@Article{, title={Selective Image Encryption Based on DCT, Hybrid Shift Coding and Randomly Generated Secret Key}, author={Loay E. George1 and Enas Kh. Hassan*2 and Sajaa G. Mohammed3 and Faisel G. Mohammed1}, journal={Iraqi Journal of Science المجلة العراقية للعلوم}, volume={61}, number={4}, pages={920-935}, year={2020}, abstract={Most of today’s techniques encrypt all of the image data, which consumes atremendous amount of time and computational payload. This work introduces aselective image encryption technique that encrypts predetermined bulks of theoriginal image data in order to reduce the encryption/decryption time and thecomputational complexity of processing the huge image data. This technique isapplying a compression algorithm based on Discrete Cosine Transform (DCT). Twoapproaches are implemented based on color space conversion as a preprocessing forthe compression phases YCbCr and RGB, where the resultant compressed sequenceis selectively encrypted using randomly generated combined secret key.The results showed a significant reduction in image quality degradation whenapplying the system based on YCbCr over RGB, where the compression ratio wasraised in some of the tested images to 50% for the same Peak Signal to Noise Ratio(PSNR). The usage of 1-D DCT reduced the transform time by 47:1 times comparedto the same transform using 2-D DCT. The values of the adaptive scalar quantizationparameters were reduced to the half for the luminance (Y band) to preserve thevisual quality, while the chrominance (Cb and Cr bands) were quantized by thepredetermined quantization parameters. In the hybrid encoder horizontal zigzag,block scanning was applied to scan the image. The Detailed Coefficient (DC)coefficients are highly correlated in this arrangement- where DC are losslesslycompressed by Differential Pulse Coding Modulation (DPCM) and theAccumulative Coefficients (AC) are compressed using Run Length Encoding(RLE). As a consequence, for the compression algorithm, the compression gainobtained was up to 95%. Three arrays are resulted from each band (DC coefficients,AC values, and AC runs), where the cipher is applied to some or all of those bulksselectively. This reduces the encryption decryption time significantly, whereencrypting the DC coefficients provided the second best randomness and the leastencryption/decryption time recorded (3 10-3 sec.) for the entire image. Although thecompression algorithm consumes time but it is more efficient than the savedencryption time.

} }