diff --git a/lib/hdkey.js b/lib/hdkey.js
index e849d38..04e93ba 100644
--- a/lib/hdkey.js
+++ b/lib/hdkey.js
@@ -43,23 +43,23 @@ var HDKey = ("object" === typeof module && exports) || {};
 (function (window, HDKey) {
   "use strict";
 
-  var crypto = require("crypto");
-  var bs58check = require("bs58check");
-  var RIPEMD160 = require("ripemd160");
-  var secp256k1 = require("secp256k1");
+  let crypto = require("crypto");
+  let bs58check = require("bs58check");
+  let RIPEMD160 = require("ripemd160");
+  let secp256k1 = require("secp256k1");
 
-  var MASTER_SECRET = Buffer.from("Bitcoin seed", "utf8");
-  var HARDENED_OFFSET = 0x80000000;
-  var LEN = 78;
+  let MASTER_SECRET = Buffer.from("Bitcoin seed", "utf8");
+  let HARDENED_OFFSET = 0x80000000;
+  let LEN = 78;
 
   // Bitcoin hardcoded by default, can use package `coininfo` for others
-  var BITCOIN_VERSIONS = { private: 0x0488ade4, public: 0x0488b21e };
+  let BITCOIN_VERSIONS = { private: 0x0488ade4, public: 0x0488b21e };
 
   HDKey.create = function (versions) {
     /** @type {hdkey} */
-    var hdkey = {};
+    let hdkey = {};
     /** @type {Buffer?} */
-    var _privateKey = null;
+    let _privateKey = null;
 
     hdkey.versions = versions || BITCOIN_VERSIONS;
     hdkey.depth = 0;
@@ -95,7 +95,7 @@ var HDKey = ("object" === typeof module && exports) || {};
       );
       assert(secp256k1.publicKeyVerify(value) === true, "Invalid public key");
       // force compressed point (performs public key verification)
-      var publicKey =
+      let publicKey =
         value.length === 65 ? secp256k1.publicKeyConvert(value, true) : value;
       hdkey._setPublicKey(publicKey);
     };
@@ -138,16 +138,16 @@ var HDKey = ("object" === typeof module && exports) || {};
         return hdkey;
       }
 
-      var entries = path.split("/");
-      var _hdkey = hdkey;
+      let entries = path.split("/");
+      let _hdkey = hdkey;
       entries.forEach(function (c, i) {
         if (i === 0) {
           assert(/^[mM]{1}/.test(c), 'Path must start with "m" or "M"');
           return;
         }
 
-        var hardened = c.length > 1 && c[c.length - 1] === "'";
-        var childIndex = parseInt(c, 10); // & (HARDENED_OFFSET - 1)
+        let hardened = c.length > 1 && c[c.length - 1] === "'";
+        let childIndex = parseInt(c, 10); // & (HARDENED_OFFSET - 1)
         assert(childIndex < HARDENED_OFFSET, "Invalid index");
         if (hardened) {
           childIndex += HARDENED_OFFSET;
@@ -160,11 +160,11 @@ var HDKey = ("object" === typeof module && exports) || {};
     };
 
     hdkey.deriveChild = function (index) {
-      var isHardened = index >= HARDENED_OFFSET;
-      var indexBuffer = Buffer.allocUnsafe(4);
+      let isHardened = index >= HARDENED_OFFSET;
+      let indexBuffer = Buffer.allocUnsafe(4);
       indexBuffer.writeUInt32BE(index, 0);
 
-      var data;
+      let data;
 
       if (isHardened) {
         // Hardened child
@@ -172,8 +172,8 @@ var HDKey = ("object" === typeof module && exports) || {};
           throw new Error("Could not derive hardened child key");
         }
 
-        var pk = _privateKey;
-        var zb = Buffer.alloc(1, 0);
+        let pk = _privateKey;
+        let zb = Buffer.alloc(1, 0);
         pk = Buffer.concat([zb, pk]);
 
         // data = 0x00 || ser256(kpar) || ser32(index)
@@ -185,14 +185,14 @@ var HDKey = ("object" === typeof module && exports) || {};
         data = Buffer.concat([hdkey.publicKey, indexBuffer]);
       }
 
-      var I = crypto
+      let I = crypto
         .createHmac("sha512", hdkey.chainCode)
         .update(data)
         .digest();
-      var IL = I.slice(0, 32);
-      var IR = I.slice(32);
+      let IL = I.slice(0, 32);
+      let IR = I.slice(32);
 
-      var hd = HDKey.create(hdkey.versions);
+      let hd = HDKey.create(hdkey.versions);
 
       // Private parent key -> private child key
       if (_privateKey) {
@@ -275,14 +275,14 @@ var HDKey = ("object" === typeof module && exports) || {};
   };
 
   HDKey.fromMasterSeed = function (seedBuffer, versions) {
-    var I = crypto
+    let I = crypto
       .createHmac("sha512", MASTER_SECRET)
       .update(seedBuffer)
       .digest();
-    var IL = I.slice(0, 32);
-    var IR = I.slice(32);
+    let IL = I.slice(0, 32);
+    let IR = I.slice(32);
 
-    var hdkey = HDKey.create(versions);
+    let hdkey = HDKey.create(versions);
     hdkey.chainCode = IR;
     hdkey.setPrivateKey(IL);
 
@@ -293,11 +293,11 @@ var HDKey = ("object" === typeof module && exports) || {};
     // => version(4) || depth(1) || fingerprint(4) || index(4) || chain(32) || key(33)
     versions = versions || BITCOIN_VERSIONS;
     skipVerification = skipVerification || false;
-    var hdkey = HDKey.create(versions);
+    let hdkey = HDKey.create(versions);
 
-    var keyBuffer = bs58check.decode(base58key);
+    let keyBuffer = bs58check.decode(base58key);
 
-    var version = keyBuffer.readUInt32BE(0);
+    let version = keyBuffer.readUInt32BE(0);
     assert(
       version === versions.private || version === versions.public,
       "Version mismatch: does not match private or public",
@@ -308,7 +308,7 @@ var HDKey = ("object" === typeof module && exports) || {};
     hdkey.index = keyBuffer.readUInt32BE(9);
     hdkey.chainCode = keyBuffer.slice(13, 45);
 
-    var key = keyBuffer.slice(45);
+    let key = keyBuffer.slice(45);
     if (key.readUInt8(0) === 0) {
       // private
       assert(
@@ -352,12 +352,12 @@ var HDKey = ("object" === typeof module && exports) || {};
    */
   function serialize(hdkey, version, key) {
     // => version(4) || depth(1) || fingerprint(4) || index(4) || chain(32) || key(33)
-    var buffer = Buffer.allocUnsafe(LEN);
+    let buffer = Buffer.allocUnsafe(LEN);
 
     buffer.writeUInt32BE(version, 0);
     buffer.writeUInt8(hdkey.depth, 4);
 
-    var fingerprint = hdkey.depth ? hdkey.parentFingerprint : 0x00000000;
+    let fingerprint = hdkey.depth ? hdkey.parentFingerprint : 0x00000000;
     buffer.writeUInt32BE(fingerprint, 5);
     buffer.writeUInt32BE(hdkey.index, 9);
 
@@ -372,7 +372,7 @@ var HDKey = ("object" === typeof module && exports) || {};
    * @returns {Buffer}
    */
   function hash160(buf) {
-    var sha = crypto.createHash("sha256").update(buf).digest();
+    let sha = crypto.createHash("sha256").update(buf).digest();
     return new RIPEMD160().update(sha).digest();
   }