cbcEncrypt :: Char -> Char -> String -> String
cbcEncrypt k iv plainText = generateCypher plainTextLength
  where
    plainTextLength  = length plainText
    generateCypher :: Int -> String
    -- Generate the cypher text based on length of the plain text
    -- Function uses the CBC model defined as
    -- c_1 = (x_1 + iv) + k
    -- c_i = (x_i + c_(i-1)) + k for 1 < i ≤ l
    -- where "+" reffers to the addition operation defined in the add Haskell
    -- function and x is the plain text string
    generateCypher 0 = []
    generateCypher currentIndex
      | currentIndex == 1
        = [add (add currentEl iv) k]
      | otherwise
        = previousList ++ [add (add currentEl previousListLastEl) k]
      where
        currentEl               = plainText !! (currentIndex - 1)
        previousList            = generateCypher (currentIndex - 1)
        previousListLastEl      = previousList !! (length previousList - 1)