-- | -- Module : Crypto.Cipher.Types.GF -- License : BSD-style -- Maintainer : Vincent Hanquez <vincent@snarc.org> -- Stability : Stable -- Portability : Excellent -- -- Slow Galois Field arithmetic for generic XTS and GCM implementation -- module Crypto.Cipher.Types.GF ( -- * XTS support xtsGFMul ) where import Control.Applicative import Data.ByteString (ByteString) import qualified Data.ByteString as B import qualified Data.ByteString.Internal as B import Data.Byteable import Foreign.Storable import Foreign.Ptr import Data.Word import Data.Bits -- block size need to be 128 bits. -- -- FIXME: add support for big endian. xtsGFMul :: ByteString -> ByteString xtsGFMul b | B.length b == 16 = B.unsafeCreate (B.length b) $ \dst -> withBytePtr b $ \src -> do (hi,lo) <- gf <$> peek (castPtr src) <*> peek (castPtr src `plusPtr` 8) poke (castPtr dst) lo poke (castPtr dst `plusPtr` 8) hi | otherwise = error "unsupported block size in GF" where gf :: Word64 -> Word64 -> (Word64, Word64) gf srcLo srcHi = ((if carryLo then (.|. 1) else id) (srcHi `shiftL` 1) ,(if carryHi then xor 0x87 else id) $ (srcLo `shiftL` 1) ) where carryHi = srcHi `testBit` 63 carryLo = srcLo `testBit` 63 {- const uint64_t gf_mask = cpu_to_le64(0x8000000000000000ULL); uint64_t r = ((a->q[1] & gf_mask) ? cpu_to_le64(0x87) : 0); a->q[1] = cpu_to_le64((le64_to_cpu(a->q[1]) << 1) | (a->q[0] & gf_mask ? 1 : 0)); a->q[0] = cpu_to_le64(le64_to_cpu(a->q[0]) << 1) ^ r; -}