simple string encoding from key

simple_cipher.rb

def encode(message, key)
  c = key.to_s.split('').map { |e| e.to_i }.cycle #setup key cycle
  letter_hash = Hash[('a'..'z').zip(1..26)] #hash containing 'a' => 1, 'b' => 2, and so on...
  message.split('').map { |e| letter_hash.fetch(e,e) + c.next} #encode vlaues
end

def decode(code, key)
  c = key.to_s.split('').map { |e| e.to_i }.cycle #setup key cycle
  h = Hash[(1..26).zip('a'..'z')] #hash containing 1 => 'a', 2=> 'b', and so on...
  code.map { |e| h.fetch((e - c.next),e) }.join('') # decode and fetch values from hash and join  
end
# encode("masterpiece", 1939)
#    m  a  s  t  e  r  p  i  e  c  e
#   13  1 19 20  5 18 16  9  5  3  5
# +  1  9  3  9  1  9  3  9  1  9  3
#   --------------------------------
#   14 10 22 29  6 27 19 18  6  12 8
# -  1  9  3  9  1  9  3  9  1  9  3
#   --------------------------------
#   13  1 19 20  5 18 16  9  5  3  5 
#    m  a  s  t  e  r  p  i  e  c  e