YubiKey two factor authentication for LUKS disks

 With this extension to the initramfs-tools, you can unlock a LUKS encrypted
 disk using your YubiKey as a second factor.
 .
 The challenge-response mechanism of the YubiKey is used to generate a response
 based on a PIN/password you have to enter.
 .
 Only the combination of the correct password and the matching YubiKey will
 generate a response, that is a valid key of the LUKS disk. Alternatively
 you can use any other LUKS passphrase when the YubiKey is not present.