Q98700: Bit Manipulation in FoxPro for Data Encryption

Article: Q98700
Product(s): Microsoft FoxPro
Version(s): 2.00 2.50 2.50a | 2.50 2.50a 3.0
Operating System(s): 
Keyword(s): kbcode
Last Modified: 25-AUG-1999

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 3.0 
- Microsoft FoxPro for MS-DOS, versions 2.0, 2.5, 2.5a 
- Microsoft FoxPro for Windows, versions 2.5, 2.5a 
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SUMMARY
=======

Because FoxPro uses characters that have values between 0 and 255 (1 byte),
these character values and thus the bit pattern can be manipulated once the
characters are converted to numeric values using the ASC() command. This sort of
operation could be used for data encryption.

The program below illustrates how the bit pattern of an entire string can be
swapped by rotating the bit patterns of each character one at a time and placing
the resulting characters in reverse order in the output string.

MORE INFORMATION
================

     *PROGRAM SHIFTSTR.PRG
     * (RUN BY TYPING 'DO SHIFTSTR.PRG WITH <STRING>')
     PARAMETERS A
     ?A
     A=shift(A)
     ?A

     PROCEDURE shift
     PARAMETERS in_str
     result=[]
     SET DECIMAL TO 0
     lngth=LEN(in_str)
     DIMENSION out_array(lngth)
     FOR char_num=1 TO lngth
        x=ASC(SUBSTR(in_str,char_num,1))
        y=0
        FOR bit=7 TO 0 STEP -1
           IF x>((2^bit)-1)
              x=x-(2^bit)
              y=y+(2^(7-bit))
           ENDIF
        ENDFOR
        out_array(lngth-char_num+1)=CHR(y)
     ENDFOR
     FOR char_num=1 TO lngth
        result=result+out_array(char_num)
     ENDFOR
     RETURN result

Additional query words: VFoxWin FoxDos FoxWin encrypt password

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Keywords          : kbcode 
Technology        : kbVFPsearch kbAudDeveloper kbFoxproSearch kbZNotKeyword3 kbFoxPro200DOS kbFoxPro250DOS kbFoxPro250aDOS kbFoxPro250 kbFoxPro250a kbVFP300
Version           : 2.00 2.50 2.50a | 2.50 2.50a 3.0

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