# Solution
1. Realize the server is using `hans` software for tunneling over ICMP. One can easily found that by googling "hans icmp".
2. How to find a password:
Option 1. Based on [hans source code](https://github.com/friedrich/hans/blob/master/src/auth.cpp#L30), crack the password. See the last lines of [solution.py](https://github.com/oioki/balccon2k20-ctf/blob/master/forensics/ping-pong/solution/solution.py)
Option 2. Brute-force:
```for PASSWORD in $(<xato-net-10-million-passwords-100.txt); do echo "### $PASSWORD" ; sudo ../src/bin/hans -p "$PASSWORD" -c "$SERVER_IP" -f -v ; done```
3. Connect with found password
```./hans -p "$PASSWORD" -c "$SERVER_IP" -f -v```
4. Do the same thing as in PCAP capture (send special pattern)
```>>> s='pleasegivemeflag'>>> print(''.join([hex(ord(c)).replace('0x','') for c in s]))706c65617365676976656d65666c6167
ping 192.168.18.1 -p 706c65617365676976656d65666c6167```
5. Observe the flag in an ICMP response payload.