Hybrid image encryption using Pseudo Random Number Generators, and transposition and substitution techniques

The importance of strong image encryption has increased hugely with the increasing stress on cryptanalysis. The protection of image data from unauthorized access is important. In the proposed work, the authors introduce a two-stage image encryption using a hybrid of two Pseudo Random Number Generators. In the first stage, an altered version of the Sophie Germain Prime Generator is used to create a set of generated pseudo random numbers, which is then used to assign new values to all the pixels of the image. In the second stage, Lehmer Random Number Generator is used to generate a set of random numbers depending on the key entered. Each pixel of the intermediate cipher image is then swapped with a different pixel using the list of the pseudo random numbers. The resultant is an encrypted image on which cryptanalysis becomes difficult since the random numbers cannot be predicted if key values for PRNGs are not known.