2 files changed, 110 insertions, 0 deletions
diff --git a/src/ZeroBin/SJCL.hs b/src/ZeroBin/SJCL.hs
new file mode 100644
index 0000000..b121546
--- /dev/null
+++ b/src/ZeroBin/SJCL.hs
@@ -0,0 +1,91 @@
+{-# LANGUAGE DeriveGeneric #-}
+
+module ZeroBin.SJCL (
+  Content(..),
+  encrypt
+) where
+
+import Crypto.Cipher.AES (AES256)
+import Crypto.Cipher.Types (ivAdd, blockSize, cipherInit, ecbEncrypt, ctrCombine, makeIV)
+import Crypto.Error (throwCryptoErrorIO)
+import Crypto.Hash.Algorithms (SHA256(..))
+import Crypto.KDF.PBKDF2 (prfHMAC)
+import Crypto.Number.Serialize (i2ospOf_)
+import Crypto.Random.Entropy (getEntropy)
+import Data.ByteString (ByteString)
+import Data.Maybe (fromJust)
+import Data.Word (Word8)
+import GHC.Generics (Generic)
+import ZeroBin.Utils (toWeb)
+import qualified Crypto.KDF.PBKDF2 as PBKDF2
+import qualified Data.Aeson as JSON
+import qualified Data.ByteArray as BA
+import qualified Data.ByteString as BS
+import qualified Data.ByteString.Char8 as C
+
+data Content = Content {
+    iv   :: String
+  , salt :: String
+  , ct   :: String
+  } deriving (Generic, Show)
+
+-- FIXME: http://stackoverflow.com/questions/33045350/unexpected-haskell-aeson-warning-no-explicit-implementation-for-tojson
+instance JSON.ToJSON Content where
+  toJSON = JSON.genericToJSON JSON.defaultOptions
+
+makeCipher :: ByteString -> IO AES256
+makeCipher = throwCryptoErrorIO . cipherInit
+
+-- SJCL uses PBKDF2-HMAC-SHA256 with 1000 iterations, 32 bytes length,
+-- but the output is truncated down to 16 bytes.
+-- https://github.com/bitwiseshiftleft/sjcl/blob/master/core/pbkdf2.js
+-- TODO: this is default, we can specify it explicitly
+--       for forward compatibility
+makeKey :: ByteString -> ByteString -> ByteString
+makeKey pwd slt = BS.take 16 $ PBKDF2.generate (prfHMAC SHA256)
+  PBKDF2.Parameters {PBKDF2.iterCounts = 1000, PBKDF2.outputLength = 32}
+  pwd slt
+
+
+chunks :: Int -> ByteString -> [ByteString]
+chunks sz = split
+  where split b | cl <= sz = [b'] -- padded
+                | otherwise = b1 : split b2
+                where cl = BS.length b
+                      (b1, b2) = BS.splitAt sz b
+                      b' = BS.take sz $ BS.append b (BS.replicate sz 0)
+
+lengthOf :: Int -> Word8
+lengthOf = ceiling . (logBase 256 :: Float -> Float) . fromIntegral
+
+-- Ref. https://tools.ietf.org/html/rfc3610
+-- SJCL uses 64-bit tag (8 bytes)
+encrypt :: String -> ByteString -> IO Content
+encrypt password plaintext = do
+  ivd    <- getEntropy 16 -- XXX it is truncated to get the nonce below
+  slt    <- getEntropy 13 -- arbitrary length
+  cipher <- makeCipher $ makeKey (C.pack password) slt
+  let tlen = 8 :: Word8
+      l = BS.length plaintext
+      eL = max 2 (lengthOf l)
+      nonce = BS.take (15 - fromIntegral eL) ivd
+      b0 = BS.concat [
+             BS.pack [8*((tlen-2) `div` 2) + (eL-1)],
+             nonce,
+             i2ospOf_ (fromIntegral eL) (fromIntegral l)
+           ]
+      mac = foldl (\ a b -> ecbEncrypt cipher $ BA.xor a b)
+                   (ecbEncrypt cipher b0)
+                   (chunks (blockSize cipher) plaintext)
+      tag = BS.take (fromIntegral tlen) mac
+      a0 = BS.concat [
+             BS.pack [eL - 1],
+             nonce,
+             BS.replicate (fromIntegral eL) 0
+           ]
+      a1iv = ivAdd (fromJust . makeIV $ a0) 1
+      ciphtext = C.append
+                  (ctrCombine cipher a1iv plaintext)
+                  (BA.xor (ecbEncrypt cipher a0) tag)
+  return Content { iv = toWeb ivd, salt = toWeb slt, ct = toWeb ciphtext }
+
diff --git a/src/ZeroBin/Utils.hs b/src/ZeroBin/Utils.hs
new file mode 100644
index 0000000..34871d2
--- /dev/null
+++ b/src/ZeroBin/Utils.hs
@@ -0,0 +1,19 @@
+module ZeroBin.Utils (
+  toWeb
+, makePassword
+) where
+
+import Crypto.Random.Entropy (getEntropy)
+import Data.ByteString (ByteString)
+import Data.ByteString.Base64 (encode)
+import Data.ByteString.Char8 (unpack)
+import Data.Char (isAlphaNum)
+
+
+toWeb :: ByteString -> String
+toWeb = takeWhile (/= '=') . unpack . encode
+
+makePassword :: Int -> IO String
+makePassword n = (map (\c -> if isAlphaNum c then c else 'X')
+                  . toWeb) `fmap` getEntropy n
+