Now that 3DES is phasing out, a new signature is need to replace the veteran X9.19. So here comes the brand new (from 2006!) AES CMAC signature. It uses AES instead of 3DES, but externally it uses the same 128bit long keys. I've programmed, with help from StackOverflow, a version in C#, and another version using the BouncyCastle library. Both ways return the same result, and I don't know which one performs better. The program is easy to understand, the only difficult step lays in the subkey generation. I've cut&pasted the RFC part that explains it to be sure I've done the correct thing.

byte[] AESEncrypt(byte[] key, byte[] iv, byte[] data)
{
    using (MemoryStream ms = new MemoryStream())
    {
	AesCryptoServiceProvider aes = new AesCryptoServiceProvider();

	aes.Mode = CipherMode.CBC;
	aes.Padding = PaddingMode.None;

	using (CryptoStream cs = new CryptoStream(ms, aes.CreateEncryptor(key, iv), CryptoStreamMode.Write))
	{
	    cs.Write(data, 0, data.Length);
	    cs.FlushFinalBlock();

	    return ms.ToArray();
	}
    }
}

/// <summary>
/// This function does:
/// x << 1
/// Left-shift of the string x by 1 bit.
/// The most significant bit disappears, and a zero
/// comes into the least significant bit.
/// 10010001 << 1 is 00100010.
/// </summary>
/// <param name="b">Array de bytes a fer shift</param>
/// <returns>El byte shiftejat</returns>
byte[] Rol(byte[] b)
{
    byte[] r = new byte[b.Length];
    byte carry = 0;

    for (int i = b.Length - 1; i >= 0; i--)
    {
	ushort u = (ushort)(b[i] << 1);
	r[i] = (byte)((u & 0xff) + carry);
	carry = (byte)((u & 0xff00) >> 8);
    }

    return r;
}

byte[] AESCMAC(byte[] key, byte[] data)
{
    /*
    // SubKey generation
    Figure 2.2 specifies the subkey generation algorithm.
 

    ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ +
    +Algorithm Generate_Subkey +
    +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
    + +
    +Input    : K(128 - bit key) +
    +Output   : K1(128 - bit first subkey) +
    +K2(128 - bit second subkey) +
    +-------------------------------------------------------------------+
    + +
    +Constants: const_Zero is 0x00000000000000000000000000000000 +
    +const_Rb is 0x00000000000000000000000000000087 +
    +Variables: L          for output of AES - 128 applied to 0 ^ 128 +
    + +
    +Step 1.L := AES - 128(K, const_Zero); +
    +Step 2.  if MSB(L) is equal to 0 +
    +then    K1:= L << 1; +
    +            else    K1:= (L << 1) XOR const_Rb; +
    +Step 3.  if MSB(K1) is equal to 0 +
    +then    K2:= K1 << 1; +
    +            else    K2:= (K1 << 1) XOR const_Rb; +
    +Step 4.  return K1, K2; +
    + +
    +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

    Figure 2.2.Algorithm Generate_Subkey

    In step 1, AES - 128 with key K is applied to an all-zero input block.

       In step 2, K1 is derived through the following operation:

		If the most significant bit of L is equal to 0, K1 is the left - shift
       of L by 1 bit.

       Otherwise, K1 is the exclusive - OR of const_Rb and the left - shift of L
       by 1 bit.

       In step 3, K2 is derived through the following operation:

		If the most significant bit of K1 is equal to 0, K2 is the left - shift
       of K1 by 1 bit.

       Otherwise, K2 is the exclusive - OR of const_Rb and the left - shift of
	   K1 by 1 bit.

       In step 4, (K1, K2) := Generate_Subkey(K) is returned.
       */


    // step 1, AES-128 with key K is applied to an all-zero input block.
    byte[] L = AESEncrypt(key, new byte[16], new byte[16]);

    // step 2, K1 is derived through the following operation:
    byte[] FirstSubkey = Rol(L); //If the most significant bit of L is equal to 0, K1 is the left-shift of L by 1 bit.
    if ((L[0] & 0x80) == 0x80)
	FirstSubkey[15] ^= 0x87; // Otherwise, K1 is the exclusive-OR of const_Rb and the left-shift of L by 1 bit.

