Study On Image Secure Communication Based On Chaos Theory

The development at full speed of the information technology brings the worldwide change with the arrival of information ages. The information network system has become the necessary infrastructure of each social realm. During the last decade, there has been an explosive growth of using computers, networks, communications and multimedia applications. Today, Internet users demand not only text but also audio, images, and video. Recently, the convergence of computers, networks, communications, and multimedia applications, have been took place. The information revolution is entering a new area where consumer products will combine the functions of telephone, personal computer, and television. In order to satisfy users demands, future consumer electronics devices, such as videophone, should be able to transmit images and video over wireless communications networks. However, more and more fraud cases on the network are reported recently with the rapid development of science and technology. It has produced important economic losses and bad effect to society in our country. Besides bandwidth and error resiliency issues present in image and video applications, the presence of a network has prompted new problems with security and privacy. Having a secure and reliable means for communicating with images and video is a necessity for many networks. Information security has become an important topic.In the last few years, network security and data encryption have become an important and high profile issues. Innovative encryption techniques need to be developed for effective data encryption for financial institutions, e-commerce, and multimedia applications. The statistics show that image information accounts for 70% of the total volume of information. Nowadays image is the important means of information exchange. With the development of network technology, more and more image information has been transmitted over the Internet. Image encryption can be also used to protect a person's right to privacy. The significance for image encryption in the field of e-government, e-commerce and military is self-evident. For future internet applications on wireless networks, besides source coding and channel coding techniques, cryptographic coding techniques for multimedia applications need to be studied and developed.Recently, there are two fundamental technologies, which have been identified for protecting digital images, namely watermarking and image encryption. Within the last several years, many achievements have been done in the area of watermarking. Image encryption, however, is still an open area for research. Image encryption, indeed, is necessary for future multimedia Internet applications. In some situations, image encryption, indeed, is necessary. Password codes to identify individual users will likely be replaced with biomedical images of fingerprints and retinal scans in the future. When such images are sent over a network, an eavesdropper may duplicate or reroute the information. So they must be encrypted at first. By encrypting these images, the content still has some degree of added security. Furthermore, by encrypting non-critical images as well, an eavesdropper is less likely to be able to distinguish between important and non-important information. Image security has become an important topic.Image encryption can also be used to protect privacy. An example for image encryption to protect privacy is in medical imaging applications. Recently, in order to reduce the cost and to improve the service, electronic forms of medical records have been sent over networks from the laboratories to medical centers or to doctors' offices. According to the law, medical records, which include many images, should not be disclosed to any unauthorized persons. Medical images, therefore, should be encrypted before they are sent over networks. Moreover, image encryption can be used to protect intellectual properties. One of concerns of the entertainment industry is that movies and videos in digital format are vulnerable to unauthorized access, theft, and replication.Entertainment industry has lost billion dollars due to the illegal copies. Recently, new technologies have been developed which allows multimedia can be delivered to millions of household very quickly. In the future, entertainment industry will utilize Internet and satellites for multimedia distributions. The threat of unauthorized access during transmission over networks and the threat of illegal copy increase significantly. Image encryption, therefore, can be used to minimize these problems.Most traditional or modem encryption methods have been designed to protect the text data such as the Data Encryption Standard (DES) algorithm and the Rivest-Shamir-Adleman (RSA) algorithm. They can also be used to encrypt images directly when the information of image is regarded as ordinary data stream. However, there are two major differences between image data and text data. One difference is that image data permit small distortion owing to the characteristic of human perception, but text data rarely do. The other is that the size of image data is usually much larger than that of text data. Therefore, some special encryption methods for image have been proposed recently. Chaotic encryption is an image encryption method attracting much attention recently.Chaos was first discovered by an America meteorologist Lorenz in 1963, and turned into a new science rapidly. Over the past decade, there has been tremendous interest in studying the behavior of chaotic systems. They are characterized by sensitive