{-# LANGUAGE DeriveDataTypeable, GeneralizedNewtypeDeriving, DeriveGeneric #-}

-- |
-- Module      : Crypto.Saltine.Core.SecretBox
-- Copyright   : (c) Joseph Abrahamson 2013
-- License     : MIT
--
-- Maintainer  : me@jspha.com
-- Stability   : experimental
-- Portability : non-portable
--
-- Secret-key authenticated encryption:
-- "Crypto.Saltine.Core.SecretBox"
--
-- The 'secretbox' function encrypts and authenticates a message
-- 'ByteString' using a secret key and a nonce. The 'secretboxOpen'
-- function verifies and decrypts a ciphertext 'ByteString' using a
-- secret key and a nonce. If the ciphertext fails validation,
-- 'secretboxOpen' returns 'Nothing'.
--
-- The "Crypto.Saltine.Core.SecretBox" module is designed to meet
-- the standard notions of privacy and authenticity for a secret-key
-- authenticated-encryption scheme using nonces. For formal
-- definitions see, e.g., Bellare and Namprempre, "Authenticated
-- encryption: relations among notions and analysis of the generic
-- composition paradigm," Lecture Notes in Computer Science 1976
-- (2000), 531–545, <http://www-cse.ucsd.edu/~mihir/papers/oem.html>.
--
-- Note that the length is not hidden. Note also that it is the
-- caller's responsibility to ensure the uniqueness of nonces—for
-- example, by using nonce 1 for the first message, nonce 2 for the
-- second message, etc. Nonces are long enough that randomly generated
-- nonces have negligible risk of collision.
--
-- "Crypto.Saltine.Core.SecretBox" is
-- @crypto_secretbox_xsalsa20poly1305@, a particular combination of
-- Salsa20 and Poly1305 specified in \"Cryptography in NaCl\"
-- (<http://nacl.cr.yp.to/valid.html>). This function is conjectured
-- to meet the standard notions of privacy and authenticity.
--
-- This is version 2010.08.30 of the secretbox.html web page.
module Crypto.Saltine.Core.SecretBox (
  Key, Nonce,
  secretbox, secretboxOpen,
  secretboxDetached, secretboxOpenDetached,
  newKey, newNonce
  ) where

import           Crypto.Saltine.Class
import           Crypto.Saltine.Internal.Util
import qualified Crypto.Saltine.Internal.ByteSizes as Bytes

import           Control.Applicative
import           Foreign.C
import           Foreign.Ptr
import qualified Data.ByteString                   as S
import           Data.ByteString                     (ByteString)
import           Data.Hashable (Hashable)
import           Data.Data (Data, Typeable)
import           GHC.Generics (Generic)

-- $types

-- | An opaque 'secretbox' cryptographic key.
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  {-# INLINE decode #-}
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encode (Key ByteString
v) = ByteString
v
  {-# INLINE encode #-}

-- | An opaque 'secretbox' nonce.
newtype Nonce = Nonce ByteString deriving (Nonce -> Nonce -> Bool
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instance IsEncoding Nonce where
  decode :: ByteString -> Maybe Nonce
decode ByteString
v = if ByteString -> Int
S.length ByteString
v Int -> Int -> Bool
forall a. Eq a => a -> a -> Bool
== Int
Bytes.secretBoxNonce
           then Nonce -> Maybe Nonce
forall a. a -> Maybe a
Just (ByteString -> Nonce
Nonce ByteString
v)
           else Maybe Nonce
forall a. Maybe a
Nothing
  {-# INLINE decode #-}
  encode :: Nonce -> ByteString
encode (Nonce ByteString
v) = ByteString
v
  {-# INLINE encode #-}

instance IsNonce Nonce where
  zero :: Nonce
zero            = ByteString -> Nonce
Nonce (Int -> Word8 -> ByteString
S.replicate Int
Bytes.secretBoxNonce Word8
0)
  nudge :: Nonce -> Nonce
nudge (Nonce ByteString
n) = ByteString -> Nonce
Nonce (ByteString -> ByteString
nudgeBS ByteString
n)

-- | Creates a random key of the correct size for 'secretbox'.
newKey :: IO Key
newKey :: IO Key
newKey = ByteString -> Key
Key (ByteString -> Key) -> IO ByteString -> IO Key
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> Int -> IO ByteString
randomByteString Int
Bytes.secretBoxKey

-- | Creates a random nonce of the correct size for 'secretbox'.
newNonce :: IO Nonce
newNonce :: IO Nonce
newNonce = ByteString -> Nonce
Nonce (ByteString -> Nonce) -> IO ByteString -> IO Nonce
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> Int -> IO ByteString
randomByteString Int
Bytes.secretBoxNonce

-- | Encrypts a message. It is infeasible for an attacker to decrypt
-- the message so long as the 'Nonce' is never repeated.
secretbox :: Key -> Nonce
          -> ByteString
          -- ^ Message
          -> ByteString
          -- ^ Ciphertext
secretbox :: Key -> Nonce -> ByteString -> ByteString
secretbox (Key ByteString
key) (Nonce ByteString
nonce) ByteString
msg =
  ByteString -> ByteString
unpad' (ByteString -> ByteString)
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. Int -> (Ptr CChar -> IO CInt) -> (CInt, ByteString)
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buildUnsafeByteString Int
len ((Ptr CChar -> IO CInt) -> ByteString)
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$ \Ptr CChar
pc ->
    [ByteString] -> ([CStringLen] -> IO CInt) -> IO CInt
forall b. [ByteString] -> ([CStringLen] -> IO b) -> IO b
constByteStrings [ByteString
key, ByteString -> ByteString
pad' ByteString
msg, ByteString
nonce] (([CStringLen] -> IO CInt) -> IO CInt)
-> ([CStringLen] -> IO CInt) -> IO CInt
forall a b. (a -> b) -> a -> b
$ \
      [(Ptr CChar
pk, Int
_), (Ptr CChar
pm, Int
_), (Ptr CChar
pn, Int
_)] ->
        Ptr CChar
-> Ptr CChar -> CULLong -> Ptr CChar -> Ptr CChar -> IO CInt
c_secretbox Ptr CChar
pc Ptr CChar
pm (Int -> CULLong
forall a b. (Integral a, Num b) => a -> b
fromIntegral Int
len) Ptr CChar
pn Ptr CChar
pk
  where len :: Int
len    = ByteString -> Int
S.length ByteString
msg Int -> Int -> Int
forall a. Num a => a -> a -> a
+ Int
Bytes.secretBoxZero
        pad' :: ByteString -> ByteString
pad'   = Int -> ByteString -> ByteString
pad Int
Bytes.secretBoxZero
        unpad' :: ByteString -> ByteString
unpad' = Int -> ByteString -> ByteString
unpad Int
Bytes.secretBoxBoxZero

-- | Encrypts a message. In contrast with 'secretbox', the result is not
-- serialized as one element and instead provided as an authentication tag and
-- ciphertext.
secretboxDetached :: Key -> Nonce
          -> ByteString
          -- ^ Message
          -> (ByteString,ByteString)
          -- ^ (Authentication Tag, Ciphertext)
secretboxDetached :: Key -> Nonce -> ByteString -> (ByteString, ByteString)
secretboxDetached (Key ByteString
key) (Nonce ByteString
nonce) ByteString
msg =
  Int -> (Ptr CChar -> IO ByteString) -> (ByteString, ByteString)
forall b. Int -> (Ptr CChar -> IO b) -> (b, ByteString)
buildUnsafeByteString Int
ctLen ((Ptr CChar -> IO ByteString) -> (ByteString, ByteString))
-> (Ptr CChar -> IO ByteString) -> (ByteString, ByteString)
forall a b. (a -> b) -> a -> b
$ \Ptr CChar
pc ->
   ((CInt, ByteString) -> ByteString)
-> IO (CInt, ByteString) -> IO ByteString
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap (CInt, ByteString) -> ByteString
forall a b. (a, b) -> b
snd (IO (CInt, ByteString) -> IO ByteString)
-> ((Ptr CChar -> IO CInt) -> IO (CInt, ByteString))
-> (Ptr CChar -> IO CInt)
-> IO ByteString
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Int -> (Ptr CChar -> IO CInt) -> IO (CInt, ByteString)
forall b. Int -> (Ptr CChar -> IO b) -> IO (b, ByteString)
buildUnsafeByteString' Int
tagLen ((Ptr CChar -> IO CInt) -> IO ByteString)
-> (Ptr CChar -> IO CInt) -> IO ByteString
forall a b. (a -> b) -> a -> b
$ \Ptr CChar
ptag ->
    [ByteString] -> ([CStringLen] -> IO CInt) -> IO CInt
forall b. [ByteString] -> ([CStringLen] -> IO b) -> IO b
constByteStrings [ByteString
key, ByteString
msg, ByteString
nonce] (([CStringLen] -> IO CInt) -> IO CInt)
-> ([CStringLen] -> IO CInt) -> IO CInt
forall a b. (a -> b) -> a -> b
$ \
      [(Ptr CChar
pk, Int
_), (Ptr CChar
pmsg, Int
_), (Ptr CChar
pn, Int
_)] ->
        Ptr CChar
-> Ptr CChar
-> Ptr CChar
-> CULLong
-> Ptr CChar
-> Ptr CChar
-> IO CInt
c_secretbox_detached Ptr CChar
pc Ptr CChar
ptag Ptr CChar
pmsg (Int -> CULLong
forall a b. (Integral a, Num b) => a -> b
fromIntegral Int
ptLen) Ptr CChar
pn Ptr CChar
pk
  where ctLen :: Int
ctLen  = Int
ptLen
        ptLen :: Int
ptLen  = ByteString -> Int
S.length ByteString
msg
        tagLen :: Int
tagLen = Int
Bytes.secretBoxMac