    // step 3, K2 is derived through the following operation:
    byte[] SecondSubkey = Rol(FirstSubkey); // If the most significant bit of K1 is equal to 0, K2 is the left-shift of K1 by 1 bit.
    if ((FirstSubkey[0] & 0x80) == 0x80)
	SecondSubkey[15] ^= 0x87; // Otherwise, K2 is the exclusive-OR of const_Rb and the left-shift of K1 by 1 bit.

    // MAC computing
    if (((data.Length != 0) && (data.Length % 16 == 0)) == true)
    {
	// If the size of the input message block is equal to a positive multiple of the block size (namely, 128 bits),
	// the last block shall be exclusive-OR'ed with K1 before processing
	for (int j = 0; j < FirstSubkey.Length; j++)
	    data[data.Length - 16 + j] ^= FirstSubkey[j];
    }
    else
    {
	//S'afegeix padding a l'ultim bloc, però en realitat és afegir padding a les dades
	data = AddPaddingAES(data);
	/*
	// Otherwise, the last block shall be padded with 10^i
	byte[] padding = new byte[16 - data.Length % 16];
	padding[0] = 0x80;

	data = data.Concat<byte>(padding.AsEnumerable()).ToArray();
	*/

	// and exclusive-OR'ed with K2, la SecondSubkey té 16 de longitud
	for (int j = 0; j < 16; j++) data[data.Length - 16 + j] ^= SecondSubkey[j];
    }

    // The result of the previous process will be the input of the last encryption.
    byte[] encResult = AESEncrypt(key, new byte[16], data);

    byte[] HashValue = new byte[16];
    Array.Copy(encResult, encResult.Length - HashValue.Length, HashValue, 0, HashValue.Length);

    return HashValue;
}

All that code from above, that seems very complex, can be reduced to a few lines using BouncyCastle. But you know, in the code lays the truth, and with the library you don't see it...

//Using BouncyCastle
Org.BouncyCastle.Crypto.Engines.AesEngine aes = new Org.BouncyCastle.Crypto.Engines.AesEngine();
Org.BouncyCastle.Crypto.Macs.CMac cMac = new Org.BouncyCastle.Crypto.Macs.CMac(aes, 64);
Org.BouncyCastle.Crypto.Parameters.KeyParameter kp = new Org.BouncyCastle.Crypto.Parameters.KeyParameter(key);
cMac.Init(kp);
int MacLenght = cMac.GetMacSize();
byte[] output = new byte[MacLenght];
cMac.BlockUpdate(data, 0, data.Length);
cMac.DoFinal(output, 0);

txtBase64.Text = ConvertByteArrayToHexString(output);

There are some examples in a RFC.

//https://tools.ietf.org/html/rfc4493
/*
CMAC EXAMPLE:
-------------
NIST publication 800 - 38B: http://csrc.nist.gov/publications/nistpubs/800-38B/Updated_CMAC_Examples.pdf

>>> key 2b7e151628aed2a6abf7158809cf4f3c
>>> plaintext 6bc1bee22e409f96e93d7e117393172a
<<< CMAC 070a16b46b4d4144f79bdd9dd04a287c

>>> key 2B7E151628AED2A6ABF7158809CF4F3C
>>> pt: 6BC1BEE22E409F96E93D7E117393172AAE2D8A57
<<< CMAC 7D85449E A6EA19C8 23A7BF78 837DFADE

>>> key 2B7E151628AED2A6ABF7158809CF4F3C
>>> pt: 6BC1BEE22E409F96E93D7E117393172AAE2D8A571E03AC9C9EB76FAC45AF8E5130C81C46A35CE411E5FBC1191A0A52EFF69F2445DF4F9B17AD2B417BE66C3710
<<< CMAC 51F0BEBF7E3B9D92FC49741779363CFE
*/

And that's all, another signature done!

Recently I had to implement a MAC ANSI X9.19 (MAC = Message Authentication Code) signature. And like all security related standards there is little information online.

A MAC signature of this type is usefull to verify that a message has not been tampered and that we receive it as it was sent. If there is a network problem and a bit flips it will be detected, or if someone "bad" tries to modify the message also will be detected. They can't calculate the signature for the modified payload because they don't know the key. The receiver of the message can verify it because he knows the key.

The signature MAC ANSI X9.19 is a banking standard made in USA. It's an evolution from X9.9 and it is also known as Retail-MAC. It's a cipher based in DES-CBC, here are the links to the wiki for DES that means "Data Encryption Standard" and CBC that means"Cipher Block Chaining". An international norm exists, that is very similar but a little more permisive called ISO 9807, it allows to use another cipher algorithms. ANSI X9.19 is a subset of ISO 9797, when the cipher block is 64 bits, MAC length is 32 and DES is used.

