Validate that n of m elections are encrypting and decrypting correctly (#315)

* Validate that n of m elections are encrypting and decrypting correctly

* Extract styleid

* Fix problem with inconsistent slashes on windows build targets

* Consistently use forward slashes on windows

* Fix slashes for all build targets

* Fix slashes one level higher

* Fix cpm source cache as well

Author: lprichar

Makefile

@@ -5,12 +5,12 @@ ELECTIONGUARD_BINDING_DIR=$(realpath .)/bindings
 ELECTIONGUARD_BINDING_LIB_DIR=$(ELECTIONGUARD_BINDING_DIR)/netstandard/ElectionGuard/ElectionGuard.Encryption
 ELECTIONGUARD_BINDING_BENCH_DIR=$(ELECTIONGUARD_BINDING_DIR)/netstandard/ElectionGuard/ElectionGuard.Encryption.Bench
 ELECTIONGUARD_BINDING_TEST_DIR=$(ELECTIONGUARD_BINDING_DIR)/netstandard/ElectionGuard/ElectionGuard.Encryption.Tests
-ELECTIONGUARD_BUILD_DIR=$(realpath .)/build
+ELECTIONGUARD_BUILD_DIR=$(subst \,/,$(realpath .))/build
 ELECTIONGUARD_BUILD_DIR_WIN=$(subst \c\,C:\,$(subst /,\,$(ELECTIONGUARD_BUILD_DIR)))
 ELECTIONGUARD_BUILD_APPS_DIR=$(ELECTIONGUARD_BUILD_DIR)/apps
 ELECTIONGUARD_BUILD_BINDING_DIR=$(ELECTIONGUARD_BUILD_DIR)/bindings
 ELECTIONGUARD_BUILD_LIBS_DIR=$(ELECTIONGUARD_BUILD_DIR)/libs
-CPM_SOURCE_CACHE=$(realpath .)/.cache/CPM
+CPM_SOURCE_CACHE=$(subst \,/,$(realpath .))/.cache/CPM
 
 # Detect operating system
 ifeq ($(OS),Windows_NT)

bindings/netstandard/ElectionGuard/ElectionGuard.Encryption.Tests/TestEncrypt.cs

@@ -2,7 +2,7 @@
 using ElectionGuard.Encryption.Utils;
 using NUnit.Framework;
 
-namespace ElectionGuard.Encrypt.Tests
+namespace ElectionGuard.Encryption.Tests
 {
     [TestFixture]
     public class TestEncrypt
@@ -88,7 +88,7 @@ public void Test_Encrypt_Ballot_Undervote_Succeeds()
             var mediator = new EncryptionMediator(internalManifest, context, device);
 
             // Act
-            var ballot = BallotGenerator.GetFakeBallot(internalManifest, 1);
+            var ballot = BallotGenerator.GetFakeBallot(internalManifest);
             var ciphertext = mediator.Encrypt(ballot);
 
             // Assert
@@ -116,6 +116,40 @@ public void Test_Encrypt_Ballot_Overvote_Succeeds()
             Assert.That(ciphertext.IsValidEncryption(context.ManifestHash, keypair.PublicKey, context.CryptoExtendedBaseHash));
         }
 
