## Coercion-Resistance and Receipt-Freeness in Electronic Voting

Stéphanie Delaune, Steve Kremer, and Mark D. Ryan. Coercion-Resistance and Receipt-Freeness in Electronic Voting. In Proceedings of the 19th IEEE Computer Security Foundations Workshop (CSFW'06), pp. 28–39, IEEE Computer Society Press, Venice, Italy, July 2006.

### Abstract

In this paper we formally study important properties of electronic voting protocols. In particular we are interested in coercion-resistance and receipt-freeness. Intuitively, an election protocol is coercion-resistant if a voter $$A$$ cannot prove to a potential coercer $$C$$ that she voted in a particular way. We assume that $$A$$ cooperates with $$C$$ in an interactive way. Receipt-freeness is a weaker property, for which we assume that $$A$$ and $$C$$ cannot interact during the protocol, but $$A$$ later provides evidence (the receipt) of how she voted. While receipt-freeness can be expressed using observational equivalence from the applied pi calculus, we need to introduce a new relation to capture coercion-resistance. Our formalization of coercion-resistance and receipt-freeness are quite different. Nevertheless, we show in accordance with intuition that coercion-resistance implies receipt-freeness, which implies privacy, the basic anonymity property of voting protocols, as defined in previous work. Finally we illustrate the definitions on a simplified version of the Lee et al. voting protocol.

### BibTeX

@inproceedings{DKR-csfw06,
abstract =      {In this paper we formally study important properties
of electronic voting protocols. In particular we are
interested in coercion-resistance and
receipt-freeness. Intuitively, an election protocol
is coercion-resistant if a voter $$A$$ cannot prove
to a potential coercer~$$C$$ that she voted in a
particular way. We assume that $$A$$ cooperates
with~$$C$$ in an interactive way. Receipt-freeness is
a weaker property, for which we assume that $$A$$
and~$$C$$ cannot interact during the protocol, but
$$A$$ later provides evidence (the receipt) of how
she voted. While receipt-freeness can be expressed
using observational equivalence from the applied pi
calculus, we need to introduce a new relation to
capture coercion-resistance. Our formalization of
coercion-resistance and receipt-freeness are quite
different. Nevertheless, we show in accordance with
intuition that coercion-resistance implies
receipt-freeness, which implies privacy, the basic
anonymity property of voting protocols, as defined in
previous work. Finally we illustrate the definitions
on a simplified version of the Lee~\emph{et~al.}\
voting protocol.},
author =        {Delaune, St{\'e}phanie and Kremer, Steve and
Ryan, Mark D.},
booktitle =     {{P}roceedings of the 19th {IEEE} {C}omputer
{S}ecurity {F}oundations {W}orkshop ({CSFW}'06)},
DOI =           {10.1109/CSFW.2006.8},
month =         jul,
pages =         {28-39},
publisher =     {{IEEE} Computer Society Press},
title =         {Coercion-Resistance and Receipt-Freeness in
Electronic Voting},
year =          {2006},
acronym =       {{CSFW}'06},
nmonth =        {7},
url =           {http://www.lsv.ens-cachan.fr/Publis/PAPERS/PDF/DKR-csfw06.pdf},
}