    -- |
    -- Module      : Network.TLS.Crypto.IES
    -- License     : BSD-style
    -- Maintainer  : Kazu Yamamoto <kazu@iij.ad.jp>
    -- Stability   : experimental
    -- Portability : unknown
    --
    module Network.TLS.Crypto.IES
        (
          GroupPublic
        , GroupPrivate
        , GroupKey
        -- * Group methods
        , groupGenerateKeyPair
        , groupGetPubShared
        , groupGetShared
        , encodeGroupPublic
        , decodeGroupPublic
        -- * Compatibility with 'Network.TLS.Crypto.DH'
        , dhParamsForGroup
        , dhGroupGenerateKeyPair
        , dhGroupGetPubShared
        ) where

    import Control.Arrow
    import Crypto.ECC
    import Crypto.Error
    import Crypto.Number.Generate
    import Crypto.PubKey.DH hiding (generateParams)
    import Crypto.PubKey.ECIES
    import qualified Data.ByteArray as B
    import Data.Proxy
    import Network.TLS.Crypto.Types
    import Network.TLS.Extra.FFDHE
    import Network.TLS.Imports
    import Network.TLS.RNG
    import Network.TLS.Util.Serialization (os2ip,i2ospOf_)

    data GroupPrivate = GroupPri_P256 (Scalar Curve_P256R1)
                      | GroupPri_P384 (Scalar Curve_P384R1)
                      | GroupPri_P521 (Scalar Curve_P521R1)
                      | GroupPri_X255 (Scalar Curve_X25519)
                      | GroupPri_X448 (Scalar Curve_X448)
                      | GroupPri_FFDHE2048 PrivateNumber
                      | GroupPri_FFDHE3072 PrivateNumber
                      | GroupPri_FFDHE4096 PrivateNumber
                      | GroupPri_FFDHE6144 PrivateNumber
                      | GroupPri_FFDHE8192 PrivateNumber
                      deriving (Eq, Show)

    data GroupPublic = GroupPub_P256 (Point Curve_P256R1)
                     | GroupPub_P384 (Point Curve_P384R1)
                     | GroupPub_P521 (Point Curve_P521R1)
                     | GroupPub_X255 (Point Curve_X25519)
                     | GroupPub_X448 (Point Curve_X448)
                     | GroupPub_FFDHE2048 PublicNumber
                     | GroupPub_FFDHE3072 PublicNumber
                     | GroupPub_FFDHE4096 PublicNumber
                     | GroupPub_FFDHE6144 PublicNumber
                     | GroupPub_FFDHE8192 PublicNumber
                     deriving (Eq, Show)

    type GroupKey = SharedSecret

    p256 :: Proxy Curve_P256R1
    p256 = Proxy

    p384 :: Proxy Curve_P384R1
    p384 = Proxy

    p521 :: Proxy Curve_P521R1
    p521 = Proxy

    x25519 :: Proxy Curve_X25519
    x25519 = Proxy

    x448 :: Proxy Curve_X448
    x448 = Proxy

    dhParamsForGroup :: Group -> Maybe Params
    dhParamsForGroup FFDHE2048 = Just ffdhe2048
    dhParamsForGroup FFDHE3072 = Just ffdhe3072
    dhParamsForGroup FFDHE4096 = Just ffdhe4096
    dhParamsForGroup FFDHE6144 = Just ffdhe6144
    dhParamsForGroup FFDHE8192 = Just ffdhe8192
    dhParamsForGroup _         = Nothing

