title: AES 256 program not working
body: <p>So I have been attempting to implement AES-256 in C. After lots of reading around and following the wikipedia page to implement it, I managed to code it. Only when I tested it, it seemed to give the wrong output.</p>
  
  <p>Code:</p>
  
  <pre><code>/*
  AES-256
  (c) 2017 Daniel Gee
  */
  
  #include &lt;stdio.h&gt;
  #include &lt;stdlib.h&gt;
  
  unsigned char rcon[256] = {
      0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 
      0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 
      0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 
      0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 
      0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 
      0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 
      0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 
      0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 
      0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 
      0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 
      0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 
      0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 
      0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 
      0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 
      0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 
      0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d
  };
  
  unsigned char sbox[256] = {
      0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76,
      0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0,
      0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15,
      0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75,
      0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84,
      0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf,
      0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8,
      0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2,
      0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73,
      0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb,
      0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79,
      0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08,
      0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a,
      0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e,
      0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf,
      0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16
  };
  
  void rotate(unsigned char *w){
      unsigned char t;
      t = w[0];
      w[0] = w[1];
      w[1] = w[2];
      w[2] = w[3];
      w[3] = t;
  }
  
  void key_schedule_core(unsigned char *w, unsigned char i){
      unsigned char j;
      rotate(w);
      for(j = 0; j &lt; 4; j++){
          w[j] = sbox[w[j]];
      }
      w[0] ^= rcon[i];
  }
  
  unsigned char *key_schedule(unsigned char *key){
      unsigned char n = 32, b = 240, *e = malloc(sizeof(unsigned char) * b), i = 1, j, k, t[4];
      for(k = 0; k &lt; n; k++){
          e[k] = key[k];
      }
      j = 32;
  
      while(j &lt; b){
          t[0] = e[j - 4];
          t[1] = e[j - 3];
          t[2] = e[j - 2];
          t[3] = e[j - 1];
  
          key_schedule_core(t, i);
  
          i++;
  
          t[0] ^= e[j - n];
          t[1] ^= e[j - n + 1];
          t[2] ^= e[j - n + 2];
          t[3] ^= e[j - n + 3];
  
          e[j] = t[0];
          e[j + 1] = t[1];
          e[j + 2] = t[2];
          e[j + 3] = t[3];
          j += 4;
  
          for(k = 0; k &lt; 3; k++){
              t[0] = e[j - 4];
              t[1] = e[j - 3];
              t[2] = e[j - 2];
              t[3] = e[j - 1];
  
              t[0] ^= e[j - n];
              t[1] ^= e[j - n + 1];
              t[2] ^= e[j - n + 2];
              t[3] ^= e[j - n + 3];
  
              e[j] = t[0];
              e[j + 1] = t[1];
              e[j + 2] = t[2];
              e[j + 3] = t[3];
  
              j += 4;
          }
  
          t[0] = e[j - 4];
          t[1] = e[j - 3];
          t[2] = e[j - 2];
          t[3] = e[j - 1];
  
          t[0] = sbox[t[0]];
          t[1] = sbox[t[1]];
          t[2] = sbox[t[2]];
          t[3] = sbox[t[3]];
  
          t[0] ^= e[j - n];
          t[1] ^= e[j - n + 1];
          t[2] ^= e[j - n + 2];
          t[3] ^= e[j - n + 3];
  
          e[j] = t[0];
          e[j + 1] = t[1];
          e[j + 2] = t[2];
          e[j + 3] = t[3];
  
          j += 4;
  
          if(j &gt; b){
              break;
          }
  
          for(k = 0; k &lt; 3; k++){
              t[0] = e[j - 4];
              t[1] = e[j - 3];
              t[2] = e[j - 2];
              t[3] = e[j - 1];
  
              t[0] ^= e[j - n];
              t[1] ^= e[j - n + 1];
              t[2] ^= e[j - n + 2];
              t[3] ^= e[j - n + 3];
  
              e[j] = t[0];
              e[j + 1] = t[1];
              e[j + 2] = t[2];
              e[j + 3] = t[3];
  
              j += 4;
          }
      }
  
      return e;
  }
  
  void shift_rows(unsigned char *state){
      unsigned char t;
      t = state[4];
      state[4] = state[5];
      state[5] = state[6];
      state[6] = state[7];
      state[7] = t;
  
      t = state[8];
      state[10] = t;
      t = state[9];
      state[11] = t;
  
      t = state[12];
      state[12] = state[15];
      state[15] = state[14];
      state[14] = state[13];
      state[13] = t;
  }
  
  void mix_columns(unsigned char *state){
      unsigned char a[4], b[4], c, j;
      for(j = 0; j &lt; 4; j++){
          for(c = 0; c &lt; 4; c++){
              a[c] = state[(j * 4) + c];
              b[c] = state[(j * 4) + c] &lt;&lt; 1;
              if(state[(j * 4) + c] &amp; 0x80){
                  b[c] ^= 0x1b;
              }
          }
          state[(j * 4) + 0] = b[0] ^ a[3] ^ a[2] ^ b[1] ^ a[1];
          state[(j * 4) + 1] = b[1] ^ a[0] ^ a[3] ^ b[2] ^ a[2];
          state[(j * 4) + 2] = b[2] ^ a[1] ^ a[0] ^ b[3] ^ a[3];
          state[(j * 4) + 3] = b[3] ^ a[2] ^ a[1] ^ b[0] ^ a[0];
      }
  }
  
  void encrypt(unsigned char *key, unsigned char *state){
      unsigned char *e = key_schedule(key), i, j;
      for(i = 0; i &lt; 14; i++){
          if(i == 0){
              for(j = 0; j &lt; 16; j++){
                  state[j] ^= e[(i * 16) + j];
              }
          }else if(i == 13){
              for(j = 0; j &lt; 16; j++){
                  state[j] ^= sbox[state[j]];
              }
              shift_rows(state);
              for(j = 0; j &lt; 16; j++){
                  state[j] ^= e[(i * 16) + j];
              }
          }else{
              for(j = 0; j &lt; 16; j++){
                  state[j] ^= sbox[state[j]];
              }
              shift_rows(state);
              mix_columns(state);
              for(j = 0; j &lt; 16; j++){
                  state[j] ^= e[(i * 16) + j];
              }
          }
      }
  }
  
  int main(){
      unsigned char key[] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
          message[] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
  
      encrypt(key, message);
  
      for(int i = 0; i &lt; 16; i++){
          printf("%02x ", message[i]);
      }
      printf("\n");
  }
  </code></pre>
  
  <p>Example:</p>
  
  <pre><code>key = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  message = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  output = c2 2a 26 68 a8 4a 1e f3 ac 40 23 05 25 50 00 02
  </code></pre>