Class: Arcfour

Inherits:
Object
  • Object
show all
Defined in:
lib/prawn/arcfour.rb

Overview

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.

Instance Method Summary collapse

Constructor Details

#initialize(key) ⇒ Arcfour

Returns a new instance of Arcfour.



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# 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

Instance Method Details

#encrypt(string) ⇒ Object 



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# File 'lib/prawn/arcfour.rb', line 38

def encrypt(string)
  string.unpack('c*').map{|byte| byte ^ key_byte}.pack('c*')
end