Laboratory Test and Mechanism Analysis on Electromagnetic Compromising Emanations of PS/2 Keyboard

Keyboard is the main input device of computer systems. Electromagnetic waves will be emitted while the keys are stroked. These waves may reveal the keystroke information, and it brings about information security problems. Electromagnetic compromising emanations of PS/2 keyboard are studied through laboratory test and mechanism analysis. The testing probe is placed under the control circuit to test the near field emission. Two different oscilloscopes are used to obtain time-domain signals. Based on results of the test, compromising mechanism and information recovery are studied. As a result of the open collector that is coupled to a pull-up resistor, the compromising emanation of a falling edge is much more powerful than that of a rising edge. The keystroke information is determined or partially recovered from the test results. The laboratory test not only discloses how the keystroke information is leaked, but also indicates that control circuit is the very compromising emission source of PS/2 keyboard.