fix to hex

android/src/main/java/rnpbkdf2/PBKDF2.java

@@ -31,11 +31,22 @@ public class PBKDF2 extends ReactContextBaseJavaModule {
         }
         return new String(hexChars);
     }
+    
+    public static byte[] hexStringToByteArray(String s) {
+        int len = s.length();
+        byte[] data = new byte[len / 2];
+        for (int i = 0; i < len; i += 2) {
+            data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
+                                 + Character.digit(s.charAt(i+1), 16));
+        }
+        return data;
+    }
+
 
     private static String derivationKey(String pwd, String salt, Integer cost, Integer length)
             throws NoSuchAlgorithmException, InvalidKeySpecException {
         PKCS5S2ParametersGenerator gen = new PKCS5S2ParametersGenerator(new SHA512Digest());
-        gen.init(pwd.getBytes(StandardCharsets.UTF_8), salt.getBytes(StandardCharsets.UTF_8), cost);
+        gen.init(hexStringToByteArray(pwd), hexStringToByteArray(salt), cost);
         byte[] key = ((KeyParameter) gen.generateDerivedParameters(length)).getKey();
         return bytesToHex(key);
     }