  Recently it was shown that permutation-only multimedia ciphers can completely
be broken in a chosen-plaintext scenario. Apparently, chosen-plaintext scenario
models a very resourceful adversary and does not hold in many practical
situations. To show that these ciphers are totally broken, we propose a
cipher-text only attack on these ciphers. To that end, we investigate speech
permutation-only ciphers and show that inherent redundancies of speech signal
can pave the path for a successful cipher-text only attack. For this task
different concepts and techniques are merged together. First, Short Time
Fourier Transform (STFT) is employed to extract regularities of audio signal in
both time and frequency. Then, it is shown that cipher-texts can be considered
as a set of scrambled puzzles. Then different techniques such as estimation,
image processing, branch and bound, and graph theory are fused together to
create and solve these puzzles. After extracting the keys from the solved
puzzles, they are applied on the scrambled signal. Conducted tests show that
the proposed method achieves objective and subjective intelligibility of 87.8%
and 92.9%. These scores are 50.9% and 34.6% higher than scores of previous
method.
