week1-pset1-7.hs

{-|
 - Cryptography Week 1 Problem Set #7 | Corsera
 -
 - 1. Extract One-Time-Pad key from PT and CT pair.
 - 2. Encrypt a new message using the key.
 - 3. Print the result as a Hex String.
 -}

import Text.Printf (printf)
import Data.Bits (xor)
import Data.Char (ord, chr)
import Numeric (showHex)

extractKey :: [Int] -> [Int] -> [Int]
extractKey = zipWith xor

encrypt :: [Int] -> [Int] -> [Int]
encrypt = zipWith xor

fixedHexString :: Int -> String
fixedHexString x = printf "%02X" x :: String

showHexString = map fixedHexString

main=do print $ concat . showHexString $ encrypt key m
    where 
        -- original plain text message
        om  = map ord "attack at dawn"
        -- original cipher text in hex
        oc  = [0x6c, 0x73, 0xd5, 0x24, 0x0a, 0x94, 0x8c, 0x86, 0x98, 0x1b, 0xc2, 0x94, 0x81, 0x4d]
        -- extracted otp key
        key = extractKey om oc
        -- new plain text message
        m   = map ord "attack at dusk"