dependence on initial conditions, similarity to random behavior, and continuous broad-band power spectrum. Chaos has potential applications in several functional blocks of a digital communication system: compression, encryption and modulation. The possibility for self-synchronization of chaotic oscillations has sparked an avalanche of works on application of chaos in cryptography. An attempt only to mention all related papers on chaos and cryptography in this short presentation will result in a prohibitively long list; and, therefore, we refer the reader to some recent work. Despite a huge number of papers published in the field of chaos-based cryptography, the impact that this research has made on conventional cryptography is rather marginal. This is due to two reasons:First, almost all chaos-based cryptographic algorithms use dynamical systems defined on the set of real numbers, and therefore are difficult for practical realization and circuit implementation. Second, security and performance of almost all proposed chaos-based methods are not analyzed in terms of the techniques developed in cryptography. Moreover, most of the proposed methods generate cryptographically weak and slow algorithms. Cryptography is generally acknowledged as the best method of data protection against passive and active fraud. Therefore, it is necessary that the randomness testing of the chaotic sequence is discussed.The need for random and pseudorandom numbers arises in many cryptographic applications. For example, common cryptosystems employ keys that must be generated in a random fashion. Many cryptographic protocols also require random or pseudorandom inputs at various points, e.g., for auxiliary quantities used in generating digital signatures, or for generating challenges in authentication protocols.The first type of sequence generator is a random number generator (RNG). An RNG uses a non-deterministic source, along with some processing function to produce randomness. The use of a distillation process is needed to overcome any weakness in the entropy source that results in the production of non-random numbers (e.g., the occurrence of long strings of zeros or ones). The entropy source typically consists of some physical quantity, such as the noise in an electrical circuit, the timing of user processes (e.g., key strokes or mouse movements), or the quantum effects in a semiconductor. Various combinations of these inputs may be used.The outputs of an RNG may be used directly as a random number or may be fed into a pseudorandom number generator (PRNG). To be used directly (i.e., without further processing),the output of any RNG needs to satisfy strict randomness criteria as measured by statistical tests in order to determine that the physical sources of the RNG inputs appear random. For example, a physical source such as electronic noise may contain a superposition of regular structures, such as waves or other periodic phenomena, which may appear to be random, yet are determined to be non-random using statistical tests.For cryptographic purposes, the output of RNGs needs to be unpredictable. However, some physical sources (e.g., date/time vectors) are quite predictable. These problems may be mitigated by combining outputs from different types of sources to use as the inputs for an RNG. However, the resulting outputs from the RNG may still be deficient when evaluated by statistical tests. In addition, the production of high-quality random numbers may be too time consuming, making such production undesirable when a large quantity of random numbers is needed. To produce large quantities of random numbers, pseudorandom number generators may be preferable.A PRNG uses one or more inputs and generates multiple"pseudorandom"numbers. Inputs to PRNGs are called seeds. In contexts in which unpredictability is needed, the seed itself must be random and unpredictable. Hence, by default, a PRNG should obtain its seeds from the outputs of an RNG; i.e., a PRNG requires a RNG as a companion.The outputs of a PRNG are typically deterministic functions of the seed; i.e., all true randomness is confined to seed generation. The deterministic nature of the process leads to the term"pseudorandom."Since each element of a pseudorandom sequence is reproducible from its seed, only the seed needs to be saved if reproduction or validation of the pseudorandom sequence is required.Ironically, pseudorandom numbers often appear to be more random than random numbers obtained from physical sources. If a pseudorandom sequence is properly constructed, each value in the sequence is produced from the previous value via transformations which appear to introduce additional randomness. A series of such transformations can eliminate statistical auto-correlations between input and output. Thus, the outputs of a PRNG may have better statistical properties and be produced faster than an RNG.Chaotic signals are usually noise-like and chaos system is very sensitive to initial condition and parameters. Encryption and chaos, in fact, exhibit remarkably similar features. The chaos encryption system has wide application prospects.In this paper, chaotic theory and parameters for judging chaos are researched deeply. The cryptology characteristics of the chaotic map are described, and the method of key design based on logistic-map is introduced. A set of randomness tests described by NIST(National Institute of Standards and Technology) are used for the statistical analysis of binary chaotic sequence. Finally, an image secure communication scheme based on chaos theory is proposed, and image transmission technique based MATLAB and VB is introduced.