# Information Security and Cryptography Research Group

## New Perspectives on Weak Oblivious Transfer

### Ueli Maurer and João Ribeiro

2016 IEEE International Symposium on Information Theory (ISIT), pp. 790–794, Jul 2016.

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{MauRib16,
author       = {Ueli Maurer and João Ribeiro},
title        = {New Perspectives on Weak Oblivious Transfer},
booktitle    = {2016 IEEE International Symposium on Information Theory (ISIT)},
pages        = 790--794,
year         = 2016,
month        = 7,
}