Cryptography method based on hill’s cipher And ECC in image processing Ali Kaffash Faculty of computer engineering Imamreza international university Mashhad, Iran alikaffash@yahoo.com Abstract —hill’s cipher is a symmetric cryptography algorithm which is based on blocking cipher and use array computation to encrypt a message.in this article we want introduce new application of hill’s cipher cryptography in digital image processing to encrypt an image and ECC to transfer the key during an unsecure channel to decrypt it. The method involves each type of images including binary , gray scale and RGB images. Keywords—hill’s cipher;symmetric algorithems; blocking cipher; modular mathematics;image processing;Elliptic Curve Cryotosystem(ECC) I. INTRODUCTION Encryption algorithms are very important for cryptography because cryptography focuses on encryption algorithms to provide security and privacy.in general encryption algorithms have been divided into three classes. The classes are symmetric and asymmetric algorithms and there another type which is called digest algorithms. Encryption is the process of disguising a message in such a way as to hide its substance. The main idea behind the encryption is to provide the receiver to decrypt the information using his/her private key. The process of encrypting a plaintext is called encryption and the process of decrypting cipher text back into plaintext is called decryption . As we have seen, there are three main materials for encryption: plaintext, key and encryption algorithm, which uses the other two materials. There are complex mathematical processes behind the encryption algorithms. The main goal in encryption is to make the relation between plaintext and cipher text irrelevant using these mathematical background and the key. In [most of the ciphers that we have studied], changing one letter in the plaintext changes exactly one letter in the cipher text. In the [Caesar], affine, and substitution ciphers, a given letter in the cipher text always comes from exactly one letter in the plaintext. In the Vigenère system, the use of blocks of letters corresponding to the length of the key, made the frequency analysis more difficult, but still possible since there was not interaction among the various letters in each block. Block ciphers avoid these problems by encrypting blocks of several letters or numbers simultaneously. A change of one character in a plaintext block should change potentially all the characters in the corresponding cipher text block. The standard way of using a block cipher is to convert blocks of plaintext to blocks of cipher text, independently and one at a time. This is called electronic code book (ECB) mode. However, there are ways to use feedback from the blocks of cipher text in the encryption of subsequent blocks of plaintext. This leads to the cipher block chaining (CBC) mode and cipher feedback (CFB) [and other modes] of operation. [1] II. RELATED WORK The visual cryptography was initially intoduced and used only on binary images. Recently, some visual cryptography schemes for gray and color image have been proposed. Again naor and shamir [9] introduced vs. (k,n), the idea of cover based semi-group to further improve the contest in 1996. Ateniese et al. [10] provided the first construction of vs. (2,n) having the best possible contest for any nl2. Verheul and Tilburg [11] are first to present a secret sharing scheme for images with c colors in 1997. The principle of this scheme is to transform one pixel of image to b sub-pixels, and each sub pixel is divided into c color regions. In each sub-pixel, there is exactly one color region colored, and all the other color regions are black. The color of one pixel depends on the interrelations between the stacked sub-pixels. A major disadvantage of this scheme is that the number of colors and the number of sub-pixels determine the resolution of the revealed secret image. If the number of colors is large, coloring the sub-pixels will become a very difficult task. III. HILL’S CIPHER The Hill cipher uses matrices to transform blocks of plaintext letters into blocks of cipher text. Here is an example that encrypts digraphs. A. Encryption method Consider the following message: