Method shiftRowsDec

src/main/java/com/thealgorithms/ciphers/AES.java:2604–2633

Cell permutation step for decryption . Shifts cells within the rows of the input and returns the result.

(BigInteger ciphertext)

     * the input and returns the result.
     */
    public static BigInteger shiftRowsDec(BigInteger ciphertext) {
        int[] cells = splitBlockIntoCells(ciphertext);
        int[] output = new int[16];

        // do nothing in the first row
        output[0] = cells[0];
        output[4] = cells[4];
        output[8] = cells[8];
        output[12] = cells[12];

        // shift the second row forwards by one cell
        output[1] = cells[13];
        output[5] = cells[1];
        output[9] = cells[5];
        output[13] = cells[9];

        // shift the third row forwards by two cell
        output[2] = cells[10];
        output[6] = cells[14];
        output[10] = cells[2];
        output[14] = cells[6];

        // shift the forth row forwards by tree cell
        output[3] = cells[7];
        output[7] = cells[11];
        output[11] = cells[15];
        output[15] = cells[3];

        return mergeCellsIntoBlock(output);
    }

    /**
     * Applies the Rijndael MixColumns to the input and returns the result.