Covert Encryption and Document Authentication using Texture Coding

Abstract

With the im provem ents in the quality of Com m ercial-Off-The-Shelf (COTS) printing and scanning devices, the ability to counterfeit docum ents has becom e a widespread problem . Consequently, there has been an increasing dem and to develop digital waterm arking techniques which can be applied to both electronic and printed im ages (and docum ents) that can be authenticated, prevent unauthorized copying and withstand abuse and degradation. In this paper, a new approach to digital waterm arking is presented and a range of possible applications are considered. The process is defined by using concepts and techniques borrowed from Cryptography. It is based on com puting a 'scram ble im age' by diffusing a waterm ark im age with a noise field (a cipher). The cover im age (covertext) is then introduced using a sim ple additive process (confusion). The waterm ark is subsequently recovered by rem oving the covertext and then correlating the output with the original (key dependent) noise field. For covert encryption, this approach provides the user with a m ethod of hiding ciphertext (the scram bled im age) in a host im age before the transm ission of t he data. With regard to dcum ent authentication, a diffusion only or ' texture coding' approach that is