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{-# LANGUAGE PatternGuards #-}
module Network.TLS.Handshake.Random (
serverRandom,
clientRandom,
isDowngraded,
) where
import qualified Data.ByteString as B
import Network.TLS.Context.Internal
import Network.TLS.Struct
-- | Generate a server random suitable for the version selected by the server
-- and its supported versions. We use an 8-byte downgrade suffix when the
-- selected version is lowered because of incomplete client support, but also
-- when a version downgrade has been forced with 'debugVersionForced'. This
-- second part allows to test that the client implementation correctly detects
-- downgrades. The suffix is not used when forcing TLS13 to a server not
-- officially supporting TLS13 (this is not a downgrade scenario but only the
-- consequence of our debug API allowing this).
serverRandom :: Context -> Version -> [Version] -> IO ServerRandom
serverRandom ctx chosenVer suppVers
| TLS13 `elem` suppVers = case chosenVer of
TLS13 -> ServerRandom <$> getStateRNG ctx 32
TLS12 -> ServerRandom <$> genServRand suffix12
_ -> ServerRandom <$> genServRand suffix11
| TLS12 `elem` suppVers = case chosenVer of
TLS13 -> ServerRandom <$> getStateRNG ctx 32
TLS12 -> ServerRandom <$> getStateRNG ctx 32
_ -> ServerRandom <$> genServRand suffix11
| otherwise = ServerRandom <$> getStateRNG ctx 32
where
genServRand suff = do
pref <- getStateRNG ctx 24
return (pref `B.append` suff)
-- | Test if the negotiated version was artificially downgraded (that is, for
-- other reason than the versions supported by the client).
isDowngraded :: Version -> [Version] -> ServerRandom -> Bool
isDowngraded ver suppVers (ServerRandom sr)
| ver <= TLS12
, TLS13 `elem` suppVers =
suffix12 `B.isSuffixOf` sr
|| suffix11 `B.isSuffixOf` sr
| ver <= TLS11
, TLS12 `elem` suppVers =
suffix11 `B.isSuffixOf` sr
| otherwise = False
suffix12 :: B.ByteString
suffix12 = B.pack [0x44, 0x4F, 0x57, 0x4E, 0x47, 0x52, 0x44, 0x01]
suffix11 :: B.ByteString
suffix11 = B.pack [0x44, 0x4F, 0x57, 0x4E, 0x47, 0x52, 0x44, 0x00]
clientRandom :: Context -> IO ClientRandom
clientRandom ctx = ClientRandom <$> getStateRNG ctx 32
|
