Can anyone help with Encrypt login?

Public Class clsEncryption
    Public Shared Function encryptThis(ByVal str As String, ByVal bt As Byte) As String
        Dim encrypt As String = ""

        'USING COALESCING OPERATOR CONDITION
        bt = If((bt > 0 AndAlso bt <= 13), bt, Convert.ToByte(13))

        Dim chr As Char() = Str.ToString().ToCharArray()

        For i As Integer = 0 To str.Length - 1
            'CONVERTING CHAR TO INT
            Dim x As Integer = Convert.ToInt32(Chr(i))
            'CONVERTING INT TO CHAR
            encrypt = encrypt + Convert.ToChar((255 - (x + bt - i)))
        Next
        Return encrypt
    End Function

    Public Shared Function decryptThis(ByVal str As String, ByVal bt As Byte) As String
        Dim encrypt As String = ""

        'USING COALESCING OPERATOR CONDITION
        bt = If((bt > 0 AndAlso bt <= 13), bt, Convert.ToByte(13))

        Dim chr As Char() = str.ToString().ToCharArray()

        For i As Integer = 0 To str.Length - 1
            Dim x As Integer = Convert.ToInt32(chr(i))
            encrypt = encrypt + Convert.ToChar(255 + (-x - bt + i))
        Next
        Return encrypt
    End Function
End Class

Private Sub cmdlogin_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdlogin.Click
       On Error Resume Next
       Dim timex As String
       Dim isigroup As DataTable
       objdata = New clsMSSQL
       isigroup = objdata.QueryDatabase("SELECT * FROM Userx WHERE Username='" & txtuser.Text & "' AND Userpass ='" & txtpassword.Text & "'")
       If isigroup.Rows.Count > 0 Then
           For i = 0 To isigroup.Rows.Count - 1
               If isigroup.Rows(i)("username") <> txtuser.Text Or isigroup.Rows(i)("userpass") <> txtpassword.Text Then
                   MsgBox("Λάθος Όνομα Χρήστη ή Κωδικού !", MsgBoxStyle.Information, "Προσοχή.....")
                   xcountx = xcountx + 1
                   If xcountx >= 3 Then
                       MsgBox("Έχεις χρησιμοποιήσει όλες τις προσπάθειες !", MsgBoxStyle.Exclamation, "Προσοχή.....")
                       End
                   End If
                Exit Sub