pam_usb

pam_usb provides hardware authentication for Linux using ordinary USB Flash Drives.

It works with any application supporting PAM, such as su and login managers (GDM, KDM).

Features

Password-less authentication. Use your USB stick for authentication, don't type passwords anymore.
Device auto probing. You don't need to mount the device, or even to configure the device location (sda1, sdb1, etc). pam_usb.so will automatically locate the device using UDisks and access its data by itself.
Two-factor authentication. Achieve greater security by requiring both the USB stick and the password to authenticate the user.
Non-intrusive. pam_usb doesn't require any modifications of the USB storage device to work (no additional partitions required).
USB Serial number, model and vendor verification.
Support for One Time Pads authentication.
You can use the same device across multiple machines.
Support for all kind of removable devices (SD, MMC, etc).

pamusb-agent: trigger actions (such as locking the screen) upon device authentication and removal.
pamusb-conf: configuration helper.
pamusb-check: integrate pam_usb's authentication engine within your scripts or applications.