SSH Network Secure Shell

Generate the RSA Key

SSH uses encryption key to secure connection. The client creates the Key pair. The public key is then added to the server authorized keys.


Generating public/private rsa key pair.
Enter file in which to save the key (/home/user/.ssh/id_rsa): <empty>
Enter passphrase (empty for no passphrase): <empty>
Enter same passphrase again: <empty>
Your identification has been saved in /home/user/.ssh/id_rsa.
Your public key has been saved in /home/user/.ssh/

The key pair associated to this user@host is located in ~/.ssh/


Download Putty from:

The full package includes PuTTYgen Key Generator that can be used to generate a key pair on Windows. Private key (.ppk) must be stored securely.

Configure the server


Install OpenSSH server (if not installed by default)

sudo apt-get install openssh-server

Import clients public keys:

Note: The authorized public key file must be write-protected: anybody that can add a key can gain SSH access!

# copy client public key ( to server host (ex: via USB key)
cat /media/usb/ >> ~/.ssh/authorized_keys
chmod 644 ~/.ssh/authorized_keys

Windows WSL (Ubuntu)

# To generate server keys
sudo dpkg-reconfigure openssh-server

# Start the server
sudo service ssh start

To start ssh server automatically:

Invoke the client


# add -X to enable X forwarding (allows to run GUI)
ssh -X user@server [cmd]


# Invoke Putty from command line:
putty.exe -ssh -i C:\Users\user\ssh\user@client.ppk user@server
# To recalled a saved session:
putty.exe -load "SSH_Server"

# Tera Term Pro can also be used:
ttermpro.exe server /ssh /auth=publickey /user=user /keyfile=\Users\user\ssh\user@client.ppk