Hovav Shacham
September 11, 2015 at 12:00 PM in 380 Soda Hall
Title: On Subnormal Floating Point and Abnormal Timing
We identify a timing channel in the floating point instructions of modern x86 processors: the running time of floating point addition and multiplication instructions can vary by two orders of magnitude depending on their operands. We develop a benchmark measuring the timing variability of floating point operations and report on its results. We use floating point data timing variability to demonstrate practical attacks on the security of the Firefox browser (versions 23 through 27) and the Fuzz differentially private database. Finally, we initiate the study of mitigations to floating point data timing channels with libfixedtimefixedpoint, a new fixed-point, constant-time math library. Modern floating point standards and implementations are sophisticated, complex, and subtle, a fact that has not been sufficiently recognized by the security community. More work is needed to assess the implications of the use of floating point instructions in security-relevant software. Joint work with Marc Andrysco, David Kohlbrenner, Keaton Mowery, Ranjit Jhala, and Sorin Lerner.
Bio: Hovav Shacham is an associate professor in UC San Diego’s Department of Computer Science and Engineering. His research interests are in applied cryptography, systems security, privacy-enhancing technologies, and tech policy. Shacham received his Ph.D. in computer science in 2005 from Stanford University, where he had also earned, in 2000, an A.B. in English. His Ph.D. advisor was Dan Boneh. In 2006 and 2007, he was a Koshland Scholars Program postdoctoral fellow at the Weizmann Institute of Science, hosted by Moni Naor. In 2007, Shacham participated in California Secretary of State Debra Bowen’s “Top-to-Bottom” review of the voting machines certified for use in California. He was a member of the team reviewing Hart InterCivic source code; the report he co-authored was cited by the Secretary in her decision to withdraw approval from Hart voting machines.