gistfile1.idr

KSA : ARC4Key n -> Vect 256 (Mod 256)
KSA {n=(n ** p)} key =
  fst (runIdentity (runStateT (nextJ (map Prelude.Classes.fromInteger (fromList [0..255])))
                              (0, 0)))
  where
    nextJ : Vect 256 (Mod 256) -> State (Mod 256, Mod 256) (Vect 256 (Mod 256))
    nextJ S = do
      (i, j) <- get
      let ind = tightmod (cast i) (cast n) (stillNotZero n p)
      let pos = index ind key
      let newJ = the (Mod 256) (j + index (cast i) S + pos)
      let newS = (swap (cast i) (cast newJ) S)
      if i == maxBound
        then
          return newS
        else do
          put (i + 1, newJ)
          nextJ newS

-- Data.Crypto.Encryption.ARC4.KSA, nextJ is possibly not total due to: Data.Crypto.Encryption.ARC4.case block in Data.Crypto.Encryption.ARC4.KSA, nextJ