Don't touch a word! A practical input eavesdropping attack against mobile touchscreen devices

@TechReport{	  maggi_iclearshot_tr_2010,
  abstract	= {Spying on a person is a subtle, yet easy and reliable
		  method to obtain sensitive information. Even if the victim
		  is well protected from digital attacks, spying may be a
		  viable option. In addition, the pervasiveness of mobile
		  devices increases an attacker's opportunities to observe
		  the victims while they are accessing or entering sensitive
		  information. This risk is exacerbated by the remarkable
		  user-friendliness of modern, mobile graphical interfaces,
		  which, for example, display visual feedback to improve the
		  user experience and make common tasks,
		  \$\ensuremath\backslashbackslash\$eg, typing, more natural.
		  Unfortunately, this turns into the well-known trade-off
		  between usability and security. In this work, we focus on
		  how usability of modern mobile interfaces may affect the
		  users' privacy. In particular, we describe a practical
		  eavesdropping attack, able to recognize the sequence of
		  keystrokes from a low-resolution video, recorded while the
		  victim is typing on a touchscreen. Our attack exploits the
		  fact that modern virtual keyboards, as opposed to
		  mechanical ones, often display magnified, virtual keys in
		  predictable positions. To demonstrate the feasibility of
		  this attack we implemented it against 2010's most popular
		  smart-phone (i.e., Apple's iPhone). Our approach works
		  under realistic conditions, because it tracks and rectifies
		  the target screen according to the victim's natural
		  movements, before performing the keystroke recognition. On
		  real-world settings, our attack can automatically recognize
		  up to 97.07% (91.03% on average) of the keystrokes, with a
		  1.15% error rate and a speed between 37 and 51 keystrokes
		  per minute. This work confirms that touchscreen keyboards
		  that magnify keys make automatic eavesdropping attacks
		  easier than in classic mobile keyboards.},
  author	= {Maggi, Federico and Volpatto, Alberto and Gasparini,
		  Simone and Boracchi, Giacomo and Zanero, Stefano},
  date		= {2010-11-01},
  file		= {files/papers/reports/maggi_iclearshot_tr_2010.pdf},
  institution	= {Politecnico di Milano},
  number	= {2010-59},
  shorttitle	= {iClearshot},
  title		= {Don't touch a word! A practical input eavesdropping attack
		  against mobile touchscreen devices}
}