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Obfuscation Project of the UMDES Group at the University of Michigan

We call this page the "Obfuscation Project". A better but less catchy name should probably be: "Opacity Enforcement and Its Application to Location Privacy".

Opacity is a general property that has been defined and studied in the context of computer security and privacy. Assuming that some information about a user is revealed to an eavesdropper with potentially malicious intentions, and assuming that a portion of that information needs to be kept "secret", opacity roughly means that the user can always maintain plausible deniability about its secret information. Let's say that someone is tracking your movements and that your secret information is that you are at the bank, then the tracking should not reveal with certainty that you are at the bank; perhaps you could also be at the coffee shop next to the bank. For an overview of the study of opacity, please refer to [1]. For some historical remarks regarding the study of opacity in a branch of control engineering known as Discrete Event Systems (DES), see [2].

Our group at Michigan has been doing work on opacity and its enforcement for many years. More on this below. To illustrate our theoretical work on opacity enforcement by insertion and edit functions, we have used location privacy as an illustrative example. Let's imagine that you can send slightly altered (i.e., obfuscated) information about your location as you move around in a certain geographical area. Then how should your position information be slightly altered, as observed by the eavesdropper or other parties, so that your visits to secret locations are never revealed? This is more complicated than adding random noise to your location as you move. This is because the obfuscated trajectory is required to be a valid trajectory where you are moving. Inside a building, the obfuscated trajectory should not go through wall. If you are moving around town, then it should not go through buildings, etc.

The paper [3] gives an example on


[1] Overview of opacity: Jacob et al.

[2] History of opacity

[3] Location privacy: WODES 2014

[4] Demonstration of opacity: IFAC 2017

[3] [4] [5]

Yi-Chin Wu: opacity enforcement: TAC, optimal, JAR

[6] [7]

Yiding Ji: opacity enforcement: public-private insertion; public-private edit

[8] Xiang

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