DES is a very old cipher algorithm that uses 56 bit keys but X9.19 uses 128bit keys like 3DES. Here are the process steps:

1. The incoming message is padded with 00. As padding will not be removed later there's no need of adding an special padding so 00 is ok. So we add 00 until the message length is multiple of 8 bytes.
2. The 128 bit key is divided into two sub-keys. Left part is called K, and right part K'.
3. Message is divided in 8 byte blocks.
4. Firts block is cyphered with K key.
5. A XOR is applied to the result with the next block (it's the CBC).
6. Result is ciphered with K key. If it isn't the last block return to previous step.
   If it is then move to the next step.
7. To this last result a decryption is applied with K' key (nothing coherent is obtained).
8. Finally encrypt with K key. The result is the MAC.

Better an image than a thousand words:

I've made two implementations in C#, one doing things by hand and the other with system libraries. Both offer the same result (I don't know which performs better). In code comments there is an example with correct values to check if it works.

public byte[] SubArray(byte[] data, int index, int length)
{
    byte[] result = new byte[length];
    Array.Copy(data, index, result, 0, length);
    return result;
}

private void btnFirma_Click(object sender, EventArgs e)
{
    try
    {

	if (!ValidarClau()) return;

	NetejaTXTs();

	byte[] IV = new byte[8]; //empty byte array
	byte[] key = ConvertHexStringToByteArray(txtKey.Text);
	byte[] LeftKey = SubArray(key, 0, 8);
	byte[] RightKey = SubArray(key, 8, 8);
	byte[] data;

	if (chkHexString.Checked)
	{
	    data = ConvertHexStringToByteArray(Neteja(txtOriginal.Text));
	}
	else
	{
	    data = Encoding.ASCII.GetBytes(Neteja(txtOriginal.Text));
	}
	//Exemple
	//Dades = 4E6F77206973207468652074696D6520666F7220616C6C20
	//Clau = 0123456789ABCDEFFEDCBA9876543210
	//Firma = A1C72E74EA3FA9B6

	DES DESalg = DES.Create();
	DESalg.Mode = CipherMode.CBC;
	DESalg.Padding = PaddingMode.None;
	ICryptoTransform SimpleDES_Encriptador = DESalg.CreateEncryptor(LeftKey, IV);
	ICryptoTransform SimpleDES_Desencriptador = DESalg.CreateDecryptor(RightKey, IV);

	byte[] result = new byte[8];
	byte[] datablock = new byte[8];
	int remain = data.Length % 8;
	int LoopCount = data.Length / 8;

	/*
	//Padding a 0
	if (remain != 0)
	{
	    int extra = 8 - (data.Length % 8);
	    int newLength = data.Length + extra;
	    byte[] newData = new byte[newLength];
	
	    Array.Copy(data, newData, data.Length);
	    data = newData;
	}
	result = SimpleDES_Encriptador.TransformFinalBlock(data, 0, data.Length);

	byte[] block = new byte[8];
	
	// Agafem l'ultim block
	Array.Copy(result, result.Length - 8, block, 0, 8);

	// Desencriptar l'ultim bloc a la K'
	block = SimpleDES_Desencriptador.TransformFinalBlock(block, 0, 8);

	// Encriptar altra cop el resultat amb K
	block = SimpleDES_Encriptador.TransformFinalBlock(block, 0, 8);

	result = block;
	*/

	//Si el que s'ha de firmar és multiple de 8...
	if (remain == 0)
	{
	    LoopCount--;
	    remain = 8;
	}

	//Primer block
	Array.Copy(data, 0, datablock, 0, 8);
	result = EncryptBlock(SimpleDES_Encriptador, datablock);

	for (int i = 1; i < LoopCount; i++)
	{
	    datablock = new byte[8];
	    Array.Copy(data, i * 8, datablock, 0, 8);
	    //Això fa el CBC
	    datablock = XorArray(datablock, result);
	    result = EncryptBlock(SimpleDES_Encriptador, datablock);
	}

	//Ultim block
	byte[] LastBlock = new byte[8];

