Encryptor

class Encryptor
  def cypher(letter, rotation)
    (letter.ord + rotation).chr
  end

  def encrypt(message, rotation)
    letters = message.split("")

    letters.collect { |letter| cypher(letter, rotation) }.join
  end

  def decrypt(message, rotation)
    letters = message.split("")

    letters.collect { |letter| cypher(letter, -rotation) }.join
  end
end