### Reverse Firewalls for Actively Secure MPCs

Suvradip Chakraborty, Stefan Dziembowski, and Jesper Buus Nielsen

##### Abstract

Reverse firewalls were introduced at Eurocrypt 2015 by Mironov and Stephens-Davidowitz, as a method for protecting cryptographic protocols against attacks on the devices of the honest parties. In a nutshell: a reverse firewall is placed outside of a device and its goal is to sanitize'' the messages sent by it, in such a way that a malicious device cannot leak its secrets to the outside world. It is typically assumed that the cryptographic devices are attacked in a functionality-preserving way'' (i.e. informally speaking, the functionality of the protocol remains unchanged under this attacks). In their paper, Mironov and Stephens-Davidowitz construct a protocol for passively-secure two-party computations with firewalls, leaving extension of this result to stronger models as an open question. In this paper, we address this problem by constructing a protocol for secure computation with firewalls that has two main advantages over the original protocol from Eurocrypt 2015. Firstly, it is a multiparty computation protocol (i.e. it works for an arbitrary number $n$ of the parties, and not just for $2$). Secondly, it is secure in much stronger corruption settings, namely in the actively corruption model. More precisely: we consider an adversary that can fully corrupt up to $n-1$ parties, while the remaining parties are corrupt in a functionality-preserving way. Our core techniques are: malleable commitments and malleable non-interactive zero-knowledge, which in particular allow us to create a novel protocol for multiparty augmented coin-tossing into the well with reverse firewalls (that is based on a protocol of Lindell from Crypto 2001).

Available format(s)
Category
Cryptographic protocols
Publication info
A minor revision of an IACR publication in CRYPTO 2020
Keywords
Contact author(s)
stefan dziembowski @ gmail com
jbn @ cs au dk
History
2020-08-21: last of 2 revisions
See all versions
Short URL
https://ia.cr/2019/1317

CC BY

BibTeX

@misc{cryptoeprint:2019/1317,
author = {Suvradip Chakraborty and Stefan Dziembowski and Jesper Buus Nielsen},
title = {Reverse Firewalls for Actively Secure MPCs},
howpublished = {Cryptology ePrint Archive, Paper 2019/1317},
year = {2019},
note = {\url{https://eprint.iacr.org/2019/1317}},
url = {https://eprint.iacr.org/2019/1317}
}

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