#include <Windows.h>
#include <stdio.h>
using namespace std;

BYTE buffer[65535], key[] = "BitDefender Test\0";
DWORD bRead, bWrite, size, seed, functions[] = { 1, 2, 3, 1, 4 };

DWORD getRandom() {
    DWORD nr = seed;
    nr *= 214013;
    nr += 2531011;
    seed = nr;
    nr >>= 16;
    nr &= 32767;
    return nr;
}

BYTE ROR(BYTE ch, BYTE key) {
    return (ch >> key) | (ch << (8 - key));
}

BYTE f1(BYTE ch, DWORD keyIndex, BYTE prec) {
    return ROR(ch, (key[keyIndex] + prec) % 8);
}

BYTE f2(BYTE ch, DWORD keyIndex, BYTE prec) {
    return (ch ^ key[keyIndex]) - prec;
}

BYTE f3(BYTE ch, DWORD keyIndex, BYTE prec) {
    return (ch - key[keyIndex]) + prec;
}

BYTE f4(BYTE ch, DWORD keyIndex, BYTE prec) {
    return (ch - key[keyIndex]) ^ prec;
}

int main() {
    BYTE prec;
    DWORD i, random1, random2, aux, keyIndex;
    HANDLE hFileR, hFileW;

    hFileR = CreateFile("out.txt", GENERIC_READ, 0, 0, 3, 0, 0);
    size = GetFileSize(hFileR, 0);
    ReadFile(hFileR, buffer, size, &bRead, 0);
    buffer[size] = 0;
    CloseHandle(hFileR);

    for (i = 0; i < 20; ++i) {
        random1 = getRandom() % 5;
        random2 = getRandom() % 5;
        aux = functions[random1];
        functions[random1] = functions[random2];
        functions[random2] = aux;
    }

    for (i = 0; i < 5; ++i)
        printf("%d ", functions[i]);

    // ordinea functiilor pentru decriptare: 1 4 2 3 1
    keyIndex = 0;
    for (i = size; i > 0; --i) {
        prec = buffer[i - 1];
        buffer[i] = f1(buffer[i], keyIndex, prec);
        buffer[i] = f3(buffer[i], keyIndex, prec);
        buffer[i] = f2(buffer[i], keyIndex, prec);
        buffer[i] = f4(buffer[i], keyIndex, prec);
        buffer[i] = f1(buffer[i], keyIndex, prec);
        ++keyIndex;
        if (!key[keyIndex])
            keyIndex = 0;
    }
    prec = 0;
    buffer[i] = f1(buffer[i], keyIndex, prec);
    buffer[i] = f3(buffer[i], keyIndex, prec);
    buffer[i] = f2(buffer[i], keyIndex, prec);
    buffer[i] = f4(buffer[i], keyIndex, prec);
    buffer[i] = f1(buffer[i], keyIndex, prec);

    hFileW = CreateFile("in.txt", GENERIC_WRITE, 0, 0, 2, 0, 0);
    WriteFile(hFileW, buffer, size, 0, 0);
    CloseHandle(hFileW);
}