Paper 2009/043

Image Encryption by Pixel Property Separation

Karthik Chandrashekar Iyer and Aravinda Subramanya

Abstract

Pixels in an image are essentially constituted of two properties, position and colour. Pixel Property Separation, a radically different approach for Symmetric-key image encryption, separates these properties to disturb the semantics of the image. The scheme operates in two orthogonal stages each requiring an encryption key. The first stage creates the Position Vector, an ordered set of Pixel Position Information controlled by a set of plaintext dependent Random Permutations. A bitmap flagging the presence of all the 24 bit colours is generated. The second stage randomly positions the image width and height within the ciphertext and finally applies a byte transposition on the ciphertext bytes. The complete set of image properties including width, height and pixel position-colour correlation are obscured, resulting in a practically unbreakable encryption. The orthogonality of the stages acts as an anti-catalyst for cryptanalysis. The information retrieved from compromising a stage is totally independent and cannot be used to derive the other. Classical cryptanalytic techniques demand huge number of attempts, most failing to generate valid encryption information. Plaintext attacks are rendered ineffective due to the dependency of the Random Permutations on the plaintext. Linear and Differential cryptanalysis are highly inefficient due to high Diffusion and Confusion. Although the paper describes the algorithm as applied to images, its applicability is not limited to images only. The cryptographic strength and the efficiency of operation is independent of the nature of the plaintext.

Note: Although the paper describes the algorithm as applied to images, its applicability is not limited to images only. The cryptographic strength and the efficiency of operation is independent of the nature of the plaintext. For example, in the case of a non-image plaintext, each set of 3 bytes shall represent a 24 bit pixel.