Bug fixes; Encryption/Rerandomization tests pass

meerkat-common/build.gradle

@@ -153,6 +153,8 @@ task fatCapsule(type: FatCapsule){
 
 repositories {
 
+        mavenLocal();
+        
         // Prefer the local nexus repository (it may have 3rd party artifacts not found in mavenCentral)
         maven { 
             url nexusRepository

meerkat-common/src/main/java/meerkat/crypto/concrete/ECElGamalEncryption.java

@@ -22,6 +22,7 @@ import org.slf4j.LoggerFactory;
 import qilin.primitives.concrete.ECElGamal;
 import qilin.primitives.concrete.ECGroup;
 import qilin.primitives.PseudorandomGenerator;
+import qilin.primitives.generic.ElGamal;
 import qilin.util.PRGRandom;
 import qilin.util.Pair;
 
@@ -49,6 +50,12 @@ public class ECElGamalEncryption extends GlobalCryptoSetup implements Encryption
 
     ECGroup group;
 
+    public ECGroup getGroup() { return group; }
+
+    public ECElGamal.PK getElGamalPK() {
+        return elGamalPK;
+    }
+
     public void init(ConcreteCrypto.ElGamalPublicKey serializedPk) throws InvalidKeySpecException {
         AsymmetricKeyParameter keyParam;
 

meerkat-common/src/test/java/meerkat/crypto/concrete/ECElGamalEncryptionTest.java

@@ -4,18 +4,32 @@ import meerkat.protobuf.BulletinBoardAPI;
 import meerkat.protobuf.ConcreteCrypto;
 import meerkat.protobuf.Crypto;
 import meerkat.protobuf.Voting;
+import org.bouncycastle.math.ec.ECPoint;
+import org.junit.Assert;
 import org.junit.Before;
 import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import qilin.primitives.concrete.ECElGamal;
 import qilin.primitives.concrete.ECGroup;
+import qilin.primitives.generic.ElGamal;
+import qilin.util.Pair;
 
 import java.math.BigInteger;
 import java.util.Random;
 
+import static org.junit.Assert.*;
+
 /**
  * Test class for {@link ECElGamalEncryption}
  */
 public class ECElGamalEncryptionTest {
+    final Logger logger = LoggerFactory.getLogger(getClass());
+    /**
+     * Number of times to repeat probabilistic tests.
+     */
+    public final static int CONFIDENCE = 10;
+
     Random rand = new Random(0); // Insecure deterministic random for testing.
 
     ECElGamal.SK key;
@@ -37,25 +51,75 @@ public class ECElGamalEncryptionTest {
         enc.init(serializedPk);
     }
 
+
+    Voting.PlaintextBallot genRandomBallot(int numQuestions, int numAnswers, int maxAnswer) {
+        Voting.PlaintextBallot.Builder ballot = Voting.PlaintextBallot.newBuilder();
+        ballot.setSerialNumber(rand.nextInt(1000000));
+        for (int i = 0; i < numQuestions; ++i) {
+            Voting.BallotAnswer.Builder answers = ballot.addAnswersBuilder();
+            for (int j = 0; j < numAnswers; ++j) {
+                answers.addAnswer(rand.nextInt(maxAnswer));
+            }
+        }
+        return ballot.build();
+    }
+
+    /**
+     * Testing just the key management
+     * @throws Exception
+     */
     @Test
-    public void testEncrypt() throws Exception {
+    public void testPkSerialization() throws Exception {
-        Voting.PlaintextBallot msg = Voting.PlaintextBallot.newBuilder()
+        ECElGamal.PK pk = enc.getElGamalPK();
-                .setSerialNumber(1)
+
-                .addAnswers( Voting.BallotAnswer.newBuilder()
+        ECPoint point = enc.getGroup().sample(rand);
-                    .addAnswer(2)
+        Pair<ECPoint, ECPoint> cipher = pk.encrypt(point, pk.getRandom(rand));
-                    .addAnswer(3)
+
-                    .addAnswer(0)
+        ECPoint decrypted = key.decrypt(cipher);
-                )
+
-                .addAnswers( Voting.BallotAnswer.newBuilder()
+        assertEquals("Decrypted value not equal to encrypted value!", point, decrypted);
-                        .addAnswer(5)
+    }
-                        .addAnswer(6)
+
-                        .addAnswer(7)
+    @Test
-                )
+    public void testEncryption() throws Exception {
-                .build();
+        for (int i = 0; i < CONFIDENCE; ++i) {
+            Voting.PlaintextBallot msg = genRandomBallot(2,3,16); // 2 questions with 3 answers each, in range 0-15.
+            if (msg.getSerializedSize() > enc.getGroup().getInjectiveEncodeMsgLength()) {
+                logger.error("Test Message too big (|msg|={} > max={}), expect failure.",
+                        msg.getSerializedSize(), enc.getGroup().getInjectiveEncodeMsgLength());
+            }
 
