Description:
Install the rpm
sudo apt install libpam-google-authenticator
Install google-authenticator
google-authenticator
Initialize google authenticator (How to add google authenticator to ssh [centos] )
google-authenticator
Do you want authentication tokens to be time-based (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) 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
Before starting step 5 and later step, please ensure you kept at least one logged in session. The reason for keeping session is to reset the setting if any unexpected issue happened. If missing the session, maybe never get back to server. Try to login to the ssh with new putty process and flowing step 5 and 6, until the the login behaviour match our target (publickey + google authenticator).
Edit pam.d/sshd
sudo vim /etc/pam.d/sshd
#####################
###Comment below line
#@include common-auth
#Append below line
auth required pam_google_authenticator.so nullok
#nullok means the pam_google_authenticator.so is no mandatory
#if all user using totp then the nullok can be removed
//Restart sshd service
sudo systemctl restart sshd
Edit ssh_config
sudo vim /etc/ssh/sshd_config
####################
#change ChallengeResponseAuthentication to yes
ChallengeResponseAuthentication yes
#Seem missing or not mandatory setting
PubkeyAuthentication yes
#define the authentication method as publickey + keyboard-interactive
AuthenticationMethods publickey,keyboard-interactive
####################
#restart sshd
sudo systemctl restart sshd