simple Vigenere-cipher

Vigenere.hs

module Vigenere where

import Data.Char
import Test.QuickCheck.Test (quickCheck)

encrypt :: String -> String -> String
encrypt key = zipWith (shiftChar (+)) (cycle key)

decrypt :: String -> String -> String
decrypt key = zipWith (shiftChar (flip (-))) (cycle key)

shiftChar :: (Int -> Int -> Int) -> Char -> Char -> Char
shiftChar op a b = chr . wrap $ op (ord a) (ord b)
  where wrap c = c `mod` maxValue
        maxValue = 1 + ord (maxBound :: Char)

-- test if decrypt . encrypt = id
decryptIsInverseOfEncrypt :: String -> IO ()
decryptIsInverseOfEncrypt key = 
  quickCheck (\s -> s == (decrypt key . encrypt key) s)

main :: IO ()
main =
  -- run 100 tests with a sample key
  decryptIsInverseOfEncrypt "my Key"