    groupGenerateKeyPair :: MonadRandom r => Group -> r (GroupPrivate, GroupPublic)
    groupGenerateKeyPair P256   =
        (GroupPri_P256,GroupPub_P256) `fs` curveGenerateKeyPair p256
    groupGenerateKeyPair P384   =
        (GroupPri_P384,GroupPub_P384) `fs` curveGenerateKeyPair p384
    groupGenerateKeyPair P521   =
        (GroupPri_P521,GroupPub_P521) `fs` curveGenerateKeyPair p521
    groupGenerateKeyPair X25519 =
        (GroupPri_X255,GroupPub_X255) `fs` curveGenerateKeyPair x25519
    groupGenerateKeyPair X448 =
        (GroupPri_X448,GroupPub_X448) `fs` curveGenerateKeyPair x448
    groupGenerateKeyPair FFDHE2048 = gen ffdhe2048 exp2048 GroupPri_FFDHE2048 GroupPub_FFDHE2048
    groupGenerateKeyPair FFDHE3072 = gen ffdhe3072 exp3072 GroupPri_FFDHE3072 GroupPub_FFDHE3072
    groupGenerateKeyPair FFDHE4096 = gen ffdhe4096 exp4096 GroupPri_FFDHE4096 GroupPub_FFDHE4096
    groupGenerateKeyPair FFDHE6144 = gen ffdhe6144 exp6144 GroupPri_FFDHE6144 GroupPub_FFDHE6144
    groupGenerateKeyPair FFDHE8192 = gen ffdhe8192 exp8192 GroupPri_FFDHE8192 GroupPub_FFDHE8192

    dhGroupGenerateKeyPair :: MonadRandom r => Group -> r (Params, PrivateNumber, PublicNumber)
    dhGroupGenerateKeyPair FFDHE2048 = addParams ffdhe2048 (gen' ffdhe2048 exp2048)
    dhGroupGenerateKeyPair FFDHE3072 = addParams ffdhe3072 (gen' ffdhe3072 exp3072)
    dhGroupGenerateKeyPair FFDHE4096 = addParams ffdhe4096 (gen' ffdhe4096 exp4096)
    dhGroupGenerateKeyPair FFDHE6144 = addParams ffdhe6144 (gen' ffdhe6144 exp6144)
    dhGroupGenerateKeyPair FFDHE8192 = addParams ffdhe8192 (gen' ffdhe8192 exp8192)
    dhGroupGenerateKeyPair grp       = error ("invalid FFDHE group: " ++ show grp)

    addParams :: Functor f => Params -> f (a, b) -> f (Params, a, b)
    addParams params = fmap $ \(a, b) -> (params, a, b)

    fs :: MonadRandom r
       => (Scalar a -> GroupPrivate, Point a -> GroupPublic)
       -> r (KeyPair a)
       -> r (GroupPrivate, GroupPublic)
    (t1, t2) `fs` action = do
        keypair <- action
        let pub = keypairGetPublic keypair
            pri = keypairGetPrivate keypair
        return (t1 pri, t2 pub)

    gen :: MonadRandom r
        => Params
        -> Int
        -> (PrivateNumber -> GroupPrivate)
        -> (PublicNumber -> GroupPublic)
        -> r (GroupPrivate, GroupPublic)
    gen params expBits priTag pubTag = (priTag *** pubTag) <$> gen' params expBits

    gen' :: MonadRandom r
         => Params
         -> Int
         -> r (PrivateNumber, PublicNumber)
    gen' params expBits = (id &&& calculatePublic params) <$> generatePriv expBits

    groupGetPubShared :: MonadRandom r => GroupPublic -> r (Maybe (GroupPublic, GroupKey))
    groupGetPubShared (GroupPub_P256 pub) =
        fmap (first GroupPub_P256) . maybeCryptoError <$> deriveEncrypt p256 pub
    groupGetPubShared (GroupPub_P384 pub) =
        fmap (first GroupPub_P384) . maybeCryptoError <$> deriveEncrypt p384 pub
    groupGetPubShared (GroupPub_P521 pub) =
        fmap (first GroupPub_P521) . maybeCryptoError <$> deriveEncrypt p521 pub
    groupGetPubShared (GroupPub_X255 pub) =
        fmap (first GroupPub_X255) . maybeCryptoError <$> deriveEncrypt x25519 pub
    groupGetPubShared (GroupPub_X448 pub) =
        fmap (first GroupPub_X448) . maybeCryptoError <$> deriveEncrypt x448 pub
    groupGetPubShared (GroupPub_FFDHE2048 pub) = getPubShared ffdhe2048 exp2048 pub GroupPub_FFDHE2048
    groupGetPubShared (GroupPub_FFDHE3072 pub) = getPubShared ffdhe3072 exp3072 pub GroupPub_FFDHE3072
    groupGetPubShared (GroupPub_FFDHE4096 pub) = getPubShared ffdhe4096 exp4096 pub GroupPub_FFDHE4096
    groupGetPubShared (GroupPub_FFDHE6144 pub) = getPubShared ffdhe6144 exp6144 pub GroupPub_FFDHE6144
    groupGetPubShared (GroupPub_FFDHE8192 pub) = getPubShared ffdhe8192 exp8192 pub GroupPub_FFDHE8192

