Dual Image based LSB Steganography

A new steganographic model using dual image has been proposed to increase the obscurity of the secret as well as to make it more secure. It uses two different images namely reference image and cover image along with a secret embed key ( stego key). Reference image is divided into blocks with assigned block-codes. Total number of blocks and other embedding parameters(block traversing direction, starting block etc.) are stored in the embed key. Secret message converted to binary and bit pairs are made. Bit pairs of secret message are encoded using the bit pairs of different blocks of reference image and sometimes updating a few LSB bits in the reference image. As an optional capacity enhancement module for text only secret messages dictionary word indexing based encoding is applied. Finally encoded bit stream is embedded into the cover image using any standard LSB technique with its own merits and demerits. LSB changes in the reference image are almost negligible. Embedding key is encrypted using public key of the receiver hence even if someone gets the encoded message it is not possible to get the secret message. As this model can use any existing LSB replacement scheme to embed encoded message into the cover image the state of the art security and other quality features are by default available to it. This is made more secure by using different dictionary word indexing scheme every time based on a random secret key that is appended in the embed key.