From 79d2776d417909e4af5f171d8a951dd334184688 Mon Sep 17 00:00:00 2001
From: Manuel Thalmann <m@nuth.ch>
Date: Tue, 14 Nov 2023 08:32:32 +0100
Subject: [PATCH] Implement `expandKey`

---
 aes/aes.cpp | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/aes/aes.cpp b/aes/aes.cpp
index 95418b9..c388c64 100644
--- a/aes/aes.cpp
+++ b/aes/aes.cpp
@@ -139,8 +139,24 @@ void mixColumns(t_state s) {
 * to 11 round keys (11*4*32b)
 * each round key is 4*32b
 */
+// Taken from: https://www.brainkart.com/article/AES-Key-Expansion_8410/
 void expandKey(uint8_t k[16], uint32_t ek[44]) {
-    /* ??? */
+    for (uint8_t i = 0; i < 4; i++) {
+        for (uint8_t j = 0; j < 4; j++) {
+            *(((uint8_t*)(&(ek[i]))) + j) = k[i * 4 + j];
+        }
+    }
+
+    for (uint8_t i = 4; i < 44; i++) {
+        uint32_t key = ek[i - 1];
+
+        if (i % 4 == 0) {
+            key = (key >> 8) | (key << 24);
+            key = subWord(key) ^ rCon[i / 4];
+        }
+
+        ek[i] = ek[i - 4] ^ key;
+    }
 }