A device strengthens a user password while the password occupies the keyboard input buffer of an authenticating system. The device masquerades to the system as a second keyboard. The device strengthens the user password by sending keyboard scan codes, altering the user password by inserting and deleting characters. The device is small, portable, and self-contained. The device is Operating System neutral, and can be constructed to be used with any system that supports compounding plug-and-play keyboards, such as USB keyboards and Bluetooth keyboards. The device can be embedded into common input devices such as mice to impersonate a second keyboard. Use of the device improves overall system security by enforcing strong system passwords without encouraging users to write down passwords that are difficult to remember.