Added encrypted message protobuf, and updated encryption API.

meerkat-common/src/main/java/meerkat/crypto/Encryption.java

@@ -7,6 +7,14 @@ import static meerkat.protobuf.Crypto.*;
  * Created by talm on 11/2/15.
  */
 public interface Encryption {
-    Message encrypt(Message plaintext, EncryptionRandomness rnd);
+    /**
+     * Encrypt the serialized form of a message plaintext.
+     * @param plaintext
+     * @param rnd
+     * @return
+     */
+    RerandomizableEncryptedMessage encrypt(Message plaintext, EncryptionRandomness rnd); // TODO: type of exception; throws
+
+    RerandomizableEncryptedMessage rerandomize(RerandomizableEncryptedMessage msg, EncryptionRandomness rnd);
 
 }

meerkat-common/src/main/java/meerkat/crypto/mixnet/Mixer.java

@@ -1,8 +1,7 @@
 package meerkat.crypto.mixnet;
 
-import meerkat.voting.EncryptedBallot;
-
 import java.util.List;
+import static meerkat.protobuf.Voting.*;
 
 /**
  * Created by talm on 25/10/15.

meerkat-common/src/main/java/meerkat/voting/EncryptedBallot.java

@@ -1,16 +0,0 @@
-package meerkat.voting;
-
-import com.google.protobuf.Message;
-
-/**
- * Created by talm on 25/10/15.
- */
-public interface EncryptedBallot {
-    /**
-     * Return the public portion of the ballot (this can be published to the bulletin board without violating privacy).
-     * @return
-     */
-    Message getPublicPortion();
-
-
-}

meerkat-common/src/main/proto/meerkat/crypto.proto

@@ -41,4 +41,10 @@ message EncryptionRandomness {
 // A proof that randomness is correctly generated
 message RandomnessGenerationProof {
     bytes data = 1;
-}
+}
+
+// An encrypted message (rerandomizable)
+message RerandomizableEncryptedMessage {
+    bytes data = 1;
+}
+

meerkat-common/src/main/proto/meerkat/voting.proto

@@ -49,6 +49,12 @@ message PlaintextBallot {
     repeated BallotAnswer answers = 2;
 }
 
+message EncryptedBallot {
+    uint64 serialNumber = 1; // Ballot serial number
+
+    RerandomizableEncryptedMessage data = 2;
+}
+
 message BallotSecrets {
     PlaintextBallot plaintext_ballot = 1;