{-# LANGUAGE DeriveAnyClass #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE DerivingStrategies #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE UndecidableInstances #-}
module Voting.Protocol.Tally where
import Control.DeepSeq (NFData)
import Control.Monad (Monad(..), mapM, unless)
import Control.Monad.Trans.Except (Except, ExceptT, throwE)
import Data.Aeson (ToJSON(..),FromJSON(..),(.:),(.=))
import Data.Eq (Eq(..))
import Data.Function (($), (.))
import Data.Functor ((<$>))
import Data.Maybe (maybe)
import Data.Semigroup (Semigroup(..))
import Data.Tuple (fst, snd)
import GHC.Generics (Generic)
import Numeric.Natural (Natural)
import Text.Show (Show(..))
import qualified Data.Aeson as JSON
import qualified Data.Aeson.Types as JSON
import qualified Data.Aeson.Encoding as JSON
import qualified Control.Monad.Trans.State.Strict as S
import qualified Data.ByteString as BS
import qualified Data.List as List
import qualified Data.Map.Strict as Map
import Voting.Protocol.Utils
import Voting.Protocol.FFC
import Voting.Protocol.Credential
import Voting.Protocol.Election
data Tally c = Tally
{ tally_countMax :: !Natural
, tally_encByChoiceByQuest :: !(EncryptedTally c)
, tally_decShareByTrustee :: ![DecryptionShare c]
, tally_countByChoiceByQuest :: ![[Natural]]
} deriving (Eq,Show,Generic,NFData)
deriving instance Reifies c FFC => ToJSON (Tally c)
deriving instance Reifies c FFC => FromJSON (Tally c)
type EncryptedTally c = [[Encryption c]]
encryptedTally :: Reifies c FFC => [Ballot c] -> (EncryptedTally c, Natural)
encryptedTally = List.foldr insertEncryptedTally emptyEncryptedTally
emptyEncryptedTally :: Reifies c FFC => (EncryptedTally c, Natural)
emptyEncryptedTally = (List.repeat (List.repeat zero), 0)
insertEncryptedTally :: Reifies c FFC => Ballot c -> (EncryptedTally c, Natural) -> (EncryptedTally c, Natural)
insertEncryptedTally Ballot{..} (encTally, numBallots) =
( List.zipWith
(\Answer{..} -> List.zipWith (+) (fst <$> answer_opinions))
ballot_answers
encTally
, numBallots+1
)
type DecryptionShareCombinator c =
EncryptedTally c -> [DecryptionShare c] -> Except ErrorTally [[DecryptionFactor c]]
proveTally ::
Reifies c FFC =>
(EncryptedTally c, Natural) -> [DecryptionShare c] ->
DecryptionShareCombinator c ->
Except ErrorTally (Tally c)
proveTally
(tally_encByChoiceByQuest, tally_countMax)
tally_decShareByTrustee
decShareCombinator = do
decFactorByChoiceByQuest <-
decShareCombinator
tally_encByChoiceByQuest
tally_decShareByTrustee
dec <- isoZipWithM (throwE ErrorTally_NumberOfQuestions)
(maybe (throwE ErrorTally_NumberOfChoices) return `o2`
isoZipWith (\Encryption{..} decFactor -> encryption_vault / decFactor))
tally_encByChoiceByQuest
decFactorByChoiceByQuest
let logMap = Map.fromList $ List.zip groupGenPowers [0..tally_countMax]
let log x =
maybe (throwE ErrorTally_CannotDecryptCount) return $
Map.lookup x logMap
tally_countByChoiceByQuest <- (log `mapM`)`mapM`dec
return Tally{..}
verifyTally ::
Reifies c FFC =>
Tally c -> DecryptionShareCombinator c ->
Except ErrorTally ()
verifyTally Tally{..} decShareCombinator = do
decFactorByChoiceByQuest <- decShareCombinator tally_encByChoiceByQuest tally_decShareByTrustee
isoZipWith3M_ (throwE ErrorTally_NumberOfQuestions)
(isoZipWith3M_ (throwE ErrorTally_NumberOfChoices)
