string message;
       string key;
 
       key = this.key.Text;
       message = this.message.Text;
 
       System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();
 
       byte[] keyByte = encoding.GetBytes(key);
 
        HMACSHA1 hmacsha1 = new HMACSHA1(keyByte);
        byte[] messageBytes = encoding.GetBytes(message);
        byte[] hashmessage = hmacmd5.ComputeHash(messageBytes);
        this.hmac1.Text = ByteToString(hashmessage);
        hashmessage = hmacsha1.ComputeHash(messageBytes);
        this.hmac2.Text = ByteToString(hashmessage);

   Imports System.Security.Cryptography
 
        Dim key As String = "schlüssel"
        Dim message As String = "Text"        
        Dim encoding As System.Text.ASCIIEncoding = New _
          System.Text.ASCIIEncoding()
        Dim keyByte As Byte() = System.Text.ASCIIEncoding.ASCII.GetBytes(key)
        Dim HMACSHA1 As HMACSHA1 = New HMACSHA1(keyByte)
        Dim messageBytes As Byte() = encoding.GetBytes(message)
        Dim hashmessage As Byte() = HMACSHA1.ComputeHash(messageBytes)
        mac.Text = System.Text.Encoding.Default.GetString(hashmessage)

Joachim