Lagrangian E-Voting: e-Voting Concept Our contribution - PowerPoint PPT Presentation

Lagrangian E-Voting Lagrangian E-Voting: e-Voting Concept Our contribution Verifiability on Demand and Strong Privacy Scheme Description Registration Ballot Structure Casting a Vote Łukasz Krzywiecki, Mirosław Kutyłowski Mixing Cascades Verification by a Voter Verification Institute of Mathematics and Computer Science Wrocław University of Technology TRUST 2010 21-23 June 2010, Berlin

Outline Lagrangian E-Voting e-Voting 1 e-Voting Concept Concept Our contribution Our contribution Scheme Description Registration Ballot Structure Scheme Description 2 Casting a Vote Mixing Cascades Registration Verification by a Voter Verification Ballot Structure Casting a Vote Mixing Cascades Verification by a Voter Verification

Remote Voting motivation Lagrangian E-Voting Necessity of remote voting e-Voting Concept mobility of voters Our contribution Scheme (polling stations model and voting at the place of Description Registration residence is a 19 century model) Ballot Structure Casting a Vote a growing number of disabled and/or aged people Mixing Cascades Verification by a Voter Verification increasing the number of democratic decisions? Solutions postal voting remote voting

Postal Voting properties Lagrangian E-Voting Advantages e-Voting Concept usability Our contribution Scheme simple, transparent Description Registration Ballot Structure no electronics involved Casting a Vote Mixing Cascades Verification by a Voter Verification Threats requires very reliable post system (so it may work in Switzerland, but not in Poland) vote selling so easy . . . coercion problems

Postal Voting properties Lagrangian E-Voting Advantages e-Voting Concept usability Our contribution Scheme simple, transparent Description Registration Ballot Structure no electronics involved Casting a Vote Mixing Cascades Verification by a Voter Verification Threats requires very reliable post system (so it may work in Switzerland, but not in Poland) vote selling so easy . . . coercion problems

Remote Voting advantages and disadvantages Lagrangian E-Voting Advantages e-Voting instantaneous confirmation about arrival of a vote Concept Our contribution once deployed cheap in operation Scheme Description Registration scalable Ballot Structure Casting a Vote Mixing Cascades Verification by a Voter Threats Verification how can you trust your computer?! (vote modified, no confidentiality,...) vote selling so easy . . . (downloading software, digital reward...) coercion problems

Remote Voting advantages and disadvantages Lagrangian E-Voting Advantages e-Voting instantaneous confirmation about arrival of a vote Concept Our contribution once deployed cheap in operation Scheme Description Registration scalable Ballot Structure Casting a Vote Mixing Cascades Verification by a Voter Threats Verification how can you trust your computer?! (vote modified, no confidentiality,...) vote selling so easy . . . (downloading software, digital reward...) coercion problems

Remote Voting solutions Lagrangian E-Voting e-Voting Concept Idea 1 - blind computer Our contribution Scheme the computer performs some operations but does not Description Registration know their meaning Ballot Structure Casting a Vote the voter has some information from an independent Mixing Cascades channel hidden from the PC Verification by a Voter Verification no possibility to change a vote by the computer not even to a random one no possibility to betray the voter’s preferences

Remote Voting solutions Lagrangian E-Voting e-Voting Concept Our contribution Idea 2 - local verifiability Scheme Description some information published on bulletin board Registration Ballot Structure Casting a Vote a voter obtains some information that can be checked Mixing Cascades Verification by a Voter against bulletin board Verification the voter can check that her/his vote has been counted ... but cannot prove anything about the vote cast

Remote Voting solutions Lagrangian E-Voting e-Voting Concept Our contribution Scheme Description Idea 3 - redoing Registration Ballot Structure a voter can change his vote until the end of election day Casting a Vote Mixing Cascades Verification by a Voter coercion requires physical supervision during the whole Verification election period

Remote Voting weakening crypto Lagrangian E-Voting What happens in 10 years? e-Voting Concept Our contribution sensitive informations published on bulletin board in Scheme order to enable verifiability Description Registration Ballot Structure well protected according to the crypto’s state-of-the-art Casting a Vote Mixing Cascades ... but in 10 years cryptanalysis may break it and reveal Verification by a Voter Verification voter’s preferences Threat the voters can be scared to vote against some parties as they make revenge in 10 years

