HOWTO: Use a Custom Class to Encrypt Passwords (130005)


The information in this article applies to:

  • Microsoft Visual FoxPro for Windows 3.0
  • Microsoft Visual FoxPro for Windows 5.0
  • Microsoft Visual FoxPro for Windows 6.0
This article was previously published under Q130005

SUMMARY

Many applications require a level of security that necessitates password protection. Password validation requires comparing passwords to a list of acceptable passwords, normally stored in table form. This article demonstrates how to create a custom class that encrypts passwords and allows passwords to be manipulated in encrypted form, allowing a higher level of security.

MORE INFORMATION

The following code sample demonstrates how to use a Custom Class to encrypt and decrypt a password. The password can then be used in encrypted form for added security.

Code Sample

* Beginning of pwdclass.prg
*
* To use this program, run it; then type the password in the upper-left
* text box, and press ENTER. The Encrypt_It procedure in the FxtoolFormdes
* instance of the PASS_WORD class is called in the valid of the text box.
* The encrypted password is displayed in the lower-left text.
* Pressing the Decrypt It! button calls the Decrypt_It procedure
* in the custPassword instance of the PASS_WORD class. The resulting
* value is displayed in the text box below the Decrypt It! button.
*************

frmPwdform = CREATEOBJECT("pwdform") && Instantiate class from pwdform.

frmPwdform.VISIBLE = .T.
READ EVENTS

* Define Form Class:

DEFINE CLASS pwdform AS FORM

   CAPTION = "Password Encryption Example"
   ADD OBJECT custPassword AS PASS_WORD  && Add Password object to form.

   HEIGHT = 130
   WIDTH = 350
   AUTOCENTER = .T.

   ADD OBJECT txtText1 AS TEXTBOX WITH ;
      HEIGHT = 25, ;
      LEFT = 25, ;
      TOP = 20, ;
      WIDTH = 125, ;
      PASSWORDCHAR = "*", ;
      NAME = "txtText1"

   ADD OBJECT txtText2 AS TEXTBOX WITH ;
      HEIGHT = 25, ;
      LEFT = 25, ;
      TOP = 72, ;
      WIDTH = 125, ;
      READONLY = .T., ;
      NAME = "txtText2"

* Command button to demonstrate the call to Decrypt_It procedure is
* contained in cmdCommand1.click in the following procedure:

   ADD OBJECT cmdCommand1 AS COMMANDBUTTON WITH ;
      TOP = 20, ;
      LEFT = 200, ;
      HEIGHT = 29, ;
      WIDTH = 125, ;
      CAPTION = "Decrypt It!", ;
      NAME = "cmdCommand1"

* Textbox to display Unencrypted password:

   ADD OBJECT txtText3 AS TEXTBOX WITH ;
      CONTROLSOURCE = "THISFORM.custPassword.cUnencrypted", ;
      HEIGHT = 25, ;
      LEFT = 200, ;
      READONLY = .T., ;
      TOP = 72, ;
      WIDTH = 125, ;
      NAME = "Text3"

   PROCEDURE txtText1.LOSTFOCUS
      THISFORM.custPassword.Encrypt_It(TRIM(THIS.VALUE))
      THISFORM.txtText2.VALUE = THISFORM.custPassword.cEncrypted
      THISFORM.cmdCommand1.SETFOCUS
   ENDPROC

   PROCEDURE cmdCommand1.CLICK
      THISFORM.custPassword.Decrypt_It(THISFORM.custPassword.cEncrypted)
      THISFORM.REFRESH
      THISFORM.txtText1.SETFOCUS
   ENDPROC

   PROCEDURE DESTROY
      CLEAR EVENTS
   ENDPROC

ENDDEFINE

DEFINE CLASS PASS_WORD AS CUSTOM

   HEIGHT = 17
   WIDTH = 100
   cUnencrypted = ""
   cEncrypted = ""
   NAME = "Password"

   PROCEDURE Encrypt_It     && Call this to encrypt password
      PARAMETERS cPassword
      cEncrypted_password = ''
      FOR i = 1 TO LEN(cPassword)
         cLetter = SUBSTR(cPassword, i, 1)
         cEncrypted_password = cEncrypted_password + ;
            CHR((ASC(cLetter)*2)+5)      && Arbitrary encryption formula
      NEXT i
      THIS.cEncrypted = cEncrypted_password

   ENDPROC

   PROCEDURE Decrypt_It     && Call this to Decrypt password
      PARAMETERS cPassword
      cUnencrypted_password = ''
      FOR i = 1 TO LEN(cPassword)
         cLetter = SUBSTR(cPassword, i, 1)
         cUnencrypted_password = cUnencrypted_password + ;
            CHR((ASC(cLetter)-5)/2)    && Reverse of encryption formula
      NEXT i
      THIS.cUnencrypted = cUnencrypted_password

   ENDPROC

ENDDEFINE
* End of pwdclass.prg
Modification Type:MinorLast Reviewed:7/13/2004
Keywords:kbcode kbhowto KB130005
©2004 Microsoft Corporation. All rights reserved.