def encryption(plaintext, keyword):
    txt_len = len(plaintext)
    keyword *= txt_len // len(keyword) + 1
    keyword = keyword[:txt_len]
    encoded = ""
    for c in range(txt_len):
        newchar = ord(plaintext[c]) + ord(keyword[c]) - 194
        newchar %= 25
        encoded += chr(newchar + 97)
    return encoded

def decrypt(key, ciphertext):
    from itertools import cycle
    ALPHA = 'abcdefghijklmnopqrstuvwxyz'
    pairs = zip(ciphertext, cycle(key))
    result = ''
    for pair in pairs:
        total = reduce(lambda x, y: ALPHA.index(x) - ALPHA.index(y), pair)
        result += ALPHA[total % 26]
    return result

module VigenereCipher
 
  BASE = 'A'.ord
  SIZE = 'Z'.ord - BASE + 1
 
  def encrypt(text, key)
    crypt(text, key, :+)
  end
 
  def decrypt(text, key)
    crypt(text, key, :-)
  end
 
  def crypt(text, key, dir)
    text = text.upcase.gsub(/[^A-Z]/, '')
    key_iterator = key.upcase.gsub(/[^A-Z]/, '').chars.map{|c| c.ord - BASE}.cycle
    text.each_char.inject('') do |ciphertext, char|
      offset = key_iterator.next
      ciphertext << ((char.ord - BASE).send(dir, offset) % SIZE + BASE).chr
    end
  end
 
end