void shift_rows(unsigned char* state) {
    unsigned char temp = state[1];
    state[1] = state[5];
    state[5] = state[9];
    state[9] = state[13];
    state[13] = temp;

    for (int i = 0; i < 2; i++) {
        temp = state[2];
        state[2] = state[6];
        state[6] = state[10];
        state[10] = state[14];
        state[14] = temp;
    }

    for (int i = 0; i < 3; i++) {
        temp = state[3];
        state[3] = state[7];
        state[7] = state[11];
        state[11] = state[15];
        state[15] = temp;
    }
}