Chen, Ang

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Now showing 1 - 2 of 2
  • Publication
    Fault Tolerance and the Five-Second Rule
    (2015-05-01) Chen, Ang; Xiao, Hanjun; Haeberlen, Andreas; Phan, Linh T.X.
    We propose a new approach to fault tolerance that we call bounded-time recovery (BTR). BTR is intended for systems that need strong timeliness guarantees during normal operation but can tolerate short outages in an emergency, e.g., when they are under attack. We argue that BTR could be a good fit for many cyber-physical systems. We also sketch a technical approach to providing BTR, and we discuss some challenges that still remain.
  • Publication
    Detecting Covert Timing Channels with Time-Deterministic Replay
    (2014-10-01) Chen, Ang; Haeberlen, Andreas; Moore, W. Brad; Phan, Linh T.X.; Xiao, Hanjun; Sherr, Micah; Zhou, Wenchao
    This paper presents a mechanism called timedeterministic replay (TDR) that can reproduce the execution of a program, including its precise timing. Without TDR, reproducing the timing of an execution is difficult because there are many sources of timing variability – such as preemptions, hardware interrupts, cache effects, scheduling decisions, etc. TDR uses a combination of techniques to either mitigate or eliminate most of these sources of variability. Using a prototype implementation of TDR in a Java Virtual Machine, we show that it is possible to reproduce the timing to within 1.85% of the original execution, even on commodity hardware. The paper discusses several potential applications of TDR, and studies one of them in detail: the detection of a covert timing channel. Timing channels can be used to exfiltrate information from a compromised machine; they work by subtly varying the timing of the machine’s outputs, and it is this variation that can be detected with TDR. Unlike prior solutions, which generally look for a specific type of timing channel, our approach can detect a wide variety of channels with high accuracy.