Refactoring in LMS

Author: peterdettman

core/src/main/java/org/bouncycastle/pqc/crypto/lms/HSSPrivateKeyParameters.java

@@ -129,7 +129,7 @@ else if (src instanceof byte[])
                 {
                     // old style single LMS key.
                     LMSPrivateKeyParameters lmsKey = LMSPrivateKeyParameters.getInstance(src);
-                    return new HSSPrivateKeyParameters(lmsKey, lmsKey.getIndex(), lmsKey.getIndex() + lmsKey.getUsagesRemaining());
+                    return new HSSPrivateKeyParameters(lmsKey, lmsKey.getIndex(), lmsKey.getIndexLimit());
                 }
             }
             finally
@@ -212,7 +212,7 @@ long getIndexLimit()
 
     public long getUsagesRemaining()
     {
-        return indexLimit - index;
+        return getIndexLimit() - getIndex();
     }
 
     LMSPrivateKeyParameters getRootKey()
@@ -233,32 +233,33 @@ public HSSPrivateKeyParameters extractKeyShard(int usageCount)
     {
         synchronized (this)
         {
-
-            if (getUsagesRemaining() < usageCount)
+            if (usageCount < 0)
+            {
+                throw new IllegalArgumentException("usageCount cannot be negative");
+            }
+            if (usageCount > indexLimit - index)
             {
                 throw new IllegalArgumentException("usageCount exceeds usages remaining in current leaf");
             }
 
-            long maxIndexForShard = index + usageCount;
-            long shardStartIndex = index;
+            long shardIndex = index;
+            long shardIndexLimit = index + usageCount;
 
-            //
-            // Move this keys index along
-            //
-            index += usageCount;
+            // Move this key's index along
+            index = shardIndexLimit;
 
             List<LMSPrivateKeyParameters> keys = new ArrayList<LMSPrivateKeyParameters>(this.getKeys());
             List<LMSSignature> sig = new ArrayList<LMSSignature>(this.getSig());
 
-            HSSPrivateKeyParameters shard = makeCopy(new HSSPrivateKeyParameters(l, keys, sig, shardStartIndex, maxIndexForShard, true));
+            HSSPrivateKeyParameters shard = makeCopy(
+                new HSSPrivateKeyParameters(l, keys, sig, shardIndex, shardIndexLimit, true));
 
             resetKeyToIndex();
 
             return shard;
         }
     }
 
-
     synchronized List<LMSPrivateKeyParameters> getKeys()
     {
         return keys;

core/src/main/java/org/bouncycastle/pqc/crypto/lms/LMSPrivateKeyParameters.java

@@ -253,14 +253,22 @@ public LMSPrivateKeyParameters extractKeyShard(int usageCount)
     {
         synchronized (this)
         {
-            if (q + usageCount >= maxQ)
+            if (usageCount < 0)
+            {
+                throw new IllegalArgumentException("usageCount cannot be negative");
+            }
+            if (usageCount > maxQ - q)
             {
                 throw new IllegalArgumentException("usageCount exceeds usages remaining");
             }
-            LMSPrivateKeyParameters keyParameters = new LMSPrivateKeyParameters(this, q, q + usageCount);
-            q += usageCount;
 
-            return keyParameters;
+            int shardIndex = q;
+            int shardIndexLimit = q + usageCount;
+
+            // Move this key's index along
+            q = shardIndexLimit;
+
+            return new LMSPrivateKeyParameters(this, shardIndex, shardIndexLimit);
         }
     }
 
@@ -284,9 +292,15 @@ public byte[] getMasterSecret()
         return Arrays.clone(masterSecret);
     }
 
+    public int getIndexLimit()
+    {
+        return maxQ;
+    }
+
+    // TODO Only needs 'int'
     public long getUsagesRemaining()
     {
-        return maxQ - getIndex();
+        return getIndexLimit() - getIndex();
     }
 
     public LMSPublicKeyParameters getPublicKey()

core/src/test/java/org/bouncycastle/pqc/crypto/lms/HSSTests.java

@@ -543,6 +543,7 @@ else if (line.startsWith("Signature:"))
 
         assertEquals(1024, keyPair.getUsagesRemaining());
         assertEquals(1024, keyPair.getIndexLimit());
+        assertEquals(0, keyPair.getIndex());
 
         //
         // Split the space up with a shard.
@@ -555,7 +556,6 @@ else if (line.startsWith("Signature:"))
         HSSPrivateKeyParameters pair = shard1;
 
         int c = 0;
-        String exhaustionMessage = null;
         for (int i = 0; i < keyPair.getIndexLimit(); i++)
         {
             if (i == 500)
@@ -640,6 +640,7 @@ public void testRemaining()
 
         HSSPrivateKeyParameters shard = keyPair.extractKeyShard(10);
 
+        assertEquals(10, shard.getUsagesRemaining());
         assertEquals(15, shard.getIndexLimit());
         assertEquals(5, shard.getIndex());
 

core/src/test/java/org/bouncycastle/pqc/crypto/test/LMSTest.java

@@ -112,6 +112,7 @@ public void testKeyGenAndSignTwoSigsWithShard()
         LMSSigner signer = new LMSSigner();
 
         assertEquals(2, privKey.getUsagesRemaining());
+        assertEquals(2, privKey.getIndexLimit());
         assertEquals(0, privKey.getIndex());
 
         signer.init(true, privKey);