GAMBAS BOOK 3.19.5

In this project, you can encrypt or decrypt a file using a high-quality encryption algorithm. It is always checked whether the system supports the key used.

If the selected file was encrypted with a strong password, then the encrypted file is saved under the original name with a new extension .enc in the same directory. The original file is not deleted in the presented project.

Figure 6.10.2.1: Main programme

In the dialogue you can select the file to be encrypted:

Figure 6.10.2.2: File selection dialogue box

In another dialogue the password has to be entered:

Figure 6.10.2.3: Password request

You will be informed about the success or failure in encrypting or decrypting the file:

Figure 6.10.2.4: Success message

Figure 6.10.2.5: Error message

The source codes are given in full:

' Gambas class file
 
Private sMethod As String = "BF-CBC" ' Definition of the encryption algorithm
Private sCurrentFile As String
 
Public Sub Form_Open()
  FMain.Caption = ("Encrypting and decrypting files")
  FMain.Resizable = False
 
  If Cipher.List.Find(sMethod) = -1 Then
     Message.Error(Subst("\n&1 &2 &3", ("The system does not support the Cipher-Method:"), sMethod, "!"))
     FMain.Close()
  Else
     lblMethod.Text = Subst("&1 &2", ("Cipher-Method is"), sMethod)
  Endif
End
 
Public Sub btnEncryptFile_Click()
 
  Dim sPassword, sSalt, sPath, sMessage As String
 
  Dialog.Title = ("Select a file!")
  Dialog.Path = Application.Dir
  If Dialog.OpenFile() Then Return
 
  sPassword = GetPassword() ' Password from a password dialog
  If sPassword Then
     sSalt = "123Abc#*" ' Free defined string (8 bytes)
     sPath = Dialog.Path & ".enc"
     btnEncryptFile.Text = ("Encrypt a selected file ... in progress")
       File.Save(sPath, Cipher[sMethod].EncryptSalted(File.Load(Dialog.Path), sPassword, sSalt))
       Wait 1
     btnEncryptFile.Text = ("Encrypt a selected file ...")
     sMessage = Subst("&1\n&2\n&3", ("File"), File.Name(Dialog.Path), ("has been successfully encrypted!"))
     Message.Info(sMessage)
  Else
     Message.Warning(("The password dialog was aborted by the user\nor the password is empty!"))
     Return
  Endif
 
  Catch
    Message.Error(Error.Text)
    btnEncryptFile.Text = ("Encrypt a selected file ...")
End
 
Public Sub btnDecryptFile_Click()
 
  Dim sPassword, sPath, sMessage As String
 
  Dialog.Title = ("Select a file!")
  Dialog.Path = Application.Dir
  If Dialog.OpenFile() Then Return
 
  sPassword = GetPassword() ' Password from a password dialog
  If sPassword Then
     If Dialog.Path Ends ".enc" Then
        sPath = Replace(Dialog.Path, ".enc", "")
     Else
        sPath = Dialog.Path
     Endif
     btnDecryptFile.Text = ("Decrypt a selected file... in progress")
       File.Save(sPath, Cipher[sMethod].DecryptSalted(File.Load(Dialog.Path), sPassword))
       Wait 1
     btnDecryptFile.Text = ("Decrypt a selected file ...")
     sMessage = Subst("&1\n&2\n&3", ("File"), File.Name(Dialog.Path), ("has been successfully decrypted!"))
     Message.Info(sMessage)
  Else
     Message.Warning(("The password dialog was aborted by the user\nor the password is empty!"))
     Return
  Endif
 
  Catch
    Message.Error(Error.Text)
    btnDecryptFile.Text = ("Decrypt a selected file ...")
End
 
Public Sub btnPWInformation_Click()
  ShowPWInformation()
End
 
Public Sub btnHelp_Click()
  ShowHelp()
End
 
Public Sub Form_Resize()
  Separator1.Width = FMain.ClientWidth
End
 
Private Sub ShowPWInformation()
 
  Dim sMessage As String
 
  sMessage = "<hr>"
  sMessage &= "<p>"
  sMessage &= Subst("&1 ", ("A"))
  sMessage &= "<font color='red'>" & ("strong") & "</font>"
  sMessage &= Subst(" &1", ("password contains at least:"))
  sMessage &= "<p>"
  sMessage &= ("- 8 characters,") & "<br>"
  sMessage &= ("- a small letter,") & "<br>"
  sMessage &= ("- one uppercase letter,") & "<br>"
  sMessage &= ("- one digit and") & "<br>"
  sMessage &= ("- a special character from the set {+ # _ @ ! ? § $ % *}")
  sMessage &= "<hr>"
 
  Message.Info(sMessage)
 
End
 
Private Sub ShowHelp()
 
  Dim sMessage As String
 
  sMessage = "<hr>"
  sMessage &= "<p>"
  sMessage &= ("The encrypted file retains its original name,\n")
  sMessage &= ("to which the extension 'enc' is appended.")
  sMessage &= "<hr><p>"
  sMessage &= ("The decrypted file gets its original name. \n")
  sMessage &= ("An existing file with the original name will be overwritten!")
  sMessage &= "<hr>"
 
  Message.Info(sMessage)
 
End
 
Private Function GetPassword() As String
 
  Dim hFormLogin As New FLogin
 
  Return hFormLogin(("Enter a password!")) ' Start dialog ...
 
End
 
Public Sub btnClose_Click()
  FMain.Close()
End

The source code of the dialogue for entering the password can be found in the file FLogin.class, whose most important procedure is _call(…):

' Gambas class file
 
Public Sub _call(sMessage As String) As String
  lblMessage.Text = sMessage
  ' Returns when one of the buttons is clicked! The return value is specified in the Me.Close() call and
  ' indicates whether or not it was canceled.
  Select Me.ShowModal()
    Case 1
      Return txtPassword.Text
    Case 0
      Return ""
  End Select
 
End
 
Public Sub btnOK_Click()
  Me.Close(1)
End
 
Public Sub btnCancel_Click()
' 0 is also indicated by the cross in the window bar is returned - this corresponds to an abort.
  Me.Close(0)
End
 
Public Sub txtPassword_Activate()
  btnOK_Click() ' Me.Close(1)
End