Ruby implementation of a Vigenere Cipher

vigenere_cipher.rb

class VigenereCipher
  attr_reader :input
  attr_reader :key
  attr_reader :output

  def initialize(input, key)
    @input = input
    @key = key.downcase.gsub(/\W|\d|_/, "")

    while @key.size < @input.length
      @key = @key * 2
    end

    @key = @key[0, @input.size]

    @output = @input

    tabula_recta
  end


  def alphabet
    @alphabet ||= ('a'..'z').to_a.join
  end

  def upper_alphabet
    @upper_alphabet ||= ('A'..'Z').to_a.join
  end

  def tabula_recta
    @table ||= generate_table
  end

  def generate_table
    base = ('a'..'z').to_a

    rect = []

    26.times do |i|
      rect << base.rotate(i)
    end

    rect
  end

  def encode
    output = ""

    @output.each_char.with_index do |c, i|
      x = alphabet.index(@key[i])
      y = alphabet.index(c) || upper_alphabet.index(c)

      ciphered = (y.nil? ? c : tabula_recta[x][y].dup)

      ciphered.upcase! if c == c.upcase

      output << ciphered
    end

    @output = output
  end

  def decode
    output = ""

    @output.each_char.with_index do |c, i|
      x = alphabet.index(@key[i])
      y = tabula_recta[x].index(c.downcase)

      ciphered = (y.nil? ? c : alphabet[y].dup)

      ciphered.upcase! if c == c.upcase

      output << ciphered
    end

    @output = output
  end

end