Python RC4 Script - Printable Version

Code:
import struct



class RC4:

    def __init__(self, InitializeKeyStream = []):

        #Place the keystream in the following array

        #The following is just an example of a keystream

        if InitializeKeyStream == []:

             self.keystream = [0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF]

        else:

             self.keystream = InitializeKeyStream



        self.state = range(256)

        length = len(self.keystream)

        x = 0

        for i in range(256):

            #Randomization step

            x = (self.keystream[i % length] + self.state[i] + x) & 0xFF



            #Swap the array index i and x in the "state" array

            self.state[i], self.state[x] = (self.state[x], self.state[i])



    

    def crypt(self, string):

        #Create an array filled with 0's the same size as the length

        #of the string

        output = [0] * len(string)



        #Change the string into an array of numbers

        string = struct.unpack('%dB' % len(string), string)



        #Copy the keystream over to a local variable

        keys = [i for i in self.state]



        #Begin PRGA

        x = 0 ; y = 0

        for i, character in enumerate(string):

            x = (x + 1) & 0xFF

            y = (y + keys[x]) & 0xFF

            keys[x], keys[y] = (keys[y], keys[x])

            output[i] = character ^ keys[(keys[x] + keys[y]) & 0xFF]



        #Change the numbers into a string

        return struct.pack('%dB' % len(output), *output)