TouchLogger: Inferring Keystrokes On Touch Screen From Smartphone
Motion

Liang Cai and Hao Chen

Attacks that use side channels, such as sound and electromagnetic
emanation, to infer keystrokes on physical keyboards are ineffective
on smartphones without physical keyboards.  We describe a new side
channel, motion, on touch screen smartphones with only soft keyboards.
Since typing on different locations on the screen causes different
vibrations, motion data can be used to infer the keys being typed.  To
demonstrate this attack, we developed TouchLogger, an Android
application that extracts features from device orientation data to
infer keystrokes.  TouchLogger correctly inferred more than 70 of
the keys typed on a number-only soft keyboard on a smartphone.  We
hope to raise the awareness of motion as a significant side channel
that may leak confidential data.