Caveat Coercitor: Coercion-Evidence in Electronic Voting

Abstract

The balance between coercion-resistance, election verifiability and usability remains unresolved in remote electronic voting despite significant research over the last few years. We propose a change of perspective, replacing the requirement of coercion-resistance with a new requirement of coercionevidence: there should be public evidence of the amount of coercion that has taken place during a particular execution of the voting system. We provide a formal definition of coercion-evidence that has two parts. Firstly, there should be a coercion-evidence test that can be performed against the bulletin board to accurately determine the degree of coercion that has taken place in any given run. Secondly, we require coercer independence, that is the ability of the voter to follow the protocol without being detected by the coercer. To show how coercion-evidence can be achieved, we propose a new remote voting scheme, Caveat Coercitor, and we prove that it satisfies coercion-evidence. Moreover, Caveat Coercitor makes weaker trust assumptions than other remote voting systems, such as JCJ/Civitas and Helios, and has better usability properties.

APTE: An Algorithm for Proving Trace Equivalence

“…Moreover, we would like to include new cryptographic primitives such as XOR, blind signature and re-encryption used in very interesting protocols e.g. Caveat Coercitor [11].…”

Receipt-freeness and coercion resistance in remote E-voting systems

“…This process includes following buyers' instructions and communicating with buyers during the voting process [25]. Traditionally, vote-selling is considered illegal and is prohibited in elections.…”

“…Instead of considering voter-coercion resistance, Caveat Coercitor [25] proposed a protocol which satisfies coercion-evidence. Unlike voter-coercion resistant systems, Caveat Coercitor tolerates coercions but records unforgeable evidence for voter-coercions.…”

Analysis of privacy in mobile telephony systems

“…Formal methods have proved to be effective in highlighting weaknesses of protocols and hence enabling designers and programmers to patch them and strengthen their security guarantees, as well as in giving strong assurance on the properties a protocol achieves by proving the absence of attacks undermining the stated security properties. For example, conference management [1], electronic voting [2][3][4], single-sign-on [5,6], cloud storage [7], RFID [8], TPM [9,10] and mobile telephony protocols [11] have been scrutinized using manual and automatic verification techniques. Manual proof methods are lengthy and error prone, while automatic verification tools have to compromise in order to achieve decidability (at least for some subclass of processes) by bounding the number of agents and sessions and/or restricting the considered class of cryptographic functions.…”