"In particular, we show a practical Keyboard JitterBug that solves the data exfiltration problem for keystroke loggers by leaking captured passwords through small variations in the precise times at which keyboard events are delivered to the host. Whenever an interactive communication application (such as SSH, Telnet, instant messaging, etc) is running, a receiver monitoring the host's network traffic can recover the leaked data, even when the session or link is encrypted."
http://static.usenix.org/events/sec06/tech/shah/shah_html/jb...
"In particular, we show a practical Keyboard JitterBug that solves the data exfiltration problem for keystroke loggers by leaking captured passwords through small variations in the precise times at which keyboard events are delivered to the host. Whenever an interactive communication application (such as SSH, Telnet, instant messaging, etc) is running, a receiver monitoring the host's network traffic can recover the leaked data, even when the session or link is encrypted."