Differentially private multi-agent constraint optimization

Distributed constraint optimization (DCOP) is a framework in which multiple agents with private constraints (or preferences) cooperate to achieve a common goal optimally. DCOPs are applicable in several multi-agent coordination/allocation problems, such as vehicle routing, radio frequency assignments, and distributed scheduling of meetings. However, optimization scenarios may involve multiple agents wanting to protect their preferences' privacy. Researchers propose privacy-preserving algorithms for DCOPs that provide improved privacy protection through cryptographic primitives such as partial homomorphic encryption, secret-sharing, and secure multiparty computation. These privacy benefits come at the expense of high computational complexity. Moreover, such an approach does not constitute a rigorous privacy guarantee for optimization outcomes, as the result of the computation may compromise agents' preferences. In this work, we show how to achieve privacy, specifically Differential Privacy, by randomizing the solving process. In particular, we present P-Gibbs, which adapts the current state-of-the-art algorithm for DCOPs, namely SD-Gibbs, to obtain differential privacy guarantees with much higher computational efficiency. Experiments on benchmark problems such as Ising, graph-coloring, and meeting-scheduling show P-Gibbs' privacy and performance trade-off for varying privacy budgets and the SD-Gibbs algorithm. More concretely, we empirically show that P-Gibbs provides fair solutions for competitive privacy budgets.