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|
-- |
-- Module : Crypto.Data.AFIS
-- License : BSD-style
-- Maintainer : Vincent Hanquez <vincent@snarc.org>
-- Stability : experimental
-- Portability : unknown
--
-- Haskell implementation of the Anti-forensic information splitter
-- available in LUKS. <http://clemens.endorphin.org/AFsplitter>
--
-- The algorithm bloats an arbitrary secret with many bits that are necessary for
-- the recovery of the key (merge), and allow greater way to permanently
-- destroy a key stored on disk.
--
{-# LANGUAGE ScopedTypeVariables #-}
module Crypto.Data.AFIS
( split
, merge
) where
import Crypto.Hash
import Crypto.Random.Types
import Crypto.Internal.Compat
import Control.Monad (forM_, foldM)
import Data.Word
import Data.Bits
import Foreign.Storable
import Foreign.Ptr
import Crypto.Internal.ByteArray (ByteArray, Bytes, MemView(..))
import qualified Crypto.Internal.ByteArray as B
import Data.Memory.PtrMethods (memSet, memCopy)
-- | Split data to diffused data, using a random generator and
-- an hash algorithm.
--
-- the diffused data will consist of random data for (expandTimes-1)
-- then the last block will be xor of the accumulated random data diffused by
-- the hash algorithm.
--
-- ----------
-- - orig -
-- ----------
--
-- ---------- ---------- --------------
-- - rand1 - - rand2 - - orig ^ acc -
-- ---------- ---------- --------------
--
-- where acc is :
-- acc(n+1) = hash (n ++ rand(n)) ^ acc(n)
--
split :: (ByteArray ba, HashAlgorithm hash, DRG rng)
=> hash -- ^ Hash algorithm to use as diffuser
-> rng -- ^ Random generator to use
-> Int -- ^ Number of times to diffuse the data.
-> ba -- ^ original data to diffuse.
-> (ba, rng) -- ^ The diffused data
{-# NOINLINE split #-}
split hashAlg rng expandTimes src
| expandTimes <= 1 = error "invalid expandTimes value"
| otherwise = unsafeDoIO $ do
(rng', bs) <- B.allocRet diffusedLen runOp
return (bs, rng')
where diffusedLen = blockSize * expandTimes
blockSize = B.length src
runOp dstPtr = do
let lastBlock = dstPtr `plusPtr` (blockSize * (expandTimes-1))
memSet lastBlock 0 blockSize
let randomBlockPtrs = map (plusPtr dstPtr . (*) blockSize) [0..(expandTimes-2)]
rng' <- foldM fillRandomBlock rng randomBlockPtrs
mapM_ (addRandomBlock lastBlock) randomBlockPtrs
B.withByteArray src $ \srcPtr -> xorMem srcPtr lastBlock blockSize
return rng'
addRandomBlock lastBlock blockPtr = do
xorMem blockPtr lastBlock blockSize
diffuse hashAlg lastBlock blockSize
fillRandomBlock g blockPtr = do
let (rand :: Bytes, g') = randomBytesGenerate blockSize g
B.withByteArray rand $ \randPtr -> memCopy blockPtr randPtr blockSize
return g'
-- | Merge previously diffused data back to the original data.
merge :: (ByteArray ba, HashAlgorithm hash)
=> hash -- ^ Hash algorithm used as diffuser
-> Int -- ^ Number of times to un-diffuse the data
-> ba -- ^ Diffused data
-> ba -- ^ Original data
{-# NOINLINE merge #-}
merge hashAlg expandTimes bs
| r /= 0 = error "diffused data not a multiple of expandTimes"
| originalSize <= 0 = error "diffused data null"
| otherwise = B.allocAndFreeze originalSize $ \dstPtr ->
B.withByteArray bs $ \srcPtr -> do
memSet dstPtr 0 originalSize
forM_ [0..(expandTimes-2)] $ \i -> do
xorMem (srcPtr `plusPtr` (i * originalSize)) dstPtr originalSize
diffuse hashAlg dstPtr originalSize
xorMem (srcPtr `plusPtr` ((expandTimes-1) * originalSize)) dstPtr originalSize
return ()
where (originalSize,r) = len `quotRem` expandTimes
len = B.length bs
-- | inplace Xor with an input
-- dst = src `xor` dst
xorMem :: Ptr Word8 -> Ptr Word8 -> Int -> IO ()
xorMem src dst sz
| sz `mod` 64 == 0 = loop 8 (castPtr src :: Ptr Word64) (castPtr dst) sz
| sz `mod` 32 == 0 = loop 4 (castPtr src :: Ptr Word32) (castPtr dst) sz
| otherwise = loop 1 (src :: Ptr Word8) dst sz
where loop _ _ _ 0 = return ()
loop incr s d n = do a <- peek s
b <- peek d
poke d (a `xor` b)
loop incr (s `plusPtr` incr) (d `plusPtr` incr) (n-incr)
diffuse :: HashAlgorithm hash
=> hash -- ^ Hash function to use as diffuser
-> Ptr Word8 -- ^ buffer to diffuse, modify in place
-> Int -- ^ length of buffer to diffuse
-> IO ()
diffuse hashAlg src sz = loop src 0
where (full,pad) = sz `quotRem` digestSize
loop s i
| i < full = do h <- hashBlock i s digestSize
B.withByteArray h $ \hPtr -> memCopy s hPtr digestSize
loop (s `plusPtr` digestSize) (i+1)
| pad /= 0 = do h <- hashBlock i s pad
B.withByteArray h $ \hPtr -> memCopy s hPtr pad
return ()
| otherwise = return ()
digestSize = hashDigestSize hashAlg
-- Hash [ BE32(n), (p .. p+hashSz) ]
hashBlock n p hashSz = do
let ctx = hashInitWith hashAlg
return $! hashFinalize $ hashUpdate (hashUpdate ctx (be32 n)) (MemView p hashSz)
be32 :: Int -> Bytes
be32 n = B.allocAndFreeze 4 $ \ptr -> do
poke ptr (f8 (n `shiftR` 24))
poke (ptr `plusPtr` 1) (f8 (n `shiftR` 16))
poke (ptr `plusPtr` 2) (f8 (n `shiftR` 8))
poke (ptr `plusPtr` 3) (f8 n)
where
f8 :: Int -> Word8
f8 = fromIntegral
|
