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99 | Shumran & Al-Hussein
Fig. 20. Block diagram of speech encryption system using FPSCM-SC, adapted from [48].
domain by using the inverse discrete cosine transform (IDCT). in the unified chaotic map to (0.485935,0.481211,0.624137)
in the proposed system.
In 2017, Mahmood K. Ibrahem et al [52], introduced a
voice-over-internet protocol (VOIP) speech encryption sys- G. Chaotic Systems Based on Hybrid Chaotic Generators
tem by using Lorenz chaotic map as a pseudo-random num- systems
ber (PRN) by solving the three-dimensional equations of the
Lorenz system using fourth-order Runge Kutta (RK4) and In 2013, Mohamed Salah Azzaz, et al [54], suggested an in-
the output is converted to binary with 64 bits. By applying novative chaotic pseudo-random number generator known as
a different test for different voices, the best residual intelli- the Hybrid Continuous Chaotic System, or HDCCS. A new
gibility measure results are MSE=172313540.6 and SNR= method for creating chaos-based cryptosystems can be devel-
1.385901466 and the throughput of the system is 1876 bps. oped thanks to this chaotic generator. approach is based on
the perturbation technique, which uses two different kinds of
In 2015, Sattar B. Sadkhan et al [53], introduced a new chaotic systems: discrete (Henon Map, Logistic Map, etc.)
stream cipher system by XORing the voice signal with PRBG and continuous (Lorenz, Chen, Chua, etc.) chaotic systems.
that is generated from the random unified chaotic map (RUM) Their scheme, the continuous chaotic system perturbs the
which is modified from the Unified chaotic map by using a uni- discrete system and makes the transmitter and receiver syn-
form distribution to get expanded and other values of the map. chronized. Chaotic encryption keys with intricate and er-
To achieve random properties such as (nonlinear, sensitivity ratic behaviors are generated by the disrupted discrete system.
to the initial condition, and deterministic) the mod operation Real-time wireless chaos-based speech encryption based on
is used. Three PRBGs are generated and compared with each the suggested HDCCS has been developed and implemented
other. The results show that the Lyapunov exponents (LE), on FPGA technology in order to verify the efficacy and prin-
which is the most important tool that is used to measure the ciple of their scheme encryption. Secure real-time embedded
sensitivity to initial condition and the non-chaotic behavior applications in digital cryptosystems heavily depend on the
for the non-linear system and which its value must be larger use of a good chaotic generator with desirable dynamical sta-
than zero are increased from (0.341353,0.346251,0.389717) tistical properties and high performance (speed, cost, power,
