DOCUMENT:Q130005  13-AUG-1999  [foxpro]
TITLE   :HOWTO: Use a Custom Class to Encrypt Passwords
PRODUCT :Microsoft FoxPro
PROD/VER:
OPER/SYS:
KEYWORDS:kbcode kbnokeyword kbvfp300 kbvfp500 kbvfp600

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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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