Implement AES algorithm

HWBTutorials.code-workspace

@@ -106,5 +106,8 @@
             }
         ],
         "compounds": []
+    },
+    "settings": {
+        "cortex-debug.variableUseNaturalFormat": false
     }
 }

aes/aes.cpp

@@ -11,6 +11,8 @@ http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf
 */
 
 /* AES Constants */
+// AES polynomial
+const uint16_t POLYNOMIAL = 0b100011011;
 
 // forward sbox
 const uint8_t SBOX[256] = {
@@ -78,26 +80,58 @@ 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]);
+    }
 }
 
 
 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) {
-    return 0; /* ??? */
+    uint8_t mask;
+
+    if (a & 0b10000000) {
+        mask = POLYNOMIAL & 0xFF;
+    }
+    else {
+        mask = 0x00;
+    }
+
+    return ((a << 1) ^ mask) & 0xFF;
 }
 
 // not mandatory - mix a single column
 uint32_t mixColumn(uint32_t c) {
-    return 0; /* ??? */
+    uint32_t result = c;
+    uint8_t *source = (uint8_t*)(&c);
+    uint8_t *target = (uint8_t*)(&result);
+    uint8_t base = *source ^ *(source + 1) ^ *(source + 2) ^ *(source + 3);
+    *target ^= base ^ xtime(*source ^ *(source + 1));
+    *(target + 1) ^= base ^ xtime(*(source + 1) ^ *(source + 2));
+    *(target + 2) ^= base ^ xtime(*(source  + 2) ^ *(source + 3));
+    *(target + 3) ^= base ^ xtime(*(source + 3) ^ *source);
+    return result;
 }
 
 
 void mixColumns(t_state s) {
-    /* ??? */
+    for (uint8_t i = 0; i < 4; i++) {
+        s[i] = mixColumn(s[i]);
+    }
 }
 
 /*
@@ -105,14 +139,31 @@ 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++) {
+        ek[i] = word(k[i * 4], k[i * 4 + 1], k[i * 4 + 2], k[i * 4 + 3]);
+    }
+
+    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;
+    }
 }
 
 
 /* Adding expanded round key (prepared before) */
 void addRoundKey(t_state s, uint32_t ek[], short round) {
-    /* ??? */
+    s[0] ^= ek[round];
+    s[1] ^= ek[round + 1];
+    s[2] ^= ek[round + 2];
+    s[3] ^= ek[round + 3];
 }
 
 void aes(uint8_t *in, uint8_t *out, uint8_t *skey)
@@ -122,8 +173,9 @@ void aes(uint8_t *in, uint8_t *out, uint8_t *skey)
 
     t_state state;
 
-    state[0] = word(in[0],  in[1],  in[2],  in[3]);
+    for (uint8_t i = 0; i < 4; i++) {
-    /* ??? */
+        state[i] = word(in[i * 4], in[i * 4 + 1], in[i * 4 + 2], in[i * 4 + 3]);
+    }
 
     printf("IN:  "); printstate(state);
 
@@ -139,10 +191,25 @@ void aes(uint8_t *in, uint8_t *out, uint8_t *skey)
     addRoundKey(state, expKey, 0);
     printf("ARK: "); printstate(state);
 
-    /* ??? */
+    for (int i = 1; i <= 10; i++) {
-    /* ??? */
+        subBytes(state);
-    /* ??? */
+        printf("SB:  ");
+        printstate(state);
 
+        shiftRows(state);
+        printf("SR:  ");
+        printstate(state);
+
+        if (i < 10) {
+            mixColumns(state);
+            printf("MC:  ");
+            printstate(state);
+        }
+
+        addRoundKey(state, expKey, 4*i);
+        printf("ARK: ");
+        printstate(state);
+    }
 
     for (int i = 0; i < 16; i++) {
         if (i < 4) out[i] = wbyte(state[0], i % 4);
@@ -265,7 +332,7 @@ int main(int argc, char* argv[])
         // test  AddRoundKey (last round)
         t_state state = { 0x01234567, 0x89abcdef, 0xdeadbeef, 0x00112233 };
         t_state res_state = { 0xb46d152d, 0x45e164c3, 0xa7cab335, 0x910eed36 };
-        addRoundKey(state, key_w, 10);
+        addRoundKey(state, key_w, 40);
         printf("0x%08x, 0x%08x, 0x%08x, 0x%08x\n", state[0], state[1], state[2], state[3]);
         for (int i = 0; i < 4; i++) {
             if (state[i] != res_state[i]) { printf("Mismatch at state[%d]!\n", i); }