Penyembunyian Ciphertext Algoritma Gost Pada Citra Ke Dalam Audio Dengan Metode Least Significant Bit

Abstract

Government Standard (GOST) is a 64-bit block cipher algorithm with 32 round, use a 256-bit key. The weakness of this algorithm is the keys so simple, than make cryptanalyst easy to break this algorithm. Least Significant Bit (LSB) use to insert message into another form without changing the form of the cover after insertion. This research does by hiding encrypted ciphertext to image and hiding image into audio. This research use grayscale and RBG image with BMP and PNG format. Audio using music with wav format. Security analysis using differential analysis NPCR and UACI. Security analysis aims to calculate percentage from cover after hiding the message. The smaller the NPCR and UACI values, the higher the level of security the message is hidden. The results of the analysis of concealment in the image obtained by the average values of NPCR and UACI were 99.98% and 3.46% respectively. While the results of the analysis of hiding in audio obtained the average value of NPCR and UACI were 83.78% and 12.66% respectively.

Image Steganography Analysis Using GOST Algorithm and PRNG Based on LSB

“…The GOST algorithm accepts a 256-bit key and 64-bit text (plaintext/ciphertext) per block [15]. If there is a text that is longer than 64 bits, then the text will be broken into several blocks and added padding if needed.…”

“…Break the binary number into 4 digits so that 4 digits are produced sequentially, namely "1111" (15), "0000" (0), "0001" (1), and "0011" (3) 2.…”

“…For the first order, namely "1111" (15), then look for the intersection of column 15 and row 1 so that "0001" is produced (1) 3.…”

“…This method hides information by inserting a message at the rightmost bit of an image pixel (or file) [12]. Various attacks against GOST have been carried out in previous studies, where the best attack requires 2 32 data and 2 36 memory with a time complexity is 2 224 [13] [15]. To overcome the weaknesses of GOST and LSB, further modifications were made to the LSB using the XOR and PRNG logic functions [16].…”