yubikey-ksm binary package in Ubuntu Xenial amd64

 YubiKeys are USB tokens that act like keyboards and generate one-time
 passwords. This package contains a server written in PHP for use
 with Apache that decrypt YubiKey One-Time Passwords (OTPs), normally
 only used by YubiKey OTP validation servers. The architecture is
 that a set of validation servers manage the token counters and
 respond to OTP requests from clients, and utilize a set of back-end
 YubiKey Key Storage Module (KSM) servers to perform the actual AES
 key decryption. The protocols are openly published. This implementation
 store the AES keys in a database unencrypted, which can be protected
 using file-system encryption mechanisms Another KSM implementation
 is available in the yhsm-yubikey-ksm package that use the YubiHSM hardware
 to protect the decryption process. Sometimes the KSM runs on another
 server than the validation server, but it is possible to run both on
 the same machine. After installing and configuring this package you
 will have a YubiKey KSM server up and running via Apache.

Source package