lib/{merkle,mrkl}: rename createBranch to createPath. improve mrkl.de…

…riveRoot.

lib/merkle.js

@@ -155,14 +155,14 @@ function createRoot(alg, leaves) {
 }
 
 /**
- * Collect a merkle branch from vector index.
+ * Collect a merkle path from leaf index.
  * @param {Object} alg
  * @param {Number} index
  * @param {Buffer[]} leaves
- * @returns {Buffer[]} branch
+ * @returns {Buffer[]} path
  */
 
-function createBranch(alg, index, leaves) {
+function createPath(alg, index, leaves) {
   assert(alg && typeof alg.root === 'function');
   assert((index >>> 0) === index);
   assert(Array.isArray(leaves));
@@ -171,14 +171,14 @@ function createBranch(alg, index, leaves) {
   let size = leaves.length;
 
   const [nodes] = createTree(alg, leaves);
-  const branch = [];
+  const path = [];
 
   let i = 0;
 
   while (size > 1) {
     const j = Math.min(index ^ 1, size - 1);
 
-    branch.push(nodes[i + j]);
+    path.push(nodes[i + j]);
 
     index >>>= 1;
 
@@ -187,27 +187,27 @@ function createBranch(alg, index, leaves) {
     size = (size + 1) >>> 1;
   }
 
-  return branch;
+  return path;
 }
 
 /**
- * Derive merkle root from branch.
+ * Derive merkle root from path.
  * @param {Object} alg
  * @param {Buffer} hash
- * @param {Buffer[]} branch
+ * @param {Buffer[]} path
  * @param {Number} index
  * @returns {Buffer} root
  */
 
-function deriveRoot(alg, hash, branch, index) {
+function deriveRoot(alg, hash, path, index) {
   assert(alg && typeof alg.root === 'function');
   assert(Buffer.isBuffer(hash));
-  assert(Array.isArray(branch));
+  assert(Array.isArray(path));
   assert((index >>> 0) === index);
 
   let root = hash;
 
-  for (const hash of branch) {
+  for (const hash of path) {
     if ((index & 1) && hash.equals(root))
       return alg.zero;
 
@@ -219,6 +219,9 @@ function deriveRoot(alg, hash, branch, index) {
     index >>>= 1;
   }
 
+  if (index !== 0)
+    return alg.zero;
+
   return root;
 }
 
@@ -228,5 +231,6 @@ function deriveRoot(alg, hash, branch, index) {
 
 exports.createTree = createTree;
 exports.createRoot = createRoot;
-exports.createBranch = createBranch;
+exports.createPath = createPath;
+exports.createBranch = createPath;
 exports.deriveRoot = deriveRoot;

lib/mrkl.js

@@ -82,19 +82,19 @@ function createRoot(alg, leaves) {
 }
 
 /**
- * Collect a merkle branch from vector index.
+ * Collect a merkle path from leaf index.
  * @param {Object} alg
  * @param {Number} index
  * @param {Buffer[]} leaves
- * @returns {Buffer[]} branch
+ * @returns {Buffer[]} path
  */
 
-function createBranch(alg, index, leaves) {
+function createPath(alg, index, leaves) {
   assert((index >>> 0) === index);
 
   const nodes = createTree(alg, leaves);
   const sentinel = hashEmpty(alg);
-  const branch = [];
+  const path = [];
 
   let size = leaves.length;
   let i = 0;
@@ -105,9 +105,9 @@ function createBranch(alg, index, leaves) {
     const j = index ^ 1;
 
     if (j < size)
-      branch.push(nodes[i + j]);
+      path.push(nodes[i + j]);
     else
-      branch.push(sentinel);
+      path.push(sentinel);
 
     index >>>= 1;
 
@@ -116,27 +116,32 @@ function createBranch(alg, index, leaves) {
     size = (size + 1) >>> 1;
   }
 
-  return branch;
+  return path;
 }
 
 /**
- * Derive merkle root from branch.
+ * Derive merkle root from path.
  * @param {Object} alg
  * @param {Buffer} leaf
- * @param {Buffer[]} branch
+ * @param {Buffer[]} path
  * @param {Number} index
  * @returns {Buffer} root
  */
 
-function deriveRoot(alg, leaf, branch, index) {
+function deriveRoot(alg, leaf, path, index) {
   assert(alg && typeof alg.multi === 'function');
   assert(Buffer.isBuffer(leaf));
-  assert(Array.isArray(branch));
+  assert(Array.isArray(path));
   assert((index >>> 0) === index);
 
+  const sentinel = hashEmpty(alg);
+
   let root = hashLeaf(alg, leaf);
 
-  for (const hash of branch) {
+  for (const hash of path) {
+    if ((index & 1) && hash.equals(sentinel))
+      return alg.zero;
+
     if (index & 1)
       root = hashInternal(alg, hash, root);
     else
@@ -145,6 +150,9 @@ function deriveRoot(alg, leaf, branch, index) {
     index >>>= 1;
   }
 
+  if (index !== 0)
+    return alg.zero;
+
   return root;
 }
 
@@ -188,7 +196,8 @@ function hashInternal(alg, left, right) {
 
 exports.createTree = createTree;
 exports.createRoot = createRoot;
-exports.createBranch = createBranch;
+exports.createPath = createPath;
+exports.createBranch = createPath;
 exports.deriveRoot = deriveRoot;
 exports.hashEmpty = hashEmpty;
 exports.hashLeaf = hashLeaf;