Debian does not provide a package for Wheezy to use Google Authenticator as a pam module. However, you can grab and install the Jessie (Debian testing) deb. Here are some steps!
First install a needed dependency:
$ sudo apt-get install libqrencode3
For 64bit grab the Jessie deb:
$ wget http://ftp.us.debian.org/debian/pool/main/g/google-authenticator/libpam-google-authenticator_20130529-2_amd64.deb
$ sudo dpkg -i libpam-google-authenticator_20130529-1_amd64.deb
Done! Next I suggest following my guide here to add two-factor authentication to your SSH logins. It works great on Wheezy:
user@brahms:~$ ssh email@example.com Password: Verification code: Linux sanfran.stmiller.org 3.2.0-4-amd64 #1 SMP Debian 3.2.41-2+deb7u2 x86_64 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. You have mail. Last login: Sun Jul 28 13:53:27 2013 from ec2-54-226-107-17.compute-1.amazonaws.com Last login: Sun Jun 2 13:20:22 2013 from 172.16.1.202 firstname.lastname@example.org:~$