	//Això fa padding a zeros
	Array.Copy(data, data.Length - remain, LastBlock, 0, remain);
	LastBlock = XorArray(LastBlock, result);

	result = EncryptBlock(SimpleDES_Encriptador, LastBlock);

	result = EncryptBlock(SimpleDES_Desencriptador, result);

	result = EncryptBlock(SimpleDES_Encriptador, result);

	if (!chkHexString.Checked) txtBase64.Text = ConvertByteArrayToHexString(data);
	txtEncrypted.Text = ConvertByteArrayToHexString(result);
	   
    }
    catch(Exception E)
    {
	MessageBox.Show(E.Message);
    }
}

public byte[] XorArray(byte[] buffer1, byte[] buffer2)
{
    for (int i = 0; i < buffer1.Length; i++)
	buffer1[i] ^= buffer2[i];
    return buffer1;
}

private byte[] EncryptBlock(ICryptoTransform crypt, byte[] toEncrypt)
{
    try
    {
	MemoryStream mStream = new MemoryStream();

	CryptoStream cStream = new CryptoStream(mStream,
	    crypt,
	    CryptoStreamMode.Write);
	cStream.Write(toEncrypt, 0, toEncrypt.Length);
	cStream.FlushFinalBlock();
	byte[] ret = mStream.ToArray();
	cStream.Close();
	mStream.Close();

	Console.WriteLine("DES OUTPUT : " + ConvertByteArrayToHexString(ret));
	return ret;
    }

    catch (CryptographicException e)
    {
	Console.WriteLine("A Cryptographic error occurred: {0}", e.Message);
	return null;
    }
}

The class clsData contains all methods needed to invoque all the stored procedures (SP) and the declaration of all the variables used by those methods. On the other hand a derived class contains only the initialization of those variables but no declarations. The program that generates the clsData only creates those derived classes filling the initializations automatically. So the next piece of code is generated by a program, not hand-made. For explanation purposes I put here an example.

