Class: Arcfour

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

Instance Method Summary collapse

Constructor Details

#initialize(key) ⇒ Arcfour

Returns a new instance of Arcfour.



11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
 
# File 'lib/prawn/security/arcfour.rb', line 11

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) ⇒ String

Encrypt string.

Parameters:

  • string (String)

Returns:

  • (String) 


41
42
43
 
# File 'lib/prawn/security/arcfour.rb', line 41

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