diff --git a/src/main/java/Main/Utils.java b/src/main/java/Main/Utils.java
index c06d7f7..29d6912 100644
--- a/src/main/java/Main/Utils.java
+++ b/src/main/java/Main/Utils.java
@@ -15,7 +15,13 @@ public class Utils {
         return hexString.toString();
     }
 
-    static byte[] stringToBytes(String hexString) {
-        return new BigInteger(hexString, 16).toByteArray();
+    static byte[] stringToBytes(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;
     }
 }