Enable proof verification without full tree (#15)

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
Co-authored-by: Francisco Giordano <fg@frang.io>

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## 1.0.3
+
+- Added `StandardMerkleTree.verify` static method for verification of a proof for given root, leaf, and leaf encoding.
+
 ## 1.0.2
 
 - Added `StandardMerkleTree` methods `verify` and `verifyMultiProof`.

README.md

@@ -149,6 +149,14 @@ Creates a standard merkle tree out of an array of the elements in the tree, alon
 > **Note**
 > Consider reading the array of elements from a CSV file for easy interoperability with spreadsheets or other data processing pipelines.
 
+### `StandardMerkleTree.verify`
+
+```typescript
+const verified = StandardMerkleTree.verify(root, ['address', 'uint'], [alice, '100'], proof);
+```
+
+Returns a boolean that is `true` when the proof verifies that the value is contained in the tree given only the proof, merkle root, and encoding.
+
 ### `tree.root`
 
 ```typescript

src/standard.test.ts

@@ -32,6 +32,26 @@ describe('standard merkle tree', () => {
     }
   });
 
+  it('generates valid single proofs for all leaves from root and encoding', () => {
+    const { t } = characters('abcdef');
+
+    for (const [, leaf] of t.entries()) {
+      const proof = t.getProof(leaf);
+
+      assert(StandardMerkleTree.verify(t.root, ['string'], leaf, proof));
+    }
+  });
+
+  it('rejects invalid proof using static verify method', () => {
+    const { t } = characters('abcdef');
+    const { t: fakeTree } = characters('xyz');
+
+    const testLeaf = ['x'];
+    const proof = fakeTree.getProof(testLeaf);
+
+    assert(!StandardMerkleTree.verify(t.root, ['string'], testLeaf, proof));
+  });
+
   it('generates valid multiproofs', () => {
     const { t, l } = characters('abcdef');
 

src/standard.ts

@@ -28,7 +28,7 @@ export class StandardMerkleTree<T extends any[]> {
     private readonly values: { value: T, treeIndex: number }[],
     private readonly leafEncoding: string[],
   ) {
-    this.hashLookup = 
+    this.hashLookup =
       Object.fromEntries(values.map(({ value }, valueIndex) => [
         hex(standardLeafHash(value, leafEncoding)),
         valueIndex,
@@ -61,6 +61,11 @@ export class StandardMerkleTree<T extends any[]> {
     );
   }
 
+  static verify<T extends any[]>(root: string, leafEncoding: string[], leaf: T, proof: string[]): boolean {
+    const impliedRoot = processProof(standardLeafHash(leaf, leafEncoding), proof.map(hexToBytes));
+    return equalsBytes(impliedRoot, hexToBytes(root));
+  }
+
   dump(): StandardMerkleTreeData<T> {
     return {
       format:      'standard-v1',