A Secure Image Transmission using Image Mosaics, 2D DWT and RSA Encryption

Security of an image when it is in transit is a serious matter of concern. The advent of computing systems, new inventions in image processing fields, Artificial Intelligence have contributed considerably for the insecurity of an image. Conceptually, a strong encryption powered by sophisticated Cryptographic algorithm can protect any type of multimedia data. But encryption changes the format of data and it is not a good idea to use it with an image. Reason being that, an encrypted noise like image attracts hacker’s attention and secondly, lossless recovery of original image is not possible from an encrypted image. An alternative for securing the image is covert communication using Steganography methods. Here, message is concealed; but if existence of data is discovered in any way, the security is compromised. Therefore, there is a need for a system which exploits the advantages of both Cryptography and Steganography. The proposed system combines those two and provides “Stenographic Encryption” security for an image being sent in the channel. An image which needs to be sent secretly and securely is called the SecretiImage. Another image which is similar to secret image in background and colour characteristics - is selected and it is called TargetiImage. The secretiimage is sliced intoismall chunks and a mosaic of target image is created (MosaiciEncryption). The mosaic encrypted image will undergo 2 levels 2 dimensional DWT (Discrete Wavelet Transform) which separates information part and details part. Also, 2D DWT compresses the image. RSA encryption is applied to information part. The detailed part and RSA encrypted information part are merged together to form the combined image. A large cover image is chosen and the combined image’s bits are embedded into pixels of cover image using advanced LSB method which gives the stego image. This stego image is sent to receiver over channel. At the receiver, combined image is extracted from the stego image. RSA decryption is applied to information part and IDWT is applied to get the mosaic image. The secret image is reconstructed using the mosaic image. The proposed method will give two levels of encryption protection (Mosaic encryption and RSA encryption), compression facility (DWT) and Stenographic facility (LSB hiding). Nearly lossless recovery of Secret image is possible. The experimental results were pleasing with high PSNR and Correlation and less RMSE. The system is implemented using MATLAB tool.