How can a machine specify a computation to another one and then, without
executing the computation, check that the other machine carried it out
correctly? And how can this be done without assumptions about the
performer (replication, trusted hardware, etc.) or restrictions on the
computation? This is the problem of _verified computation_, and it is
motivated by the cloud and other third-party computing models. It has
long been known that (1) this problem can be solved in theory using
probabilistically checkable proofs (PCPs) coupled with cryptographic
tools, and (2) the performance of these solutions is wildly impractical
(trillions of CPU-years or more to verify simple computations).
I will describe a project at UT Austin that challenges the second piece
of this folklore. We have developed an interactive protocol that begins
with an efficient argument [IKO CCC '07] and incorporates new
theoretical work to improve performance by 20+ orders of magnitude. In
addition, we have broadened the computational model from Boolean
circuits to a general-purpose model. We have fully implemented the
system, accelerated it with GPUs, and developed a compiler that
transforms computations expressed in a high-level language to
executables that implement the protocol entities.
The resulting system, while not quite ready for the big leagues, is
close enough to practicality to suggest that in the near future, PCPs
could be a real tool for building actual systems.
Talk will be based on these papers and ongoing work:
Michael Walfish is an assistant professor in the Computer Science
Department at The University of Texas at Austin. His research interests
are in systems, security, and networking. His honors include an Air
Force Young Investigator Award, an NSF CAREER Award, a Sloan Research
Fellowship, a Teaching Excellence Award from the UT College of Natural
Sciences, the Intel Early Career Faculty Honor Program, and the UT
Society for Teaching Excellence. He received his B.A. from Harvard and
his Ph.D. from MIT, both in Computer Science.