' 
' RC4crypt.inc 
' (C) 2003-10-04 Martin Wehner 
' 
' Contact:  mailto:martin.wehner@firemail.de 
' Homepage: http://mitglied.lycos.de/maweso/ 
' 
' RC4 is a stream cipher symmetric key algorithm. It was 
' developed in 1987 by Ronald Rivest and kept as a trade 
' secret by RSA Data Security. On September 9, 1994, the 
' RC4 algorithm was anonymously posted on the Internet on 
' the Cyperpunks' Anonymous Remailers List. 
' RC4 uses a variable length key from 1 to 256 bytes to 
' initialize a 256-byte state table. The state table is 
' used for subsequent generation of pseudo-random bytes 
' and then to generate a pseudo-random stream which is 
' XORed with the plaintext to give the ciphertext. Each 
' element in the state table is swapped at least once. The 
' RC4 key is often limited to 40 bits, because of export 
' restrictions but it is sometimes used as a 128 bit key. 
' It has the capability of using keys between 1 and 2048 
' bits. 
' Analysis shows that the period of the cipher is 
' overwhelmingly likely to be greater than 10^100. Eight 
' to sixteen machine operations are required per output 
' byte, and the cipher can be expected to run very quickly 
' in software. Independent analysts have scrutinized the 
' algorithm and it is considered secure. RC4 is used in 
' many commercial software packages. 
' 
' The type definition below is an adaptation of the RC4 
' algorithm to RapidQ Basic. If you want to use this 
' component then you must first create an object of type 
' QRC4. After that you must call the procedure Init() to 
' initialize the object with the key. If you now call the 
' function Pipe() with a string then the string is encoded 
' and returned by the function. 
' If you want to decode then simply execute the same steps 
' again but call the function Pipe() with the encoded 
' string. 
' This component can process data streams. Encode or 
' decode data streams by calling the function Pipe() for 
' each stream element. You are free with the size of the 
' data packets because (Pipe(s) & Pipe(t)) is always equal 
' to Pipe(s & t). 
' 
' Example: 
'   $INCLUDE "RC4crypt.inc" 
'   DEFSTR k = "1234567890"   ' This is the key 
'   DEFSTR s = "abcdefghijklmnopqrstuvwxyz" 
'   DEFSTR t = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" 
'   DIM rc4 AS QRC4 
'   rc4.Init(k)   ' Initialize RC4 object with the key 
'   s = rc4.Pipe(s)   ' Encode stream element s 
'   t = rc4.Pipe(t)   ' Encode stream element t 
'   rc4.Init(k)   ' Initialize RC4 object with the key again 
'   ShowMessage(rc4.Pipe(s & t))   ' Concatenate and decode 
' 
' DISCLAIMER: ABSOLUTELY NO WARRANTY IS GIVEN FOR THIS 
' COMPONENT! USE THIS TYPE DEFINITION AT YOUR OWN RISK! 
' 

TYPE QRC4 EXTENDS QOBJECT
  PRIVATE:
    stateTable(256) AS BYTE
    randomIndex AS BYTE
    i AS LONG
    j AS LONG
    k AS LONG
    n AS LONG

  PUBLIC:
    SUB Reset
      FOR QRC4.i = 0 TO 255
        QRC4.stateTable(QRC4.i) = QRC4.i
      NEXT

      QRC4.i = 0
      QRC4.j = 0
    END SUB

    SUB Init (key AS STRING)
      QRC4.Reset

      QRC4.n = LEN(key)
      IF 0 < QRC4.n THEN
        FOR QRC4.i = 0 TO 255
          QRC4.k = (QRC4.i MOD QRC4.n) + 1
          QRC4.j = (QRC4.j + QRC4.stateTable(QRC4.i) + ASC(key[QRC4.k])) AND 255
          SWAP QRC4.stateTable(QRC4.i), QRC4.stateTable(QRC4.j)
        NEXT

        QRC4.i = 0
        QRC4.j = 0
      END IF
    END SUB

    FUNCTION Pipe (str AS STRING) AS STRING
      result = ""

      QRC4.n = LEN(str)
      FOR QRC4.k = 1 TO QRC4.n
        QRC4.i = (QRC4.i + 1) AND 255
        QRC4.j = (QRC4.j + QRC4.stateTable(QRC4.i)) AND 255
        QRC4.randomIndex = (QRC4.stateTable(QRC4.i) + QRC4.stateTable(QRC4.j)) AND 255
        SWAP QRC4.stateTable(QRC4.i), QRC4.stateTable(QRC4.j)

        result = result & CHR$(ASC(str[QRC4.k]) XOR QRC4.stateTable(QRC4.randomIndex))
      NEXT
    END FUNCTION

  CONSTRUCTOR
    Reset
  END CONSTRUCTOR
END TYPE
 
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