Kriptos solving script (K4 is not solved)

kriptos.rb

def decode_Vigenere(keyword, source)
  s = 'KRYPTOSABCDEFGHIJLMNQUVWXZ'
  t = []
  keyword.each_char {|c|
    i = s.index(c)
    t << s[i..-1] + s[0...i]
  }
  r = []
  d = 0
  source.each_char.with_index {|c, i|
    if c.match(/[A-Z]/)
      r << s[t[(i - d) % keyword.length].index(c)]
    else
      r << c
      d += 1
    end
  }
  puts r.join('')
end

def decode_k3(source)
  source = source.gsub(/[^A-Za-z?]/, '')
  i = 191
  r = []
  while true
    r << source[i]
    i = (i + 192) % source.length
    if r.length >= source.length
      break
    end
  end
  puts r.join('')
end

def decode_k4(source)
  source = source.gsub(/[^A-Za-z]/, '')
  r = []
  source.each_char.with_index {|c, i|
    # Rewrite this line!
    r << c
  }
  a = r.join('')
  unless a[63, 11] == 'BERLINCLOCK'
    puts "NO! #{a[63, 11]}"
  end
  puts a
end

decode_Vigenere('PALIMPSEST', <<EOT
EMUFPHZLRFAXYUSDJKZLDKRNSHGNFIVJ
YQTQUXQBQVYUVLLTREVJYQTMKYRDMFD
EOT
)
decode_Vigenere('ABSCISSA', <<EOT
VFPJUDEEHZWETZYVGWHKKQETGFQJNCE
GGWHKK?DQMCPFQZDQMMIAGPFXHQRLG
TIMVMZJANQLVKQEDAGDVFRPJUNGEUNA
QZGZLECGYUXUEENJTBJLBQCRTBJDFHRR
YIZETKZEMVDUFKSJHKFWHKUWQLSZFTI
HHDDDUVH?DWKBFUFPWNTDFIYCUQZERE
EVLDKFEZMOQQJLTTUGSYQPFEUNLAVIDX
FLGGTEZ?FKZBSFDQVGOGIPUFXHHDRKF
FHQNTGPUAECNUVPDJMQCLQUMUNEDFQ
ELZZVRRGKFFVOEEXBDMVPNFQXEZLGRE
DNQFMPNZGLFLPMRJQYALMGNUVPDXVKP
DQUMEBEDMHDAFMJGZNUPLGESWJLLAETG
EOT
)
decode_k3(<<EOT
ENDyaHrOHNLSRHEOCPTEOIBIDYSHNAIA
CHTNREYULDSLLSLLNOHSNOSMRWXMNE
TPRNGATIHNRARPESLNNELEBLPIIACAE
WMTWNDITEENRAHCTENEUDRETNHAEOE
TFOLSEDTIWENHAEIOYTEYQHEENCTAYCR
EIFTBRSPAMHNEWENATAMATEGYEERLB
TEEFOASFIOTUETUAEOTOARMAEERTNRTI
BSEDDNIAAHTTMSTEWPIEROAGRIEWFEB
AECTDDHILCEIHSITEGOEAOSDDRYDLORIT
RKLMLEHAGTDHARDPNEOHMGFMFEUHE
ECDMRIPFEIMEHNLSSTTRTVDOHW?
EOT
)
decode_k4(<<EOT
                           OBKR
UOXOGHULBSOLIFBBWFLRVQQPRNGKSSO
TWTQSJQSSEKZZWATJKLUDIAWINFBNYP
VTTMZFPKWGDKZXTJCDIGKUHUAUEKCAR
EOT
)