public class clsClassificacio : clsData
{
	/// <summary>
	/// Class Constructor
	/// </summary>
	/// <param name="pCadConnBBDD">Connection string</param>
	public clsClassificacio(string pCadConnBBDD)
	{
		spINS = "DI_EXP_CLASSIFICACIO_INS";
		spUPD = "DI_EXP_CLASSIFICACIO_UPD";
		spGET = "DI_EXP_CLASSIFICACIO_GET";
		spCOUNT = "DI_EXP_CLASSIFICACIO_COUNT";
		spQUERY = "DI_EXP_CLASSIFICACIO_QUERY";
		spDEL = "DI_EXP_CLASSIFICACIO_DEL";
		HasIdentity = true;
		Identity = "PK_Classificacio";
		TableName = "DI_EXP_CLASSIFICACIO";
		UseCache = false;
		CadConnBBDD = pCadConnBBDD;
		ParamsGET = new clsColumn[7];
		for (int i = 0; i < 7; i++) ParamsGET[i] = new clsColumn();
	#region Llista params GET
		ParamsGET[0].ColName = "PK_Classificacio";
		ParamsGET[0].DB_Type = DBType.tint;
		ParamsGET[0].PK = true;
		ParamsGET[0].Identity = true;
		ParamsGET[0].Nulable = false;
		ParamsGET[1].ColName = "Nom";
		ParamsGET[1].DB_Type = DBType.nvarchar;
		ParamsGET[1].Len = 200;
		ParamsGET[1].Nulable = false;
		ParamsGET[2].ColName = "PK_Arxiu";
		ParamsGET[2].DB_Type = DBType.tint;
		ParamsGET[3].ColName = "Codi_TC";
		ParamsGET[3].DB_Type = DBType.nvarchar;
		ParamsGET[3].Len = 5;
		ParamsGET[3].Nulable = false;
		ParamsGET[4].ColName = "Nivell_Codi";
		ParamsGET[4].DB_Type = DBType.nvarchar;
		ParamsGET[4].Len = 100;
		ParamsGET[4].Nulable = false;
		ParamsGET[5].ColName = "IdPare";
		ParamsGET[5].DB_Type = DBType.tint;
		ParamsGET[5].Nulable = false;
		ParamsGET[6].ColName = "FK_TAAD";
		ParamsGET[6].DB_Type = DBType.tint;
	#endregion
		ParamsINS = new clsColumn[10];
		for (int i = 0; i < 10; i++) ParamsINS[i] = new clsColumn();
	#region Llista params INS
		ParamsINS[0].ColName = "PK_Classificacio";
		ParamsINS[0].DB_Type = DBType.tint;
		ParamsINS[0].PK = true;
		ParamsINS[0].Identity = true;
		ParamsINS[0].Nulable = false;
		ParamsINS[1].ColName = "Codi_TC";
		ParamsINS[1].DB_Type = DBType.varchar;
		ParamsINS[1].Len = 5;
		ParamsINS[1].Nulable = false;
		ParamsINS[2].ColName = "Observacions";
		ParamsINS[2].DB_Type = DBType.varchar;
		ParamsINS[2].Len = 3000;
		ParamsINS[3].ColName = "DataAlta";
		ParamsINS[3].DB_Type = DBType.datetime;
		ParamsINS[4].ColName = "DataBaixa";
		ParamsINS[4].DB_Type = DBType.datetime;
		ParamsINS[5].ColName = "Any_inici";
		ParamsINS[5].DB_Type = DBType.tint;
		ParamsINS[5].Nulable = false;
		ParamsINS[6].ColName = "Any_final";
		ParamsINS[6].DB_Type = DBType.tint;
		ParamsINS[6].Nulable = false;
		ParamsINS[7].ColName = "IdPare";
		ParamsINS[7].DB_Type = DBType.tint;
		ParamsINS[7].Nulable = false;
		ParamsINS[8].ColName = "Nom";
		ParamsINS[8].DB_Type = DBType.nvarchar;
		ParamsINS[8].Len = 200;
		ParamsINS[8].Nulable = false;
		ParamsINS[9].ColName = "Nivell_Codi";
		ParamsINS[9].DB_Type = DBType.varchar;
		ParamsINS[9].Len = 100;
		ParamsINS[9].Nulable = false;
	#endregion
		ParamsUPD = new clsColumn[10];
		for (int i = 0; i < 10; i++) ParamsUPD[i] = new clsColumn();
	#region Llista params UPD
		ParamsUPD[0].ColName = "PK_Classificacio";
		ParamsUPD[0].DB_Type = DBType.tint;
		ParamsUPD[0].PK = true;
		ParamsUPD[0].Identity = true;
		ParamsUPD[0].Nulable = false;
		ParamsUPD[1].ColName = "Codi_TC";
		ParamsUPD[1].DB_Type = DBType.varchar;
		ParamsUPD[1].Len = 5;
		ParamsUPD[1].Nulable = false;
		ParamsUPD[2].ColName = "Observacions";
		ParamsUPD[2].DB_Type = DBType.varchar;
		ParamsUPD[2].Len = 3000;
		ParamsUPD[3].ColName = "DataAlta";
		ParamsUPD[3].DB_Type = DBType.datetime;
		ParamsUPD[4].ColName = "DataBaixa";
		ParamsUPD[4].DB_Type = DBType.datetime;
		ParamsUPD[5].ColName = "Any_inici";
		ParamsUPD[5].DB_Type = DBType.tint;
		ParamsUPD[5].Nulable = false;
		ParamsUPD[6].ColName = "Any_final";
		ParamsUPD[6].DB_Type = DBType.tint;
		ParamsUPD[6].Nulable = false;
		ParamsUPD[7].ColName = "IdPare";
		ParamsUPD[7].DB_Type = DBType.tint;
		ParamsUPD[7].Nulable = false;
		ParamsUPD[8].ColName = "Nom";
		ParamsUPD[8].DB_Type = DBType.nvarchar;
		ParamsUPD[8].Len = 200;
		ParamsUPD[8].Nulable = false;
		ParamsUPD[9].ColName = "Nivell_Codi";
		ParamsUPD[9].DB_Type = DBType.varchar;
		ParamsUPD[9].Len = 100;
		ParamsUPD[9].Nulable = false;
	#endregion
		ParamsDEL = new clsColumn[7];
		for (int i = 0; i < 7; i++) ParamsDEL[i] = new clsColumn();
	#region Llista params DEL
		ParamsDEL[0].ColName = "PK_Classificacio";
		ParamsDEL[0].DB_Type = DBType.tint;
		ParamsDEL[0].PK = true;
		ParamsDEL[0].Identity = true;
		ParamsDEL[0].Nulable = false;
		ParamsDEL[1].ColName = "Nom";
		ParamsDEL[1].DB_Type = DBType.nvarchar;
		ParamsDEL[1].Len = 200;
		ParamsDEL[1].Nulable = false;
		ParamsDEL[2].ColName = "PK_Arxiu";
		ParamsDEL[2].DB_Type = DBType.tint;
		ParamsDEL[3].ColName = "Codi_TC";
		ParamsDEL[3].DB_Type = DBType.nvarchar;
		ParamsDEL[3].Len = 5;
		ParamsDEL[3].Nulable = false;
		ParamsDEL[4].ColName = "Nivell_Codi";
