For those who want the YubiKey support for KeePassX 2.0, a new stable series released a month ago, here’s a PPA built the binaries a few days ago for Ubuntu 15.10, Ubuntu 15.04, and Ubuntu 14.04.

YubiKey (a USB authentication device) support is added by configuring a YubiKey slot to operate in HMAC-SHA1 challenge-response mode. The mechanism works by submitting the database master seed as a challenge to the YubiKey which replies with a HMAC-SHA1 cryptographic hash. The resultant hash is then hashed with the other keys (password, keyfile) to generate the final key used to encrypt the database.

How to Install KeePassX 2.0 with YubiKey support:

Open terminal from Unity Dash, App Launcher, or via Ctrl+Alt+T shortcut key. When it opens, paste below command one by one and hit run:

1. Add YubiKey stable PPA:

sudo add-apt-repository ppa:yubico/stable

Type in your password when it asks, no visual feedback so just type in mind, and hit Enter to continue.

2. Add the KeePassX 2 PPA built with YubiKey support:

sudo add-apt-repository ppa:hda-me/keepassx2-yubico

3. Finally update package cache and install both keepassx and yubikey-personalization-gui:

sudo apt-get update

sudo apt-get install yubikey-personalization-gui keepassx

4. (Optional) After installation, you may keep the PPAs for receiving future updates, or disable/remove them via Software & Updates -> Other Software.

For more information: github.com/keepassx/keepassx/pull/52