title: AES decryption/ encryption implementation in C# - not using libraries
body: <p>I'm trying to implement a <strong>AES</strong> system in <strong>C#</strong> to encrypt and decrypt messages using <strong>AES</strong>. The decrypted message of an encrypted message is different from the original text. </p>
  
  <p>Where am I going wrong?</p>
  
  <p>PS: I have included the <strong>state.cs</strong> class which contains the mixcolumns, subbytes and shiftrow methods as well as the inverse of these methods.</p>
  
  <pre><code>    private byte[] readHexString(string s)
          {
              int size = s.Length / 2;
              byte[] b = new byte[size];
  
              if ((size != 16) &amp;&amp; (size != 24) &amp;&amp; (size != 32))
              {
                  throw new Exception();
              }
  
              for (int i = 0; i &lt; size; i++)
              {
                  b[i] = Convert.ToByte(s.Substring(2 * i, 2), 16);
              }
              return (b);
          }
  
          private byte[] readAsciiString(string s)
          {
              byte[] b = new byte[s.Length];
              b = System.Text.ASCIIEncoding.ASCII.GetBytes(s);
              return (b);
          }
  
          private void btnTest_Click(object sender, EventArgs e)
          {
              byte[] inputKey = readHexString(tbKey.Text);
              Key key = new Key(inputKey);
              Console.Out.WriteLine("\nkey:\n" + key);
  
              byte[] inputPlain = readAsciiString(tbPlain.Text);
              State inputState = new State(inputPlain);
  
              Console.Out.WriteLine("state:\n" + inputState.ToMatrixString());
  
              //string outplain = ConvertHex(Encrypt(inputState, key));
              string  ciphertext = Encrypt(inputState, key);
              tbCiphertext.Text = ciphertext;
  
  
              byte[] inputPlain2 = readAsciiString(tbCiphertext.Text);
              State inputState2 = new State(inputPlain2);
              string plaintext = Decrypt(inputState2, key);
              Console.Out.WriteLine(plaintext);
  
          }
  
          private string Encrypt(State _inputState, Key k)
          {
              //string ciphertext;
              byte[] ciphertext;
  
              State thisState = _inputState;
              thisState = thisState.addRoundKey(k, 0);
              Console.Out.WriteLine(thisState.ToString());
              for (int i = 1; i &lt; 10; i++)
              {
                  thisState = thisState.subBytes();
                  thisState = thisState.shiftRows();
                  thisState = thisState.mixColumns();
                  thisState = thisState.addRoundKey(k, i);
                  Console.Out.WriteLine(thisState.ToString());
              }
  
              thisState = thisState.subBytes();
              thisState = thisState.shiftRows();
              thisState = thisState.addRoundKey(k, 10);
  
              Console.Out.WriteLine(thisState.ToString());
  
              ciphertext = readHexString(thisState.ToString());
              string output = "";
              for (int i = 0; i &lt; ciphertext.Length; i++)
              {
                  output += ciphertext[i];
              }
  
              return ConvertHex(output);
          }
  
          public string Decrypt(State state, Key k)
          {
              byte[] plainText;
              State thisState = state.addRoundKey(k, 10); 
              thisState = thisState.shiftRowsInv();
              thisState = thisState.subBytesInv();
  
  
              for (int i = 9; i &gt; 0; i--)
              {
                  thisState = thisState.addRoundKey(k, i);
                  thisState = thisState.mixColumnsInv();
                  thisState = thisState.shiftRowsInv();
                  thisState = thisState.subBytesInv();
               }
              thisState = thisState.addRoundKey(k, 0);
              plainText = readHexString(thisState.ToString());
               string output = "";
               for (int i = 0; i &lt; plainText.Length; i++)
               {
                   output += plainText[i];
               }
               Console.Out.WriteLine(ConvertHex(output));
               return ConvertHex(output);
  
