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Tomáš Kroupa

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AAMAS Conference 2024 Conference Paper

Trust in Shapley: A Cooperative Quest for Global Trust in P2P Network

  • Arti Bandhana
  • Tomáš Kroupa
  • Sebastián Garcia

Modeling the trust of peers in peer-to-peer networks is pivotal in maintaining the security and functionality of the network. This trust is commonly perceived as a peer’s reliability based on past interactions and is generally classified as local and global trust values. In a traditional client-server network, the responsibility of maintaining the integrity of the network falls on the central authority responsible for enforcing the security protocols and safeguarding the network against adversarial activities. In contrast, peer-to-peer networks may lack a central authority due to their decentralized nature, needing innovative mechanisms to maintain network trust. Incorporating a trust mechanism that considers peer interactions within peer groups becomes convenient in the absence of central authority. This paper introduces a novel approach to global trust computation. We propose a transferable utility coalitional game that pools local trust values between peers. The coalitions of peers aggregate the local trust values by considering internal and external trust. Internal trust is defined as the sum of the local trust values of the peers in the coalition, and external trust is constituted by the minimal trustworthiness of peers in the coalition to the peers outside. The resulting trust game is superadditive, monotone, and has a non-empty core. The global trust values of individual peers are the Shapley values in the trust game. Our numerical experiments in three different settings show that the resulting global trust captures the peer behavior faithfully, and we compared our method to Eigentrust.

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AAAI Conference 2021 Conference Paper

Double Oracle Algorithm for Computing Equilibria in Continuous Games

  • Lukáš Adam
  • Rostislav Horčík
  • Tomáš Kasl
  • Tomáš Kroupa

Many efficient algorithms have been designed to recover Nash equilibria of various classes of finite games. Special classes of continuous games with infinite strategy spaces, such as polynomial games, can be solved by semidefinite programming. In general, however, continuous games are not directly amenable to computational procedures. In this contribution, we develop an iterative strategy generation technique for finding a Nash equilibrium in a whole class of continuous two-person zero-sum games with compact strategy sets. The procedure, which is called the double oracle algorithm, has been successfully applied to large finite games in the past. We prove the convergence of the double oracle algorithm to a Nash equilibrium. Moreover, the algorithm is guaranteed to recover an approximate equilibrium in finitely-many steps. Our numerical experiments show that it outperforms fictitious play on several examples of games appearing in the literature. In particular, we provide a detailed analysis of experiments with a version of the continuous Colonel Blotto game.

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