(\Encryption{..} decFactor count -> do
let groupGenPowCount = encryption_vault / decFactor
unless (groupGenPowCount == groupGen ^ fromNatural count) $
throwE ErrorTally_WrongProof))
tally_encByChoiceByQuest
decFactorByChoiceByQuest
tally_countByChoiceByQuest
newtype DecryptionShare c = DecryptionShare
{ unDecryptionShare :: [[(DecryptionFactor c, Proof c)]] }
deriving (Eq,Show,Generic)
deriving newtype instance NFData (DecryptionShare c)
instance ToJSON (DecryptionShare c) where
toJSON (DecryptionShare decByChoiceByQuest) =
JSON.object
[ "decryption_factors" .=
toJSONList (((toJSON . fst) <$>) <$> decByChoiceByQuest)
, "decryption_proofs" .=
toJSONList (((toJSON . snd) <$>) <$> decByChoiceByQuest)
]
toEncoding (DecryptionShare decByChoiceByQuest) =
JSON.pairs $
JSON.pair "decryption_factors"
(JSON.list (JSON.list (toEncoding . fst)) decByChoiceByQuest) <>
JSON.pair "decryption_proofs"
(JSON.list (JSON.list (toEncoding . snd)) decByChoiceByQuest)
instance Reifies c FFC => FromJSON (DecryptionShare c) where
parseJSON = JSON.withObject "DecryptionShare" $ \o -> do
decFactors <- o .: "decryption_factors"
decProofs <- o .: "decryption_proofs"
let err msg = JSON.typeMismatch ("DecryptionShare: "<>msg) (JSON.Object o)
DecryptionShare
<$> isoZipWithM (err "inconsistent number of questions")
(isoZipWithM (err "inconsistent number of choices")
(\a b -> return (a, b)))
decFactors decProofs
type DecryptionFactor = G
proveDecryptionShare ::
Monad m => Reifies c FFC => RandomGen r =>
EncryptedTally c -> SecretKey c -> S.StateT r m (DecryptionShare c)
proveDecryptionShare encByChoiceByQuest trusteeSecKey =
(DecryptionShare <$>) $
(proveDecryptionFactor trusteeSecKey `mapM`) `mapM` encByChoiceByQuest
proveDecryptionFactor ::
Monad m => Reifies c FFC => RandomGen r =>
SecretKey c -> Encryption c -> S.StateT r m (DecryptionFactor c, Proof c)
proveDecryptionFactor trusteeSecKey Encryption{..} = do
proof <- prove trusteeSecKey [groupGen, encryption_nonce] (hash zkp)
return (encryption_nonce^trusteeSecKey, proof)
where zkp = decryptionShareStatement (publicKey trusteeSecKey)
decryptionShareStatement :: Reifies c FFC => PublicKey c -> BS.ByteString
decryptionShareStatement pubKey =
"decrypt|"<>bytesNat pubKey<>"|"
data ErrorTally
= ErrorTally_NumberOfQuestions
| ErrorTally_NumberOfChoices
| ErrorTally_NumberOfTrustees
| ErrorTally_WrongProof
| ErrorTally_CannotDecryptCount
deriving (Eq,Show,Generic,NFData)
verifyDecryptionShare ::
Monad m => Reifies c FFC =>
EncryptedTally c -> PublicKey c -> DecryptionShare c ->
ExceptT ErrorTally m ()
verifyDecryptionShare encByChoiceByQuest trusteePubKey (DecryptionShare decShare) =
let zkp = decryptionShareStatement trusteePubKey in
isoZipWithM_ (throwE ErrorTally_NumberOfQuestions)
(isoZipWithM_ (throwE ErrorTally_NumberOfChoices) $
\Encryption{..} (decFactor, proof) ->
unless (proof_challenge proof == hash zkp
[ commit proof groupGen trusteePubKey
, commit proof encryption_nonce decFactor
]) $ throwE ErrorTally_WrongProof)
encByChoiceByQuest
decShare
verifyDecryptionShareByTrustee ::
Monad m => Reifies c FFC =>
EncryptedTally c -> [PublicKey c] -> [DecryptionShare c] ->
ExceptT ErrorTally m ()
verifyDecryptionShareByTrustee encTally =
isoZipWithM_ (throwE ErrorTally_NumberOfTrustees)
(verifyDecryptionShare encTally)