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How to Force ssh login via Public Key Authentication

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How to Force ssh login via Public Key Authentication

Postby tanmay.01 » Wed Jul 03, 2013 7:40 am

A main advantage of key authentication is that you can be protected against brute-force password guessing attacks. However, requiring a private key for ssh access means that you have to store the key somewhere on client system, which can be another avenue of attack.

Here is how to disable ssh password authentication so that you can force ssh login via public key only.
Open sshd configuration file, and add the following line (or uncomment it if it’s commented out).

Code: Select all
sudo nano /etc/ssh/sshd_config


PasswordAuthentication no


Make sure that you have the following in /etc/ssh/sshd_config, in order to allow private/public key authentication.

RSAAuthentication yes
PubkeyAuthentication yes


Finally, reload ssh server configuration to make the change effective.
Code: Select all
sudo /etc/init.d/ssh reload


The above setting will disable ssh login via password, system-wide. If what you want is to disable ssh password login for individual users, you can do the following.

If you want to disable ssh password authentication for specific users only, use “Match User” field as follows.

Match User theemahn,ironmahn
PasswordAuthentication no


If you want to disable ssh password login for specific Linux group(s), use “Match Group” field. For example, to disable ssh password login for all users belonging to “sudoers” group:

Match Group sudoers
PasswordAuthentication no


If you want to force ssh key authentication for non-root normal users, use “Match User” field.

Match User !root
PasswordAuthentication no
HP ENVY 15
•3rd generation Intel(R) Core(TheeMahn) i5-3210M Processor (2.5 GHz with Turbo Boost up to 3.1 GHz)
• 1GB Radeon(TheeMahn) HD 7750M GDDR5 Graphics [HDMI]
• 6GB 1600DDR3 System Memory (2 Dimm)
• 750GB 7200 rpm Hard Drive
• Intel 2x2 802.11a/b/g/n WLAN + Bluetooth(R)
• Full-size Radiance backlit keyboard.

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