-- | Decrypts a message. Returns 'Nothing' if the keys and message do
-- not match.
secretboxOpen :: Key -> Nonce 
                 -> ByteString
                 -- ^ Ciphertext
                 -> Maybe ByteString
                 -- ^ Message
secretboxOpen :: Key -> Nonce -> ByteString -> Maybe ByteString
secretboxOpen (Key ByteString
key) (Nonce ByteString
nonce) ByteString
cipher =
  let (CInt
err, ByteString
vec) = Int -> (Ptr CChar -> IO CInt) -> (CInt, ByteString)
forall b. Int -> (Ptr CChar -> IO b) -> (b, ByteString)
buildUnsafeByteString Int
len ((Ptr CChar -> IO CInt) -> (CInt, ByteString))
-> (Ptr CChar -> IO CInt) -> (CInt, ByteString)
forall a b. (a -> b) -> a -> b
$ \Ptr CChar
pm ->
        [ByteString] -> ([CStringLen] -> IO CInt) -> IO CInt
forall b. [ByteString] -> ([CStringLen] -> IO b) -> IO b
constByteStrings [ByteString
key, ByteString -> ByteString
pad' ByteString
cipher, ByteString
nonce] (([CStringLen] -> IO CInt) -> IO CInt)
-> ([CStringLen] -> IO CInt) -> IO CInt
forall a b. (a -> b) -> a -> b
$ \
          [(Ptr CChar
pk, Int
_), (Ptr CChar
pc, Int
_), (Ptr CChar
pn, Int
_)] ->
            Ptr CChar
-> Ptr CChar -> CULLong -> Ptr CChar -> Ptr CChar -> IO CInt
c_secretbox_open Ptr CChar
pm Ptr CChar
pc (Int -> CULLong
forall a b. (Integral a, Num b) => a -> b
fromIntegral Int
len) Ptr CChar
pn Ptr CChar
pk
  in Either String ByteString -> Maybe ByteString
forall s a. Either s a -> Maybe a
hush (Either String ByteString -> Maybe ByteString)
-> (ByteString -> Either String ByteString)
-> ByteString
-> Maybe ByteString
forall b c a. (b -> c) -> (a -> b) -> a -> c
. CInt -> ByteString -> Either String ByteString
forall a. CInt -> a -> Either String a
handleErrno CInt
err (ByteString -> Maybe ByteString) -> ByteString -> Maybe ByteString
forall a b. (a -> b) -> a -> b
$ ByteString -> ByteString
unpad' ByteString
vec
  where len :: Int
len    = ByteString -> Int
S.length ByteString
cipher Int -> Int -> Int
forall a. Num a => a -> a -> a
+ Int
Bytes.secretBoxBoxZero
        pad' :: ByteString -> ByteString
pad'   = Int -> ByteString -> ByteString
pad Int
Bytes.secretBoxBoxZero
        unpad' :: ByteString -> ByteString
unpad' = Int -> ByteString -> ByteString
unpad Int
Bytes.secretBoxZero

