Arcfourを実装してみました

新山さんがここで実装してるのを見て、僕もRubyで実装してみました。

#!/usr/bin/env ruby

require 'test/unit'
require 'enumerator'

class Arcfour
  def initialize(key)
    @s = (0 .. 255).to_a
    j = 0
    @s.each_index do |i|
      j = (j + @s[i] + key[i % key.size]) % 256
      @s[i], @s[j] = @s[j], @s[i]
    end
    @i, @j = 0, 0
  end
  
  def process(data)
    data.enum_for(:each_byte).inject('') do |r, c|
      @i = (@i + 1) % 256
      @j = (@j + @s[@i]) % 256
      @s[@i], @s[@j] = @s[@j], @s[@i]
      k = @s[(@s[@i] + @s[@j]) % 256]
      r << (c ^ k)
      r
    end
  end
end

class TC_Arcfour < Test::Unit::TestCase
  def test_vector1
    key = "\x01\x23\x45\x67\x89\xAB\xCD\xEF"
    dat = "\x00\x00\x00\x00\x00\x00\x00\x00"
    enc = Arcfour.new(key).process(dat)
    assert_equal("\x74\x94\xC2\xE7\x10\x4B\x08\x79", enc)
    dec = Arcfour.new(key).process(enc)
    assert_equal(dat, dec)
  end

  def test_vector2
    key = "\x61\x8a\x63\xd2\xfb"
    dat = "\xdc\xee\x4c\xf9\x2c"
    enc = Arcfour.new(key).process(dat)
    assert_equal("\xf1\x38\x29\xc9\xde", enc)
    dec = Arcfour.new(key).process(enc)
    assert_equal(dat, dec)
  end