          }
          public string ConvertHex(String hexString)
          {
              StringBuilder sb = new StringBuilder();
              for (int i = 0; i &lt;= hexString.Length - 2; i += 2)
              {
                  sb.Append(Convert.ToString(Convert.ToChar(Int32.Parse(hexString.Substring(i, 2), System.Globalization.NumberStyles.HexNumber))));
              }
              return sb.ToString();
          }
      }
  }
  
  
  namespace Aes
  {
      public class State
      {
          private const int nrofRow = 4;
          private const int nrofCol = 4;
          private byte[,] buf;
          //multiplication tables taken from http://en.wikipedia.org/wiki/Rijndael_mix_columns
          private static byte[] mul2 = {
              0x00,0x02,0x04,0x06,0x08,0x0a,0x0c,0x0e,0x10,0x12,0x14,0x16,0x18,0x1a,0x1c,0x1e,
              0x20,0x22,0x24,0x26,0x28,0x2a,0x2c,0x2e,0x30,0x32,0x34,0x36,0x38,0x3a,0x3c,0x3e,
              0x40,0x42,0x44,0x46,0x48,0x4a,0x4c,0x4e,0x50,0x52,0x54,0x56,0x58,0x5a,0x5c,0x5e,
              0x60,0x62,0x64,0x66,0x68,0x6a,0x6c,0x6e,0x70,0x72,0x74,0x76,0x78,0x7a,0x7c,0x7e,
              0x80,0x82,0x84,0x86,0x88,0x8a,0x8c,0x8e,0x90,0x92,0x94,0x96,0x98,0x9a,0x9c,0x9e,
              0xa0,0xa2,0xa4,0xa6,0xa8,0xaa,0xac,0xae,0xb0,0xb2,0xb4,0xb6,0xb8,0xba,0xbc,0xbe,
              0xc0,0xc2,0xc4,0xc6,0xc8,0xca,0xcc,0xce,0xd0,0xd2,0xd4,0xd6,0xd8,0xda,0xdc,0xde,
              0xe0,0xe2,0xe4,0xe6,0xe8,0xea,0xec,0xee,0xf0,0xf2,0xf4,0xf6,0xf8,0xfa,0xfc,0xfe,
              0x1b,0x19,0x1f,0x1d,0x13,0x11,0x17,0x15,0x0b,0x09,0x0f,0x0d,0x03,0x01,0x07,0x05,
              0x3b,0x39,0x3f,0x3d,0x33,0x31,0x37,0x35,0x2b,0x29,0x2f,0x2d,0x23,0x21,0x27,0x25,
              0x5b,0x59,0x5f,0x5d,0x53,0x51,0x57,0x55,0x4b,0x49,0x4f,0x4d,0x43,0x41,0x47,0x45,
              0x7b,0x79,0x7f,0x7d,0x73,0x71,0x77,0x75,0x6b,0x69,0x6f,0x6d,0x63,0x61,0x67,0x65,
              0x9b,0x99,0x9f,0x9d,0x93,0x91,0x97,0x95,0x8b,0x89,0x8f,0x8d,0x83,0x81,0x87,0x85,
              0xbb,0xb9,0xbf,0xbd,0xb3,0xb1,0xb7,0xb5,0xab,0xa9,0xaf,0xad,0xa3,0xa1,0xa7,0xa5,
              0xdb,0xd9,0xdf,0xdd,0xd3,0xd1,0xd7,0xd5,0xcb,0xc9,0xcf,0xcd,0xc3,0xc1,0xc7,0xc5,
              0xfb,0xf9,0xff,0xfd,0xf3,0xf1,0xf7,0xf5,0xeb,0xe9,0xef,0xed,0xe3,0xe1,0xe7,0xe5
          };
  
