Keystroke logging
Keystroke logging can be achieved by both hardware and software means. Hardware key loggers are commercially available devices which come in three types: inline devices that are attached to the keyboard cable (see picture), devices which can be installed inside standard keyboards, and actual replacement keyboards that contain the key logger already built-in.
Writing software applications for keylogging is trivial, and like any computer program can be distributed as a trojan horse or as part of a virus. What is not trivial however, is installing a keystroke logger without getting caught and downloading data that has been logged without being traced. An attacker that manually connects to a host machine to download logged keystrokes risks being traced. A trojan that sends keylogged data to a fixed e-mail address or IP address risks exposing the attacker.
Contrary to common understanding, software keyloggers are simple to write. With a working knowledge of C or C++ and a knowledge of the API's provided by the target's operating system it is straight forward do this. Software keyloggers fall into the following categories :-
1) Kernel based: This method is most difficult both to write, and combat. Such keyloggers reside at the kernel level and are thus practically invisible. They almost always subvert the OS kernel and gain unauthorised access to the hardware which makes them very powerful. A keylogger using this method can act as a keyboard driver for example, and thus gain access to any information typed on the keyboard as it goes to the Operating System.
2) Hook based: Such keyloggers hook the keyboard with functions provided by the OS. The OS warns them any time a key is pressed and it records it.
3) Creative Methods: Here the coder uses functions like GetAsyncKeyState, GetForegroundWindow, etc.
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