Q130005: HOWTO: Use a Custom Class to Encrypt Passwords

Article: Q130005
Product(s): Microsoft FoxPro
Version(s): 
Operating System(s): 
Keyword(s): kbcode kbnokeyword kbvfp300 kbvfp500 kbvfp600
Last Modified: 13-AUG-1999

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, versions 3.0, 5.0, 6.0 
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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


Additional query words:

======================================================================
Keywords          : kbcode kbnokeyword kbvfp300 kbvfp500 kbvfp600 
Technology        : kbVFPsearch kbAudDeveloper kbVFP300 kbVFP500 kbVFP600
Issue type        : kbhowto

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