Comments on: Ron’s Cipher #4

By: VaporWarning» Blog Archive » Learning Python by example: RC4

VaporWarning» Blog Archive » Learning Python by example: RC4 — Mon, 21 Sep 2009 05:54:33 +0000

[...] in point, I’ll use the recent kata from Programming Praxis for this Python exercise, as they provide straightforward pseudocode. Here’s the encryption [...]

By: Posts about Programming from google blogs as of September 4, 2009 « tryfly.com

Sat, 05 Sep 2009 00:02:22 +0000

[...] [...]

By: Remco Niemeijer

Remco Niemeijer — Fri, 04 Sep 2009 19:32:59 +0000

My Haskell solution (see http://bonsaicode.wordpress.com/2009/09/04/programming-praxis-ron%E2%80%99s-cipher-4/ for a version with comments):

import Data.Bits
import Data.Char
import Data.IntMap ((!), fromList, insert, size, IntMap)

swap :: Int -> Int -> IntMap a -> IntMap a
swap i j a = insert j (a ! i) $ insert i (a ! j) a

rc4init :: IntMap Char -> IntMap Int
rc4init key = snd $ foldl (\(j, a) i ->
    let j' = mod (j + a ! i + ord (key ! mod i (size key))) 256
    in (j', swap i j' a)) (0, s) [0..255] where
    s = fromList $ zip [0..] [0..255]
  
rc4 :: String -> String -> String
rc4 key = map chr . zipWith xor (stream key) . map ord where
    stream = s 0 0 . rc4init . fromList . zip [0..]
    s i' j' k' = k ! (mod (k ! i + k ! j) 256) : s i j k where
                 i = mod (i' + 1) 256
                 j = mod (j' + k' ! i) 256
                 k = swap i j k'

By: Programming Praxis – Ron’s Cipher #4 « Bonsai Code

Programming Praxis – Ron’s Cipher #4 « Bonsai Code — Fri, 04 Sep 2009 19:32:45 +0000

[...] Praxis – Ron’s Cipher #4 By Remco Niemeijer In today’s Programming Praxis problem, we have to implement the RC4 cipher, which is often used in protocols [...]