bytExpression1 = Encoding.ASCII.GetBytes(Expression1)

 Private Function MD5(ByVal Key As String) As String
        Dim tmpSource() As Byte
        Dim tmpHash() As Byte
        Dim md As New MD5CryptoServiceProvider
        tmpSource = ASCIIEncoding.ASCII.GetBytes(Key)
 
        tmpHash = md.ComputeHash(tmpSource)
 
        Return ByteArrayToString(tmpHash)
 
    End Function
    Private Function ByteArrayToString(ByVal arrInput() As Byte) As String
        Dim i As Integer
        Dim sOutput As New StringBuilder(arrInput.Length)
        For i = 0 To arrInput.Length - 1
            sOutput.Append(arrInput(i).ToString("x2"))
        Next
        Return sOutput.ToString()
    End Function

Private Function MD5(Key As String) As String
    Dim strHash           As String
    Dim lngResult         As Long
    Dim lngHHash          As Long
    Dim lngHCryptProvider As Long
    Dim lngHashLength     As Long
    Dim i                 As Long
    Dim abytBuffer()      As Byte
    '
    Const cstBufferSize As Long = 256
    '
    ReDim abytBuffer(0 To cstBufferSize)
    '
    lngResult = CryptAcquireContext(lngHCryptProvider, vbNullString, _
      MS_ENHANCED_PROV, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT)
    If lngResult = 1 Then
        lngResult = CryptCreateHash(lngHCryptProvider, CALG_MD5, 0, 0, lngHHash)
        If lngResult = 1 Then
            lngResult = CryptHashData(lngHHash, Key, Len(Key), 0)
            If lngResult = 1 Then
                lngResult = CryptGetHashParam(lngHHash, HP_HASHSIZE, abytBuffer( _
                  0), cstBufferSize, 0)
                If lngResult = 1 Then
                    lngHashLength = abytBuffer(0)
                    lngResult = CryptGetHashParam(lngHHash, HP_HASHVAL, _
                      abytBuffer(0), cstBufferSize, 0)
                    If lngResult = 1 Then
                        For i = 0 To (lngHashLength - 1)
                            If abytBuffer(i) < 16 Then
                                strHash = strHash & "0"
                            End If
                            strHash = strHash & LCase(Hex(abytBuffer(i)))
                        Next i
                    End If
                End If
            End If
        End If
    End If
    '
    MD5 = strHash
End Function
 
'Private Function HMAC_MD5(Key As String, Data As String) As String
    Dim iPad As String
    Dim oPad As String
    '
    Const MD5_BLOCK_LEN As Long = &H40&
    '
    If Len(Key) > MD5_BLOCK_LEN Then
        Key = Pack(MD5(Key))
    End If
    '
    Key = Key & String((MD5_BLOCK_LEN - Len(Key)), vbNullChar)
    '
    iPad = String(MD5_BLOCK_LEN, Chr$(&H36))
    oPad = String(MD5_BLOCK_LEN, Chr$(&H5C))
    '
    iPad = StrXor(Key, iPad)
    oPad = StrXor(Key, oPad)
    '
    HMAC_MD5 = MD5(oPad & Pack(MD5(iPad & Data)))
End Function
 
Private Function StrXor(Expression1 As String, Expression2 As String) As String
    Dim strReturn        As String
    Dim i                As Long
    Dim bytReturn()      As Byte
    Dim bytExpression1() As Byte
    Dim bytExpression2() As Byte
    '
    If Len(Expression1) = Len(Expression2) Then
        bytExpression1() = StrConv(Expression1, vbFromUnicode)
        bytExpression2() = StrConv(Expression2, vbFromUnicode)
        '
        ReDim bytReturn(LBound(bytExpression1()) To UBound(bytExpression1()))
        '
        For i = LBound(bytExpression1()) To UBound(bytExpression1())
            bytReturn(i) = bytExpression1(i) Xor bytExpression2(i)
        Next i
        '
        strReturn = StrConv(bytReturn(), vbUnicode)
    End If
    '
    StrXor = strReturn
End Function
 
Private Function Pack(strData As String) As String
    Dim strPack As String
    Dim lngLen  As Long
    Dim lngPos  As Long
    '
    lngLen = Len(strData)
    lngPos = 1
    '
    Do While (lngPos < lngLen)
        strPack = strPack & Chr$(Val("&H" & Mid(strData, lngPos, 2)))
        lngPos = lngPos + 2
    Loop
    '
    Pack = strPack
End Function