		ParamsDEL[4].DB_Type = DBType.nvarchar;
		ParamsDEL[4].Len = 100;
		ParamsDEL[4].Nulable = false;
		ParamsDEL[5].ColName = "IdPare";
		ParamsDEL[5].DB_Type = DBType.tint;
		ParamsDEL[5].Nulable = false;
		ParamsDEL[6].ColName = "FK_TAAD";
		ParamsDEL[6].DB_Type = DBType.tint;
	#endregion
		ParamsQUERY = new clsColumn[7];
		for (int i = 0; i < 7; i++) ParamsQUERY[i] = new clsColumn();
	#region Llista params QUERY
		ParamsQUERY[0].ColName = "PK_Classificacio";
		ParamsQUERY[0].DB_Type = DBType.tint;
		ParamsQUERY[0].PK = true;
		ParamsQUERY[0].Identity = true;
		ParamsQUERY[0].Nulable = false;
		ParamsQUERY[1].ColName = "Nom";
		ParamsQUERY[1].DB_Type = DBType.nvarchar;
		ParamsQUERY[1].Len = 200;
		ParamsQUERY[1].Nulable = false;
		ParamsQUERY[2].ColName = "PK_Arxiu";
		ParamsQUERY[2].DB_Type = DBType.tint;
		ParamsQUERY[3].ColName = "Codi_TC";
		ParamsQUERY[3].DB_Type = DBType.nvarchar;
		ParamsQUERY[3].Len = 5;
		ParamsQUERY[3].Nulable = false;
		ParamsQUERY[4].ColName = "Nivell_Codi";
		ParamsQUERY[4].DB_Type = DBType.nvarchar;
		ParamsQUERY[4].Len = 100;
		ParamsQUERY[4].Nulable = false;
		ParamsQUERY[5].ColName = "IdPare";
		ParamsQUERY[5].DB_Type = DBType.tint;
		ParamsQUERY[5].Nulable = false;
		ParamsQUERY[6].ColName = "FK_TAAD";
		ParamsQUERY[6].DB_Type = DBType.tint;
	#endregion
		ResultColumns = new clsColumn[10];
		for (int i = 0; i < 10; i++) ResultColumns[i] = new clsColumn();
	#region Result columns
		ResultColumns[0].ColName = "PK_Classificacio";
		ResultColumns[0].DB_Type = DBType.tint;
		ResultColumns[0].PK = true;
		ResultColumns[0].Identity = true;
		ResultColumns[0].Nulable = false;
		ResultColumns[1].ColName = "Codi_TC";
		ResultColumns[1].DB_Type = DBType.varchar;
		ResultColumns[1].Len = 5;
		ResultColumns[1].Nulable = false;
		ResultColumns[2].ColName = "Observacions";
		ResultColumns[2].DB_Type = DBType.varchar;
		ResultColumns[2].Len = 3000;
		ResultColumns[3].ColName = "DataAlta";
		ResultColumns[3].DB_Type = DBType.datetime;
		ResultColumns[4].ColName = "DataBaixa";
		ResultColumns[4].DB_Type = DBType.datetime;
		ResultColumns[5].ColName = "Any_inici";
		ResultColumns[5].DB_Type = DBType.tint;
		ResultColumns[5].Nulable = false;
		ResultColumns[6].ColName = "Any_final";
		ResultColumns[6].DB_Type = DBType.tint;
		ResultColumns[6].Nulable = false;
		ResultColumns[7].ColName = "IdPare";
		ResultColumns[7].DB_Type = DBType.tint;
		ResultColumns[7].Nulable = false;
		ResultColumns[8].ColName = "Nom";
		ResultColumns[8].DB_Type = DBType.nvarchar;
		ResultColumns[8].Len = 200;
		ResultColumns[8].Nulable = false;
		ResultColumns[9].ColName = "Nivell_Codi";
		ResultColumns[9].DB_Type = DBType.varchar;
		ResultColumns[9].Len = 100;
		ResultColumns[9].Nulable = false;
	#endregion
		Serialitzar = new clsColumn[10];
		for (int i = 0; i < 10; i++) Serialitzar[i] = new clsColumn();
	#region Serializable columns
		Serialitzar[0].ColName = "PK_Classificacio";
		Serialitzar[0].DB_Type = DBType.tint;
		Serialitzar[1].ColName = "Codi_TC";
		Serialitzar[1].DB_Type = DBType.varchar;
		Serialitzar[1].Len = 5;
		Serialitzar[2].ColName = "Observacions";
		Serialitzar[2].DB_Type = DBType.varchar;
		Serialitzar[2].Len = 3000;
		Serialitzar[3].ColName = "DataAlta";
		Serialitzar[3].DB_Type = DBType.datetime;
		Serialitzar[4].ColName = "DataBaixa";
		Serialitzar[4].DB_Type = DBType.datetime;
		Serialitzar[5].ColName = "Any_inici";
		Serialitzar[5].DB_Type = DBType.tint;
		Serialitzar[6].ColName = "Any_final";
		Serialitzar[6].DB_Type = DBType.tint;
		Serialitzar[7].ColName = "IdPare";
		Serialitzar[7].DB_Type = DBType.tint;
		Serialitzar[8].ColName = "Nom";
		Serialitzar[8].DB_Type = DBType.nvarchar;
		Serialitzar[8].Len = 200;
		Serialitzar[9].ColName = "Nivell_Codi";
		Serialitzar[9].DB_Type = DBType.varchar;
		Serialitzar[9].Len = 100;
	#endregion
		Deserialitzar = new clsColumn[9];
		for (int i = 0; i < 9; i++) Deserialitzar[i] = new clsColumn();
	#region Deserializable columns
		Deserialitzar[0].ColName = "Codi_TC";
		Deserialitzar[0].DB_Type = DBType.varchar;
		Deserialitzar[0].Len = 5;
		Deserialitzar[1].ColName = "Observacions";
		Deserialitzar[1].DB_Type = DBType.varchar;
		Deserialitzar[1].Len = 3000;
		Deserialitzar[2].ColName = "DataAlta";
		Deserialitzar[2].DB_Type = DBType.datetime;
		Deserialitzar[3].ColName = "DataBaixa";
		Deserialitzar[3].DB_Type = DBType.datetime;
		Deserialitzar[4].ColName = "Any_inici";
		Deserialitzar[4].DB_Type = DBType.tint;
		Deserialitzar[5].ColName = "Any_final";
		Deserialitzar[5].DB_Type = DBType.tint;
		Deserialitzar[6].ColName = "IdPare";
		Deserialitzar[6].DB_Type = DBType.tint;
		Deserialitzar[7].ColName = "Nom";
		Deserialitzar[7].DB_Type = DBType.nvarchar;
		Deserialitzar[7].Len = 200;
		Deserialitzar[8].ColName = "Nivell_Codi";
		Deserialitzar[8].DB_Type = DBType.varchar;
		Deserialitzar[8].Len = 100;
	#endregion
	}
}