Our goal Lagrangian E-Voting e-Voting Concept Forward security in e-voting Our contribution Scheme 1 limit verification to its primary purpose - avoiding Description Registration election frauds Ballot Structure Casting a Vote Mixing Cascades 2 verification possible only in front of a judge Verification by a Voter Verification (and OECD ... observers) 3 minimal information principle - destroy verification keys as soon as the legal situation cannot change

Our contribution Lagrangian E-Voting e-Voting Concept On top approach Our contribution We do not design a new scheme but provide a method for Scheme Description securing schemes for which: Registration Ballot Structure Casting a Vote the voter has to fill a number a bubbles on the screen of Mixing Cascades his PC Verification by a Voter Verification all security features are already granted, except for forward security

Our contribution Lagrangian E-Voting PC ID card System (BB,CA) e-Voting Concept Our contribution Court (Verification) Scheme Description Registration Ballot Structure Casting a Vote Mixing Cascades Verification by a Voter Basic Properties Verification 1 some computations are done inside a personal ID card (the voters know that borrowing an ID card is very risky!) 2 verification can be performed only in an election court, 3 verification cannot be used outside the court due to its zero knowledge properties

Registration Interaction: ID card – RA Lagrangian E-Voting ID card Registartion Authority e-Voting Concept Our contribution Scheme Description Registration Ballot Structure Casting a Vote Mixing Cascades Verification by a Voter Verification

Registration Key Generation Lagrangian E-Voting ID card Registartion Authority e-Voting Generates keys: ( cs,cp ) Concept Our contribution Scheme Description Registration Ballot Structure Casting a Vote Mixing Cascades Verification by a Voter Verification

Registration Request Signing Lagrangian E-Voting ID card Registartion Authority e-Voting Generates keys: ( cs,cp ) Concept Our contribution cp,Sign(cp) Scheme Description Registration Ballot Structure Casting a Vote Mixing Cascades Verification by a Voter Verification

Registration Passing Request to RA Lagrangian E-Voting ID card Registartion Authority e-Voting Generates keys: ( cs,cp ) Concept Our contribution cp,Sign(cp) Scheme Description Registration Ballot Structure Casting a Vote Mixing Cascades Verification by a Voter Verification

Registration Request Verification Lagrangian E-Voting ID card Registartion Authority e-Voting Generates keys: ( cs,cp ) Concept Our contribution cp,Sign(cp) Scheme Description Ver(Sign(cp) Registration Ballot Structure Casting a Vote Mixing Cascades Verification by a Voter Verification

Registration Blind Signature Computing Lagrangian E-Voting ID card Registartion Authority e-Voting Generates keys: ( cs,cp ) Concept Our contribution cp,Sign(cp) Scheme Description Ver(Sign(cp) Registration Ballot Structure Casting a Vote Mixing Cascades s:= Blind_Sign(cp) Verification by a Voter Verification

Registration Passing Blind Signature to ID card Lagrangian E-Voting ID card Registartion Authority e-Voting Generates keys: ( cs,cp ) Concept Our contribution cp,Sign(cp) Scheme Description Ver(Sign(cp) Registration Ballot Structure Casting a Vote Mixing Cascades s:= Blind_Sign(cp) Verification by a Voter Verification

Registration Token Creation Lagrangian E-Voting ID card Registartion Authority e-Voting Generates keys: ( cs,cp ) Concept Our contribution cp,Sign(cp) Scheme Description Ver(Sign(cp) Registration Ballot Structure Casting a Vote Mixing Cascades s:= Blind_Sign(cp) Verification by a Voter Verification x:= (cp,s)

Ballot Structure Lagrangian E-Voting Ballot e-Voting Concept Our contribution Scheme Description Registration Ballot Structure Casting a Vote Mixing Cascades Verification by a Voter Verification

Ballot Structure Triple Lagrangian E-Voting Ballot e-Voting t := ( x, y, z ) Concept Our contribution Scheme Description Registration Ballot Structure Casting a Vote Mixing Cascades Verification by a Voter Verification

Ballot Structure Token Lagrangian E-Voting Ballot e-Voting t := ( x, y, z ) Concept Our contribution Scheme Description Registration Token Ballot Structure Casting a Vote ( cp, s ) Mixing Cascades Verification by a Voter Verification