Add method verifyProof to Tree

packages/lib/src/helpers/tree.ts

@@ -1,7 +1,6 @@
 import { IncrementalMerkleTree } from "@zk-kit/incremental-merkle-tree";
 import { Poseidon } from "./poseidon";
 import { MerkleProof } from "../types";
-import { bytesToBigInt } from "./utils";
 
 export class Tree {
   depth: number;
@@ -38,17 +37,14 @@ export class Tree {
 
   createProof(index: number): MerkleProof {
     const proof = this.treeInner.createProof(index);
-
-    const siblings = proof.siblings.map(s =>
-      typeof s[0] === "bigint" ? s : bytesToBigInt(s[0])
-    );
-
     return {
-      siblings,
+      siblings: proof.siblings,
       pathIndices: proof.pathIndices,
       root: proof.root
     };
   }
 
-  // TODO: Add more functions that expose the IncrementalMerkleTree API
+  verifyProof(proof: MerkleProof, leaf: bigint): boolean {
+    return this.treeInner.verifyProof({ ...proof, leaf });
+  }
 }

packages/lib/src/types.ts

@@ -5,7 +5,7 @@ import { PublicInput } from "./helpers/public_input";
 // library users can choose whatever merkle tree management method they want.
 export interface MerkleProof {
   root: bigint;
-  siblings: bigint[];
+  siblings: [bigint][];
   pathIndices: number[];
 }
 export interface EffECDSAPubInput {

packages/lib/tests/tree.test.ts

@@ -0,0 +1,31 @@
+import { Tree, Poseidon } from "../src/lib";
+
+describe("Merkle tree prove and verify", () => {
+  let poseidon: Poseidon;
+  let tree: Tree;
+  const members = new Array(10).fill(0).map((_, i) => BigInt(i));
+
+  beforeAll(async () => {
+    // Init Poseidon
+    poseidon = new Poseidon();
+    await poseidon.initWasm();
+    const treeDepth = 20;
+
+    tree = new Tree(treeDepth, poseidon);
+    for (const member of members) {
+      tree.insert(member);
+    }
+  });
+
+  it("should prove and verify a valid Merkle proof", async () => {
+    const proof = tree.createProof(0);
+    expect(tree.verifyProof(proof, members[0])).toBe(true);
+  });
+
+  it("should assert an invalid Merkle proof", async () => {
+    const proof = tree.createProof(0);
+    proof.siblings[0][0] = proof.siblings[0][0] += BigInt(1);
+    expect(tree.verifyProof(proof, members[0])).toBe(false);
+    proof.siblings[0][0] = proof.siblings[0][0] -= BigInt(1);
+  });
+});