68 lines
2.4 KiB
Haskell
68 lines
2.4 KiB
Haskell
-- |
|
|
-- Module : Crypto.Number.Generate
|
|
-- License : BSD-style
|
|
-- Maintainer : Vincent Hanquez <vincent@snarc.org>
|
|
-- Stability : experimental
|
|
-- Portability : Good
|
|
|
|
module Crypto.Number.Generate
|
|
( generateMax
|
|
, generateBetween
|
|
, generateOfSize
|
|
, generateBits
|
|
) where
|
|
|
|
import Crypto.Internal.Imports
|
|
import Crypto.Number.Basic
|
|
import Crypto.Number.Serialize
|
|
import Crypto.Random.Types
|
|
import Data.Bits ((.|.), (.&.), shiftR)
|
|
import Crypto.Internal.ByteArray (Bytes, ScrubbedBytes)
|
|
import qualified Crypto.Internal.ByteArray as B
|
|
|
|
|
|
-- | generate a positive integer x, s.t. 0 <= x < m
|
|
generateMax :: MonadRandom m => Integer -> m Integer
|
|
generateMax 1 = return 0
|
|
generateMax m
|
|
| m <= 0 = error "negative value for generateMax"
|
|
| otherwise = do
|
|
result <- randomInt bytesLength
|
|
let result' = result `shiftR` bitsPoppedOff
|
|
if result' >= m
|
|
then generateMax m
|
|
else return result'
|
|
where
|
|
bytesLength = lengthBytes m
|
|
bitsLength = log2 (m-1) + 1
|
|
bitsPoppedOff = 8 - (bitsLength `mod` 8)
|
|
|
|
randomInt nbBytes = os2ipBytes <$> getRandomBytes nbBytes
|
|
|
|
-- | generate a number between the inclusive bound [low,high].
|
|
generateBetween :: MonadRandom m => Integer -> Integer -> m Integer
|
|
generateBetween low high = (low +) <$> generateMax (high - low + 1)
|
|
|
|
-- | generate a positive integer of a specific size in bits.
|
|
-- the number of bits need to be multiple of 8. It will always returns
|
|
-- an integer that is close to 2^(1+bits/8) by setting the 2 highest bits to 1.
|
|
generateOfSize :: MonadRandom m => Int -> m Integer
|
|
generateOfSize bits = os2ip . setHighest <$> getRandomBytes (bits `div` 8)
|
|
where
|
|
setHighest :: ScrubbedBytes -> ScrubbedBytes
|
|
setHighest ran = case B.unpack ran of
|
|
[] -> B.empty
|
|
(w:ws) -> B.pack ((w .|. 0xc0) : ws)
|
|
|
|
-- | Generate a number with the specified number of bits
|
|
generateBits :: MonadRandom m => Int -> m Integer
|
|
generateBits nbBits = modF . os2ipBytes <$> getRandomBytes nbBytes'
|
|
where (nbBytes, strayBits) = nbBits `divMod` 8
|
|
nbBytes' | strayBits == 0 = nbBytes
|
|
| otherwise = nbBytes + 1
|
|
modF | strayBits == 0 = id
|
|
| otherwise = (.&.) (2^nbBits - 1)
|
|
|
|
os2ipBytes :: Bytes -> Integer
|
|
os2ipBytes = os2ip
|