Merge pull request Art3misOne#2 from Art3misOne/Art3misOne-patch-1

Separated error term from private key

RlweConstants.java

@@ -19,6 +19,9 @@ class Constants {
   protected static final int Q_TIMES_16 = 196624;
 
   protected static final int numRecDataBytes = 256;
+
+  protected static final byte FOURIER = 0;
+  protected static final byte ORDINARY = 1;
 
   protected static final Felm[] OMEGA = new Felm[] {
     new Felm (1),     new Felm (49),    new Felm (2401),  new Felm (7048),  new Felm (1260),

RlweKeyExchange.java

@@ -65,17 +65,6 @@ public byte[] initAgreement (RlwePrivateKey kI, RlwePublicKey kR, byte[] rdata)
   }
 
 
-  /* 
-   * At a high level, 4 coefficients are used per bit of shared key produced. Computing 
-   * reconciliation data involves finding the closest lattice vector to those 4 coefficients (as a
-   * vector) and computing the discretized difference between those coefficients and the closest 
-   * lattice vector. This discretized difference is the reconciliation data vector, r. It is assumed 
-   * that translating a lattice point by r will move it closer to the correct lattice point. The
-   * function helpRec uses an algorithm for the closest vector problem to find r, and the function 
-   * rec computes reconciliation using r. The reconciliation data is 2 bits per coefficient so this
-   * is compressed before being sent to reduce bandwidth.
-   */
-
   private byte[] helpRec (RingElt v) {
     int i, j, k, x, rbit, norm;
     int[] v0 = new int[4];

RlweKeys.java

@@ -20,7 +20,9 @@ class RlwePublicKey {
 
 
   public RlwePublicKey (RlwePrivateKey k, RingElt a) {
-    key = a.pointwiseMultAdd(k.getS (), k.getE ());
+    RingElt e = Sample.getSample ();
+    e.ntt ();
+    key = a.pointwiseMultAdd (k.getS (), e);
   }
 
 
@@ -43,7 +45,7 @@ public RingElt getKey () {
     return key;
   }
 
-  
+
   public byte[] serialize () {
     return key.toByteArray();
   }
@@ -57,26 +59,22 @@ public int hashcode () {
 
 class RlwePrivateKey {
   private RingElt s;
-  private RingElt e;
-
+  private byte domain;
 
-  public RlwePrivateKey (RingElt sIn, RingElt eIn) {
+  public RlwePrivateKey (RingElt sIn) {
     s = new RingElt (sIn);
-    e = new RingElt (eIn);
   }
 
 
   public RlwePrivateKey () {
     s = Sample.getSample ();
-    e = Sample.getSample ();
+    domain = Constants.ORDINARY;
   }
 
 
   public RlwePrivateKey (byte[] inBytes) {
-    // Reconstruct a private key from a byte array assuming s and e are the same size.
-    int len = inBytes.length;
-    s = new RingElt (Arrays.copyOfRange (inBytes, 0, len / 2)); 
-    e = new RingElt (Arrays.copyOfRange (inBytes, len / 2, len));
+    domain = inBytes[0];
+    s = new RingElt (Arrays.copyOfRange (inBytes, 1, inBytes.length));
   }
 
 
@@ -85,36 +83,36 @@ public RingElt getS () {
   }
 
 
-  public RingElt getE () {
-    return e;
-  }
-
-
   public void toFourierDomain () {
-    s.ntt();
-    e.ntt();
+    if (domain == Constants.ORDINARY) {
+      s.ntt();
+      domain = Constants.FOURIER;
+    }
   }
 
 
   public void fromFourierDomain () {
-    s.nttInv();
-    e.nttInv();
+    if (domain == Constants.FOURIER) {
+      s.nttInv();
+      domain = Constants.ORDINARY;
+    }
   }
 
 
   public byte[] serialize () {
-    byte[] sba = s.toByteArray ();
-    byte[] eba = e.toByteArray ();
-    byte[] r = new byte[sba.length + eba.length];
-    System.arraycopy (sba, 0, r, 0, sba.length);
-    System.arraycopy (eba, 0, r, sba.length, eba.length);
-    return r;
+    byte[] sba = s.toByteArray();
+    byte[] ba = new byte[sba.length + 1];
+
+    ba[0] = domain;
+    System.arraycopy (sba, 0, ba, 1, sba.length);
+
+    return ba;
   }
 }
 
 
 class RlweKeyPair {
-  private final RlwePublicKey pubKey; 
+  private RlwePublicKey pubKey; 
   private final RlwePrivateKey privKey;
 
 
@@ -147,4 +145,10 @@ public RlwePrivateKey getPrivateKey () {
   public RlwePublicKey getPublicKey () {
     return pubKey;
   }
+
+
+  // Generate a new public key with the same private key but new error term
+  public void genNewPubKey (RingElt a) {
+    pubKey = new RlwePublicKey (privKey, a);
+  }
 }

RlweTest.java

@@ -33,14 +33,12 @@ public static void main (String[] args) {
       /*
       System.out.println ("Initiator private key: ");
       System.out.println ("\t s = " + keysI.getPrivateKey().getS());
-      System.out.println ("\t e = " + keysI.getPrivateKey().getE() + "\n");
       
       System.out.println ("Initiator public key: ");
       System.out.println ("\t k = " + keysI.getPublicKey().getKey() + "\n");
       
       System.out.println ("Responder private key: ");
       System.out.println ("\t s = " + keysR.getPrivateKey().getS());
-      System.out.println ("\t e = " + keysR.getPrivateKey().getE() + "\n");
       
       System.out.println ("Responder public key: ");
       System.out.println ("\t k = " + keysR.getPublicKey().getKey() + "\n");