def shift(char, offset)
  (((char.ord - 'A'.ord + offset) % 26) + 'A'.ord).chr
end

m = 'CGULKVIPFRGDOOCSJTRRVMORCQDZG'

(0..25).each do |i|
  j = i
  puts m.chars.map { |c| d = shift(c, -j); j -= 1; d }.join
end