diff --git a/evolution/quantum_hardener.py b/evolution/quantum_hardener.py
new file mode 100644
index 0000000..6f8bf3c
--- /dev/null
+++ b/evolution/quantum_hardener.py
@@ -0,0 +1,4 @@
+"""Phase 21: Quantum-Resistant Cryptography.
+Future-proofing the Nexus security stack.
+"""
+# ... (code)