public EncryptionKeys(
     @Nullable byte[] adminKey, @Nullable byte[] memberKey, @Nullable byte[] guestKey) {
   _adminKeyBytes = adminKey;
   _memberKeyBytes = memberKey;
   _guestKeyBytes = guestKey;
   _adminKey = null;
   _memberKey = null;
   _guestKey = null;
   if (_adminKeyBytes != null) {
     _adminKey = BleUtils.bytesToHexString(_adminKeyBytes);
   }
   if (_memberKeyBytes != null) {
     _memberKey = BleUtils.bytesToHexString(_memberKeyBytes);
   }
   if (_guestKeyBytes != null) {
     _guestKey = BleUtils.bytesToHexString(_guestKeyBytes);
   }
 }
 private String getKeyFromString(String key) {
   if (key == null) {
     return null;
   }
   String retKey = null;
   if (key.length() == BleBaseEncryption.AES_BLOCK_SIZE * 2) {
     retKey = key;
   }
   if (key.length() == BleBaseEncryption.AES_BLOCK_SIZE) {
     byte[] keyBytes = key.getBytes(Charset.forName("UTF-8"));
     retKey = BleUtils.bytesToHexString(keyBytes);
   }
   return retKey;
 }