![]() ![]() This will permit for a time skew of up to 4 minutes If youĮxperience problems with poor time synchronization, you can increase the windowįrom its default size of 3 permitted codes (one previous code, the currentĬode, the next code) to 17 permitted codes (the 8 previous codes, the currentĬode, and the 8 next codes). Time skew of up to 30 seconds between authentication server and client. We allow an extra token before and after the current time. In order to compensate for possible time-skew between the client and the server, Your chances to notice or even prevent man-in-the-middle attacks (y/n) yīy default, a new token is generated every 30 seconds by the mobile app. Token? This restricts you to one login about every 30s, bit it increases Warning: pasting the following URL into your browser exposes the OTP secret to Google:įailed to use libqrencode to show QR code visually for scanning.Ĭonsider typing the OTP secret into your app manually.ĭo you want me to update your "/home/$USER/.google_authenticator" file? (y/n) yĭo you want to disallow multiple uses of the same authentication $ google-authenticator Do you want authentication tokens to be time-based (y/n) y The command output will look something like this: They will type the OTP secret generated into their authenticator app and hand write their 5 scratch codes to store in a secure location. Instruct all users whom you wish to use the one time passes to login to their account and run the google-authenticator command to setup their secrets. This is very useful because you can restart sshd and open an additional connection to test config changes, if you make a typo error, you can use the first connection to make corrections or revert changes to get sshd running again.īefore proceeding further, take the time to ensure your sshd is allowing you to log in with your username/password without TOTP as usual and fix any issues. Tip: If you are logged into your system remotely, restarting sshd will not kill your current connection. In order for the changes above to take effect, run as the root user: More options can be found in the google-authenticator manpage or on their github. ![]() It is recommended you remove this option after all of your users have created secret keys. This option is recommended during the initial roll-out process of google authenticator on your server, it allows users who have not created a secret key to bypass the verification code prompt. In the example above, we are passing a few useful options to the google authenticator pam module:Īllows the user to see their verification code as they type it, reducing the chance it is entered incorrectly.ĭefines a grace period in seconds during which a user login attempt from the same IP address will not be asked for the verification code. Please consult the sshd_config manpage, particularly the AuthenticationMethods directive, if you would like to use public key authentication.Ĭonfigure the google-authenticator PAM moduleĪs root, create the /etc/pam.d/sshd file and create a link to it called /etc/pam.d/sshd.pam:Įlevate your preferred text editor to root and edit the /etc/pam.d/sshd file, it will contain the following lines at a minimum:Īuth required pam_google_authenticator.so echo_verification_code grace_period=57600 nullok There are three directives which need to be altered or added if not present:ĪuthenticationMethods keyboard-interactive Use sudo, su, or doas to elevate your preferred text editor to root privileges, and then edit the /etc/ssh/sshd_config file. Please see the article Setting up a SSH server if you have not done so Note: This article assumes that you have already done basic setup of OpenSSH relying on username and password to login. ![]()
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