add scrypt pbkdf

lib/pbkdf.js

@@ -0,0 +1,20 @@
+'use strict';
+
+const { scrypt } = require ('scrypt-js');
+
+/**
+ * creates a scrypt hash
+ *
+ * @param {string} str string input
+ * @param {string} salt salt
+ * @returns {Promise<string>} hash
+ */
+async function pbkdf_scrypt (str, salt) {
+  const bstr = Buffer.from (str.normalize ('NFKC'), 'utf-8');
+  const bsalt = Buffer.from (salt.normalize ('NFKC'), 'utf-8');
+  const hash = await scrypt (bstr, bsalt, 65536, 8, 1, 64);
+  return Buffer.from (hash)
+    .toString ('hex');
+}
+
+module.exports = { pbkdf_scrypt };