-- | Decrypts a message. Returns 'Nothing' if the keys and message do
-- not match.
secretboxOpenDetached :: Key -> Nonce
                 -> ByteString
                 -- ^ Auth Tag
                 -> ByteString
                 -- ^ Ciphertext
                 -> Maybe ByteString
                 -- ^ Message
secretboxOpenDetached :: Key -> Nonce -> ByteString -> ByteString -> Maybe ByteString
secretboxOpenDetached (Key ByteString
key) (Nonce ByteString
nonce) ByteString
tag ByteString
cipher
    | ByteString -> Int
S.length ByteString
tag Int -> Int -> Bool
forall a. Eq a => a -> a -> Bool
/= Int
Bytes.secretBoxMac = Maybe ByteString
forall a. Maybe a
Nothing
    | Bool
otherwise =
  let (CInt
err, ByteString
vec) = Int -> (Ptr CChar -> IO CInt) -> (CInt, ByteString)
forall b. Int -> (Ptr CChar -> IO b) -> (b, ByteString)
buildUnsafeByteString Int
len ((Ptr CChar -> IO CInt) -> (CInt, ByteString))
-> (Ptr CChar -> IO CInt) -> (CInt, ByteString)
forall a b. (a -> b) -> a -> b
$ \Ptr CChar
pm ->
        [ByteString] -> ([CStringLen] -> IO CInt) -> IO CInt
forall b. [ByteString] -> ([CStringLen] -> IO b) -> IO b
constByteStrings [ByteString
key, ByteString
cipher, ByteString
tag, ByteString
nonce] (([CStringLen] -> IO CInt) -> IO CInt)
-> ([CStringLen] -> IO CInt) -> IO CInt
forall a b. (a -> b) -> a -> b
$ \
          [(Ptr CChar
pk, Int
_), (Ptr CChar
pc, Int
_), (Ptr CChar
pt, Int
_), (Ptr CChar
pn, Int
_)] ->
            Ptr CChar
-> Ptr CChar
-> Ptr CChar
-> CULLong
-> Ptr CChar
-> Ptr CChar
-> IO CInt
c_secretbox_open_detached Ptr CChar
pm Ptr CChar
pc Ptr CChar
pt (Int -> CULLong
forall a b. (Integral a, Num b) => a -> b
fromIntegral Int
len) Ptr CChar
pn Ptr CChar
pk
  in Either String ByteString -> Maybe ByteString
forall s a. Either s a -> Maybe a
hush (Either String ByteString -> Maybe ByteString)
-> (ByteString -> Either String ByteString)
-> ByteString
-> Maybe ByteString
forall b c a. (b -> c) -> (a -> b) -> a -> c
. CInt -> ByteString -> Either String ByteString
forall a. CInt -> a -> Either String a
handleErrno CInt
err (ByteString -> Maybe ByteString) -> ByteString -> Maybe ByteString
forall a b. (a -> b) -> a -> b
$ ByteString
vec
  where len :: Int
len    = ByteString -> Int
S.length ByteString
cipher

-- | The secretbox C API uses 0-padded C strings. Always returns 0.
foreign import ccall "crypto_secretbox"
  c_secretbox :: Ptr CChar
              -- ^ Cipher 0-padded output buffer
              -> Ptr CChar
              -- ^ Constant 0-padded message input buffer
              -> CULLong
              -- ^ Length of message input buffer (incl. 0s)
              -> Ptr CChar
              -- ^ Constant nonce buffer
              -> Ptr CChar
              -- ^ Constant key buffer
              -> IO CInt

-- | The secretbox_detached C API uses C strings. Always returns 0.
foreign import ccall "crypto_secretbox_detached"
  c_secretbox_detached
              :: Ptr CChar
              -- ^ Ciphertext output buffer
              -> Ptr CChar
              -- ^ Authentication tag output buffer
              -> Ptr CChar
              -- ^ Constant message input buffer
              -> CULLong
              -- ^ Length of message input buffer (incl. 0s)
              -> Ptr CChar
              -- ^ Constant nonce buffer
              -> Ptr CChar
              -- ^ Constant key buffer
              -> IO CInt

-- | The secretbox C API uses 0-padded C strings. Returns 0 if
-- successful or -1 if verification failed.
foreign import ccall "crypto_secretbox_open"
  c_secretbox_open :: Ptr CChar
                   -- ^ Message 0-padded output buffer
                   -> Ptr CChar
                   -- ^ Constant 0-padded message input buffer
                   -> CULLong
                   -- ^ Length of message input buffer (incl. 0s)
                   -> Ptr CChar
                   -- ^ Constant nonce buffer
                   -> Ptr CChar
                   -- ^ Constant key buffer
                   -> IO CInt

-- | The secretbox C API uses C strings. Returns 0 if
-- successful or -1 if verification failed.
foreign import ccall "crypto_secretbox_open_detached"
  c_secretbox_open_detached
                   :: Ptr CChar
                   -- ^ Message output buffer
                   -> Ptr CChar
                   -- ^ Constant ciphertext input buffer
                   -> Ptr CChar
                   -- ^ Constant auth tag input buffer
                   -> CULLong
                   -- ^ Length of ciphertext input buffer
                   -> Ptr CChar
                   -- ^ Constant nonce buffer
                   -> Ptr CChar
                   -- ^ Constant key buffer
                   -> IO CInt