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O'Reilly Network: Time and Tide Wait for No Protocol: The SSH Keystroke Timing Attack

Nov 09, 2001, 16:45 (3 Talkback[s])
(Other stories by Richard Silverman)
"At the 10th Usenix Security Symposium (Washington D.C., August 2001), U.C. Berkeley researchers Dawn Song, David Wagner, and Xuqing Tian presented a paper titled, Timing Analysis of Keystrokes and Timing Attacks on SSH . The paper describes their research into applying traffic-analysis techniques to interactive SSH connections in order to infer information about the encrypted connection contents. The paper concludes that the keystroke timing data observable from today's SSH implementations reveals a dangerously significant amount of information about user terminal sessions--enough to locate typed passwords in the session data stream and reduce the computational work involved in guessing those passwords by a factor of 50.

Not surprisingly, this paper initiated a great deal of discussion among SSH users, developers, and the security community in general, especially in public forums such as Slashdot. In this article, I will summarize the issues involved, discuss the paper's methods and conclusions, and dispel some of the often-repeated misconceptions in the public's reaction to this research.

The paper revolves around the notion of traffic analysis, and while it uses SSH as a concrete example, the techniques involved are not specific to SSH, but rather apply to most interactive remote-terminal protocols as they are implemented today. The principle of traffic analysis is that there is a lot of useful information to be gleaned from the amount, timing, and direction of network traffic, even if you can't actually read the traffic content itself. Suppose I'm monitoring the network port leading to a system administrator's office."

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