Original research articleColor image encryption scheme using coupled hyper chaotic system with multiple impulse injections
Introduction
In design of symmetric cryptographic algorithms, some important aspects, such as easy to implement, high security, resistant to crypt analysis, real-time encryption and decryption speed [1], must be considered.
Generally, hyper chaotic systems have more complex dynamical characteristics than their chaotic systems[2], and have been applied in designing image encryption algorithms. Niu et al. [3] presented an image encryption scheme on the basics of formal model of DNA computing-splicing system and hyper-chaotic system, while programming the method, the instinct properties of hyper-chaotic system and splicing model are utilized.Yuan et al. [4] designed an efficient image encryption scheme based on 2D hyper-chaotic system, the confusion and the diffusion procedures of the proposed scheme are interacted on each other, the cryptosystem with the interacted structure is steadier and harder to decipher. Tan et al. [5] designed a quantum color image encryption algorithm based on a hyper-chaotic system, the quantum Fourier transform is exploited to fulfill the encryption.
Short-period behavior of chaotic system after too many times iteration can lead to degeneration of dynamics [6], these problems can be solved by random noise impulse injection during the iteration process [7], [8], because chaotic system is extremely sensitive to the initial conditions, a tiny deviation in iterating can result in significantly different trajectory. The injection times can be determined by the size of plain-text, and the injection moments can be random numbers, and the value of state variable after injection should not exceed the original interval of the state variable.
Some image encryption schemes based on chaotic systems or hyper chaotic systems have designed the mechanism of keys changing and distribution [9]. According to Shannon’s theory, only those schemes based on one-time keys can be regarded as theoretically absolute security and can make differential attack ineffective. The best quantum attack against generic symmetric-key systems is an application of Grover's algorithm [10], which requires work proportional to the square root of the size of the key space. It is clear that symmetric-key systems offer the smallest key sizes for post-quantum cryptography [11]. One-time keys can be sampled from natural noise [12], such as the call of cicadas, the sounds of wind, thunder and rain.
The paper proposes a color image encryption scheme using coupled hyper chaotic Lorenz system, to enhance the complexity of trajectory, the impulse noise signals of true random numbers are sampled from noise and being injected into one of the state variables, the injection moment and times are random. Fast and bitwise operations of XOR and left or right cyclic shift are applied to encrypt three color components. Larger and variable key space can make the algorithm more secure. Security and statistical analysis demonstrate the effectiveness of the image encryption scheme.
Section snippets
The coupled hyper chaotic Lorenz system
The coupled hyper chaotic Lorenz system was obtained by coupling two identical Lorenz systems, which is proposed by Grassi et al., [13], and the corresponding differential equation can be described in Eq. (1).Here is the state variable vector, and , and are control parameters, are coupling parameters. When , , , and , the system exhibits
Design of encryption algorithm
Input: Color plain image with the size of ; randomly sampled noise signals .
Output: The ciphered color image with the same size.
Step 1. Randomly select six signals of , , …, from to serve as six initial values of system (3), and two other values to serve as impulse signals of and .
Step 2. Iterating system (3) for 1200 times to remove the transient process, and then continue to iterate it for times. When the iterating times and
Experimental results
The keys are noise signal intercepted in randomly sampled environmental noise through digital voice recorder, and the corresponding time domain and frequency domain characteristic charts of sampled noise signal are shown in Fig. 6.
The plain images have identical size of , as shown in Fig. 7, and their corresponding ciphered images are shown in Fig. 8.
System evaluation
In this section, security and statistical analyses are applied to test the cryptographic algorithm, including the variable key space, key sensitivity, correlation coefficients of adjacent pixels, differential attack and information entropy evaluation.
Conclusion
The paper proposes a color image encryption scheme based on coupled hyper chaotic Lorenz system, and the novelty is multiple impulse injections of true random signals sampled from noise during the iteration process, to make the coupled hyper chaotic Lorenz system produce more complex trajectory. Time-saving operations of bitwise XOR and cyclic shift are applied to encrypt the red, green and blue components. The injection times can be designed to depend upon the image size. The simulation
Acknowledgments
This research is supported by the National Natural Science Foundation of China (Nos: 61363082, 61662073) and Minority Nationality Technology Talent Cultivation Plan of Xinjiang (No.201123116).
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