rubyzip/lib/zip/crypto/traditional_encryption.rb

module Zip
  module TraditionalEncryption
    def initialize(password)
      @password = password
      reset_keys!
    end

    def header_bytesize
      12
    end

    def gp_flags
      1
    end

    protected

    def reset_keys!
      @key0 = 0x12345678
      @key1 = 0x23456789
      @key2 = 0x34567890
      @password.each_byte do |byte|
        update_keys(byte.chr)
      end
    end

    def update_keys(n)
      @key0 = ~Zlib.crc32(n, ~@key0)
      @key1 = ((@key1 + (@key0 & 0xff)) * 134775813 + 1) & 0xffffffff
      @key2 = ~Zlib.crc32((@key1 >> 24).chr, ~@key2)
    end

    def decrypt_byte
      temp = (@key2 & 0xffff) | 2
      ((temp * (temp ^ 1)) >> 8) & 0xff
    end
  end

  class TraditionalEncrypter < Encrypter
    include TraditionalEncryption

    def header(crc32)
      [].tap do |header|
        (header_bytesize - 1).times do
          header << rand(0..255)
        end
        header << (crc32 >> 24)
      end.map{|x| encode x}.pack("C*")
    end

    def encrypt(data)
      data.unpack("C*").map{|x| encode x}.pack("C*")
    end

    def reset!
      reset_keys!
    end

    private

    def encode(n)
      t = decrypt_byte
      update_keys(n.chr)
      t ^ n
    end
  end

  class TraditionalDecrypter < Decrypter
    include TraditionalEncryption

    def decrypt(data)
      data.unpack("C*").map{|x| decode x}.pack("C*")
    end

    def reset!(header)
      reset_keys!
      header.each_byte do |x|
        decode x
      end
    end

    private

    def decode(n)
      n ^= decrypt_byte
      update_keys(n.chr)
      n
    end
  end
end

# Copyright (C) 2002, 2003 Thomas Sondergaard
# rubyzip is free software; you can redistribute it and/or
# modify it under the terms of the ruby license.