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|
-- |
-- Module : Crypto.Random.API
-- License : BSD-style
-- Maintainer : Vincent Hanquez <vincent@snarc.org>
-- Stability : experimental
-- Portability : Good
module Crypto.Random.API
( CPRG(..)
, ReseedPolicy(..)
, genRandomBytes
, genRandomBytes'
, withRandomBytes
, getSystemEntropy
-- * System Random generator
, SystemRandom
, getSystemRandomGen
) where
import Control.Applicative
import qualified Data.ByteString as B
import Data.ByteString (ByteString)
import qualified System.Entropy as SE
import System.IO.Unsafe (unsafeInterleaveIO)
import Data.Word
-- | This is the reseed policy requested by the CPRG
data ReseedPolicy =
NeverReseed -- ^ there is no need to reseed as either
-- the RG doesn't supports it, it's done automatically
-- or pratically the reseeding period exceed a Word64 type.
| ReseedInBytes Word64 -- ^ the RG need to be reseed in the number
-- of bytes joined to the type. it should be done before
-- the number reached 0, otherwise an user of the RG
-- might request too many bytes and get repeated random bytes.
deriving (Show,Eq)
-- | A class of Cryptographic Secure Random generator.
--
-- The main difference with the generic haskell RNG is that
-- it return bytes instead of integer.
--
-- It is quite similar to the CryptoRandomGen class in crypto-api
-- except that error are not returned to the user. Instead
-- the user is suppose to handle reseeding by using the NeedReseed
-- and SupplyEntropy methods. For other type of errors, the user
-- is expected to generate bytes with the parameters bounds explicity
-- defined here.
--
-- The CPRG need to be able to generate up to 2^20 bytes in one call,
--
class CPRG g where
-- | Provide a way to query the CPRG to calculate when new entropy
-- is required to be supplied so the CPRG doesn't repeat output, and
-- break assumptions. This returns the number of bytes before
-- which supply entropy should have been called.
cprgNeedReseed :: g -> ReseedPolicy
-- | Supply entropy to the CPRG, that can be used now or later
-- to reseed the CPRG. This should be used in conjunction to
-- NeedReseed to know when to supply entropy.
cprgSupplyEntropy :: ByteString -> g -> g
-- | Generate bytes using the CPRG and the number specified.
--
-- For user of the API, it's recommended to use genRandomBytes
-- instead of this method directly. the CPRG need to be able
-- to supply at minimum 2^20 bytes at a time.
cprgGenBytes :: Int -> g -> (ByteString, g)
-- | Generate bytes using the cprg in parameter.
--
-- If the number of bytes requested is really high,
-- it's preferable to use 'genRandomBytes' for better memory efficiency.
genRandomBytes :: CPRG g => Int -- ^ number of bytes to return
-> g -- ^ CPRG to use
-> (ByteString, g)
genRandomBytes len rng = (\(lbs,g) -> (B.concat lbs, g)) $ genRandomBytes' len rng
-- | Generate bytes using the cprg in parameter.
--
-- This is not tail recursive and an excessive len (>= 2^29) parameter would
-- result in stack overflow.
genRandomBytes' :: CPRG g => Int -- ^ number of bytes to return
-> g -- ^ CPRG to use
-> ([ByteString], g)
genRandomBytes' len rng
| len < 0 = error "genBytes: cannot request negative amount of bytes."
| otherwise = loop rng len
where loop g len
| len == 0 = ([], g)
| otherwise = let itBytes = min (2^20) len
(bs, g') = cprgGenBytes itBytes g
(l, g'') = genRandomBytes' (len-itBytes) g'
in (bs:l, g'')
-- | this is equivalent to using Control.Arrow 'first' with 'genRandomBytes'.
--
-- namely it generate @len bytes and map the bytes to the function @f
withRandomBytes :: CPRG g => g -> Int -> (ByteString -> a) -> (a, g)
withRandomBytes rng len f = (f bs, rng')
where (bs, rng') = genRandomBytes len rng
-- | Return system entropy using the entropy package 'getEntropy'
getSystemEntropy :: Int -> IO ByteString
getSystemEntropy = SE.getEntropy
-- | This is a simple generator that pull bytes from the system entropy
-- directly. Its randomness and security properties are absolutely
-- depends on the underlaying system implementation.
data SystemRandom = SystemRandom [B.ByteString]
-- | Get a random number generator based on the standard system entropy source
getSystemRandomGen :: IO SystemRandom
getSystemRandomGen = do
ch <- SE.openHandle
let getBS = unsafeInterleaveIO $ do
bs <- SE.hGetEntropy ch 8192
more <- getBS
return (bs:more)
SystemRandom <$> getBS
instance CPRG SystemRandom where
cprgNeedReseed _ = NeverReseed
cprgSupplyEntropy _ g = g
cprgGenBytes n (SystemRandom l) = (B.concat l1, SystemRandom l2)
where (l1, l2) = lbsSplitAt n l
lbsSplitAt rBytes (x:xs)
| xLen >= rBytes =
let (b1,b2) = B.splitAt rBytes x
in ([b1], b2:xs)
| otherwise =
let (l1,l2) = lbsSplitAt (rBytes-xLen) xs
in (x:l1,l2)
where xLen = B.length x
|
