commit 892e529ea8cd73b8c927125c0aae1ab7c842230d
parent ff01c61677c0e9206e7e0549fede3f3571b5c04c
Author: Jared Tobin <jared@jtobin.io>
Date: Wed, 2 Aug 2023 22:14:04 -0230
Add 4.25.
Diffstat:
4 files changed, 153 insertions(+), 1 deletion(-)
diff --git a/README.md b/README.md
@@ -11,4 +11,5 @@ to build binaries. Use `cabal install` to (I think) dump them in
* [Problem Set 1](docs/s1.md)
* [Problem Set 2](docs/s2.md)
* [Problem Set 3](docs/s3.md)
+* [Problem Set 4](docs/s4.md)
diff --git a/data/s4/q25_input.txt b/data/s4/q25_input.txt
@@ -0,0 +1,64 @@
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diff --git a/docs/s4.md b/docs/s4.md
@@ -0,0 +1,26 @@
+### Set 4
+
+#### 4.25
+
+If we can control the offset and plaintext input, then we can ask
+the oracle to encrypt a plaintext with the same length of the
+ciphertext at offset 0. *Et voilà*, there's our keystream, which we
+can just xor with the original ciphertext in order to decrypt it.
+Cryptopals.Stream.Attacks.rawrCtrAttack implements such an "attack":
+
+ rawrCtrAttack :: IO BS.ByteString
+ rawrCtrAttack = do
+ cip <- rawrCtrOracle (maxBound :: Int) mempty
+ let l = BS.length cip
+ p = BS.replicate l 65
+
+ new <- rawrCtrOracle 0 p
+ let ks = new `CU.fixedXor` p
+
+ pure $ ks `CU.fixedXor` cip
+
+Which gives the expected plaintext:
+
+ > fmap (BS.take 33) rawrCtrAttack
+ "I'm back and I'm ringin' the bell"
+
diff --git a/lib/Cryptopals/Stream/Attacks.hs b/lib/Cryptopals/Stream/Attacks.hs
@@ -1,18 +1,37 @@
module Cryptopals.Stream.Attacks where
import Control.Monad
+import Control.Monad.Primitive
import qualified Control.Monad.ST as ST
import qualified Data.Binary.Put as BP
import qualified Data.ByteString as BS
+import qualified Data.ByteString.Char8 as B8
import qualified Data.ByteString.Base64 as B64
import qualified Data.ByteString.Lazy as BSL
import qualified Data.Text as T
import qualified Data.Time.Clock.System as TS
+import qualified Cryptopals.AES as AES
import qualified Cryptopals.Stream.RNG.MT19937 as MT
import qualified Cryptopals.Util as CU
-import GHC.Word (Word16, Word8)
+import GHC.Word (Word64, Word16, Word8)
import qualified System.Random.MWC as MWC
+bytes :: PrimMonad m => Int -> MWC.Gen (PrimState m) -> m BS.ByteString
+bytes n gen = fmap BS.pack $ replicateM n (MWC.uniform gen)
+
+-- | An unknown AES key.
+consistentKey :: BS.ByteString
+consistentKey = ST.runST $ do
+ gen <- MWC.create
+ bytes 16 gen
+
+consistentNonce :: Word64
+consistentNonce = ST.runST $ do
+ gen <- MWC.create
+ MWC.uniformR (0, 0xffffffffffffffff) gen
+
+-- MT19937-related attacks
+
keystream :: Int -> MT.Gen -> BS.ByteString
keystream nb g =
let l = nb `quot` 4 + nb `rem` 4
@@ -72,3 +91,45 @@ isPwnt token = do
let g = MT.seed s
ks = keystream 16 g
pure $ token == B64.encodeBase64 ks
+
+-- CTR attacks
+
+ctrEdit
+ :: BS.ByteString
+ -> BS.ByteString
+ -> Word64
+ -> Int
+ -> BS.ByteString
+ -> BS.ByteString
+ctrEdit cip key non off new =
+ let (pre, _) = BS.splitAt off cip
+ ced = AES.encryptCtrAES128 non key new
+ in pre <> ced
+
+rawrCtrInput :: IO BS.ByteString
+rawrCtrInput = do
+ raw <- B8.readFile "data/s4/q25_input.txt"
+ let bs = B64.decodeBase64Lenient . mconcat .B8.lines $ raw
+ let pay = AES.decryptEcbAES128 "YELLOW SUBMARINE" bs
+ pure $ AES.encryptCtrAES128 consistentNonce consistentKey pay
+
+rawrCtrOracle :: Int -> BS.ByteString -> IO BS.ByteString
+rawrCtrOracle off pay = do
+ let k = consistentKey
+ n = consistentNonce
+
+ cip <- rawrCtrInput
+
+ pure $ ctrEdit cip k n off pay
+
+rawrCtrAttack :: IO BS.ByteString
+rawrCtrAttack = do
+ cip <- rawrCtrOracle (maxBound :: Int) mempty
+ let l = BS.length cip
+ p = BS.replicate l 65
+
+ new <- rawrCtrOracle 0 p
+ let ks = new `CU.fixedXor` p
+
+ pure $ ks `CU.fixedXor` cip
+
