Add voter_id to NIZK proofs in ballots (client-side)

Backported from Helios-C branch. Only ballot generation code is
updated (not verification code).

media/booth/boothworker.js

@@ -35,7 +35,7 @@ function do_setup(message) {
 function do_encrypt(message) {
     console.log("encrypting answer for question " + ELECTION.questions[Q_NUM]);
 
-    var encrypted_answer = new HELIOS.EncryptedAnswer(ELECTION.questions[Q_NUM], message.answer, ELECTION.public_key);
+    var encrypted_answer = new HELIOS.EncryptedAnswer(ELECTION.questions[Q_NUM], message.answer, ELECTION.public_key, message.voter_id);
 
     console.log("done encrypting");
 

media/booth/js/jscrypto/elgamal.js

@@ -525,7 +525,7 @@ ElGamal.DLogProof.fromJSONObject = function(d) {
 
 // a challenge generator based on a list of commitments of
 // proofs of knowledge of plaintext. Just appends A and B with commas.
-ElGamal.disjunctive_challenge_generator = function(commitments) {
+ElGamal.disjunctive_challenge_generator = function(id) { return function(commitments) {
   var strings_to_hash = [];
 
   // go through all proofs and append the commitments
@@ -537,8 +537,8 @@ ElGamal.disjunctive_challenge_generator = function(commitments) {
   
   // console.log(strings_to_hash);
   // STRINGS = strings_to_hash;
-  return new BigInt(hex_sha1(strings_to_hash.join(",")), 16);
-};
+  return new BigInt(hex_sha1("prove|" + id + "|" + strings_to_hash.join(",")), 16);
+}};
 
 // a challenge generator for Fiat-Shamir
 ElGamal.fiatshamir_challenge_generator = function(commitment) {

media/booth/js/jscrypto/helios.js

@@ -216,7 +216,7 @@ UTILS.generate_plaintexts = function(pk, min, max) {
 
 
 HELIOS.EncryptedAnswer = Class.extend({
-  init: function(question, answer, pk, progress) {    
+  init: function(question, answer, pk, id, progress) {
     // if nothing in the constructor
     if (question == null)
       return;
@@ -226,7 +226,7 @@ HELIOS.EncryptedAnswer = Class.extend({
     this.answer = answer;
 
     // do the encryption
-    var enc_result = this.doEncryption(question, answer, pk, null, progress);
+    var enc_result = this.doEncryption(question, answer, pk, id, null, progress);
 
     this.choices = enc_result.choices;
     this.randomness = enc_result.randomness;
@@ -234,7 +234,7 @@ HELIOS.EncryptedAnswer = Class.extend({
     this.overall_proof = enc_result.overall_proof;    
   },
   
-  doEncryption: function(question, answer, pk, randomness, progress) {
+  doEncryption: function(question, answer, pk, id, randomness, progress) {
     var choices = [];
     var individual_proofs = [];
     var overall_proof = null;
@@ -278,7 +278,7 @@ HELIOS.EncryptedAnswer = Class.extend({
       // generate proof
       if (generate_new_randomness) {
         // generate proof that this ciphertext is a 0 or a 1
-        individual_proofs[i] = choices[i].generateDisjunctiveProof(zero_one_plaintexts, plaintext_index, randomness[i], ElGamal.disjunctive_challenge_generator);        
+        individual_proofs[i] = choices[i].generateDisjunctiveProof(zero_one_plaintexts, plaintext_index, randomness[i], ElGamal.disjunctive_challenge_generator(id));
       }
       
       if (progress)
@@ -306,7 +306,7 @@ HELIOS.EncryptedAnswer = Class.extend({
       if (question.min)
         overall_plaintext_index -= question.min;
       
-      overall_proof = hom_sum.generateDisjunctiveProof(plaintexts, overall_plaintext_index, rand_sum, ElGamal.disjunctive_challenge_generator);
+      overall_proof = hom_sum.generateDisjunctiveProof(plaintexts, overall_plaintext_index, rand_sum, ElGamal.disjunctive_challenge_generator(id));
 
       if (progress) {
         for (var i=0; i<question.max; i++)

media/booth/vote.html

@@ -167,6 +167,7 @@ BOOTH.setup_election = function(raw_json) {
   // appears to be safer.
   BOOTH.election = HELIOS.Election.fromJSONString(raw_json);
   BOOTH.election.cast_url = "/election/cast?uuid=" + BOOTH.election.uuid
+  BOOTH.voter_id = "ID"; // placeholder for later
 
   // FIXME: we shouldn't need to set both, but right now we are doing so
   // because different code uses each one. Bah. Need fixing.
@@ -205,6 +206,7 @@ BOOTH.launch_async_encryption_answer = function(question_num) {
    BOOTH.workers[question_num].postMessage({
       'type' : 'encrypt',
       'answer' : BOOTH.ballot.answers[question_num],
+      'voter_id' : BOOTH.voter_id,
       'id' : BOOTH.answer_timestamps[question_num]
    });
 };
@@ -464,7 +466,7 @@ BOOTH.seal_ballot_raw = function() {
     if (BOOTH.synchronous) {
       BOOTH.progress = new UTILS.PROGRESS();
       var progress_interval = setInterval("BOOTH.check_encryption_status()", 500);
-      BOOTH.encrypted_ballot = new HELIOS.EncryptedVote(BOOTH.election, BOOTH.ballot.answers, BOOTH.progress);
+      BOOTH.encrypted_ballot = new HELIOS.EncryptedVote(BOOTH.election, BOOTH.ballot.answers, BOOTH.progress, BOOTH.voter_id);
       clearInterval(progress_interval);
       BOOTH._after_ballot_encryption();
     } else {