fix(incremental-merkle-tree): merkle tree supports zero leaves. Merkle proof fails for zero value

The incremental-merkle-tree can be constructed with any value, including zeros. The generation of
merkle proof will fail for zero value.


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packages/incremental-merkle-tree/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@zk-kit/incremental-merkle-tree",
-  "version": "0.4.2",
+  "version": "0.4.3",
   "description": "Incremental Merkle tree implementation in TypeScript.",
   "license": "MIT",
   "iife": "dist/index.js",

packages/incremental-merkle-tree/src/insert.ts

@@ -11,10 +11,6 @@ export default function insert(
 ): Node {
   checkParameter(leaf, "leaf", "number", "string", "bigint")
 
-  if (leaf === zeroes[0]) {
-    throw new Error("The leaf cannot be a zero value")
-  }
-
   if (nodes[0].length >= arity ** depth) {
     throw new Error("The tree is full")
   }

packages/incremental-merkle-tree/tests/index.test.ts

@@ -37,18 +37,12 @@ describe("Incremental Merkle Tree", () => {
         expect(tree.arity).toEqual(arity)
       })
 
-      it("Should not insert a zero leaf", () => {
-        const fun = () => tree.insert(BigInt(0))
-
-        expect(fun).toThrow("The leaf cannot be a zero value")
-      })
-
       it("Should not insert a leaf in a full tree", () => {
         const fullTree = new IncrementalMerkleTree(poseidon, 1, BigInt(0), 3)
 
+        fullTree.insert(BigInt(0))
         fullTree.insert(BigInt(1))
         fullTree.insert(BigInt(2))
-        fullTree.insert(BigInt(3))
 
         const fun = () => fullTree.insert(BigInt(4))
 

packages/protocols/package.json

@@ -38,7 +38,7 @@
     "@ethersproject/bytes": "^5.5.0",
     "@ethersproject/solidity": "^5.5.0",
     "@ethersproject/strings": "^5.5.0",
-    "@zk-kit/incremental-merkle-tree": "^0.4.2",
+    "@zk-kit/incremental-merkle-tree": "^0.4.3",
     "circomlibjs": "0.0.8",
     "ffjavascript": "0.2.38",
     "snarkjs": "^0.4.13"

packages/protocols/src/utils.ts

@@ -64,6 +64,8 @@ export function generateMerkleProof(
   leaves: StrBigInt[],
   leaf: StrBigInt
 ): MerkleProof {
+  if (leaf === zeroValue) throw new Error("Can't generate a proof for a zero leaf")
+
   const tree = generateMerkleTree(depth, zeroValue, arity, leaves)
 
   const leafIndex = tree.leaves.indexOf(BigInt(leaf))

packages/protocols/tests/rln.test.ts

@@ -48,6 +48,16 @@ describe("RLN", () => {
       expect(typeof witness).toBe("object")
     })
 
+    it("Should throw an exception for a zero leaf", () => {
+      const zeroIdCommitment = BigInt(0)
+      const leaves = Object.assign([], identityCommitments)
+      leaves.push(zeroIdCommitment)
+
+      const fun = () => generateMerkleProof(15, zeroIdCommitment, 2, leaves, zeroIdCommitment)
+
+      expect(fun).toThrow("Can't generate a proof for a zero leaf")
+    })
+
     // eslint-disable-next-line jest/no-disabled-tests
     it.skip("Should generate rln proof and verify it", async () => {
       const identity = new ZkIdentity()