SSH wiki for Ants.md

SSH Wiki for Ants

Basics

ssh [email protected] // Basic ssh connection
ssh [email protected] -p 33 // Using port 33
ssh [email protected] -v // log more info on connection

Authentication

When connecting to a remote device, authentication is needed by default (this can be bypassed through config files). The remote needs to know the client device trying to connect.

On client

Generate RSA public/private keys pair, which will be located in ~/.ssh/

ssh-keygen -t rsa

Copy RSA public key (the private key needs to stay private) of your client device

cat ~/.ssh/id_rsa.pub

On server

Paste client RSA public key into

~/.ssh/authorized_keys

The home folder used for authorized_keys needs to be the home folder of the user you want to be connected as on the server

Config Files

SSH connection established from your local machine

/etc/ssh/ssh_config

SSH connection established to your local machine

There is a SSH daemon that listens to incoming connection request via SSH. You can configure the daemon with this file.

/etc/ssh/sshd_config

For authentication to work, Protocol 2needs to be set, simply with

Protocol 2

, enabling the host keys type you will be using. You can choose to have only one type of key.

HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key

Verify sshd status

On ArchLinux

journalctl -u sshd | tail -100

Client side connections customization

You can set up different connection configurations to remote hosts.

On your local machine (the client),

• Go to ~/.ssh/
• Create a config file vim config, and fill in:

Host name-of-the-remote // only for you, not server-related
  User myUser // user you want to log in as onto the remote server
  Hostname 111.222.333.444 // address of the remote server
  Port 9999 // Optional. SSH port of the remote server. Default is 22, but can be changed on the server for security reasons

Reverse SSH connection

SSH reverse connections are used in different situations, to bypass a firewall on a remote machine for instance.
In this particular case, the remote device (or server) you want to access to is the Ant device, and the client device from which you access is the Ants server, named Kerrigan.

On server (the Ant device)

ssh -N -R 2222:localhost:22 kerrigan

With this command, you're digging a tunnel from the Ant to queen Kerrigan. Startpoint (port 22 of the Ant) is opened, but the endpoint (port 2222 of Kerrigan) is not yet opened.
In reality, you're telling Kerrigan to forward any SSH connection that she will receive on port 2222 to the port 22 of the Ant. Be careful, port 2222 of Kerrigan should be available, and port 22 is the default SSH port of the Ant, but can be different.

On client (the Ants server, Kerrigan)

ssh -l userOnAnt -p 2222 localhost

Here, you're just opening the endpoint of the tunnel that was dug before, allowing SSH connection from queen Kerrigan to the Ant.
In reality, you're opening an SSH connection from Kerrigan to Kerrigan on port 2222, which is forwarded automatically to port 22 of the Ant. You are now connected to the Ant device from Kerrigan.

Sources

https://wiki.archlinux.org/index.php/Secure_Shell
http://www.snailbook.com/faq/ssh-1-vs-2.auto.html
http://unix.stackexchange.com/questions/46235/how-does-reverse-ssh-tunneling-work
http://www.tunnelsup.com/raspberry-pi-phoning-home-using-a-reverse-remote-ssh-tunnel