On the Cryptographic Hardness of Finding a Nash Equilibrium Nir Bitansky∗ Omer Panethy Alon Rosenz August 14, 2015 Abstract We prove that finding a Nash equilibrium of a game is hard, assuming the existence of indistin- guishability obfuscation and one-way functions with sub-exponential hardness. We do so by showing how these cryptographic primitives give rise to a hard computational problem that lies in the complexity class PPAD, for which finding Nash equilibrium is complete. Previous proposals for basing PPAD-hardness on program obfuscation considered a strong “virtual black-box” notion that is subject to severe limitations and is unlikely to be realizable for the programs in question. In contrast, for indistinguishability obfuscation no such limitations are known, and recently, several candidate constructions of indistinguishability obfuscation were suggested based on different hardness assumptions on multilinear maps. Our result provides further evidence of the intractability of finding a Nash equilibrium, one that is extrinsic to the evidence presented so far. ∗MIT. Email:
[email protected]. yBoston University. Email:
[email protected]. Supported by the Simons award for graduate students in theoretical computer science and an NSF Algorithmic foundations grant 1218461. zEfi Arazi School of Computer Science, IDC Herzliya, Israel. Email:
[email protected]. Supported by ISF grant no. 1255/12 and by the ERC under the EU’s Seventh Framework Programme (FP/2007-2013) ERC Grant Agreement n. 307952. 1 Introduction The notion of Nash equilibrium is fundamental to game theory. While a mixed Nash equilibrium is guar- anteed to exist in any game [Nas51], there is no known polynomial-time algorithm for finding one.