Microsoft’s popular text, audio and video messaging service Skype can be used to record keystrokes and reveal what a user has typed, researchers say.
According to researchers from the University of California Irvine (UCI) and two Italian Universities, an attack where keystrokes are recorded during a Skype call and then reassembled as text is possible because of the acoustic emanations of computer keyboards, already a proven privacy issue.
Unlike previous research, which was based on an adversary’s physical proximity to the victim, profiling of the victim’s typing style, and/or victim’s typed information being available to the adversary, the new study proposes a new keyboard acoustic eavesdropping attack, one based on Voice-over-IP (VoIP), or the core technology behind Skype (and many other chat services out there, we might add).
In their paper (PDF), the UCI researchers argue that users typing on their desktop or laptop computer’s keyboard while participating in a Skype call become vulnerable to the demonstrated electronic eavesdropping. The VoIP software acquires acoustic emanations of pressed keystrokes and transmits them to the others involved in the VoIP call, thus creating a vulnerability.
The issue, the researchers argue, is that people often engage into secondary activities while in a VoIP call, and that some of these activities include typing. They also say that Skype conveys enough audio information to reconstruct the victim’s input with an accuracy of 91.7% if the victim’s typing style and keyboard are known (the accuracy drops to 41.89% if they aren’t known).
However, the attack is not possible if the victim uses a touchscreen or a holographic keyboard and keypad. Moreover, the researchers explain that, because Skype is encrypted, an attacker who is not part of the call can’t easily pilfer keystrokes.
“Skype is used by a huge number of people worldwide. We have shown that during a Skype video or audio conference, your keystrokes are subject to recording and analysis by your call partners. They can learn exactly what you type, including confidential information such as passwords and other very personal stuff,” co-author Gene Tsudik, Chancellor’s Professor of computer science at UCI, said.
This type of attack is possible because various brands of keyboards emit distinct sounds and because different letters on the same keyboard emit different sounds. If someone’s typing is recorded, each keystroke can then be analyzed and matched to a specific key. Thus, an attacker with some knowledge of a user’s typing style could re-create entire texts.
Unlike previous studies, which relied on getting a recording device close to the victim’s keyboard, the new research reveals how VoIP technology eliminates this impediment. “Our work is yet another nail in the coffin of traditional physical keyboards that are common in modern laptop and desktop computers. It clearly shows previously unnoticed privacy dangers of using popular VoIP technologies in conjunction with such keyboards,” Tsudik said.
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