+        [Test]
+        public void Test_EncryptAndDecryptOfBallot_WithMultipleVotesAllowed()
+        {
+            // Arrange
+            var keypair = ElGamalKeyPair.FromSecret(Constants.TWO_MOD_Q);
+            var manifest = ManifestGenerator.GetManifestFromFile();
+            var internalManifest = new InternalManifest(manifest);
+            var context = new CiphertextElectionContext(
+                1UL, 1UL, keypair.PublicKey, Constants.TWO_MOD_Q, internalManifest.ManifestHash);
+            var device = new EncryptionDevice(12345UL, 23456UL, 34567UL, "Location");
+            var mediator = new EncryptionMediator(internalManifest, context, device);
+            const string styleId = "congress-district-7-arlington-pismo-beach";
+            var ballot = BallotGenerator.GetFakeBallotWithContest(internalManifest, "pismo-beach-school-board-contest", 3, styleId);
+
+            // Act
+            var ciphertext = mediator.Encrypt(ballot);
+
+            // Assert
+            Assert.AreEqual(5, ciphertext.ContestsSize);
+            var pismoBeach = FindContestOrDefault(ciphertext, i => i.ObjectId == "pismo-beach-school-board-contest");
+            Assert.IsNotNull(pismoBeach);
+            Assert.AreEqual(1L, DecryptSelection(pismoBeach, keypair, 0));
+            Assert.AreEqual(1L, DecryptSelection(pismoBeach, keypair, 1));
+            Assert.AreEqual(1L, DecryptSelection(pismoBeach, keypair, 2));
+            Assert.AreEqual(0L, DecryptSelection(pismoBeach, keypair, 3));
+            Assert.AreEqual(0L, DecryptSelection(pismoBeach, keypair, 4));
+        }
+
+        private static ulong? DecryptSelection(CiphertextBallotContest pismoBeach, ElGamalKeyPair keypair, int index)
+        {
+            var selection = pismoBeach.GetSelectionAt((ulong)index);
+            return selection.Ciphertext.Decrypt(keypair.SecretKey);
+        }
+
         [Test]
         public void Test_Compact_Encrypt_Ballot_Simple_Succeeds()
         {
@@ -168,7 +202,7 @@ public void Test_EncryptMediator_Hashes_Match()
                 var mediator = new EncryptionMediator(internalManifest, context, device);
                 Assert.IsNotNull(mediator);     // should not be null if it gets created
             }
-            catch (Exception ex)
+            catch (Exception)
             {
                 // if there is an exception then the manifest hash would not be equal
                 Assert.AreNotEqual(context.ManifestHash.ToHex(), internalManifest.ManifestHash.ToHex());
@@ -189,13 +223,27 @@ public void Test_EncryptMediator_Hashes_Dont_Match()
                 var mediator = new EncryptionMediator(internalManifest, context, device);
                 Assert.IsNull(mediator);    // should not be created, so null at best
             }
-            catch (Exception ex)
+            catch (Exception)
             {
                 // if there is an exception then the manifest hash would not be equal
                 Assert.AreNotEqual(context.ManifestHash.ToHex(), internalManifest.ManifestHash.ToHex());
             }
         }
 
 
+        private static CiphertextBallotContest FindContestOrDefault(CiphertextBallot ballot, Func<CiphertextBallotContest, bool> func)
+        {
+            var contestSize = (int)ballot.ContestsSize;
+            for (int i = 0; i < contestSize; i++)
+            {
+                var contest = ballot.GetContestAt((ulong)i);
+                if (func(contest))
+                {
+                    return contest;
+                }
+            }
+
+            return null;
+        }
     }
 }

bindings/netstandard/ElectionGuard/ElectionGuard.Encryption.Utils/Generators/Ballot.cs

@@ -0,0 +1,56 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+
+namespace ElectionGuard.Encryption.Utils
+{
+    public class BallotGenerator
+    {
+        public static PlaintextBallotSelection SelectionFrom(SelectionDescription description, bool isAffirmative = false, bool isPlaceholder = false)
+        {
+            return new PlaintextBallotSelection(description.ObjectId, isAffirmative ? 1UL : 0UL, isPlaceholder);
+        }
+
+        public static PlaintextBallotContest ContestFrom(ContestDescription contest, Func<string, int, bool> voteResultFunc)
+        {
+            List<PlaintextBallotSelection> selections = new List<PlaintextBallotSelection>();
+
+            for (ulong i = 0; i < contest.SelectionsSize; i++)
+            {
+                var isAffirmative = voteResultFunc(contest.ObjectId, (int)i);
+                selections.Add(SelectionFrom(contest.GetSelectionAtIndex(i), isAffirmative));
+            }
+
+            return new PlaintextBallotContest(contest.ObjectId, selections.ToArray());
+        }
+
+        public static PlaintextBallot GetFakeBallotWithContest(InternalManifest manifest, string contestId, int numberOfSelections, string styleId)
+        {
+            return GetFakeBallotInternal(manifest, styleId, (currentContestId, selectionId) =>
+            {
+                if (currentContestId == contestId)
+                    return selectionId < numberOfSelections;
+                return selectionId == 0;
+            });
+        }
+
+        public static PlaintextBallot GetFakeBallot(InternalManifest manifest, uint maxChoices = 1)
+        {
+            var styleId = manifest.GetBallotStyleAtIndex(0).ObjectId;
+            return GetFakeBallotInternal(manifest, styleId, (_, selectionId) => selectionId < maxChoices);
+        }
+
+        public static PlaintextBallot GetFakeBallotInternal(InternalManifest manifest, string styleId,
+            Func<string, int, bool> voteResultFunc)
+        {
+            List<PlaintextBallotContest> contests = new List<PlaintextBallotContest>();
+            for (ulong i = 0; i < manifest.ContestsSize; i++)
+            {
+                contests.Add(ContestFrom(manifest.GetContestAtIndex(i), voteResultFunc));
+            }
+
+            const string ballotId = "ballot-id-123";
+            return new PlaintextBallot(ballotId, styleId, contests.ToArray());
+        }
+    }
+}