diff --git a/advanced_expert/bitcoin/README.md b/advanced_expert/bitcoin/README.md
index 09b7cd3..e4ba6a8 100644
--- a/advanced_expert/bitcoin/README.md
+++ b/advanced_expert/bitcoin/README.md
@@ -3,3 +3,4 @@
 <br>
 
 * **[physical bitcoin attacks, by jloop](https://github.com/jlopp/physical-bitcoin-attacks/tree/master)**
+* **[working verify bitcoin message](https://www.verifybitcoinmessage.com/)**