A study of sybil manipulations in hedonic games

Hedonic games model agents that decide which other agents they will join, given some preferences on other agents. We study Sybil attacks on such games, by a malicious agent which introduces multiple false identities, so that the outcome of the game is more interesting for itself. First taking Nash stability as the solution concept, we consider two simple manipulations, and show that they are essentially the only possible Sybil manipulations. Moreover, small experiments show that they are seldom possible in random games. We exhibit another simple manipulation on the concepts of (contractual) individual stability afterwards. Then we show that such hedonic games are very sensitive to Sybil manipulations, which contrasts sharply with the Nash case.

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