduce an audio encryption scheme based on the cosine number transform (CNT). The transform, which is defined over a finite field, is recursively applied to blocks of samples of a noncompressed digital audio signal. The blocks are selected using a simple overlapping rule, which provides diffusion of the ciphered data to all processed blocks. A secret-key is used to specify the number of times the transform is applied to each one of such blocks. Computer experiments are carried out and security aspects of the proposed scheme are discussed. Our analysis indicates that the method meets the main security requirements of secret-key cryptography. More specifically, after the encryption of 16-bit audio signals, correlation coefficients significantly close to 0 and entropy values close to 16 were obtained. Furthermore, the flexibility of the method easily allows key space sizes greater than 2256 and provides robustness against differential, known-plaintext and chosen-plaintext attacks.
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Notes
The multiplicative order of an element ζ in the finite field GF(p) is the least positive integer l such that ζ l≡1 (mod p).
The index of the component selected in the secret-key has to be reduced modulo K because the number of audio blocks to be processed throughout the encryption procedure is usually greater than the key-length K. In this sense, the K-th block is processed using the component of index K (mod K)≡0 (mod K) of the secret-key; the (K+1)-th block is processed using the component of index K+1 (mod K)≡1 (mod K) of the secret-key and so on.
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This research was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) under Grants 307686/2014-0 and 456744/2014-2.
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Lima, J.B., da Silva Neto, E.F. Audio encryption based on the cosine number transform. Multimed Tools Appl 75, 8403–8418 (2016). https://doi.org/10.1007/s11042-015-2755-6
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DOI: https://doi.org/10.1007/s11042-015-2755-6