Writing all this code by hand is error prone and very boring (a lethal task), that's the reason why a program generates it. SP parameters are obtained from the meta information of the SP that is stored in the database, but this means that the SPs must be in place when this class is generated. The other parameters are obtained from the user interface of the generator software. If a column is checked to serialize then it will appear in the list "Serialitzar", and so on. From this example one can see that the database access layer is formed by the clsData and a ton of derived classes (one for each table).

clsData is a class that covers a lot of functionality. There are parts that deal with web projects, but cause some troubles when used in other kind of project (WinForms for example). For that reason I use conditional compilation.

This conditional compilation affects to serialization and deserialization because those to features are not used in projects that are not web. For this reason I define a symbol in Project -> Properties -> Build -> Conditional Compilation symbols. The symbol must be defined in all configurations (Debug, Release...).

clsData holds the declaration of all variables involved in stored procedure calling and some more. Most of them are arrays of clsColumn. We can review the code to see the purpose of each variable. Classes that inherite from clsData initialices all those variables with the correct values, need to invoke a SP. An inherited class usually belongs to a one table.

    public class clsData
    {
        /// <summary>
        /// Prefix used in stored procedures parameters, 
        /// used to differentiate them from variables deffined inside SP.
        /// </summary>
        public string Prefix = "p";

        /// <summary>
        /// GET SP parameters, are the same of GETTOP.
        /// </summary>
        public clsColumn[] ParamsGET; 

        /// <summary>
        /// INS SP parameters
        /// </summary>
        public clsColumn[] ParamsINS;

