1. INTRODUCTION:

Internet based communications are evolving at a tremendous rate. Encryption of data has become an important way to protect data resources especially on the Internet, intranets and extranets. Encryption involves applying special mathematical algorithms and keys to transform digital data into cipher code before they are transmitted and decryption involves the application of mathematical algorithms and keys to get back the original data from cipher code. The goal of security management is to provide authentication of users, and integrity, accuracy and safety of data resources.

The model for encryption and decryption of an image is designed with the objectives to have confidentiality and security in transmission of the image based data as well as storage in the data warehouse, with the help of auto generated key which is extracted by original/encrypted image.

This technique can considerably improve the efficiency of data transmission, and it is particularly suitable for the image transmission via the Internet.[01]

After encryption of image it will segment into four parts will be transmitted another end, an image-based data requires more effort during encryption and decryption. The model for encryption and decryption of an image using auto generated key which is generated by image.

Through electronic mail / voice mail / video mail it is possible to solicit the Telemedicine is becoming popular in the specialties of radiology, pathology, critical care and psychiatry, where data is in the form of image. It is required to ensure confidentiality and security for transmitting certain image-based data over the Internet. The aim of security management is to provide authentication of users and integrity, accuracy & safety of data resources. The model for encryption & decryption of an image is designed with the same purposes.

Basic operations that can be carried out in encryption/decryption are: substitution and transposition. Due to advent of computers, these operations are carried out on binary bits.[01]

Considerations of privacy and confidentially in a computer environment have given recognition to the need for protecting certain communications and stored data from theft and misuse. A suitable methodology for protecting communicated or stored data involves the use of cryptographic techniques. Cryptography is the study of mathematical techniques related to aspects of information security such as confidentiality, data integrity, entity authentication and data origin authentication. A message is plaintext An encryption method which depends on the secrecy of the encryption algorithm is not considered to be a true encryption method. An encryption method which depends on the secrecy of the encryption algorithm is not considered to be a true encryption method [02].

The amount of digital medical images has increased rapidly in the Internet. The necessity of fast and secure diagnosis isvital in the medical world. Nowadays, the transmission of images is a daily routine and it is necessary to find an efficient way to transmit them over the net. In this paper we propose a new technique to cipher an image for safe transmission. There are several methods to encrypt binary or grey level images [10]

The encryption can be done by block or by stream. But the encryption block methods applied to image, have presented two inconvenient. The first one was when you have homogeneous zones, all blocks of this kind are encrypted on the same manner. The second problem was that block encryption methods are not robust to noise. The stream cipher method is robust to moderate noise like JPEG compression with high quality factor. To embed the encrypted secret key in the image we have used a new DCT-based watermarking method [9].

Along with the fast progression of data exchange in electronic way, it is important to protect the confidentiality of data from unauthorized access. Security breaches may affect user's privacy and reputation. So, data encryption is widely used to confirm security in open networks such as the internet. Due to the substantial increase in digital data transmission via internet, the security of digital images has become more prominent and attracted much attention in the digital world today. Also, the extension of multimedia technology in our society has promoted digital images to play a more significant role than the traditional texts, which demand serious protection of users' privacy for all applications. Each type of data has its own features; therefore, different techniques should be used to protect confidential image data from unauthorized access.

Most of the available encryption algorithms are used for text data. However, due to large data size and real time requirement, the algorithms that are appropriate for textual data may not be suitable for multimedia data.[03]

To ensure the security of a cryptosystem the cipher must have some properties such as good distribution, long period, high complexity and efficiency. In particular, the outputs of a cryptosystem must be unpredictable in the absence of knowledge of the inputs. Recently, the NIST designed a set of different statistical tests to justify randomness of binary sequences produced by either hardware or software based cryptographic random or pseudorandom number generators. These tests focus on a variety of different types of nonrandomness that could exist in a sequence. The mathematical description of each test can be found at[05]

Many researchers proposed different image encryption schemes to overcome image encryption problems. In this research we have tried to find a simple, fast and secure algorithm for image encryption using the characteristics of chaotic functions and the LFSRbased stream ciphers. According to key's large space in the chaotic functions, this method is very robust. Finally, this algorithm is very sensitive to small changes in key so even with the knowledge of the key approximate values; there is no possibility for the attacker to break the cipher.[07,08]

Also many algorithms and architectures based on various transforms and digital holography were reported for optical image encryption[20]

2. ARCHITECTURE:

For encryption and decryption a symmetric key model has been used. The architecture of image encryption and decryption model is described in Figure –1:

Figure 1: Pixel encryption by stream cipher.

3. STREAM CIPHER:

3.1 The general method

Algorithms of flux ciphering (stream ciphers) can be defined as being algorithms of ciphering by blocks, where the block has an unitary dimension (1 bit, 1 byte, etc.) or relatively small. Their main advantages are their extreme speeds and their capacity to change every symbol of the plaintext. Besides, they are less numerous than those of ciphering by blocks, they are useful in an environment where mistakes are frequents, because they have the advantage of not propagate them (diffusion) [04]. The most widespread and used coding stream ciphers are the synchronous, and the most widely used is the RC4 [05].

The algorithm RC4 has been thought in 1987 by Ron Rivest and has been developed for the RSA Security. It is based on the random permutations into the byte. The algorithm has avariable key length (of 1 to 256 bytes). The key is used to initialize a table of 256-byte states. This table is used for the pseudo-random byte generation to produce a random pseudo flux with which the plaintext will be transformed. Current interest in stream ciphers is most commonly attributed to properties of the one-time pad, called the Vernam cipher [05]. It uses a string of bits that is completely random generated. The key stream has the same length as the plaintext message. The random string is combined using exclusive OR operations with the plaintext to produce the cipher text. The Linear Feedback Shift Register (LFSR) is a mechanism very often applied in applications that require very fast generation of a pseudo-random sequence. The symmetrical ciphering uses LFSR to generate some pseudo-random bit sequences called register’s vector. This vector is generally the key of the ciphering process and I t is defined in relation to a meter. For every iteration, the content of the register is baffled toward the right of a position, and the XOR operation is applied on one under whole of bits whose result is placed to the left extreme of the register.

3.2 Image encryption by stream cipher

Generally, the private key length of the stream ciphering can be eventually as long as the length of the message. The method detail resides in the fact that for every pixel the encryption depends previously of the original pixel value of the key. For every pixel p(n) of the original image pixel value p’(n) of the ciphered image using the equation:

The chosen value of k must be larger enough to turn the system safe. Suppose key size depends upon size of image,

4. CONCLUSION

This paper presented for image security and encrypt image for image safe transmission Purpose, auto key generation is safe instead of sending public key or private key, The image encryption and decryption model is designed and implemented to provide confidentiality and security in transmission of the image based data as well as in storage in the data warehouse, with the help of auto generated key.

5. REFENRENCES:

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Received on 29.04.2013 Accepted on 15.05.2013

Int. J. Tech. 3(1): Jan.-June. 2013; Page 15-18