Autenticación con segundo factor de autenticación en SSH

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$ sudo apt install libpam-google-authenticator

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$ sudo vim /etc/pam.d/sshd

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auth required pam_google_authenticator.so

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$ sudo vim /etc/ssh/sshd_config

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UsePAM yes
ChallengeResponseAuthentication yes

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pi@raspberrypi:~ $ 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/pi@raspberrypi%3Fsecret%3DZDLUAXH4UI3AJIX6EPHVQSVD5E%26issuer%3Draspberrypi
                                                                                  
                                                                                  
                                                                                  
                                                                                  
                                                                                  
Your new secret key is: ZDLUAXH4UI3AJIX6EPHVQSVD5E
Your verification code is 998007
Your emergency scratch codes are:
  46891237
  64319086
  49832138
  91155656
  34340292

Do you want me to update your "/home/pi/.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) 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
pi@raspberrypi:~ $ 

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$ sudo systemctl restart sshd.service

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[picodotdev@archlinux ~]$ ssh-copy-id -i "/home/picodotdev/pico.dev@gmail.com" pi@192.168.1.101
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/home/picodotdev/pico.dev@gmail.com.pub"
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
(pi@192.168.1.101) Password: 
(pi@192.168.1.101) Verification code: 

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'pi@192.168.1.101'"
and check to make sure that only the key(s) you wanted were added.

[picodotdev@archlinux ~]$ 

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#@include common-auth

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AuthenticationMethods publickey,keyboard-interactive

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$ sudo systemctl restart sshd.service

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[picodotdev@archlinux ~]$ ssh pi@192.168.1.101
(pi@192.168.1.101) Password: 
(pi@192.168.1.101) Verification code: 
Linux raspberrypi 5.10.17+ #1403 Mon Feb 22 11:26:13 GMT 2021 armv6l

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Fri Mar 26 16:49:20 2021 from 192.168.1.4

SSH is enabled and the default password for the 'pi' user has not been changed.
This is a security risk - please login as the 'pi' user and type 'passwd' to set a new password.

pi@raspberrypi:~ $ 

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[picodotdev@archlinux ~]$ ssh pi@192.168.1.101
(pi@192.168.1.101) Verification code: 
Linux raspberrypi 5.10.17+ #1403 Mon Feb 22 11:26:13 GMT 2021 armv6l

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Fri Mar 26 16:47:26 2021 from 192.168.1.4

SSH is enabled and the default password for the 'pi' user has not been changed.
This is a security risk - please login as the 'pi' user and type 'passwd' to set a new password.

pi@raspberrypi:~ $