How Do Hardware Keyloggers Work?
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The Process
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A keylogger is small device attached to the signal path between your keyboard and your computer. Older models had an incoming and outgoing PS/2-style keyboard jack. Newer models feature a male and female USB port so that the keyboard plugs into the keylogger, and the keylogger plugs into the computer. Each keystroke entered on the keyboard is recorded in the flash memory of the keylogger. Exactly how the keystroke data is retrieved depends on the specific model, but most employ the recognition of a specific keystroke pattern to launch a menu in your word processor or simple text editor. Some models use custom software to access the keylogger data and functions. USB keyloggers will work with any computing platform and operating system.
Physical Components
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A keylogger consists of a molded plastic shell that houses a small circuit board coupled with a flash memory chip. The amount of keystroke data the keylogger can store depends on the size of the flash memory chip. The circuit board connects to data input and data output jacks.
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Functions
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Just as the circuit can receive and store keystrokes, it can also transmit simulated keystrokes. This function is used to display information using a word processor or text editor. This information is formatted as a menu. The menu is used to communicate which keystroke commands will perform what functions. The menu indicates commands available to initialize (erase) the flash memory, download the logged keystrokes or change the access password. Should the flash memory become full, keyloggers are programmed to simply overwrite the oldest recorded memory with new data, so the most recent keystroke activity is retained.
Stealth
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The central advantage of a hardware keylogger is its stealth. Workplace keyboards normally plug into the back of computers. As a result, the keylogger is seldom noticed. The hardware keylogger has no interaction with the computer memory or central processing unit (CPU), so it is undetectable by any software installed on the host computer. Because the signal path is short and the circuit is relatively simple, there is no perceptible delay caused by its presence between the keyboard and computer.
Limitations
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By design, the keylogger must install between the keyboard and computer; therefore hardware keyloggers will not function with a laptop unless used with an external keyboard, eliminating the stealth advantage. Older keyloggers using a PS/2-style interface will not work with Apple Mac computers using USB interfaces.
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