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This paper presents a solution for secure and efficient image encryption with the help of self-adaptive permutation–diffusion and DNA random encoding. The plain image is firstly converted to DNA sequence using random encoding rules, so as to disarrange the bit distribution of the plaintext. A self-adaptive permutation–diffusion procedure is subsequently introduced for further encryption. The quantization processes of the permutation and diffusion procedures are disturbed by the intrinsic features of the plaintext, with the introduced disturbances can be automatically retrieved in the decryption end. The security of the system originates from the plaintext-related quantization of the encryption process which makes the cryptosystem secure against plaintext attack. Besides, the reusability of the random variables can dramatically promote the efficiency of the cryptosystem, which renders great potential for real-time secure image applications.

Nowadays, the increasing requirement for telemedicine services has raised more concerns in real-time medical image encryption. However, traditional block ciphers have been found poorly fit this requirement. Considering this, we propose an efficient cryptosystem for medical image encryption in the present study. Chaos-based permutation-diffusion architecture is adopted, whereas an improved image confusion strategy is developed based on the intrinsic feature of medical images. The improved confusion approach can bring about not only satisfactory permutation performance but also bit distribution balancing effect for medical images. Simulations and extensive security analyses indicate that the proposed cryptosystem provides an efficient approach for real-time secure medical image transmission and storage over public networks.

Recently, intrinsic image features in bit-level (e.g., higher bit-planes carry more information than lower bit-planes) have been widely accepted for building bit-level image cryptosystems. Higher bit-planes are generally handled with enhanced encryption, whereas light attention is paid to lower ones. However, the existing achievements on bit-level image features are solely based on the analyses of standard test images, and they do not hold for some special images, such as medical images. When ciphering these images, such cryptosystems may leak the important information of lower bit-planes, and other inadaptability also exists. In this paper, we firstly give out the inapplicability of the existing bit-level achievements, and then a novel chaos-based image encryption scheme using nonlinear inter-pixel computing and swapping based permutation approach is presented. Simulations and extensive security analyses demonstrate the high level of security for practical secret applications.

This paper presents a solution to satisfy the increasing requirement of real-time secure image transmission over public networks. The main advantage of the proposed cryptosystem is high efficiency. The confusion and diffusion operations are both performed based on a lookup table. Therefore, the time-consuming floating point arithmetic in chaotic map iteration and quantization procedures of traditional chaos-based image cipher can be avoided. Besides, this cryptosystem possesses satisfactory resistance to noise perturbation and loss of cipher data, which are inevitable and unpredictable in real-world channels. The channel disturbance and the deliberate damage from the opponents are both tolerated. The recovered image from the damaged cipher data has satisfactory visual perception. Simulations prove the advantages of the proposed scheme, which render it a good candidate for real-time secure image applications.

In recent years, the operation efficiency of chaos-based image cryptosystems has drawn much more concerns. However, the workload arised from floating point arithmetic in chaotic map iteration prevents the efficiency promotion of these cryptosystems. In this paper, we present a novel image encryption scheme using Gray code based permutation approach. The new permutation strategy takes full advantage of (n, p, k)-Gray-code achievements, and is performed with high efficiency. A plain pixel-related image diffusion scheme is introduced to compose a complete cryptosystem. Simulations and extensive security analyses have been carried out and the results demonstrate the high security and operation efficiency of the proposed scheme.

In recent years, a variety of chaos-based image cryptosystems have been investigated to meet the increasing demand for real-time secure image transmission. Most of them are based on permutation–diffusion architecture, in which permutation and diffusion are two independent procedures with fixed control parameters. This property results in two flaws. (1) At least two chaotic state variables are required for encrypting one plain pixel, in permutation and diffusion stages respectively. Chaotic state variables produced with high computation complexity are not sufficiently used. (2) The key stream solely depends on the secret key, and hence the cryptosystem is vulnerable against known/chosen-plaintext attacks. In this paper, a fast chaos-based image encryption scheme with a dynamic state variables selection mechanism is proposed to enhance the security and promote the efficiency of chaos-based image cryptosystems. Experimental simulations and extensive cryptanalysis have been carried out and the results prove the superior security and high efficiency of the scheme.