  def test_vector3
    key = 
      "\x29\x04\x19\x72\xfb\x42\xba\x5f" +
      "\xc7\x12\x77\x12\xf1\x38\x29\xc9"
    dat =
      "\x52\x75\x69\x73\x6c\x69\x6e\x6e" +
      "\x75\x6e\x20\x6c\x61\x75\x6c\x75" +
      "\x20\x6b\x6f\x72\x76\x69\x73\x73" +
      "\x73\x61\x6e\x69\x2c\x20\x74\xe4" +
      "\x68\x6b\xe4\x70\xe4\x69\x64\x65" +
      "\x6e\x20\x70\xe4\xe4\x6c\x6c\xe4" +
      "\x20\x74\xe4\x79\x73\x69\x6b\x75" +
      "\x75\x2e\x20\x4b\x65\x73\xe4\x79" +
      "\xf6\x6e\x20\x6f\x6e\x20\x6f\x6e" +
      "\x6e\x69\x20\x6f\x6d\x61\x6e\x61" +
      "\x6e\x69\x2c\x20\x6b\x61\x73\x6b" +
      "\x69\x73\x61\x76\x75\x75\x6e\x20" +
      "\x6c\x61\x61\x6b\x73\x6f\x74\x20" +
      "\x76\x65\x72\x68\x6f\x75\x75\x2e" +
      "\x20\x45\x6e\x20\x6d\x61\x20\x69" +
      "\x6c\x6f\x69\x74\x73\x65\x2c\x20" +
      "\x73\x75\x72\x65\x20\x68\x75\x6f" +
      "\x6b\x61\x61\x2c\x20\x6d\x75\x74" +
      "\x74\x61\x20\x6d\x65\x74\x73\xe4" +
      "\x6e\x20\x74\x75\x6d\x6d\x75\x75" +
      "\x73\x20\x6d\x75\x6c\x6c\x65\x20" +
      "\x74\x75\x6f\x6b\x61\x61\x2e\x20" +
      "\x50\x75\x75\x6e\x74\x6f\x20\x70" +
      "\x69\x6c\x76\x65\x6e\x2c\x20\x6d" +
      "\x69\x20\x68\x75\x6b\x6b\x75\x75" +
      "\x2c\x20\x73\x69\x69\x6e\x74\x6f" +
      "\x20\x76\x61\x72\x61\x6e\x20\x74" +
      "\x75\x75\x6c\x69\x73\x65\x6e\x2c" +
      "\x20\x6d\x69\x20\x6e\x75\x6b\x6b" +
      "\x75\x75\x2e\x20\x54\x75\x6f\x6b" +
      "\x73\x75\x74\x20\x76\x61\x6e\x61" +
      "\x6d\x6f\x6e\x20\x6a\x61\x20\x76" +
      "\x61\x72\x6a\x6f\x74\x20\x76\x65" +
      "\x65\x6e\x2c\x20\x6e\x69\x69\x73" +
      "\x74\xe4\x20\x73\x79\x64\xe4\x6d" +
      "\x65\x6e\x69\x20\x6c\x61\x75\x6c" +
      "\x75\x6e\x20\x74\x65\x65\x6e\x2e" +
      "\x20\x2d\x20\x45\x69\x6e\x6f\x20" +
      "\x4c\x65\x69\x6e\x6f"
    enc = Arcfour.new(key).process(dat)
    assert_equal(
      "\x35\x81\x86\x99\x90\x01\xe6\xb5" +
      "\xda\xf0\x5e\xce\xeb\x7e\xee\x21" +
      "\xe0\x68\x9c\x1f\x00\xee\xa8\x1f" +
      "\x7d\xd2\xca\xae\xe1\xd2\x76\x3e" +
      "\x68\xaf\x0e\xad\x33\xd6\x6c\x26" +
      "\x8b\xc9\x46\xc4\x84\xfb\xe9\x4c" +
      "\x5f\x5e\x0b\x86\xa5\x92\x79\xe4" +
      "\xf8\x24\xe7\xa6\x40\xbd\x22\x32" +
      "\x10\xb0\xa6\x11\x60\xb7\xbc\xe9" +
      "\x86\xea\x65\x68\x80\x03\x59\x6b" +
      "\x63\x0a\x6b\x90\xf8\xe0\xca\xf6" +
      "\x91\x2a\x98\xeb\x87\x21\x76\xe8" +
      "\x3c\x20\x2c\xaa\x64\x16\x6d\x2c" +
      "\xce\x57\xff\x1b\xca\x57\xb2\x13" +
      "\xf0\xed\x1a\xa7\x2f\xb8\xea\x52" +
      "\xb0\xbe\x01\xcd\x1e\x41\x28\x67" +
      "\x72\x0b\x32\x6e\xb3\x89\xd0\x11" +
      "\xbd\x70\xd8\xaf\x03\x5f\xb0\xd8" +
      "\x58\x9d\xbc\xe3\xc6\x66\xf5\xea" +
      "\x8d\x4c\x79\x54\xc5\x0c\x3f\x34" +
      "\x0b\x04\x67\xf8\x1b\x42\x59\x61" +
      "\xc1\x18\x43\x07\x4d\xf6\x20\xf2" +
      "\x08\x40\x4b\x39\x4c\xf9\xd3\x7f" +
      "\xf5\x4b\x5f\x1a\xd8\xf6\xea\x7d" +
      "\xa3\xc5\x61\xdf\xa7\x28\x1f\x96" +
      "\x44\x63\xd2\xcc\x35\xa4\xd1\xb0" +
      "\x34\x90\xde\xc5\x1b\x07\x11\xfb" +
      "\xd6\xf5\x5f\x79\x23\x4d\x5b\x7c" +
      "\x76\x66\x22\xa6\x6d\xe9\x2b\xe9" +
      "\x96\x46\x1d\x5e\x4d\xc8\x78\xef" +
      "\x9b\xca\x03\x05\x21\xe8\x35\x1e" +
      "\x4b\xae\xd2\xfd\x04\xf9\x46\x73" +
      "\x68\xc4\xad\x6a\xc1\x86\xd0\x82" +
      "\x45\xb2\x63\xa2\x66\x6d\x1f\x6c" +
      "\x54\x20\xf1\x59\x9d\xfd\x9f\x43" +
      "\x89\x21\xc2\xf5\xa4\x63\x93\x8c" +
      "\xe0\x98\x22\x65\xee\xf7\x01\x79" +
      "\xbc\x55\x3f\x33\x9e\xb1\xa4\xc1" +
      "\xaf\x5f\x6a\x54\x7f", enc)
    dec = Arcfour.new(key).process(enc)
    assert_equal(dat, dec)
  end
end

参照: ストリーム暗号アルゴリズム "Arcfour"