Quick introduction to reverse engineering for beginners

};
fread (buf, flen, 1, f);
fclose (f);
crypt (buf, flen_aligned, pw);
f=fopen(fout, "wb");
fwrite ("QR9", 3, 1, f);
fwrite (&flen, 4, 1, f);
fwrite (buf, flen_aligned, 1, f);
fclose (f);
free (buf);
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 crypted!\n");
return;
};
memcpy (&real_flen, buf+3, 4);
decrypt (buf+(3+4), flen-(3+4), pw);
f=fopen(fout, "wb");
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