Dark Blue with Orange

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A remote voting systembased on Prêt à
Votercoded byDavid LundinJohannes Clos
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Design goals

• End-to-end verifiable (if...)?
• Offload authentication to host organization
• Easy to set up, maintain and use
• Use publicly available mix servers (when...)?

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Limitations

• Unsupervised voting
• No coercion resistance
• No guarantee of response from server
• Someone has to authenticate users
• We use host organization (could use our server)?
• Some parts not quite complete
• Threshold decryption
• SSL certificates (time/money)?

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Operational overview
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Election setup phase

• Create election on EE
• Don't declare voters!
• Retrieve shared secret
• Retrieve signed applet
• Integrate host auth

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Client authentication phase

• Voter logs on normally
• Host serves applet
• PHP script gets authentication information

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Voting phase

• Vote using applet
• Applet encrypts vote
• ElGamal encryption
• Ciphertexts à la Hea07
• Packaged as XML
• Committed to
• Audit or vote
• Vote sent back to host
• Host signs XML
• Sent back to ee.com
• Signed receipt given

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Auditing
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Voting and auditing

• Voting applet
• constructs XML
• reveals XML and hash
• offers vote or audit
• Voter then can either
• audit, and uncover details of encryptions
• vote, and get signed hash
• Audit gives confidence in applet's fairness

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Decryption/tallying after polls close

• Use mix nets
• PRC to audit mixes
• Anyone can audit
• Public mix servers
• Votes decrypted
• Threshold decryption
• CP proofs
• Anyone can check
• Lazily decrypt (STV)?
• Anyone can tally

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Auditing the mix nets

• A mix net
• re-encrypts votes
• randomly shuffles
• Twice, with PRC
• Links chosen by hash of output
• Can be re-run

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Conclusion

• Pretty much plug-and-play
• Any organization hosting a web site can use
• End-to-end verifiable
• ...on various seemingly unavoidable assumptions