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Vigenère cipher method

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  • #1

    Vigenère cipher method

    Reading the thread Easy hide strings from casual viewing of Wayne Diamond I remembered one of my first programs that I wrote. This program was made by requeriment of a computer center manager to obfuscate the payroll file of own computer center in order to hide the information contained to his night operators.

    I can remember some details about the method used on this program, was a variation of Vigenère method for EBCDIC code, written with Assembler/360 on card punch, for a IBM main frame. Was in 1967. During the 60's decade this method was considered robust.

    Here is the version for ASCII using PB as language. Has a limitation, only is valid for first 127 ASCII characters.


    Code:
    '¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤
' Vigenere.bas                  by Jordi Vallès        version 1a     11/07/2008
'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
' Simple but efective and fast cypher method. Appropriate to hide information to
' operators or employees for prevent casual viewing of some critical information
' like payroll data, personnel files, etc.
' It's based on polyalphabetic substitution. This method is not inteded to
' protect sensitive data to experienced crackers and spies.
'
' This program works only for 127 first ASCII characters. For complete 256 chars
' need some modifications.
'
' Interesting information and history about Blaise de Vigenère (1523-1596) and
' cipher methods based on polyalphabetic substitution can be found on:
'   [URL="http://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher"]Wikipedia: Vigenère cipher[/URL] and
'   [URL="http://en.wikipedia.org/wiki/Polyalphabetic_cipher"]Wkipedia: Polyalphabetic cipher[/URL]
'
'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
'  - Program developed and tested with PowerBASIC for Windows (PB/Win 8.04) on
'    PC HP Pavilion m7760 1.80 GHz with Windows Vista Home Premium.
'¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤
' SED_PBWIN

#COMPILE EXE "Vigenere.exe"
#DIM ALL

'¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤
FUNCTION PBMAIN() AS LONG
   LOCAL textI, textC, textD, tkey AS STRING

   textI = "Go placidly amid the noise & haste, and remember what peace there may be in silence. " + _
           "As far as possible, without surrender, be on good terms with all persons. Speak your " + _
           "truth quietly and clearly; And listen to others, even the dull and ignorant; they too " + _
           "have their story."

   tkey = "This is my Key"

   CALL Cypher(tkey, textI, textC)

   CALL DeCypher(tkey, textC, textD)

   MSGBOX "- Original text:" + $CRLF + textI + $CRLF + $CRLF + _
          "- Text Cyphered:" + $CRLF + textC + $CRLF + $CRLF + _
          "- Text DeCyphered:" + $CRLF + textD
END FUNCTION

'¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤
SUB Cypher(keyt AS STRING, text1 AS STRING, text2 AS STRING)
   LOCAL i, j, k, n AS LONG
   LOCAL letter AS BYTE PTR

   letter = STRPTR(text1)
   text2  = SPACE$(LEN(text1))

   'loop through all characters of the text to be cyphered
   FOR j = 1 TO LEN(text1)
      'get the current character of the key
      k =  ASC(MID$(keyt, j MOD LEN(keyt)+1, 1))
      'get the numeric value of the current key character
      i = k - 31
      'shift the character of the text, rotate if necessary
      n = @letter + i
      IF n > 126 THEN n = n - 95
      'append to the ciphered string
      MID$(text2,j) = CHR$(n)
      INCR letter
   NEXT j
END SUB

'¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤
SUB DeCypher(keyt AS STRING, text1 AS STRING, text2 AS STRING)
   LOCAL i, j, k, n AS LONG
   LOCAL letter AS BYTE PTR

   letter = STRPTR(text1)
   text2  = SPACE$(LEN(text1))

   'loop through all characters of the encrypted string
   FOR j = 1 TO LEN(text1)
      'get the current character of the key
      k =  ASC(MID$(keyt, j MOD LEN(keyt)+1, 1))
      'get the numeric value of the current key character
      i = k - 31
      'shift the character of the text, rotate if necessary
      n = @letter - i
      IF n < 32 THEN n = n + 95
      'append to the deciphered string
      MID$(text2,j) = CHR$(n)
      INCR letter
   NEXT j
END SUB

'¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤
'eof
    Tags: None
  • #2
    Thank you very much,

    till know I just read about this cypher, now I can finally understand it

    Here comes little performance tweak, I get 7x - 8x faster execution speed comparing to original.

    Whole trick is in my favourite technique of array memory overlays.
    When tested with 8000 repetitions of original string ( ~= 2MB of data ), speed gain in this version is about 7x to 8x.


