At work, we are currently testing 2 factor authentication for desktops/workstations. As we are already using some nfc based cards, we want to use them. Some quick research brought up pam_nfc which utilizes libnfc.
So we bought an ACR122U reader which is supported by libnfc
compile and install
Checkout source code and create a debian package for further automated distribution (e.g. Puppet,…)
svn checkout http://nfc-tools.googlecode.com/svn/trunk/ nfc-tools-read-only
Now we need to adjust some requirements for libraries if we’re using Ubuntu as the debian control file requires libnfc2 (>= 1.5.0) which is not present in Ubuntu. Instead it’s called libnfc5 (1.7.0-3 atm in trusty)
cd nfc-tools-read-only/pam_nfc sed -i 's,libnfc2 (>= 1.5.0),libnfc5 (1.7.0-3),' debian/control
Next, install some packages and headers for compiling the source
sudo apt-get install devscripts autoconf dh-autoreconf build-essential fakeroot libnfc-dev libpam0g-dev -y
Finally, build the package
debuild -us -uc
Answer this question with yes as the package will be built:
> This package has a Debian revision number but there does not seem to be > an appropriate original tar file or .orig directory in the parent directory; > (expected one of libpam-nfc_0.1.4.orig.tar.gz, libpam-nfc_0.1.4.orig.tar.bz2, > libpam-nfc_0.1.4.orig.tar.lzma, libpam-nfc_0.1.4.orig.tar.xz or pam_nfc.orig) > continue anyway? (y/n)
Now we’ve got a deb package to install one folder up.
Grab the package built above and install it (or add it to your existing repo like freight or reprepro). This command might differ in version numbers and architecture and assumes you’re still in the current pam_nfc directory. Adjust to your needs.
sudo apt-get install ../libpam-nfc_0.1.4-0_amd64.deb
Now we can add pam directives to the configuration files in /etc/pam.d/ to make it work. But in the past, we’ve encountered some problems with pam-auth-update in automated installations (via Puppet) so let’s create a description file for pam-auth-update to have it working the clean way.
Create /usr/share/pam-configs/nfc with content like this:
Name: NFC Default: yes Priority: 257 Auth-Type: Primary Auth: required pam_nfc.so Auth-Initial: required pam_nfc.so
This example is adding pam_nfc.so as required (so NFC tag and password will be asked) just before pam_unix.so. In our case, we are using Priority 251 so it skips local users (below pam_unix.so) but before pam_lsass.so (Active Directory using PowerBroker, you might not have this). If you want to use either username/password or nfc tag (ok, then it’s no more 2 factor auth ;) ), just change required to sufficient.
Now we need to enroll tags for users, this is done via
Pairings will be put into /etc/pam_nfc.conf which can be enrolled company wide.
As always when testing PAM, keep an existing root shell to revert the settings in case it does not work.