Bering-uClibc 6.x - User Guide - Advanced Topics - Setting Up SSH password-less login and Port Knocking

SSH (dropbear) allows password-less login by using RSA security key pairs. To set it up you will have to generate the RSA key pairs on your client machine and copy the public key in your router file /root/.ssh/authorized_keys. If you have more than one client machine, repeat the same process on each of them, and append their respective public keys in your router file /root/.ssh/authorized_keys.

Make sure you have this format:

firewall# pwd
/root/.ssh
firewall# cat authorized_keys
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDtKYa9MqShtRkJDa....
...
...
ICxqcbjMXktnN3cygsf3cIU+f/SJ9r7 mywife@macbookpro.private.network
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCrpgezG0X9RhuDBBQ...
...
... 
l7bUlGYoouP3tpqfXxIBbQEeMr/2X99 me@ProBook-6560b
firewall#

You can now login in your firewall without a password from those client machines obviously. You could disable password login but be careful not to lock yourself out... I prefer to use a very very very strong password anyways, you never know when you might have to login from none of your prepared client machines. But you can always keep, at your own risks, a copy of one of the private keys on a portable secure medium..., phone, earrings ...

If you intend to login from the internet, you have to add the following rule to /etc/shorewall/rules

SSH(ACCEPT) net fw

You can always choose another port like 65022 for SSH to listen to. The port scanners wont usually reach there. There are ongoing debates about the questionable security of this obfuscation... Anyway, if you do, add this rule then:

ACCEPT  net fw tcp 65022

and tell dropbear to listen on port 65022...

lrcfg -> 3) -> 13) -> 1)
*DB_PORT=22
DB_PORT=65022

If you don't like or remember to type ssh -p 65022 root@your.ipaddrs.router everytime you login, you could always use the default SSH port 22, but keep it hidden with a technique called "port knocking". The port 22 is kept normally closed until you send a proper sequence of random port connection attempts on normally closed ports, using TCP or UDP, hence the name Port Knocking. When the port knocking software detects the right combination sequence, it will then open up port 22 for 60 seconds for instance, thus giving you time enough to make your SSH login connection attempt.

Near the end of this article: " http://shorewall.org/Events.html " you will find in Examples a simple Port Knocking setup that works quite well.

Well using this last example you will still have to remember to type:

ssh -p 1600 root@your.ipaddrs.router   # knock on port 1600
ssh root@your.ipaddrs.router           # to connect...

I'm not sure this is a typing gain :-) !, but it is a lot more secure, and you won't fill your logs with port 22 scanners attempts... anyways !!!

herrrr... don't forget to save Doctor Freeman !!!

lrcfg -> s)