Abstract: The well known multiple letter encryption cipher is the Playfair cipher. Here the digrams in the plaintext are treated as single units and converted into corresponding cipher text digrams. However because of the drawbacks inherent in the 5*5 Playfair cipher which adversely affects the security we proposed an 8*8 Playfair cipher. For details one can refer to [1]. This paper analyses the new proposed system. For this we have carried out cryptanalysis and through the avalanche effect we find out that the proposed cipher is a strong one.

Abstract: Steganography deals with hiding of data in images and steganalysis reveals the presence of data and also the data. In this paper, we propose a steganography technique that is based on randomizing the sequence of cipher bits. We compute the suitability measure of the various random sequences of the cipher bits against a given image and select the random sequence closest to the image. We generate these random sequences by the use of an L.F.S.R. We then embed these random sequences of cipher bits in the image. One advantage of this technique is there is no one-to-one mapping between a given cipher text and an image. Secondly, for successful cryptanalysis, along with an attack on the encryption system one has to get hold of information of the L.F.S.R that generated this random.

Abstract: In this paper we are proposing a new Image steganography technique for secure communication between sender and receiver. At the sender we follow two steps. In the first step we encrypt the secret information by blowfish algorithm and in second step we embed the cipher text in LSB minus one and LSB (least significant bit) locations of some of the selected pixels (bytes) of the carrier image. One pixel is 8 bits in 8-bit gray scale. The selection of the pixels is done by a dynamic evaluation function. Depending on the cipher text bits, the dynamic evaluation function decides on which pixels the different cipher text bits are to be embedded. At the receiver also two steps are followed, first the cipher bits are retrieved from the image from the said locations and then it is decrypted by using the blowfish algorithm to get the secret information. As the embedding byte locations are decided based on bits of the cipher text, so it is dynamic steganography. This approach provides two levels of security, one at the cryptography level and the other at the steganography level. The proposed technique is experimented through a large number of experiments.

Abstract: In this paper we propose a technique for secure communication between sender and receiver. We use both cryptography and steganography. We take image as the carrier to use steganography. We have extended the existing hill cipher to increase its robustness and used it as our cryptography algorithm. By using this extended hill cipher (a new block cipher) which uses a 128 bit key, we encrypt the secret message. Then the cipher text of the secret message is embedded into the carrier image in 6th, 7th and 8th bit locations of some of the selected pixels (bytes). The 8th bit in a pixel (byte) is called as the least significant bit (LSB). The pixel selection is done depending on the bit pattern of the cipher text. So for different messages the embedding pixels will be different. That means to know the pixels of the image where the cipher text is embedded we should know the cipher text bits. Thus it becomes a stronger steganography. As the pixels where we embed are chosen during the run time of the algorithm, so we say that it is dynamic steganography. After embedding the resultant image will be sent to the receiver, the receiver will apply the reverse process what the sender has done and get the secret message.

Abstract: In the last two decades, Chaos theory has received a great deal of attention from the cryptographic community. This paper presents two ideas. First idea is using chaotic functions to overcome the weaknesses of the classical Hill cipher. The second idea is proposing a new encoder-decoder architecture, called ChaoEncoDeco, for securing JPEG images. An extra stage of encryption is embedded within the traditional JPEG codec to improve security level of such system. This security stage uses one of the chaotic functions called Logistic Map. This map is used to enhance the Hill cipher and achieve more secure encryption key. The properties of both chaotic system and of the Hill cipher encryption key are all utilized to obtain ultimate secure systems. The proposed encryption algorithm is crypto-analyzed and compared to the standard Hill cipher algorithm. Complete evaluation for the proposed architecture is also performed which indicates the effectiveness of the proposed system.

