diff --git a/aes/aes.cpp b/aes/aes.cpp
index 5a95573..c5cde46 100644
--- a/aes/aes.cpp
+++ b/aes/aes.cpp
@@ -78,7 +78,9 @@ uint32_t subWord(uint32_t w) {
 }
 
 void subBytes(t_state s) {
-    s[0] = 0; /* ??? */
+    for (uint8_t i = 0; i < 4; i++) {
+        s[i] = subWord(s[i]);
+    }
 }