Recently, a double-image encryption scheme using local pixel scrambling technique and gyrator transform has been proposed [Opt Lasers Eng 2013; 51: 1327–31]. Through our simulations, there is serious cross-talk disturbance in the phase-based image when the encrypted data undergoes noise perturbation or occlusion attack. The disturbance will cause serious deterioration in the retrieved phase-based image and bring about visibility ambiguities to the receiver, and hence downgrades the practicability of the cryptosystem. In this paper, detailed analysis of the cross-talk disturbance in the original scheme will be firstly given out, and then the corresponding improvement is subsequently proposed. Numerical simulations results indicate that the improved scheme well address the cross-talk disturbance and further enhance the security of the original cryptosystem.

This paper presents a solution to satisfy the increasing requirements for secure medical image transmission and storage over public networks. The proposed scheme can simultaneously encrypt and compress the medical image using compressive sensing (CS) and pixel swapping based permutation approach. In the CS phase, the plain image is compressed and encrypted by chaos-based Bernoulli measurement matrix, which is generated under the control of the introduced Chebyshev map. The quantized measurements are then encrypted by permutation-diffusion type chaotic cipher for the second level protection. Simulations and extensive security analyses have been performed. The results demonstrate that at a large scale of compression ratio the proposed cryptosystem can provide satisfactory security level and reconstruction quality.

Recently, a number of double-image cryptosystems have been developed. However, there are notable security performance differences between the two encryption channels in these algorithms. This weakness downgrades the security level and practicability of these cryptosystems, as the cryptosystems cannot guarantee all the input images be transmitted in the channel with higher security level. In this paper, we propose a novel double-image encryption scheme based on cross-image pixel scrambling in gyrator domains. The two input images are firstly shuffled by the proposed cross-image pixel scrambling approach, which can well balance the pixel distribution across the input images. The two scrambled images will be encoded into the real and imaginary parts of a complex function, and then converted into gyrator domains. An iterative architecture is designed to enhance the security level of the cryptosystem, and the cross-image pixel scrambling operation is performed to the real and imaginary parts of the generated complex encrypted data in each round. Numerical simulation results prove that a satisfactory and balanced security performance can be achieved in both channels.

In recent years, amounts of permutation-diffusion architecture-based image cryptosystems have been proposed. However, the key stream elements in the diffusion procedure are merely depending on the secret key that is usually fixed during the whole encryption process. Cryptosystems of this type suffer from unsatisfactory encryption speed and are considered insecure upon known/chosen plaintext attacks. In this paper, an efficient diffusion scheme is proposed. This scheme consists of two diffusion procedures, with a supplementary diffusion procedure padded after the normal diffusion. In the supplementary diffusion module, the control parameter of the selected chaotic map is altered by the resultant image produced after the normal diffusion operation. As a result, a slight difference in the plain image can be transferred to the chaotic iteration and bring about distinct key streams, and hence totally different cipher images will be produced. Therefore, the scheme can remarkably accelerate the diffusion effect of the cryptosystem and will effectively resist known/chosen plaintext attacks. Theoretical analyses and experimental results prove the high security performance and satisfactory operation efficiency of the proposed scheme.

In this paper, we evaluate the security of an enhanced double random phase encoding (DRPE) image encryption scheme (2013 J. Lightwave Technol. 31 2533). The original system employs a chaotic Baker map prior to DRPE to provide more protection to the plain image and hence promote the security level of DRPE, as claimed. However, cryptanalysis shows that this scheme is vulnerable to a chosen-plaintext attack, and the ciphertext can be precisely recovered. The corresponding improvement is subsequently reported upon the basic premise that no extra equipment or computational complexity is required. The simulation results and security analyses prove its effectiveness and security. The proposed achievements are suitable for all cryptosystems under permutation and, following that, the DRPE architecture, and we hope that our work can motivate the further research on optical image encryption.