Starting from the final b_16 = 0x4e5c0d3a3c1e0b2f and working backwards, we can recover each c_i . The easiest way is to brute‑force the 16‑byte input by forward simulation because the search space is tiny (each character is limited to printable ASCII that after - '0' stays in the range 0‑9; however the original code does not enforce that – any byte works). Therefore we can simply .
If you prefer a more “classic” approach (useful when the flag printing routine is more complex), the steps are: ipzz-447
$ unzip ipzz-447.zip Archive: ipzz-447.zip inflating: ipzz Starting from the final b_16 = 0x4e5c0d3a3c1e0b2f and
The code. IPZZ-447 . It wasn't a room number; it was a designation. A target identifier. ipzz-447