Recipe 11.20. Gathering Entropy from the Keyboard

11.20.1. Problem

You need entropy in a low-entropy environment and can prompt the user to type in order to collect it.

11.20.2. Solution

On Unix, read directly from the controlling terminal (/dev/tty). On Windows, process all keyboard events. Mix into an entropy pool the key pressed, along with the timestamp at which each one was processed. Estimate entropy based upon your operating environment; see the considerations in Recipe 11.19.