Optimality of Non-Adaptive Strategies: The Case of Parallel Games
Grégory Demay, Peter Gaži, Ueli Maurer, and Björn Tackmann
Most cryptographic security proofs require showing that two systems are indistinguishable. A central tool in such proofs is that of a game, where winning the game means provoking a certain condition, and it is shown that the two systems considered cannot be distinguished unless this condition is provoked. Upper bounding the probability of winning such a game, i.e., provoking this condition, for an arbitrary strategy is usually hard, except in the special case where the best strategy for winning such a game is known to be non-adaptive.
A sufficient criterion for ensuring the optimality of non-adaptive strategies is that of conditional equivalence to a system, a notion introduced in [Mau02]. In this paper, we show that this criterion is not necessary to ensure the optimality of non-adaptive strategies by giving two results of independent interest: 1) the optimality of non-adaptive strategies is not preserved under parallel composition; 2) in contrast, conditional equivalence is preserved under parallel composition.
BibTeX Citation
@inproceedings{DGMT14,
author = {Grégory Demay and Peter Gaži and Ueli Maurer and Björn Tackmann},
title = {Optimality of Non-Adaptive Strategies: The Case of Parallel Games},
booktitle = {2014 IEEE International Symposium on Information Theory (ISIT)},
pages = 1707-1711,
year = 2014,
month = 6,
}