          private static byte[] mul3 = {
              0x00,0x03,0x06,0x05,0x0c,0x0f,0x0a,0x09,0x18,0x1b,0x1e,0x1d,0x14,0x17,0x12,0x11,
              0x30,0x33,0x36,0x35,0x3c,0x3f,0x3a,0x39,0x28,0x2b,0x2e,0x2d,0x24,0x27,0x22,0x21,
              0x60,0x63,0x66,0x65,0x6c,0x6f,0x6a,0x69,0x78,0x7b,0x7e,0x7d,0x74,0x77,0x72,0x71,
              0x50,0x53,0x56,0x55,0x5c,0x5f,0x5a,0x59,0x48,0x4b,0x4e,0x4d,0x44,0x47,0x42,0x41,
              0xc0,0xc3,0xc6,0xc5,0xcc,0xcf,0xca,0xc9,0xd8,0xdb,0xde,0xdd,0xd4,0xd7,0xd2,0xd1,
              0xf0,0xf3,0xf6,0xf5,0xfc,0xff,0xfa,0xf9,0xe8,0xeb,0xee,0xed,0xe4,0xe7,0xe2,0xe1,
              0xa0,0xa3,0xa6,0xa5,0xac,0xaf,0xaa,0xa9,0xb8,0xbb,0xbe,0xbd,0xb4,0xb7,0xb2,0xb1,
              0x90,0x93,0x96,0x95,0x9c,0x9f,0x9a,0x99,0x88,0x8b,0x8e,0x8d,0x84,0x87,0x82,0x81,
              0x9b,0x98,0x9d,0x9e,0x97,0x94,0x91,0x92,0x83,0x80,0x85,0x86,0x8f,0x8c,0x89,0x8a,
              0xab,0xa8,0xad,0xae,0xa7,0xa4,0xa1,0xa2,0xb3,0xb0,0xb5,0xb6,0xbf,0xbc,0xb9,0xba,
              0xfb,0xf8,0xfd,0xfe,0xf7,0xf4,0xf1,0xf2,0xe3,0xe0,0xe5,0xe6,0xef,0xec,0xe9,0xea,
              0xcb,0xc8,0xcd,0xce,0xc7,0xc4,0xc1,0xc2,0xd3,0xd0,0xd5,0xd6,0xdf,0xdc,0xd9,0xda,
              0x5b,0x58,0x5d,0x5e,0x57,0x54,0x51,0x52,0x43,0x40,0x45,0x46,0x4f,0x4c,0x49,0x4a,
              0x6b,0x68,0x6d,0x6e,0x67,0x64,0x61,0x62,0x73,0x70,0x75,0x76,0x7f,0x7c,0x79,0x7a,
              0x3b,0x38,0x3d,0x3e,0x37,0x34,0x31,0x32,0x23,0x20,0x25,0x26,0x2f,0x2c,0x29,0x2a,
              0x0b,0x08,0x0d,0x0e,0x07,0x04,0x01,0x02,0x13,0x10,0x15,0x16,0x1f,0x1c,0x19,0x1a
          };
  
