Blowfish encryption wrapper

encryption.rb

require 'rubygems'
require 'crypt/blowfish'
require 'base64'

# simple wrapper for blowfish encryption. Assumes all string IO in base64.
module Encryption

  extend self

  class NilKey     < StandardError; end
  class InvalidKey < StandardError; end

  @@key = nil
  @@cypher = nil

  def self.key(value=false)
    Encryption.validate_key(value == false ? @@key : value)
    unless value == false
      @@key = value
      @@cypher = nil
    end
    @@key
  end

  def self.validate_key(value)
    raise NilKey,     "Set Encryption.encryption_key 'some_key'." if value.nil?
    raise InvalidKey, "Bad encryption_key length: the encryption_key must be 1-56 bytes." unless (value.length.between?(1,56))
    value
  end

  def self.cypher
    @@cypher ||= Crypt::Blowfish.new(Encryption.key)
  end

  def encrypt_string str
    Base64.encode64( Encryption.cypher.encrypt_string(str) )
  end

  def decrypt_string str
    Encryption.cypher.decrypt_string( Base64.decode64(str) )
  end

  def encrypt_file( plain_file_name, crypted_output_file_name )
    Encryption.cypher.encrypt_file(plain_file_name, crypted_output_file_name)
  end

  def decrypt_file( crypted_file_name, plain_output_file_name )
    Encryption.cypher.decrypt_file(crypted_file_name, plain_output_file_name)
  end
end

if __FILE__ == $0
  require 'test/unit'

  class TestEncryptionModule < Test::Unit::TestCase

    def test_nil_key_raised
      assert_raise Encryption::NilKey do
        Encryption.key nil
      end
    end

    def test_invalid_key_raised
      assert_raise Encryption::InvalidKey do
        Encryption.key ""
      end
      assert_raise Encryption::InvalidKey do
        Encryption.key("x" * 57)
      end
    end

    def test_encrypt_and_decrypt_string
      Encryption.key 'some_key'
      plain = "this is some text"
      crypted = Encryption.encrypt_string plain
      assert plain != crypted
      assert_equal plain, Encryption.decrypt_string(crypted)
    end

    def test_changing_key
      plain = "this is some text"
      Encryption.key 'some_key'
      crypted = Encryption.encrypt_string plain

      Encryption.key "a_different_key"
      other_crypted = Encryption.encrypt_string plain
      assert_equal plain, Encryption.decrypt_string(other_crypted)

      Encryption.key 'some_key'
      assert_equal plain, Encryption.decrypt_string(crypted)
    end

  end
end