From 196df267f5e1ef94b1906a0014c414d73f1d66c7 Mon Sep 17 00:00:00 2001
From: Oleg Babin <babinoleg@mail.ru>
Date: Wed, 19 Jun 2024 18:17:15 +0400
Subject: [PATCH] fix invalid poseidon hash usage

We need to pad high-order bytes with zeros in case if result is less than 32 bytes.
---
 hasher.go              | 7 +++----
 tests/codetrie_test.go | 9 +++------
 2 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/hasher.go b/hasher.go
index 4b4881f..5686437 100755
--- a/hasher.go
+++ b/hasher.go
@@ -42,11 +42,10 @@ func init() {
 }
 
 func poseidonSum(input []byte) []byte {
+	output := make([]byte, 32)
 	res := poseidon.Sum(input)
-	if rest := len(res) % 32; rest != 0 {
-		res = append(res, zeroBytes[:32-rest]...)
-	}
-	return res
+	copy(output[32-len(res):], res)
+	return output
 }
 
 // HashWithDefaultHasher hashes a HashRoot object with a Hasher from
diff --git a/tests/codetrie_test.go b/tests/codetrie_test.go
index 2b529dc..7ff20bb 100644
--- a/tests/codetrie_test.go
+++ b/tests/codetrie_test.go
@@ -11,14 +11,11 @@ import (
 	"github.com/iden3/go-iden3-crypto/poseidon"
 )
 
-var zeroBytes = make([]byte, 32)
-
 func poseidonSum(input []byte) []byte {
+	output := make([]byte, 32)
 	res := poseidon.Sum(input)
-	if len(res) != 32 {
-		res = append(res, zeroBytes[:32-len(res)]...)
-	}
-	return res
+	copy(output[32-len(res):], res)
+	return output
 }
 
 func TestVerifyMetadataProof(t *testing.T) {