From 87f3102a451aabbb91d8342ece9a5f106cf57dd6 Mon Sep 17 00:00:00 2001
From: Manuel Thalmann <m@nuth.ch>
Date: Tue, 7 Nov 2023 19:25:49 +0100
Subject: [PATCH] Implement `shiftRows`

---
 aes/aes.cpp | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/aes/aes.cpp b/aes/aes.cpp
index c5cde46..82ba954 100644
--- a/aes/aes.cpp
+++ b/aes/aes.cpp
@@ -85,7 +85,18 @@ void subBytes(t_state s) {
 
 
 void shiftRows(t_state s) {
-    /* ??? */
+    for (uint8_t i = 0; i < 4; i++) {
+        uint32_t mask = 0xFF << (i * 8);
+
+        for (uint8_t shiftCount = 0; shiftCount < i; shiftCount++) {
+            for (uint8_t currentByte = 0; currentByte < 3; currentByte++) {
+                // Swap s[currentByte] and s[currentByte + 1]
+                s[currentByte] = s[currentByte] ^ (mask & s[currentByte + 1]);
+                s[currentByte + 1] = s[currentByte + 1] ^ (mask & s[currentByte]);
+                s[currentByte] = s[currentByte] ^ (mask & s[currentByte + 1]);
+            }
+        }
+    }
 }
 
 uint8_t xtime(uint8_t a) {