diff --git a/learning_python3.md b/learning_python3.md
index a4bbc54..80245b3 100644
--- a/learning_python3.md
+++ b/learning_python3.md
@@ -1469,6 +1469,12 @@ if __name__ == "__main__":
 
 To make things more interesting you can add a decode function.
 Plus you could add a prompt that asks how big the shift should be (ROT13, ROT16, ...).
+You can make the cypher a **lot** harder to break if you use a word (or phrase as a key).
+For example, if the key is `abc` and the message is `hello world` the first letter will be offset by a ROT0 (will remain `h`).
+The second letter, `e` will be offset by a ROT1 so will become `f`.
+The third letter by ROT2 so will become `n`.
+Now, the fourth letter will be offset again by `a` so ROT0 and will become `l`.
+And so on...
 
 # List comprehension