    dhGroupGetPubShared :: MonadRandom r => Group -> PublicNumber -> r (Maybe (PublicNumber, SharedKey))
    dhGroupGetPubShared FFDHE2048 pub = getPubShared' ffdhe2048 exp2048 pub
    dhGroupGetPubShared FFDHE3072 pub = getPubShared' ffdhe3072 exp3072 pub
    dhGroupGetPubShared FFDHE4096 pub = getPubShared' ffdhe4096 exp4096 pub
    dhGroupGetPubShared FFDHE6144 pub = getPubShared' ffdhe6144 exp6144 pub
    dhGroupGetPubShared FFDHE8192 pub = getPubShared' ffdhe8192 exp8192 pub
    dhGroupGetPubShared _         _   = return Nothing

    getPubShared :: MonadRandom r
                 => Params
                 -> Int
                 -> PublicNumber
                 -> (PublicNumber -> GroupPublic)
                 -> r (Maybe (GroupPublic, GroupKey))
    getPubShared params expBits pub pubTag | not (valid params pub) = return Nothing
                                           | otherwise = do
        mypri <- generatePriv expBits
        let mypub = calculatePublic params mypri
        let SharedKey share = getShared params mypri pub
        return $ Just (pubTag mypub, SharedSecret share)

    getPubShared' :: MonadRandom r
                  => Params
                  -> Int
                  -> PublicNumber
                  -> r (Maybe (PublicNumber, SharedKey))
    getPubShared' params expBits pub
        | not (valid params pub) = return Nothing
        | otherwise = do
            mypri <- generatePriv expBits
            let share = stripLeadingZeros (getShared params mypri pub)
            return $ Just (calculatePublic params mypri, SharedKey share)

    groupGetShared ::  GroupPublic -> GroupPrivate -> Maybe GroupKey
    groupGetShared (GroupPub_P256 pub) (GroupPri_P256 pri) = maybeCryptoError $ deriveDecrypt p256 pub pri
    groupGetShared (GroupPub_P384 pub) (GroupPri_P384 pri) = maybeCryptoError $ deriveDecrypt p384 pub pri
    groupGetShared (GroupPub_P521 pub) (GroupPri_P521 pri) = maybeCryptoError $ deriveDecrypt p521 pub pri
    groupGetShared (GroupPub_X255 pub) (GroupPri_X255 pri) = maybeCryptoError $ deriveDecrypt x25519 pub pri
    groupGetShared (GroupPub_X448 pub) (GroupPri_X448 pri) = maybeCryptoError $ deriveDecrypt x448 pub pri
    groupGetShared (GroupPub_FFDHE2048 pub) (GroupPri_FFDHE2048 pri) = calcShared ffdhe2048 pub pri
    groupGetShared (GroupPub_FFDHE3072 pub) (GroupPri_FFDHE3072 pri) = calcShared ffdhe3072 pub pri
    groupGetShared (GroupPub_FFDHE4096 pub) (GroupPri_FFDHE4096 pri) = calcShared ffdhe4096 pub pri
    groupGetShared (GroupPub_FFDHE6144 pub) (GroupPri_FFDHE6144 pri) = calcShared ffdhe6144 pub pri
    groupGetShared (GroupPub_FFDHE8192 pub) (GroupPri_FFDHE8192 pri) = calcShared ffdhe8192 pub pri
    groupGetShared _ _ = Nothing

    calcShared :: Params -> PublicNumber -> PrivateNumber -> Maybe SharedSecret
    calcShared params pub pri
        | valid params pub = Just $ SharedSecret share
        | otherwise        = Nothing
      where
        SharedKey share = getShared params pri pub