          private static byte[] mul09 = {
              0x00,0x09,0x12,0x1b,0x24,0x2d,0x36,0x3f,0x48,0x41,0x5a,0x53,0x6c,0x65,0x7e,0x77,
              0x90,0x99,0x82,0x8b,0xb4,0xbd,0xa6,0xaf,0xd8,0xd1,0xca,0xc3,0xfc,0xf5,0xee,0xe7,
              0x3b,0x32,0x29,0x20,0x1f,0x16,0x0d,0x04,0x73,0x7a,0x61,0x68,0x57,0x5e,0x45,0x4c,
              0xab,0xa2,0xb9,0xb0,0x8f,0x86,0x9d,0x94,0xe3,0xea,0xf1,0xf8,0xc7,0xce,0xd5,0xdc,
              0x76,0x7f,0x64,0x6d,0x52,0x5b,0x40,0x49,0x3e,0x37,0x2c,0x25,0x1a,0x13,0x08,0x01,
              0xe6,0xef,0xf4,0xfd,0xc2,0xcb,0xd0,0xd9,0xae,0xa7,0xbc,0xb5,0x8a,0x83,0x98,0x91,
              0x4d,0x44,0x5f,0x56,0x69,0x60,0x7b,0x72,0x05,0x0c,0x17,0x1e,0x21,0x28,0x33,0x3a,
              0xdd,0xd4,0xcf,0xc6,0xf9,0xf0,0xeb,0xe2,0x95,0x9c,0x87,0x8e,0xb1,0xb8,0xa3,0xaa,
              0xec,0xe5,0xfe,0xf7,0xc8,0xc1,0xda,0xd3,0xa4,0xad,0xb6,0xbf,0x80,0x89,0x92,0x9b,
              0x7c,0x75,0x6e,0x67,0x58,0x51,0x4a,0x43,0x34,0x3d,0x26,0x2f,0x10,0x19,0x02,0x0b,
              0xd7,0xde,0xc5,0xcc,0xf3,0xfa,0xe1,0xe8,0x9f,0x96,0x8d,0x84,0xbb,0xb2,0xa9,0xa0,
              0x47,0x4e,0x55,0x5c,0x63,0x6a,0x71,0x78,0x0f,0x06,0x1d,0x14,0x2b,0x22,0x39,0x30,
              0x9a,0x93,0x88,0x81,0xbe,0xb7,0xac,0xa5,0xd2,0xdb,0xc0,0xc9,0xf6,0xff,0xe4,0xed,
              0x0a,0x03,0x18,0x11,0x2e,0x27,0x3c,0x35,0x42,0x4b,0x50,0x59,0x66,0x6f,0x74,0x7d,
              0xa1,0xa8,0xb3,0xba,0x85,0x8c,0x97,0x9e,0xe9,0xe0,0xfb,0xf2,0xcd,0xc4,0xdf,0xd6,
              0x31,0x38,0x23,0x2a,0x15,0x1c,0x07,0x0e,0x79,0x70,0x6b,0x62,0x5d,0x54,0x4f,0x46
          };
  
          private static byte[] mul11 = {
              0x00,0x0b,0x16,0x1d,0x2c,0x27,0x3a,0x31,0x58,0x53,0x4e,0x45,0x74,0x7f,0x62,0x69,
              0xb0,0xbb,0xa6,0xad,0x9c,0x97,0x8a,0x81,0xe8,0xe3,0xfe,0xf5,0xc4,0xcf,0xd2,0xd9,
              0x7b,0x70,0x6d,0x66,0x57,0x5c,0x41,0x4a,0x23,0x28,0x35,0x3e,0x0f,0x04,0x19,0x12,
              0xcb,0xc0,0xdd,0xd6,0xe7,0xec,0xf1,0xfa,0x93,0x98,0x85,0x8e,0xbf,0xb4,0xa9,0xa2,
              0xf6,0xfd,0xe0,0xeb,0xda,0xd1,0xcc,0xc7,0xae,0xa5,0xb8,0xb3,0x82,0x89,0x94,0x9f,
              0x46,0x4d,0x50,0x5b,0x6a,0x61,0x7c,0x77,0x1e,0x15,0x08,0x03,0x32,0x39,0x24,0x2f,
              0x8d,0x86,0x9b,0x90,0xa1,0xaa,0xb7,0xbc,0xd5,0xde,0xc3,0xc8,0xf9,0xf2,0xef,0xe4,
              0x3d,0x36,0x2b,0x20,0x11,0x1a,0x07,0x0c,0x65,0x6e,0x73,0x78,0x49,0x42,0x5f,0x54,
              0xf7,0xfc,0xe1,0xea,0xdb,0xd0,0xcd,0xc6,0xaf,0xa4,0xb9,0xb2,0x83,0x88,0x95,0x9e,
              0x47,0x4c,0x51,0x5a,0x6b,0x60,0x7d,0x76,0x1f,0x14,0x09,0x02,0x33,0x38,0x25,0x2e,
              0x8c,0x87,0x9a,0x91,0xa0,0xab,0xb6,0xbd,0xd4,0xdf,0xc2,0xc9,0xf8,0xf3,0xee,0xe5,
              0x3c,0x37,0x2a,0x21,0x10,0x1b,0x06,0x0d,0x64,0x6f,0x72,0x79,0x48,0x43,0x5e,0x55,
              0x01,0x0a,0x17,0x1c,0x2d,0x26,0x3b,0x30,0x59,0x52,0x4f,0x44,0x75,0x7e,0x63,0x68,
              0xb1,0xba,0xa7,0xac,0x9d,0x96,0x8b,0x80,0xe9,0xe2,0xff,0xf4,0xc5,0xce,0xd3,0xd8,
              0x7a,0x71,0x6c,0x67,0x56,0x5d,0x40,0x4b,0x22,0x29,0x34,0x3f,0x0e,0x05,0x18,0x13,
              0xca,0xc1,0xdc,0xd7,0xe6,0xed,0xf0,0xfb,0x92,0x99,0x84,0x8f,0xbe,0xb5,0xa8,0xa3
              };
  
