diff --git a/crypto_stream_chacha20.js b/crypto_stream_chacha20.js
index 0b73d9a..a22ef4f 100644
--- a/crypto_stream_chacha20.js
+++ b/crypto_stream_chacha20.js
@@ -21,7 +21,7 @@ exports.crypto_stream_chacha20_xor = function (c, cpos, m, mpos, clen, n, k) {
   assert(k.byteLength === exports.crypto_stream_chacha20_KEYBYTES,
     'k should be crypto_stream_chacha20_KEYBYTES')
 
-  var xor = new Chacha20(n, k)
+  const xor = new Chacha20(n, k)
   xor.update(c, m)
   xor.final()
 }
@@ -32,7 +32,7 @@ exports.crypto_stream_chacha20_xor_ic = function (c, m, mlen, n, ic, k) {
   assert(k.byteLength === exports.crypto_stream_chacha20_KEYBYTES,
     'k should be crypto_stream_chacha20_KEYBYTES')
 
-  var xor = new Chacha20(n, k, ic)
+  const xor = new Chacha20(n, k, ic)
   xor.update(c, m)
   xor.final()
 }
@@ -57,7 +57,7 @@ exports.crypto_stream_chacha20_ietf_xor = function (c, cpos, m, mpos, clen, n, k
   assert(k.byteLength === exports.crypto_stream_chacha20_ietf_KEYBYTES,
     'k should be crypto_stream_chacha20_ietf_KEYBYTES')
 
-  var xor = new Chacha20(n, k)
+  const xor = new Chacha20(n, k)
   xor.update(c, m)
   xor.final()
 }
@@ -68,7 +68,7 @@ exports.crypto_stream_chacha20_ietf_xor_ic = function (c, m, mlen, n, ic, k) {
   assert(k.byteLength === exports.crypto_stream_chacha20_ietf_KEYBYTES,
     'k should be crypto_stream_chacha20_ietf_KEYBYTES')
 
-  var xor = new Chacha20(n, k, ic)
+  const xor = new Chacha20(n, k, ic)
   xor.update(c, m)
   xor.final()
 }
@@ -117,14 +117,14 @@ Chacha20.prototype.update = function (output, input) {
   assert(output.byteLength >= input.byteLength,
     'output cannot be shorter than input.')
 
-  var len = input.length
-  var offset = this.pos % 64
+  let len = input.length
+  let offset = this.pos % 64
   this.pos += len
 
   // input position
-  var j = 0
+  let j = 0
 
-  var keyStream = chacha20_block(this.state)
+  let keyStream = chacha20_block(this.state)
 
   // try to finsih the current block
   while (offset > 0 && len > 0) {
@@ -162,33 +162,28 @@ Chacha20.prototype.final = function () {
   this.finalized = true
 }
 
-module.exports.keystream = function (output, key, nonce, counter) {
-  var c = new Chacha20(key, nonce, counter)
-  c.update(output, Buffer.alloc(output.length))
-  c.final()
-}
-
 function chacha20_block (state) {
-  var workingState = new Uint32Array(16)
-  for (let i = 16; i--;) workingState[i] = state[i]
+  // working state
+  const ws = new Uint32Array(16)
+  for (let i = 16; i--;) ws[i] = state[i]
 
   for (let i = 0; i < 20; i += 2) {
-    QR(workingState, 0, 4, 8, 12) // column 0
-    QR(workingState, 1, 5, 9, 13) // column 1
-    QR(workingState, 2, 6, 10, 14) // column 2
-    QR(workingState, 3, 7, 11, 15) // column 3
+    QR(ws, 0, 4, 8, 12) // column 0
+    QR(ws, 1, 5, 9, 13) // column 1
+    QR(ws, 2, 6, 10, 14) // column 2
+    QR(ws, 3, 7, 11, 15) // column 3
 
-    QR(workingState, 0, 5, 10, 15) // diagonal 1 (main diagonal)
-    QR(workingState, 1, 6, 11, 12) // diagonal 2
-    QR(workingState, 2, 7, 8, 13) // diagonal 3
-    QR(workingState, 3, 4, 9, 14) // diagonal 4
+    QR(ws, 0, 5, 10, 15) // diagonal 1 (main diagonal)
+    QR(ws, 1, 6, 11, 12) // diagonal 2
+    QR(ws, 2, 7, 8, 13) // diagonal 3
+    QR(ws, 3, 4, 9, 14) // diagonal 4
   }
 
   for (let i = 0; i < 16; i++) {
-    workingState[i] += state[i]
+    ws[i] += state[i]
   }
 
-  return Buffer.from(workingState.buffer)
+  return Buffer.from(ws.buffer, ws.byteOffset, ws.byteLength)
 }
 
 function rotl (a, b) {