class Arcfour

Implementation of the “ARCFOUR” algorithm (“alleged RC4 (tm)”). Implemented as described at: www.mozilla.org/projects/security/pki/nss/draft-kaukonen-cipher-arcfour-03.txt

“RC4” is a trademark of RSA Data Security, Inc.

Copyright August 2009, Brad Ediger. All Rights Reserved.

This is free software. Please see the LICENSE and COPYING files for details.

Public Class Methods

new(key) click to toggle source
# File lib/prawn/arcfour.rb, line 12
def initialize(key)
  # Convert string key to Array of integers
  key = key.unpack('c*') if key.is_a?(String)

  # 1. Allocate an 256 element array of 8 bit bytes to be used as an S-box
  # 2. Initialize the S-box.  Fill each entry first with it's index
  @sbox = (0..255).to_a
  
  # 3. Fill another array of the same size (256) with the key, repeating
  #    bytes as necessary.
  s2 = []
  while s2.length < 256
    s2 += key
  end
  s2 = s2[0, 256]

  # 4. Set j to zero and initialize the S-box
  j = 0
  (0..255).each do |i|
    j = (j + @sbox[i] + s2[i]) % 256
    @sbox[i], @sbox[j] = @sbox[j], @sbox[i]
  end

  @i = @j = 0
end

Public Instance Methods

encrypt(string) click to toggle source
# File lib/prawn/arcfour.rb, line 38
def encrypt(string)
  string.unpack('c*').map{|byte| byte ^ key_byte}.pack('c*')
end