A New Bi-Level Encoding and Decoding Scheme for Pixel Expansion Based Visual Cryptography

Introduction

Demand of information exchange in heavy data traffic is increasing day by day with the influence of digital media over internet. Information security in modern era is a major concern for many mathematicians, computer scientists. For abstracting the secret from malicious access, third party attack there are many algorithms and mathematics was being proposed in last three decade. Usage of Mathematics makes many cryptographic algorithms robust. Today’s world is roaming behind the information operated in electronic media and internet technology starting from banking sector (both offline and online banking) to multimedia industry. As advancement of electronic media, digital communication makes the world is in finger press at the same time misuse of information is a big threat to modern world. Cryptography makes the secret information into an unreadable format and plays a vital role in presence of third parties or eavesdropper for secure communication. In the last three decades, popular cryptographic algorithms RSA, AES, DES, Blowfish, Secret Sharing etc. using private key and public key concepts provides security to text-based information. Day by day evolution of digital multimedia information system demands to build new cryptographic algorithm to cope with current technological arena. Steganography, Visual Cryptography, QR Code are emerging areas of security over modern multimedia technology. Visual Cryptography combines secret sharing scheme proposed by (Shamir 1979) with visual transparencies into n number of shares. The concept of visual cryptography is combined with visual secret sharing, threshold secret sharing scheme to produce a robust encryption and decryption method which has the broad areas of application. To divide secret data into shares which generate random shares of (k-1) polynomial degree using modulus based arithmetic where (k ≤ n). f(x) can be derived in equation (1) as

Secret data is , is the prime number and. From the integer values of uniformly distributed [1; p) the coefficients are chosen randomly. Mathematically Lagrange's interpolation is used in secret sharing scheme which is represented in equation (2), (3) and (4) using Lagrange's interpolation , I = 1, 2…n.

Figure 1.

Shows the (2, n) secret sharing scheme

Visual Cryptography gives a new dimension to information security arena using secret sharing scheme among a set of trusted participants. Beauty of this security concept is that unlike other highly computational with bigger complexity method such as RSA, AES, DES the decoding of the corresponding secret can be achieve using normal human perception without performing the computation at receivers end. Visual Cryptography has versatile application areas starting from banking sector to other security area.