    encodeGroupPublic :: GroupPublic -> ByteString
    encodeGroupPublic (GroupPub_P256 p) = encodePoint p256 p
    encodeGroupPublic (GroupPub_P384 p) = encodePoint p384 p
    encodeGroupPublic (GroupPub_P521 p) = encodePoint p521 p
    encodeGroupPublic (GroupPub_X255 p) = encodePoint x25519 p
    encodeGroupPublic (GroupPub_X448 p) = encodePoint x448 p
    encodeGroupPublic (GroupPub_FFDHE2048 p) = enc ffdhe2048 p
    encodeGroupPublic (GroupPub_FFDHE3072 p) = enc ffdhe3072 p
    encodeGroupPublic (GroupPub_FFDHE4096 p) = enc ffdhe4096 p
    encodeGroupPublic (GroupPub_FFDHE6144 p) = enc ffdhe6144 p
    encodeGroupPublic (GroupPub_FFDHE8192 p) = enc ffdhe8192 p

    enc :: Params -> PublicNumber -> ByteString
    enc params (PublicNumber p) = i2ospOf_ ((params_bits params + 7) `div` 8) p

    decodeGroupPublic :: Group -> ByteString -> Either CryptoError GroupPublic
    decodeGroupPublic P256   bs = eitherCryptoError $ GroupPub_P256 <$> decodePoint p256 bs
    decodeGroupPublic P384   bs = eitherCryptoError $ GroupPub_P384 <$> decodePoint p384 bs
    decodeGroupPublic P521   bs = eitherCryptoError $ GroupPub_P521 <$> decodePoint p521 bs
    decodeGroupPublic X25519 bs = eitherCryptoError $ GroupPub_X255 <$> decodePoint x25519 bs
    decodeGroupPublic X448 bs = eitherCryptoError $ GroupPub_X448 <$> decodePoint x448 bs
    decodeGroupPublic FFDHE2048 bs = Right . GroupPub_FFDHE2048 . PublicNumber $ os2ip bs
    decodeGroupPublic FFDHE3072 bs = Right . GroupPub_FFDHE3072 . PublicNumber $ os2ip bs
    decodeGroupPublic FFDHE4096 bs = Right . GroupPub_FFDHE4096 . PublicNumber $ os2ip bs
    decodeGroupPublic FFDHE6144 bs = Right . GroupPub_FFDHE6144 . PublicNumber $ os2ip bs
    decodeGroupPublic FFDHE8192 bs = Right . GroupPub_FFDHE8192 . PublicNumber $ os2ip bs

    -- Check that group element in not in the 2-element subgroup { 1, p - 1 }.
    -- See RFC 7919 section 3 and NIST SP 56A rev 2 section 5.6.2.3.1.
    valid :: Params -> PublicNumber -> Bool
    valid (Params p _ _) (PublicNumber y) = 1 < y && y < p - 1

    -- strips leading zeros from the result of getShared, as required
    -- for DH(E) premaster secret in SSL/TLS before version 1.3.
    stripLeadingZeros :: SharedKey -> B.ScrubbedBytes
    stripLeadingZeros (SharedKey sb) = snd $ B.span (== 0) sb

    -- Use short exponents as optimization, see RFC 7919 section 5.2.
    generatePriv :: MonadRandom r => Int -> r PrivateNumber
    generatePriv e = PrivateNumber <$> generateParams e (Just SetHighest) False

    -- Short exponent bit sizes from RFC 7919 appendix A, rounded to next
    -- multiple of 16 bits, i.e. going through a function like:
    -- let shortExp n = head [ e | i <- [1..], let e = n + i, e `mod` 16 == 0 ]
    exp2048 :: Int
    exp3072 :: Int
    exp4096 :: Int
    exp6144 :: Int
    exp8192 :: Int
    exp2048 = 240 -- shortExp 225
    exp3072 = 288 -- shortExp 275
    exp4096 = 336 -- shortExp 325
    exp6144 = 384 -- shortExp 375
    exp8192 = 416 -- shortExp 400