          private static byte[] mul13 = {
              0x00,0x0d,0x1a,0x17,0x34,0x39,0x2e,0x23,0x68,0x65,0x72,0x7f,0x5c,0x51,0x46,0x4b,
              0xd0,0xdd,0xca,0xc7,0xe4,0xe9,0xfe,0xf3,0xb8,0xb5,0xa2,0xaf,0x8c,0x81,0x96,0x9b,
              0xbb,0xb6,0xa1,0xac,0x8f,0x82,0x95,0x98,0xd3,0xde,0xc9,0xc4,0xe7,0xea,0xfd,0xf0,
              0x6b,0x66,0x71,0x7c,0x5f,0x52,0x45,0x48,0x03,0x0e,0x19,0x14,0x37,0x3a,0x2d,0x20,
              0x6d,0x60,0x77,0x7a,0x59,0x54,0x43,0x4e,0x05,0x08,0x1f,0x12,0x31,0x3c,0x2b,0x26,
              0xbd,0xb0,0xa7,0xaa,0x89,0x84,0x93,0x9e,0xd5,0xd8,0xcf,0xc2,0xe1,0xec,0xfb,0xf6,
              0xd6,0xdb,0xcc,0xc1,0xe2,0xef,0xf8,0xf5,0xbe,0xb3,0xa4,0xa9,0x8a,0x87,0x90,0x9d,
              0x06,0x0b,0x1c,0x11,0x32,0x3f,0x28,0x25,0x6e,0x63,0x74,0x79,0x5a,0x57,0x40,0x4d,
              0xda,0xd7,0xc0,0xcd,0xee,0xe3,0xf4,0xf9,0xb2,0xbf,0xa8,0xa5,0x86,0x8b,0x9c,0x91,
              0x0a,0x07,0x10,0x1d,0x3e,0x33,0x24,0x29,0x62,0x6f,0x78,0x75,0x56,0x5b,0x4c,0x41,
              0x61,0x6c,0x7b,0x76,0x55,0x58,0x4f,0x42,0x09,0x04,0x13,0x1e,0x3d,0x30,0x27,0x2a,
              0xb1,0xbc,0xab,0xa6,0x85,0x88,0x9f,0x92,0xd9,0xd4,0xc3,0xce,0xed,0xe0,0xf7,0xfa,
              0xb7,0xba,0xad,0xa0,0x83,0x8e,0x99,0x94,0xdf,0xd2,0xc5,0xc8,0xeb,0xe6,0xf1,0xfc,
              0x67,0x6a,0x7d,0x70,0x53,0x5e,0x49,0x44,0x0f,0x02,0x15,0x18,0x3b,0x36,0x21,0x2c,
              0x0c,0x01,0x16,0x1b,0x38,0x35,0x22,0x2f,0x64,0x69,0x7e,0x73,0x50,0x5d,0x4a,0x47,
              0xdc,0xd1,0xc6,0xcb,0xe8,0xe5,0xf2,0xff,0xb4,0xb9,0xae,0xa3,0x80,0x8d,0x9a,0x97
          };
  
