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How to enable SSH 2FA on AlmaLinux

 In this tutorial, How to enable two-factor authentication (2FA) for SSH logins.

 Install the Google Authenticator on AlmaLinux

sudo dnf install epel-release -y
sudo dnf install google-authenticator qrencode qrencode-libs -y

After install completes, I will create a new secret key in ~/.ssh directory

Run command as follows

google-authenticator -s ~/.ssh/google_authenticator
The output terminal as below

[[email protected] ~]# google-authenticator -s ~/.ssh/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=200x200&chld=M|0&cht=qr&chl=otpauth://totp/[email protected]%3Fsecret%3DDXFSMCJ42VQ7FPMS2VAJ3CIJIE%26issuer%3DDevopsRoles.com

Your new secret key is: DXFSMCJ42VQ7FPMS2VAJ3CIJIE
Your verification code is 222214
Your emergency scratch codes are:
  36072722
  12212187
  31577834
  31344084
  92578576

Do you want me to update your "/root/.ssh/google_authenticator" file? (y/n) y

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) y

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) y

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
[[email protected] ~]#

You use mobile device to Get verification codes with Google Authenticator.


 

Configure SSH and PAM

Configure SSH

sudo vi /etc/ssh/sshd_config
make sure both UsePAM and ChallengeResponseAuthentication are set to Yes

The output as below:

[[email protected] ~]# egrep "ChallengeResponseAuthentication|UsePAM yes" /etc/ssh/sshd_config | grep -v "#"
ChallengeResponseAuthentication yes
UsePAM yes
Setting PAM

sudo vi /etc/pam.d/sshd

Add the following line at the bottom:

auth required pam_google_authenticator.so secret=${HOME}/.ssh/google_authenticator
Restart ssh
sudo systemctl restart sshd
Login into server

My example, login root account as the picture.


Conclusion

You have enabled SSH 2FA on AlmaLinux . I hope will this your helpful. Thank you for reading the DevopsRoles page!

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