    Petr

    Code:
    '¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤
' Vigenere.bas                  by Jordi Valle`s        version 1b     13/07/2008
'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
' Simple but efective and fast cypher method. Appropriate to hide information to
' operators or employees for prevent casual viewing of some critical information
' like payroll data, personnel files, etc.
' It's based on polyalphabetic substitution. This method is not inteded to
' protect sensitive data to experienced crackers and spies.
'
' This program works only for 127 first ASCII characters. For complete 256 chars
' need some modifications.
'
' Interesting information and history about Blaise de Vigene`re (1523-1596) and
' cipher methods based on polyalphabetic substitution can be found on:
'   Wikipedia: Vigene`re cipher and
'   Wkipedia: Polyalphabetic cipher
'
'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
'  - Program developed and tested with PowerBASIC for Windows (PB/Win 8.04) on
'    PC HP Pavilion m7760 1.80 GHz with Windows Vista Home Premium.
'¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤
' v1b - Minor tweaks in performance of the algo, speed gain about 7x - 8x
'       by Petr Schreiber
'¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤
' SED_PBWIN

#COMPILE EXE "Vigenere.exe"
#DIM ALL

'¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤
FUNCTION PBMAIN() AS LONG
   LOCAL textI, textC, textD, tkey AS STRING

   textI = "Go placidly amid the noise & haste, and remember what peace there may be in silence. " + _
           "As far as possible, without surrender, be on good terms with all persons. Speak your " + _
           "truth quietly and clearly; And listen to others, even the dull and ignorant; they too " + _
           "have their story."

   tkey = "This is my Key"

   CALL Cypher(tkey, textI, textC)

   CALL DeCypher(tkey, textC, textD)

   MSGBOX "- Original text:" + $CRLF + textI + $CRLF + $CRLF + _
          "- Text Cyphered:" + $CRLF + textC + $CRLF + $CRLF + _
          "- Text DeCyphered:" + $CRLF + textD

END FUNCTION

'¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤
SUB Cypher(keyt AS STRING, text1 AS STRING, text2 AS STRING)
   REGISTER j AS LONG, i AS LONG
   LOCAL n AS LONG

   DIM ByteKeyT(1 TO LEN(keyt)) AS LOCAL BYTE AT STRPTR(keyt)
   DIM ByteTextIn(1 TO LEN(Text1)) AS LOCAL BYTE AT STRPTR(text1)

   'preallocate characters
   text2  = SPACE$(LEN(text1))

   DIM ByteTextOut(1 TO LEN(text2)) AS LOCAL BYTE AT STRPTR(text2)


   'loop through all characters of the text to be cyphered
   FOR j = 1 TO LEN(text1)

      'get the current character of the key
      i = ByteKeyT(j MOD LEN(keyt)+1)-31

      'get the numeric value of the current key character
      n = ByteTextIn(j) + i
      
      'shift the character of the text, rotate if necessary
      IF n > 126 THEN n = n - 95

      'insert character to the ciphered string
      ByteTextOut(j) = n

   NEXT j

END SUB

'¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤
SUB DeCypher(keyt AS STRING, text1 AS STRING, text2 AS STRING)
   REGISTER j AS LONG, i AS LONG
   LOCAL n AS LONG

   DIM ByteKeyT(1 TO LEN(keyt)) AS LOCAL BYTE AT STRPTR(keyt)
   DIM ByteTextIn(1 TO LEN(Text1)) AS LOCAL BYTE AT STRPTR(text1)

   'preallocate characters
   text2  = SPACE$(LEN(text1))

   DIM ByteTextOut(1 TO LEN(text2)) AS LOCAL BYTE AT STRPTR(text2)

   'loop through all characters of the encrypted string
   FOR j = 1 TO LEN(text1)
      'get the current character of the key
      i = ByteKeyT(j MOD LEN(keyt)+1) - 31

      'get the numeric value of the current key character
      n = ByteTextIn(j) - i
      'shift the character of the text, rotate if necessary
      IF n < 32 THEN n = n + 95

      'insert to the deciphered string
      ByteTextOut(j) = n

   NEXT j

END SUB

'¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤
'eof
    [email protected]

    Comment

    • #3
      Petr, a great lesson for programmers about speed. On my PC the gain speed is 7x times. Using sentences like
      Code:
      DIM ByteTextIn(1 TO LEN(Text1)) AS LOCAL BYTE AT STRPTR(text1)
      is not necessary to use pointers and simplify a lot the code. Thanks.
      Jordi
      Last edited by Jordi Vallès; 16 Jul 2008, 06:11 AM.

      Comment

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