Generate Key using Cipher Block Chaining MAC

[danishce]

I want to encrypt the ASCII message using Cipher Block Chaining MAC and generate the 8 byte key.How can i achieve this?
Thanks:
Danish Majid

[danishce]

Basically i am developing a message interface document and send/receive data to server from my application using winsock TCP/IP. There is a MAC field in the document which apply CBC MAC encryption to plain text that i send to server and return 8 byte key in output.Then i send this 8 byte key with my plain text and the server check my message with their interface. At the server end their is a third party involved which developed server interface so they check my message and gives reply to me either transaction is OK/CANCEL.
When i am using TripleDES it generate 8 byte MAC Key but i want to generate CBC MAC key using DES.The code for TripleDES key is:
dim plaintext as string
plainText = "46546544798752 123449879843132 187984132146546 4"
Dim data As Byte() = ASCIIEncoding.A SCII.GetBytes(p lainText)
Dim mac3des As New MACTripleDES
Dim result As Byte() = mac3des.Compute Hash(data)
output=(result= 52637299) 8 byte

Code for DES key is:
'Dim DES As New DESCryptoServic eProvider
'' Set the cipher mode.
'DES.Mode = CipherMode.CBC
'Dim data As Byte() = ASCIIEncoding.A SCII.GetBytes(p lainText)
'If key Is Nothing Then
' DES.GenerateKey ()
' DES.GenerateIV( )
' key = DES.Key
' iv = DES.IV
'Else
' DES.Key = key
' DES.IV = iv
'End If

'Dim DESEncrypt As ICryptoTransfor m = DES.CreateEncry ptor()
'Dim ms As New MemoryStream
'Dim cs As CryptoStream = New CryptoStream(ms , DESEncrypt, CryptoStreamMod e.Write)
'cs.Write(data, 0, data.Length)
'cs.FlushFinalB lock()
'ms.Position = 0
'Dim result(ms.Lengt h - 1) As Byte
'ms.Read(result , 0, ms.Length)
'cs.Close()
'Dim keyout As Byte()
'keyout = result
output=same length as plain text,i want keyout should be 8 byte.
I hope you understand this.