Configure Google Authenticator SSH on CentOS 7

I. Overview

What is 2-factor authentication?
Two-Factor Authentication, known as 2FA (Two-Factor Authentication) for short, is an extra step in your regular sign-in. Without 2FA, you will only enter your username and password to log into the system, your account. The password section will be the only layer of protection for the account. Meanwhile, the added second layer of security will help you better protect your account.

Why use 2-layer security?

2-layer security is the best way to protect yourself from attacks that steal user sensitive account information, fake login pages, and other account takeover methods. With 2-layer security, you can rest assured that if your account information is accidentally exposed, it will be difficult for others to access your account because there will be obstacles in security step 2. class. .
In this article, I will show you how to set up 2-factor authentication when SSHing into  a VPS server  , this helps increase the security of your VPS if your root information is accidentally exposed. Specifically, please see the steps in Part II.

II. Setup Guide

To set up Google Authenticator, you can follow these 4 steps.

Step 1: SSH into your server

First you need to SSH into your VPS with Root privileges.
After SSH is successful, you continue to see Step 2.

Step 2: Set up Google Authenticator

 

  • Install the epel-release repo
yum install -y epel-release 
Configure Google Authenticator SSH on CentOS 7
  • Install package google-authenticator
yum install -y google-authenticator
Configure Google Authenticator SSH on CentOS 7
  • Run the following command after the installation is done to generate the secret key.
google-authenticator
  • Next, the system will ask you to confirm and provide a QR code

[[email protected] ~]# google-authenticator

Do you want authentication tokens to be time-based (y/n) y
Warning: pasting the following URL into your browser exposes the OTP secret to Google:
https://www.google.com/chart?chs=200×200&chld=M|0&cht=qr&chl=otpauth://totp/[email protected]%3Fsecret%3DVEAYBDZLLA5MUVTNRPB23LN5CQ%26issuer%3DTamtest

Verification Code 

Your new secret key is: VEAYBDZLLA5MUVTNRPB23LN5CQ
Your verification code is 189929
Your emergency scratch codes are:
52330830
63691329
27023088
50185762
60605272

Do you want me to update your “/root/.google_authenticator” file? (y/n) Your new secret key is: VEAYBDZLLA5MUVTNRPB23LN5CQ
Your verification code is 189929
Your emergency scratch codes are:
52330830
63691329
27023088
50185762
60605272

Do you want me to update your “/root/.google_authenticator” file? (y/n)
Do you want to disallow multiple uses of the same authentication
token? This restricts you to one login about every 30s, but it increases
your chances to notice or even prevent man-in-the-middle attacks (y/n)
By default, a new token is generated every 30 seconds by the mobile app.
In order to compensate for possible time-skew between the client and the server,
we allow an extra token before and after the current time. This allows for a
time skew of up to 30 seconds between authentication server and client. If you
experience problems with poor time synchronization, you can increase the window
from its default size of 3 permitted codes (one previous code, the current
code, the next code) to 17 permitted codes (the 8 previous codes, the current
code, and the 8 next codes). This will permit for a time skew of up to 4 minutes
between client and server.
Do you want to do so? (y/n)
If the computer that you are logging into isn’t hardened against brute-force
login attempts, you can enable rate-limiting for the authentication module.
By default, this limits attackers to no more than 3 login attempts every 30s.
Do you want to enable rate-limiting? (y/n) If the computer that you are logging into isn’t hardened against brute-force
login attempts, you can enable rate-limiting for the authentication module.
By default, this limits attackers to no more than 3 login attempts every 30s.
Do you want to enable rate-limiting? (y/n) If the computer that you are logging into isn’t hardened against brute-force
login attempts, you can enable rate-limiting for the authentication module.
By default, this limits attackers to no more than 3 login attempts every 30s.
Do you want to enable rate-limiting? (y/n) If the computer that you are logging into isn’t hardened against brute-force
login attempts, you can enable rate-limiting for the authentication module.
By default, this limits attackers to no more than 3 login attempts every 30s.
Do you want to enable rate-limiting? (y/n) If the computer that you are logging into isn’t hardened against brute-force
login attempts, you can enable rate-limiting for the authentication module.
By default, this limits attackers to no more than 3 login attempts every 30s.
Do you want to enable rate-limiting? (y/n) If the computer that you are logging into isn’t hardened against brute-force
login attempts, you can enable rate-limiting for the authentication module.
By default, this limits attackers to no more than 3 login attempts every 30s.
Do you want to enable rate-limiting? (y/n) If the computer that you are logging into isn’t hardened against brute-force
login attempts, you can enable rate-limiting for the authentication module.
By default, this limits attackers to no more than 3 login attempts every 30s.
. Do you want to enable rate limiting? (y / n) y

Configure Google Authenticator SSH on CentOS 7
  • You open App Authenticator and proceed to Scan the QR code displayed on your VPS.
    • Google Play Link:  Here
    • Link Appstore:  Here
    • Chrome Link Extensions:  Here

When scanning the above QR code, we will receive a 6-digit code, these 6 digits will continuously change after 30 seconds.

Configure Google Authenticator SSH on CentOS 7

 

Step 3: Set up VPS to allow authentication through Google Authenticator 

To set up a VPS that allows  Google Authenticator to authenticate  during SSH, move and edit the file  /etc/pam.d/sshd

vi /etc/pam.d/sshd
  • Add and compliment the following lines in the file  /etc/pam.d/sshd

Add line:  require auth pam_google_authenticator.so nullok
Comment line:  auth substack password-auth  .

Configure Google Authenticator SSH on CentOS 7

 

  • Edit the file   /etc/ssh/sshd_config
    • Find the line   ChallengeResponseAuthentication  , change the setting from   no   to   yes
    • Add new line   AuthenticationMethods public key, interact with keyboard  .
Configure Google Authenticator SSH on CentOS 7
  • Restart the sshd service after editing.
systemctl restart sshd

Step 4: Check the operation of Authenticator when SSH

After the configuration is complete, you need to exit the VPS and log back in to test. When Login OTP code will be generated on Google Authenticator App, you just need to enter this code to be able to SSH.

As shown, I have successfully tested.

 

III. summary

So in this article, I have shown you how to install 2-factor authentication when SSHing into VPS, this helps to increase security and reduce the risk of password sniffing attacks. With 2-factor authentication, you can rest assured that even if your original information is accidentally exposed, others won’t be able to SSH into your VPS without the 2-factor authentication code. If you find this article interesting and useful, you can share it widely for everyone to do.
To see some other useful articles about Linux VPS administration, you can visit the link below.


Support 24/24h with coupon code: 1DOLLAROFF 10% discount. Click now! 👆
On this page