Implement buffer Xor

hcryptopals.cabal

@@ -17,6 +17,7 @@ library
   hs-source-dirs:      src
   exposed-modules:     Lib
   other-modules:       Crypto.Pals.Encoding
+                     , Crypto.Pals.Xor
                      , Crypto.Pals.BitStream
   build-depends:       base >= 4.7 && < 5
                      , bytestring

src/Crypto/Pals/BitStream.hs

@@ -44,7 +44,7 @@ groupByN n xs =
 data BitChunk  = BitChunk
   { size    :: Int
   , getBits :: Word8
-  } deriving (Show)
+  } deriving (Show, Eq)
 
 type BitStream = [BitChunk]
 

src/Crypto/Pals/Encoding.hs

@@ -17,7 +17,7 @@ generateBytesToBitsTable symbols padding = V.generate 127 gen
     gen i =
       case chr i `elemIndex` symbols of
         Just n ->  BitChunk padding (fromIntegral n)
-        Nothing -> BitChunk 0 0
+        Nothing -> error "This character is not valid for the given encoding"
 
 
 generateBitsToBytesTable :: String -> VU.Vector Word8

src/Crypto/Pals/Xor.hs

@@ -0,0 +1,10 @@
+
+module Crypto.Pals.Xor where
+
+import qualified Data.Bits as Bits
+import qualified Data.ByteString.Lazy as B
+
+xor :: B.ByteString -> B.ByteString -> Maybe B.ByteString
+xor bs1 bs2
+  | B.length bs1 /= B.length bs2 = Nothing
+  | otherwise = Just . B.pack . B.zipWith Bits.xor bs1 $ bs2

src/Lib.hs

@@ -1,7 +1,9 @@
 module Lib
   ( module Crypto.Pals.Encoding
   , module Crypto.Pals.BitStream
+  , module Crypto.Pals.Xor
   ) where
 
 import Crypto.Pals.Encoding
 import Crypto.Pals.BitStream
+import Crypto.Pals.Xor

test/Spec.hs

@@ -17,6 +17,7 @@ symbolsToWord8 = map (fromIntegral . ord)
 
 
 forAllB64 = forAll $
+  Gen.filter (\b64 -> length b64 `mod` 3 == 0) $
   Gen.list (Range.linear 1 100) (Gen.element $ symbolsToWord8 b64Symbols)
   where
     b64Symbols = ['0'..'9'] ++ ['A'..'Z'] ++ ['a'..'z'] ++ ['/', '+']
@@ -39,24 +40,26 @@ prop_groupByN =
         Gen.list (Range.linear 1 100) (Gen.word8 $ Range.linear 0 255)
 
       let bitStream = map (BitChunk 8) words
-      let groups = map (BitChunk n) $ groupByN n bitStream
-      toList groups === toList bitStream
+      let bitStream2 = map (BitChunk n) $ groupByN n bitStream
+      let bitStream3 = map (BitChunk 8) $ groupByN 8 bitStream2
+      bitStream === bitStream3
+      toList bitStream3 === toList bitStream
 
 
 prop_hex :: Property
 prop_hex =
     property $ do
-      hex <- forAllHex
-      let packed = B.pack hex
-      packed === (bitsToHex . hexToBits $ packed)
+      str <- forAllHex
+      let packed = B.pack str
+      packed === (unhex . hex $ packed)
 
 
 prop_base64 :: Property
 prop_base64 =
     property $ do
-      b64 <- forAllB64
-      let packed = B.pack b64
-      packed === (bitsToB64 . b64ToBits $ packed)
+      str <- forAllB64
+      let packed = B.pack str
+      packed === (unb64 . b64 $ packed)
 
 
 prop_hex2b64 :: Property