        /// <summary>
        /// UPD SP parameters
        /// </summary>
        public clsColumn[] ParamsUPD;

        /// <summary>
        /// DEL SP parameters
        /// </summary>
        public clsColumn[] ParamsDEL;

        /// <summary>
        /// QUERY SP parameters
        /// </summary>
        public clsColumn[] ParamsQUERY;

        /// <summary>
        /// Columns returned by GET SP as a result of the SELECT
        /// </summary>
        public clsColumn[] ResultColumns;

        /// <summary>
        /// Connection string
        /// </summary>
        public string CadConnBBDD;

        /// <summary>
        /// GET SP full name, p. ex: CLIENTS_GET
        /// </summary>
        public string spGET;

        /// <summary>
        /// INS SP full name, p. ex: CLIENTS_INS
        /// </summary>
        public string spINS;

        /// <summary>
        /// UPD SP full name, p. ex: CLIENTS_UPD
        /// </summary>
        public string spUPD;

        /// <summary>
        /// DEL SP full name, p. ex: CLIENTS_DEL
        /// </summary>
        public string spDEL;

        /// <summary>
        /// QUERY SP full name, p. ex: CLIENTS_QUERY
        /// </summary>
        public string spQUERY;

        /// <summary>
        /// COUNT SP full name, p. ex: CLIENTS_COUNT
        /// </summary>
        public string spCOUNT;

        /// <summary>
        /// SqlConnection object. this is used if the programmer wants
        /// to use the same connection all time, without closing and opening it every time.
        /// </summary>
        public SqlConnection SQLConn = null;

        /// <summary>
        /// Transaction object. Optional, if null is not used.
        /// </summary>
        public SqlTransaction SQLTrans = null;

        /// <summary>
        /// Boolean that indicates if the table has an identity column
        /// </summary>
        public bool HasIdentity = false;

        /// <summary>
        /// Boolean that indicates if the table uses a the cache system.
        /// </summary>
        public bool UseCache = false;

        /// <summary>
        /// Boolean that indicates if the cache is automanaged.
        /// </summary>
        public bool AutoManageCache = true;

        /// <summary>
        /// Table name
        /// </summary>
        public string TableName = "";

        /// <summary>
        /// Name of the identity column
        /// </summary>
        public string Identity = "";

        /// <summary>
        /// List of columns that are serialized and send to the browser
        /// </summary>
        public clsColumn[] Serialitzar = null;

        /// <summary>
        /// List of columns that are deserialized when values arrive from the browser
        /// </summary>
        public clsColumn[] Deserialitzar = null;

        //SP Cache name, usually changes from project to project.
        //It must have the following parameters: Tablename varchar(50) and URL varchar(500)
        private string SP_Cache = "DI_EXP_CACHE_DEL";
}

When developing web applications an infraestructure to access the database is needed. In other words, a piece to connect the bussines logic to the database, to invoke the stored procedures (SP) that works with data. This layer has to be easy to work with, automated at maximum to avoid messing with the boring task of building the parameter list of the SPs by hand (a process also prone to errors). For this reason I've build the clsData.

clsData is the principal class of the data layer, it holds all of the methods to acces the database. It invokes the SPs, but as every SP has different parameters, other clases creates the definition for those parameters and inherite from clsData to add the methods to invoke the SPs.

So, clsData has the methods to acces and other clases that use inheritance has the definition needed to fill the methods of clsData. For this reason clsData has the declaration of the variables that later the other classes will initialize with the correct values. Those variables, in fact, are lists of objects that has information to build a SQL parameter. First of all I use a simple class to store type information (and when I say type I'm refering to database type), the DBType class.

    public static class DBType
    {
        public const int bit = 1;
        public const int tint = 2;
        public const int bigint = 3;
        public const int nvarchar = 4;
        public const int datetime = 5;
        public const int nchar = 6;
        public const int dec = 7;
        public const int varchar = 8;
        public const int chr = 9;
        public const int date = 10;
        public const int time = 11;
    }

There's also a class that describes a datatable column (that generates a SP parameter of the same type and name): clsColumn

    public class clsColumn
    {
        public string ColName= "";
        public bool Nullable = true;
        public int DB_Type;
        public string Format = "";
        public int Len = 0;
        public bool PK = false;
        public bool Identity = false;
        public byte Precision = 0;
        public byte Scale = 0;
    }

From now on, I will describe with more detail all the variables involved in the class clsData, and its inner workings.