Abstract: Problem statement: The Hill cipher is the first polygraph cipher which has a few advantages in data encryption. However, it is vulnerable to known plaintext attack. Besides, an invertible key matrix is needed for decryption. It may become problematic since an invertible key matrix does not always exist. Approach: In this study, a robust Hill algorithm (Hill++) has been proposed. The algorithm is an extension of Affine Hill cipher. A random matrix key, RMK is introduced as an extra key for encryption. An algorithm proposed for involutory key matrix generation is also implemented in the proposed algorithm. Results: A comparative study has been made between the proposed algorithm and the existing algorithms. The encryption quality of the proposed algorithm is also measured by using the maximum deviation factor and correlation coefficient factor. Conclusion/Recommendations: The proposed algorithm introduced a random matrix key which is computed based on the previous ciphertext blocks and a multiplying factor. A modified of Hill Cipher is free from the all-zero plaintext blocks vulnerability. Usage of involutory key for encryption and decryption managed to solve the non invertible key matrix problem. It also simplify the computational complexity in term of generating the inverse key matrix.

Abstract: Steganography is the science of hiding information. Whereas the goal of cryptography is to make data unreadable by a third party, the goal of steganography is to hide the data from a third party. Briefly stated, steganography is the term applied to any number of processes that will hide a message within an object, where the hidden message will not be apparent to an observer. The original steganographic applications used “null ciphers”, or clear text. A null cipher conveys that the message has not been encrypted in any way, whether it is using basic character shifting, substitution or advanced modern day encryption algorithm. So, the message is often in plain view but for a reason can either not be detected as being present or cannot be seen once detected. As is common with cryptography, steganography has its roots in military and government applications and has advanced in ingenuity and complexity. In this paper, Network Based Public Key Method for Steganography is proposed under RSA cryptographic assumptions.

Abstract: Cryptography is the practice and study of hiding information. Cryptanalysis is the study of how to crack encryption algorithms or their implementations. This paper describes an effortless method of a cryptanalyst for a knapsack cipher. The describing method is based on simple programming and calculations to crack the knapsack cipher.

Abstract: With the increased use of digital images in numerous fields, especially sensitive ones like medicine and military where confidentiality is extremely important, their encryption has become mandatory. This paper depicts our proposed digital image encryption technique which employs two types of non-linear pixel transformation and the traditional Hill cipher which is a Matrix Transformation (MT). While the Hill cipher achieves good amount of diffusion, the two non-linear pixel transformations namely the All Pixel Transformation (APT) and the Interleaved Pixel Transformation (IPT) makes sure that confusion, avalanche effect, and completeness effect occur. The pixel transformation results in the encryption scheme being collision resistive. Simulation results show high sensitivity to key, plaintext and ciphertext changes. From the cryptanalysis point of view, it is highly resistive to known/chosen plaintext and cipher text attacks. Moreover it is a lossless encryption technique and hence apt for securing medical and military imagery.

Abstract: Steganography (a rough Greek translation of the term Steganography is secret writing) has been used in various forms for 2500 years. It has found use in variously in military, diplomatic, personal and intellectual property applications. Briefly stated, steganography is the term applied to any number of processes that will hide a message within an object, where the hidden message will not be apparent to an observer. The original steganographic applications used "null ciphers", or clear text. A null cipher conveys that the message has not been encrypted in any way, whether it is using basic character shifting, substitution or advanced modern day encryption algorithm. So, the message is often in plain view but for a reason can either not be detected as being present or cannot be seen once detected. As is common with cryptography, steganography has its roots in military and government applications and has advanced in ingenuity and complexity. In this paper, Network Based Public Key Method for Steganography is proposed under RSA cryptographic assumptions.

Abstract: At IEEE GLOBECOM 2008, a lightweight cipher based on a Multiple Recursive Generator (MRG) was proposed for use in resource limited environment such as sensor nodes and RFID tags. This paper proposes two efficient attacks on this MRG cipher. A distinguishing attack is firstly introduced to identify the use of an MRG cipher that has a modulus suggested by its designers. It requires 218 words of ciphertext and the most significant bit of each corresponding plaintext word. Then an efficient known plaintext attack is proposed to construct the cipher's current state and generate subkeys used for all subsequent encryption. The known plaintext attack, when targeted at the MRG ciphers optimized for efficiency, only requires 2k words of known plaintext and trivial computation where k is the MRG order. Even the ciphers based on complicated and inefficient MRGs can be attacked with low complexity, e.g. in the magnitude of 212 words of known plaintext for all MRG ciphers with order 47, regardless of which MRG modulus is used. These two attacks indicate that the examined MRG cipher structure is seriously flawed. Copyright © 2010 John Wiley & Sons, Ltd.