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Keyboards are the most common inputting devices. Specialized keyboards, such as keypads, are widely used for specialized data input. It is significant that keypads are usually used to protect a security system. In Hong Kong, keypads are widely used in banking industries and housing estates. Side channeling keypad data may be a potential threat to the security systems. According to a research conducted by Berkeley Doug Tygar [2], a researcher of the University of California, clicks and clacks from a computer keyboard can be transposed into a startlingly accurate transcript. Imagine that you are typing your password at an automatic telling machine. The ATM produces similar electronic sounds while you are pressing the keys. You think nobody knows what you are typing since the sounds are not distinguishable to human ears. However, you have made a big mistake. In fact, hackers use the mechanical sounds emanated to guess your password!! With some microphones, a computer and a sound-processing software, the keys pressed can easily be retrieved. The fact that an attacker can use this acoustic emanation from keypads to collect confidential information has been a great concern in security and privacy communities. In this project, we stimulate the keyboard acoustic triangulation attack. Forerunners determine different keys by their frequency components. We introduced a new attack using time difference approach. This approach works even when the mechanical sound is veiled by electronic sound.
1.1 Side Channel Attack
A side channel attack is an uprising security issue in cryptography. It refers to any attack which gains the information from the physical implementation on a cryptosystem, rather than the theoretical weaknesses in algorithms. Usually, an attacker is not required to equip a thorough technical understanding in the internal operation of a system in order to perform a side channel attack.
1.2 Acoustic Cryptanalysis
Acoustic cryptanalysis is a type of side channel attack which extracts information unintentionally exploited from sounds produced during a computation or input-output operation. It is a new research area of applied cryptography that has gained more and more interest since the mid nineties. According to a book “Spycatcher”, written by a former MI5 operative Peter Wright, similar attack technique had already been used as early a s in 1956. By that time, the attack “ENGULF” is used against the Egyptian Hagelin cipher machines.
Today, hackers collect sounds produced by a computer system during computations or input-output operations. They analysis them by implementing secure mathematical algorithms on the acoustic signals. Experiments show that valuable and distinguishable information can be extracted from those sounds. An example of acoustic cryptanalysis is the experiment conducted by Adi Shamir and Eran Tromer in 2004 . They demonstrated that it may be possible to conduct a timing attack against a CPU by analyzing the variations in its humming noise.
1.3 Acoustic Triangulation Attack
Triangulation is a process of finding the distance of a point using the concept of a triangle. The distance can be treated as a side of a triangle. It is calculated by measuring angles and sides of a triangle. Triangulation is a common technique for locating an object. It is often used in surveying, navigation, metrology and astrometry. Acoustic triangulation attack means finding the location of an object based on the measurement of acoustic waves generated by a keystroke. By detecting and measuring the differences in arrival times of the sound wave at two microphones, the impact location can be found uniquely.
1.4 A Keyboard
A mechanical keyboard consists of a number of keys and a circuit board. (Figure 1.2) On the keyboard there are many rubber buttons. Each key corresponds to a button on the board. Each key in a keyboard (Figure 1.3) generally consists of three parts:
a) A head -- This is the part where we contact with the key.
b) A bottom rubber part -- The dome-shaped rubber is used to make contact with an electrical switch corresponding to the key.
c) An intermediate plastic part in between the head and the rubber.
When a key is pressed, the dome-shaped rubber is squeezed. It then pushes the electrical switch and closes the circuit. Upon strike, the keyboard plate vibrates and produces a sound.