Public Key Authentication from Windows to Linux

Table of Contents:

• About Public Key Authentication (PKA)
• Generate SSH keys on Windows
• Move public key to VPN (Linux server)
• Disable username password authentication
• Appendix: Typical sshd commands
• Appendix: Setting Putty to use PKA

About Public Key Authentication (PKA)

Public key authentication to connect to VPN Linux server means you don’t have to use passwords anymore when using ssh.

Once you set PKA, you can fully disable username password authentication.

With public key auth there are two keys:

• private key
• public key

And you need to create (have) both.

Generate SSH keys on Windows

Since I am on Windows, here is how to generate the keys on Windows:

$ ssh-keygen -t rsa -b 4096 -C "[email protected]" -f folder 

Out:

-a----        11/6/2020  12:45 AM           1675 id_rsa
-a----        11/6/2020  12:45 AM            401 id_rsa.pub

Or just run the defaults:

$ ssh-keygen

Move public key to VPN (Linux server)

Keep the private key secret and store it on your Windows computer from where you connect to the remote VPN server. Public key is to be set inside Linux:

~/.ssh/authorized_keys

We create authorized_keys if this is not present already.

mkdir -p ~/.ssh; touch ~/.ssh/authorized_keys

The command will create folder .ssh if not present and ~/.ssh/authorized_keys if not present.

touch is not able to create directories, you need mkdir for that. mkdir has the useful -p switch (parents) to create a directory structure.

Copy the content of public key to:

~/.ssh/authorized_keys

Public key has the .pub extension.

Disable username password authentication

The trick is to alter the /etc/ssh/sshd_config file.

Navigate the following lines:

# To disable tunneled clear text passwords, change to no here!
# PasswordAuthentication no
# PermitEmptyPasswords no

And uncomment the PasswordAuthentication no

# To disable tunneled clear text passwords, change to no here!
PasswordAuthentication no
# PermitEmptyPasswords no

Then restart the sshd service.

service sshd restart

Appendix: Typical sshd commands

service sshd status
service sshd stop
service sshd start
service sshd restart

Appendix: Setting Putty to use PKA

You need to have two more files inside .ssh folder on Windows generated based on id_rsa and id_rsa.pub.

-a----        11/6/2020   1:38 AM           1464 private.putty.ppk
-a----        11/6/2020   1:36 AM            477 public.putty.ppk

Create them using PuttyGen. Steps:

• Conversions => Import Key => id_rsa key on you computer
• Click “Save Private Key” without a passphrase
• Choose folder for .ppk keys same as for id_rsa and id_rsa.pub.