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Problem 85

Garbled circuit over-simplification

Due: April 19
Points: 3

Here is a short paper from (I think) a Ph.D. student at UC Davis describing a simplified version of Yao's garbled circuit protocol.

I thought about assigning it as a reference material for the class, and then realized there is a major, serious security flaw in how it handles the encryptions.

Here's the link: https://www.math.ucla.edu/~tdokos/notes_files/garbledCircuits.pdf

Find the security flaw and describe how it could be used for Bob (the circuit evaluator) to do something that he shouldn't be able to do.

(Note: I have tried to be responsible and asked the author to fix it or take down the PDF, and got no response. So I'm doing the next-best thing, which is to make a problem out of it for you to solve!)