Reverse Engineering for Beginners

CHAPTER 79. “QR9”: RUBIK’S CUBE INSPIRED AMATEUR CRYPTO-ALGORITHM CHAPTER 79. “QR9”: RUBIK’S CUBE INSPIRED AMATEUR CRYPTO-ALGORITHM

};

void decrypt_file(char fin, char fout, char pw)
{
FILE f;
int real_flen, flen;
BYTE *buf;

f=fopen(fin, "rb");

if (f==NULL)

{

printf ("Cannot open input file!\n");

return;

};

fseek (f, 0, SEEK_END);

flen=ftell (f);

fseek (f, 0, SEEK_SET);

buf=(BYTE*)malloc (flen);

fread (buf, flen, 1, f);

fclose (f);

if (memcmp (buf, "QR9", 3)!=0)

{

printf ("File is not encrypted!\n");

return;

};

memcpy (&real_flen, buf+3, 4);

decrypt (buf+(3+4), flen-(3+4), pw);

f=fopen(fout, "wb");

fwrite (buf+(3+4), real_flen, 1, f);

fclose (f);

free (buf);
};

// run: input output 0/1 password
// 0 for encrypt, 1 for decrypt

int main(int argc, char *argv[])
{
if (argc!=5)
{
printf ("Incorrect parameters!\n");
return 1;
};

if (strcmp (argv[3], "0")==0)

crypt_file (argv[1], argv[2], argv[4]);

else

if (strcmp (argv[3], "1")==0)

decrypt_file (argv[1], argv[2], argv[4]);

else

printf ("Wrong param %s\n", argv[3]);

return 0;
};