diff --git a/src/chacha.js b/src/chacha.js
--- a/src/chacha.js
+++ b/src/chacha.js
@@ -1,5 +1,5 @@
 // https://tools.ietf.org/html/rfc7539
-import {MASK,int32s2bytes,bytes2int32s} from "./util.js";
+import {MASK,int32s2bytes,bytes2int32s,zeroPad} from "./util.js";
 
 function lrot(x,shift){
 	return (x<<shift|x>>>(32-shift))&MASK;
@@ -11,10 +11,6 @@ function createNonce(){
 	return nonce;
 }
 
-function zeroPad(arr,length){
-	return arr.concat((new Array(length)).fill(0)).slice(0,length);
-}
-
 /**
  * A Chacha20 cipher class.
  * @param {Array} key Array of bytes (integers: 0<=x<256). Short keys are padded to 32B, long keys are silently truncated.