          private static byte[] mul14 = {
              0x00,0x0e,0x1c,0x12,0x38,0x36,0x24,0x2a,0x70,0x7e,0x6c,0x62,0x48,0x46,0x54,0x5a,
              0xe0,0xee,0xfc,0xf2,0xd8,0xd6,0xc4,0xca,0x90,0x9e,0x8c,0x82,0xa8,0xa6,0xb4,0xba,
              0xdb,0xd5,0xc7,0xc9,0xe3,0xed,0xff,0xf1,0xab,0xa5,0xb7,0xb9,0x93,0x9d,0x8f,0x81,
              0x3b,0x35,0x27,0x29,0x03,0x0d,0x1f,0x11,0x4b,0x45,0x57,0x59,0x73,0x7d,0x6f,0x61,
              0xad,0xa3,0xb1,0xbf,0x95,0x9b,0x89,0x87,0xdd,0xd3,0xc1,0xcf,0xe5,0xeb,0xf9,0xf7,
              0x4d,0x43,0x51,0x5f,0x75,0x7b,0x69,0x67,0x3d,0x33,0x21,0x2f,0x05,0x0b,0x19,0x17,
              0x76,0x78,0x6a,0x64,0x4e,0x40,0x52,0x5c,0x06,0x08,0x1a,0x14,0x3e,0x30,0x22,0x2c,
              0x96,0x98,0x8a,0x84,0xae,0xa0,0xb2,0xbc,0xe6,0xe8,0xfa,0xf4,0xde,0xd0,0xc2,0xcc,
              0x41,0x4f,0x5d,0x53,0x79,0x77,0x65,0x6b,0x31,0x3f,0x2d,0x23,0x09,0x07,0x15,0x1b,
              0xa1,0xaf,0xbd,0xb3,0x99,0x97,0x85,0x8b,0xd1,0xdf,0xcd,0xc3,0xe9,0xe7,0xf5,0xfb,
              0x9a,0x94,0x86,0x88,0xa2,0xac,0xbe,0xb0,0xea,0xe4,0xf6,0xf8,0xd2,0xdc,0xce,0xc0,
              0x7a,0x74,0x66,0x68,0x42,0x4c,0x5e,0x50,0x0a,0x04,0x16,0x18,0x32,0x3c,0x2e,0x20,
              0xec,0xe2,0xf0,0xfe,0xd4,0xda,0xc8,0xc6,0x9c,0x92,0x80,0x8e,0xa4,0xaa,0xb8,0xb6,
              0x0c,0x02,0x10,0x1e,0x34,0x3a,0x28,0x26,0x7c,0x72,0x60,0x6e,0x44,0x4a,0x58,0x56,
              0x37,0x39,0x2b,0x25,0x0f,0x01,0x13,0x1d,0x47,0x49,0x5b,0x55,0x7f,0x71,0x63,0x6d,
              0xd7,0xd9,0xcb,0xc5,0xef,0xe1,0xf3,0xfd,0xa7,0xa9,0xbb,0xb5,0x9f,0x91,0x83,0x8d
          };
  
  
          private State()
          {
              buf = new byte[nrofRow, nrofCol];
              for (int i = 0; i &lt; nrofRow; i++)
              {
                  for (int j = 0; j &lt; nrofCol; j++)
                  {
                      buf[i, j] = 0;
                  }
              }
          }
  
          public State(byte[] b)
          {
              buf = new byte[nrofRow, nrofCol];
              for (int i = 0; i &lt; nrofRow; i++)
              {
                  for (int j = 0; j &lt; nrofCol; j++)
                  {
                      buf[i, j] = b[i + (nrofRow * j)];
                  }
              }
          }
  
          public State subBytes()
          {
              State s = new State();
  
              for (int i = 0; i &lt; nrofRow; i++)
              {
                  for (int j = 0; j &lt; nrofCol; j++)
                  {
                      s.buf[i, j] = Sbox.sbox[buf[i, j]];
                      //Console.Out.WriteLine("state[" + i + "," + j + "]=" + buf[i, j] + "---&gt;" + s.buf[i, j]);
                  }
              }
              return (s);
          }
  
          public State shiftRows()
          {
              State s = new State();
  
              for (int i = 0; i &lt; nrofRow; i++)
              {
                  for (int j = 0; j &lt; nrofCol; j++)
                  {
                      s.buf[i, j] = buf[i, (i + j) % 4];
                      //Console.Out.WriteLine("state[" + i + "," + j + "]=" + s.buf[i, j]);
                  }
              }
              return (s);
          }
  
