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.

Linux:

ssh-keygen
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/id_rsa.pub.

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

Windows:

Download Putty from:http://www.putty.org/

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

Linux

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 (id_rsa.pub) to server host (ex: via USB key)
cat /media/usb/id_rsa_user@host.pub >> ~/.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:

Create a start script

echo "#!/bin/bash" | sudo tee /usr/local/bin/start-ssh-server
echo "service ssh start" | sudo tee -a /usr/local/bin/start-ssh-server
sudo chmod 744 /usr/local/bin/start-ssh-server

Allow to sudo run the script without password

echo "bertrand ALL= NOPASSWD: /usr/local/bin/start-ssh-server" | sudo tee /etc/sudoers.d/50-ssh-server
sudo chmod 440 /etc/sudoers.d/50-ssh-server

Create a task in windows
- Open Windows Task Scheduler
- Create a Basic Task
- Set Trigger as When the Computer Starts
- Set Action / Program as %windir%\System32\bash.exe
- Set Action / Argument as -c "sudo /usr/local/bin/start-ssh-server"

Invoke the client

Linux:

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

Windows:

# 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

22-Jun-2019