             Crypto.RerandomizableEncryptedMessage cipherText = enc.encrypt(msg, enc.generateRandomness(rand));
 
             Voting.PlaintextBallot decrypted = ECElGamalUtils.decrypt(Voting.PlaintextBallot.class, key, group, cipherText);
 
+            assertEquals("Decrypted value differs from encrypted value (i="+i+")!", msg, decrypted);
         }
     }
+
+    @Test
+    public void testRerandomizeModifiesCiphertext() throws Exception {
+        Voting.PlaintextBallot msg = genRandomBallot(2,3,16); // 2 questions with 3 answers each, in range 0-15.
+        Crypto.RerandomizableEncryptedMessage cipher1 = enc.encrypt(msg, enc.generateRandomness(rand));
+        Crypto.RerandomizableEncryptedMessage cipher2 = enc.rerandomize(cipher1, enc.generateRandomness(rand));
+        assertNotEquals("Rerandomized cipher identical to original!", cipher1, cipher2);
+    }
+
+    @Test
+    public void testRerandomizePreservesPlaintext() throws Exception {
+        for (int i = 0; i < CONFIDENCE; ++i) {
+            Voting.PlaintextBallot msg = genRandomBallot(2,3,16); // 2 questions with 3 answers each, in range 0-15.
+
+            Crypto.RerandomizableEncryptedMessage cipher = enc.encrypt(msg, enc.generateRandomness(rand));
+            Crypto.RerandomizableEncryptedMessage cipher2 = cipher;
+            for (int j = 0; j < CONFIDENCE; ++j)
+                cipher2 = enc.rerandomize(cipher2, enc.generateRandomness(rand));
+
+            Voting.PlaintextBallot decrypted = ECElGamalUtils.decrypt(Voting.PlaintextBallot.class, key, group,
+                    cipher2);
+
+            assertEquals("Decrypted value differs from original encrypted value (i="+i+")!", msg, decrypted);
+        }
+    }
+}
+

meerkat-common/src/test/java/meerkat/crypto/concrete/ECElGamalUtils.java

@@ -1,9 +1,11 @@
 package meerkat.crypto.concrete;
 
-import com.google.protobuf.*;
+import com.google.protobuf.ByteString;
+import com.google.protobuf.GeneratedMessage;
+import com.google.protobuf.InvalidProtocolBufferException;
+import com.google.protobuf.Message;
 import meerkat.protobuf.ConcreteCrypto;
 import meerkat.protobuf.Crypto;
-import org.bouncycastle.jce.provider.BouncyCastleProvider;
 import org.bouncycastle.jce.spec.ECParameterSpec;
 import org.bouncycastle.jce.spec.ECPublicKeySpec;
 import org.bouncycastle.math.ec.ECPoint;
@@ -14,13 +16,11 @@ import qilin.primitives.concrete.ECGroup;
 import qilin.primitives.generic.ElGamal;
 import qilin.util.Pair;
 
-import java.lang.reflect.*;
+import java.io.ByteArrayInputStream;
 import java.security.KeyFactory;
 import java.security.NoSuchAlgorithmException;
-import java.security.NoSuchProviderException;
 import java.security.PublicKey;
 import java.security.spec.InvalidKeySpecException;
-import java.util.Random;
 
 /**
  * utilities for ECElgamal
@@ -73,12 +73,13 @@ public class ECElGamalUtils {
 
         byte[] plaintext = group.injectiveDecode(plaintextEncoded);
 
-        CodedInputStream ci = CodedInputStream.newInstance(plaintext);
+        ByteArrayInputStream in = new ByteArrayInputStream(plaintext);
 
         try {
             java.lang.reflect.Method newBuilder = plaintextMessageType.getMethod("newBuilder");
             GeneratedMessage.Builder builder = (GeneratedMessage.Builder) newBuilder.invoke(plaintextMessageType);
-            return (T) builder.mergeFrom(ci).build();
+            builder.mergeDelimitedFrom(in);
+            return plaintextMessageType.cast(builder.build());
         } catch (Exception e) {
             logger.error("Error parsing incoming message", e);
             throw new InvalidProtocolBufferException("Plaintext protobuf error");