Visual cryptography is a secret sharing method that uses human eyes to decrypt the secret. Most visual cryptographic methods utilize the technique of pixel expansion, which causes the size of the shares to be much larger than that of the secret image. This situation is more serious for grey-level and chromatic images. In this paper, we propose a multi-pixel encoding method for grey-level and chromatic images without pixel expansion. We simultaneously encrypt r successive white or black pixels each time. The probability of these r pixels being coloured black depends on the ratio of blacks in the basis matrices. Afterward, we incorporate the techniques of colour decomposition and halftoning into the proposed scheme to handle grey-level and chromatic images. The experimental results show that the shares are not only the same size as the secret image, but also attain the requirement of security. The stacked images have good visual effect as well. Besides, our method can be easily extended to general access structure.

We propose and analyze a new type of cryptographic scheme, which extends principles of secret sharing to Morse code-like audio signals. The proposed “audio cryptography scheme ” (ACS) is perfectly secure and easy to implement. It relies on the human auditory system for decoding. “Audio sharing schemes ” (ASS) proposed earlier were based on disguising secret binary message with a cover sound. Moreover, only 2-out-of-n audio sharing schemes have ever been proposed. Our scheme correlates strongly, and is analogous to schemes in well-studied visual cryptography. Consequently, we were able to use the existing visual cryptography constructions and obtain not only k-out-of-n audio sharing schemes, but also the most general audio cryptography schemes for qualified subsets. In audio cryptography scheme for qualified subsets, a subset of participants can recover the secret audio signal only if some qualified subset of participants is its subset. 1.

Visual cryptography was introduced by Naor and Shamir as a way to allow fast visual sharing of graphic objects. No reconstruction device is required; instead reconstruction is performed by fitting slides together. Several schemes

A form of visual jam resistant coding is presented. Using Visual BBC, a modified form of BBC (Baird, Bahn, Collins) coding, it is shown that several images can be printed on clear plastic, such that when they are superimposed (i.e. a bitwise OR of the pixels is performed), the resulting image may look random, but the original images can still be recovered without any information about the original pictures, and without any secret. BBC is a complex subject to understand, and so Visual BBC aids the teaching of how BBC coding works, by giving students a concrete, physical model. Examples are shown, illustrating that it is possible for legitimate BBC codewords to actually look like recognizable images, rather than just random binary strings. This allows us to superimpose arbitrary pictures and separate them again in linear time without using any keys or channels specific to each picture. This is not possible in any other coding systems, such as error correcting codes, superimposed codes, or steganography systems. In addition, a number of analysis problems are described that can be given to students, which are motivated by the issues arising in Visual BBC, and which further increase student understanding of the system.