1 files changed, 107 insertions, 9 deletions
diff --git a/HTTP/ProofOfWork.hs b/HTTP/ProofOfWork.hs
index 45cc96d..04aec57 100644
--- a/HTTP/ProofOfWork.hs
+++ b/HTTP/ProofOfWork.hs
@@ -4,19 +4,117 @@
  -}
 
 {-# LANGUAGE DeriveGeneric #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}
 
 module HTTP.ProofOfWork where
 
 import Types
-import qualified Data.Text as T
+import Types.Cost
+import ExpensiveHash
+import Tunables
+import ByteStrings
 import GHC.Generics
+import qualified Data.Text as T
+import qualified Data.ByteString as B
+import Data.Text.Encoding (encodeUtf8)
+import Raaz.Core.Encode
+import qualified Raaz
+import Data.BloomFilter.Hash
+import Control.Monad
+import Data.Word
+import Data.Bits
+import Data.Monoid
+import Prelude
+
+-- | A value that the client has to do some work to calculate.
+data ProofOfWork = ProofOfWork B.ByteString RandomSalt
+	deriving (Show)
+
+data ProofOfWorkRequirement = ProofOfWorkRequirement
+	{ leadingZeros :: Int
+	, addedArgon2Iterations :: Word32
+	, randomSalt :: RandomSalt
+	}
+	deriving (Generic, Show)
+
+-- | Using Text and not ByteString so that ProofOfWorkRequirement can have a
+-- JSON instance.
+newtype RandomSalt = RandomSalt { fromRandomSalt :: T.Text }
+	deriving (Generic, Show, Eq)
+
+instance Hashable RandomSalt where
+	hashIO32 = hashIO32 . encodeUtf8 . fromRandomSalt
+	hashIO64 = hashIO64 . encodeUtf8 . fromRandomSalt
+
+-- | Servers should never demand a proof of work that takes longer than
+-- this to generate. Note that if a server changes its mind and doubles
+-- the proof of work, a client counts that cumulatively. So, a server
+-- should avoid any single proof of work requirement taking more than half
+-- this long.
+maxProofOfWork :: Seconds
+maxProofOfWork = Seconds (16*60)
+
+-- | How long it will take to generate a proof of work meeting the
+-- requirement, maximum.
+--
+-- Of course, a client can get lucky and find a value that works
+-- on the very first try. On average, the client will need to work for half
+-- as long as the returned number of Seconds.
+generationTime :: ProofOfWorkRequirement -> Seconds
+generationTime req = 
+	let UseArgon2 (CPUCost (Seconds s) _) _ = proofOfWorkHashTunable (addedArgon2Iterations req)
+	in Seconds ((2^(leadingZeros req)) * s)
+
+mkProofOfWorkRequirement :: Seconds -> Maybe (RandomSalt -> ProofOfWorkRequirement)
+mkProofOfWorkRequirement (Seconds n)
+	| lz < 1 = Nothing
+	| otherwise = Just $ ProofOfWorkRequirement lz its
+  where
+	lz = floor (logBase 2 (max 1 (fromIntegral n / fromIntegral s)) :: Double)
+	UseArgon2 (CPUCost (Seconds s) _) _ = proofOfWorkHashTunable its
+	its = 0
+
+mkRandomSalt :: IO RandomSalt
+mkRandomSalt = do
+	prg <- Raaz.newPRG () :: IO Raaz.SystemPRG
+	rs <- replicateM 16 (Raaz.random prg :: IO Word8)
+	return $ RandomSalt $ T.pack $ concatMap show rs
+
+instance Raaz.Random Word8
+
+isValidProofOfWork :: ProofOfWork -> ProofOfWorkRequirement -> StorableObjectIdent -> Bool
+isValidProofOfWork (ProofOfWork pow rsalt) req (StorableObjectIdent n) =
+	samesalts && enoughzeros
+  where
+	samesalts = rsalt == randomSalt req
+	enoughzeros = all (== False) (take (leadingZeros req) (setBits b))
+	tunable = proofOfWorkHashTunable (addedArgon2Iterations req)
+	salt = Salt $ POWSalt $
+		encodeUtf8 (fromRandomSalt (randomSalt req)) <> pow
+	ExpensiveHash _ hash = expensiveHash tunable salt n
+	-- Since expensiveHash generates an ascii encoded hash that
+	-- includes the parameters, take the sha256 of it to get the
+	-- bytestring that is what's checked for the neccesary number
+	-- of leading 0 bits.
+	b = Raaz.toByteString $ Raaz.sha256 $ encodeUtf8 hash
+
+setBits :: B.ByteString -> [Bool]
+setBits = concatMap go . B.unpack
+  where
+	go byte = map (uncurry testBit) (zip (repeat byte) [0..7])
+
+newtype POWSalt = POWSalt B.ByteString
 
-data ProofOfWorkRequirement t
-	= Result t
-	| ProofOfWorkRequirement
-		{ leadingZeros :: Int
-		, argon2Iterations :: Int
-		}
-	deriving (Generic)
+instance Encodable POWSalt where
+	toByteString (POWSalt n) = n
+	fromByteString = Just . POWSalt
 
-newtype ProofOfWork = ProofOfWork T.Text
+genProofOfWork :: ProofOfWorkRequirement -> StorableObjectIdent -> ProofOfWork
+genProofOfWork req i = go allByteStrings
+  where
+	go [] = error "failed to generate Proof Of Work. This should be impossible!"
+	go (b:bs)
+		| isValidProofOfWork candidate req i = candidate
+		| otherwise = go bs
+	  where
+		candidate = ProofOfWork b (randomSalt req)