count :: Char -> String -> Int
count c xs = length [c'| c' <- xs, c' == c]
let2int :: Char -> Int
let2int c = ord c - ord 'a'
int2let :: Int -> Char
int2let n = chr (ord 'a' + n)
shift :: Int -> Char -> Char
shift n c | isLower c = int2let ((let2int c + n) `mod` 26)
| otherwise = c
encode :: Int -> String -> String
encode n xs = [shift n c | c <- xs]
persent :: Int -> Int -> Float
persent n m = (fromIntegral n / fromIntegral m) * 100
freqs :: String -> [Float]
freqs xs = [persent (count c xs) n | c <- ['a'..'z']]
where n = length xs
chisqr :: [Float] -> [Float] -> Float
chisqr os es = sum [((o - e)^2) / e | (o, e) <- zip os es]
rotate :: Int -> [a] -> [a]
rotate n xs = drop n xs ++ take n xs
table :: [Float]
table = [8.2, 1.5, 2.8, 4.3, 12.7, 2.2, 2.0, 6.1, 7.0, 0.2, 0.8, 4.0, 2.4, 6.7, 7.5, 1.9, 0.1, 6.0, 6.3, 9.1, 2.8, 1.0, 2.4, 0.2, 2.0, 0.1]
crack :: String -> String
crack xs = encode (-factor) xs
where
factor = head (positions (minimum chitab) chitab)
chitab = [chisqr (rotate n table') table | n <- [0..25]]
table' = freqs xs