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Faculty Candidate Seminar

SSH Proofs, TCP Leaks, and Not-so-AccuVotes: Comuter Security from Proofs to People

Tadayoshi Kohno

Dr. Kohno is from the University of California at San Diego
One way to divide modern computer security research is by the level
of abstraction that one deals with. At one end of the spectrum
there is fundamental research on the design and analysis of
cryptographic building blocks. At the other end of the spectrum
there is research focused on the design and analysis of complex and
socially important systems. In this talk I suggest the importance
of security research spanning multiple levels of abstraction. I
motivate this discussion with three examples. (1) The Secure Shell
(SSH) protocol's core is based on an idealized cryptographic
paradigm with negative theoretical support (Encrypt-and-MAC).
Despite this fact, I found that the overall design of the SSH core
is secure. To reconcile this difference, I extend the
reduction-based provable security approach to encompass the full
goals and details of the SSH core. As part of my research I did
discover and fix a bug in the SSH protocol that could lead to a loss
of privacy. (2) I describe a new privacy issue that arises because
of an interaction between the physical properties of a device's
hardware and the properties of the device's software. By analyzing
a stream of TCP packets from a device, it is in some cases possible
to infer information about the transmitting device's clock skew.
Applications of my technique include computer forensics, counting
the number of devices behind a NAT, and de-anonymizing anonymized
network traces. (3) I describe my discovery of security problems
with Diebold's AccuVote-TS electronic voting machines. I then
describe some social and technical implications of my results.

Sponsored by

CSE Division