          public State mixColumns()
          {
              State s = new State();
              for (int c = 0; c &lt; nrofCol; c++)
              {
                  s.buf[0, c] = (byte)(mul2[buf[0, c]] ^ mul3[buf[1, c]] ^ buf[2, c] ^ buf[3, c]);
                  s.buf[1, c] = (byte)(buf[0, c] ^ mul2[buf[1, c]] ^ mul3[buf[2, c]] ^ buf[3, c]);
                  s.buf[2, c] = (byte)(buf[0, c] ^ buf[1, c] ^ mul2[buf[2, c]] ^ mul3[buf[3, c]]);
                  s.buf[3, c] = (byte)(mul3[buf[0, c]] ^ buf[1, c] ^ buf[2, c] ^ mul2[buf[3, c]]);
              }
              return (s);
          }
  
          public State subBytesInv()
          {
              // TODO
              State s = new State();
              for (int i = 0; i &lt; nrofRow; i++)
              {
                  for (int j = 0; j &lt; nrofCol; j++)
                  {
                      s.buf[i, j] = Sbox.sboxInv[buf[i, j]];
                      //Console.Out.WriteLine("state[" + i + "," + j + "]=" + buf[i, j] + "---&gt;" + s.buf[i, j]);
                  }
              }
              return (s);
            }
  
          public State shiftRowsInv()
          {
              State s = new State();
  
  
              for (int i = 0; i &lt; nrofRow; i++)
              {
                  for (int j = 0; j &lt; nrofCol; j++)
                  {
                      s.buf[i, j] = buf[i, (j - i + 4) % 4];
                      // Console.Out.WriteLine("state[" + i + "," + j + "]=" + s.buf[i, j]);
                  }
              }
              return (s);
          }
  
          public State mixColumnsInv()
          {
              State s = new State();
              for (int c = 0; c &lt; nrofCol; c++)
              {
                  s.buf[0, c] = (byte)(mul14[buf[0, c]] ^ mul11[buf[1, c]] ^ mul13[buf[2, c]] ^ mul09[buf[3, c]]);
                  s.buf[1, c] = (byte)(mul09[buf[0, c]] ^ mul14[buf[1, c]] ^ mul11[buf[2, c]] ^ mul13[buf[3, c]]);
                  s.buf[2, c] = (byte)(mul13[buf[0, c]] ^ mul09[buf[1, c]] ^ mul14[buf[2, c]] ^ mul11[buf[3, c]]);
                  s.buf[3, c] = (byte)(mul11[buf[0, c]] ^ mul13[buf[1, c]] ^ mul09[buf[2, c]] ^ mul14[buf[3, c]]);
              }
              return (s);
          }
  
          public State addRoundKey(Key key, int round)
          {
              State s = new State();
              for (int c = 0; c &lt; nrofCol; c++)
              {
                  for (int r = 0; r &lt; nrofRow; r++)
                  {
                      s.buf[r, c] = (byte)(buf[r, c] ^ key.w[r, c + 4 * round]);
                      //Console.Out.WriteLine("state[" + r + "," + c + "]=" + buf[r, c] + " XOR " + key.w[r, c + 4 * round] + " = " + s.buf[r, c]);
                  }
              }
              return (s);
          }
  
          public string ToMatrixString()
          {
              string s = "";
              for (int i = 0; i &lt; buf.GetLength(0); i++)
              {
                  for (int j = 0; j &lt; buf.GetLength(1); j++)
                  {
                      s += buf[i, j].ToString("X2") + " ";
                  }
                  s += "\n";
              }
              return (s);
          }
  
          public override string ToString()
          {
              string s = "";
              for (int i = 0; i &lt; buf.GetLength(1); i++)
              {
                  for (int j = 0; j &lt; buf.GetLength(0); j++)
                  {
                      s += buf[j, i].ToString("X2") + "";
                  }
              }`enter code here`
              return (s);
          }
      }
  }
  </code></pre>