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The article discusses truthful mechanisms for agents that examine privacy. Topics discussed include the general way of modelling privacy in the utility functions of the players and design truthful mechanisms, the interaction between mechanism design and differential privacy, and the achievement of the social welfare by the optimal mechanisms approaches as the number of n of players increases.

We construct a publicly verifiable protocol for proving computational work based on collision-resistant hash functions and a new plausible complexity assumption regarding the existence of "inherently sequential" hash functions. Our protocol is based on a novel construction of time-lock puzzles. Given a sampled "puzzle" P getsr Dn, where $n$ is the security parameter and Dn is the distribution of the puzzles, a corresponding "solution" can be generated using N evaluations of the sequential hash function, where N>n is another parameter, while any feasible adversarial strategy for generating valid solutions must take at least as much time as Ω(N) serial evaluations of the hash function after receiving $P$. Thus, valid solutions constitute a "proof" that Ω(N) parallel time elapsed since p was received. Solutions can be publicly and efficiently verified in time poly(n) ⋅ polylog(N). Applications of these "time-lock puzzles" include noninteractive timestamping of documents (where the distribution over the possible documents corresponds to the puzzle distribution Dn) and universally verifiable CPU benchmarks. Our construction is secure in the standard model under complexity assumptions (collision-resistant hash functions and inherently sequential hash functions), and makes black-box use of the underlying primitives. Consequently, the corresponding construction in the random oracle model is secure unconditionally. Moreover, as it is a public-coin protocol, it can be made non-interactive in the random oracle model using the Fiat-Shamir Heuristic. Our construction makes a novel use of "depth-robust" directed acyclic graphs---ones whose depth remains large even after removing a constant fraction of vertices---which were previously studied for the purpose of complexity lower-bounds. The construction bypasses a recent lower-bound of Mahmoody, Moran, and Vadhan (CRYPTO '11) for time-lock puzzles in the random oracle model, which showed that it is impossible to have time-lock puzzles like ours in the random oracle model if the puzzle generator also computes a solution together with the puzzle., Engineering and Applied Sciences

Recent work has constructed economic mechanisms that are both truthful and differentially private. In these mechanisms, privacy is treated separately from the truthfulness; it is not incorporated in players' utility functions (and doing so has been shown to lead to non-truthfulness in some cases). In this work, we propose a new, general way of modelling privacy in players' utility functions. Specifically, we only assume that if an outcome o has the property that any report of player i would have led to o with approximately the same probability, then o has small privacy cost to player i. We give three mechanisms that are truthful with respect to our modelling of privacy: for an election between two candidates, for a discrete version of the facility location problem, and for a general social choice problem with discrete utilities (via a VCG-like mechanism). As the number n of players increases, the social welfare achieved by our mechanisms approaches optimal (as a fraction of n)., Engineering and Applied Sciences