Computer security compromised by hardware failure: Difference between revisions

Revision as of 19:18, 16 January 2017

Revision as of 19:21, 16 January 2017

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Attacks against emanations caused by human typing have attracted interest in recent years. In particular, works showed that keyboard acoustic emanations do leak information that can be exploited to reconstruct the typed text.<ref name="[Ber1]">[[#Ber1|Berger, 2006, p.1]]</ref>

PC keyboards, notebook keyboards are vulnerable to attacks based on differentiating the sound emanated by different keys.<ref name="[Aso1]">[[#Aso1|Asonov, 2004, p.1]]</ref> This attack takes as input an audio signal containing a recording of a single word typed by a single person on a keyboard, and a dictionary of words. It is assumed that the typed word is present in the dictionary. The aim of the attack is to reconstruct the original word from the signal.<ref name="[Ber2]">[[#Ber1|Berger, 2006, p.2]]</ref> This attack, taking as input a 10-minute sound recording of a user typing English text using a keyboard, and then recovering up to 96% of typed characters.<ref name="[Zhu1]">[[#Zhu1|Zhuang, 2005, p.1]]</ref> This attack is inexpensive because the other hardware required is a parabolic microphone and non-invasive because it does not require physical intrusion into the system. The attack employs a neural network to recognize the key being pressed.<ref name="[Aso1]">[[#Aso1]]</ref> It combines signal processing and efficient data structures and algorithms, to successfully reconstruct single words of 7-13 characters from a recording of the clicks made when typing them on a keyboard.<ref name="[Ber1]">[[#Ber1]]</ref> The sound of clicks can differ slightly from key to key, because the keys are positioned at different positions on the keyboard plate, although the clicks of different keys sound similar to the human ear.<ref name="[Aso1]"/>

On average, there were only 0.5 incorrect recognitions per 20 clicks, which shows the exposure of keyboard to the eavesdropping using this attack.<ref name="[Aso2]">[[#Aso1|Asonov, 2004, p.4]]</ref>

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Electromigration, which means to physically move the atom to new locations (to physically alter the device itself) is another type of attack.<ref name="Gut1" /> It involves the relocation of metal atoms due to high current densities, a phenomenon in which atoms are carried along by an “electron wind” in the opposite direction to the conventional current, producing voids at the negative electrode and hillocks and whiskers at the positive electrode. Void formation leads to a local increase in current density and Joule heating (the interaction of electrons and metal ions to produce thermal energy), producing further electromigration effects. When the external stress is removed, the disturbed system tends to relax back to its original equilibrium state, resulting in a backflow which heals some of the electromigration damage. In the long term though, this can cause device failure, but in less extreme cases it simply serves to alter a device’s operating characteristics in noticeable ways.

For example, the excavations of voids leads to increased wiring resistance and the growth of whiskers leads to contact formation and current leakage.<ref name="Gut1Gut5">[[#Gut1|Gutmann, 2001, p.5]]</ref> An example of a conductor which exhibits whisker growth due to electromigration is shown in the figure below:

[[File:Whisker growth.jpg|thumb|center|969px|alt=|Whisker growth due to electromigration]]