diff --git a/packages/circuits/tests/splitBytesToWords.test.ts b/packages/circuits/tests/splitBytesToWords.test.ts
new file mode 100644
index 000000000..93019abd7
--- /dev/null
+++ b/packages/circuits/tests/splitBytesToWords.test.ts
@@ -0,0 +1,33 @@
+import { wasm as wasm_tester } from "circom_tester";
+import path from "path";
+import { bigIntToChunkedBytes, Uint8ArrayToCharArray } from "@zk-email/helpers/src/binary-format";
+
+
+describe("SplitBytesToWords Helper unit test", () => {
+    jest.setTimeout(0.1 * 60 * 1000);
+    let circuit: any;
+
+    beforeAll(async () => {
+        circuit = await wasm_tester(
+            path.join(__dirname, "./test-circuits/splitBytesToWords-test.circom"),
+            {
+                recompile: true,
+                include: path.join(__dirname, "../../../node_modules"),
+                // output: path.join(__dirname, "./compiled-test-circuits"),
+            }
+        );
+
+    });
+
+    it("should split correctly according to bigIntToChunkedBytes function", async function () {
+        const bytes = new Uint8Array(256).map(() => Math.floor(Math.random() * 256));
+        const bytesBigInt = bytes.reduce((acc, val) => (acc << 8n) | BigInt(val), 0n);
+        const ts_split_to_words = bigIntToChunkedBytes(bytesBigInt, 121, 17);
+        const ts_split_to_words_bigint = ts_split_to_words.map((word) => BigInt(word));
+        const witness = await circuit.calculateWitness({
+            in: Uint8ArrayToCharArray(bytes)
+        });
+        await circuit.assertOut(witness, { out: ts_split_to_words_bigint });
+    });
+
+});
diff --git a/packages/circuits/tests/test-circuits/splitBytesToWords-test.circom b/packages/circuits/tests/test-circuits/splitBytesToWords-test.circom
new file mode 100644
index 000000000..c0c65a5d9
--- /dev/null
+++ b/packages/circuits/tests/test-circuits/splitBytesToWords-test.circom
@@ -0,0 +1,6 @@
+pragma circom 2.1.6;
+
+include "../../utils/bytes.circom";
+
+component main = SplitBytesToWords(256,121,17);
+
diff --git a/packages/circuits/utils/bytes.circom b/packages/circuits/utils/bytes.circom
index 2091d076e..d4d96027b 100644
--- a/packages/circuits/utils/bytes.circom
+++ b/packages/circuits/utils/bytes.circom
@@ -111,3 +111,39 @@ template DigitBytesToInt(n) {
 
     out <== sums[n];
 }
+
+
+// NOTE: this circuit is unaudited and should not be used in production
+/// @title SplitBytesToWords
+/// @notice split an array of bytes into an array of words
+/// @notice useful for casting a message or modulus before RSA verification
+/// @param l: number of bytes in the input array
+/// @param n: number of bits in a word
+/// @param k: number of words
+/// @input in: array of bytes
+/// @output out: array of words
+template SplitBytesToWords (l,n,k) {
+    signal input in[l];
+    signal output out[k];
+
+    component num2bits[l];
+    for (var i = 0 ; i < l ; i++){
+        num2bits[i] = Num2Bits(8);
+        num2bits[i].in <== in[i];
+    }
+    component bits2num[k];
+    for (var i = 0 ; i < k ; i++){
+        bits2num[i] = Bits2Num(n);
+        for(var j = 0 ; j < n ; j++){
+            if(i*n + j >=  8 * l){
+                bits2num[i].in[j] <==  0;
+            }
+            else{
+                bits2num[i].in[j] <== num2bits[l - (( i * n + j) \ 8) - 1].out[ ((i * n + j) % 8)];
+            }
+        }
+    }
+    for( var i = 0 ; i< k ; i++){
+    out[i] <== bits2num[i].out;
+    }
+}