How to Decrypt rom-0 file

Download the  lzs compress and decompress tools from http://git.kopf-tisch.de/?p=zyxel-revert;a=summary

After clicking on the link given above, click on snapshot link in front of support firmwareupdate master  

 Once you have down loaded the zyxel-revert-779bfd5.tar.gz  file to your Desktop, perform the following steps

root@kali1:~/Desktop# tar -xzf zyxel-revert-779bfd5.tar.gz
root@kali1:~/Desktop# cd zyxel-revert-779bfd5/
root@kali1:~/Desktop/zyxel-revert-779bfd5# ls

Compile the source code with makefile.

root@kali1:~/Desktop/zyxel-revert-779bfd5# make -f Makefile

To decompress rom-0 file

root@kali1:~/Desktop/zyxel-revert-779bfd5# ./decompress /root/Desktop/rom-0

The result of decompressed file is rom-0.decomp (original-filename.decomp).

Show printable strings from decompressed file.

root@kali1:~/Desktop/zyxel-revert-779bfd5# strings /root/Desktop/rom-0.decomp

Password usually on first line