This module is for instantiating cryptographically strong determinitic random bit generators (DRBGs, aka PRNGs)
For the simple use case of using the system random number generator (
System.Crypto.Random) to seed the DRBG:
g <- newGenIO
Users needing to provide their own entropy can call
entropy <- getEntropy nrBytes let generator = newGen entropy
- class CryptoRandomGen g where
- data GenError
- splitGen :: CryptoRandomGen g => g -> Either GenError (g, g)
- data SystemRandom
A class of random bit generators that allows for the possibility of failure, reseeding, providing entropy at the same time as requesting bytes
Instantiate a new random bit generator. The provided bytestring should
be of length >= genSeedLength. If the bytestring is shorter
then the call may fail (suggested error:
NotEnoughEntropy). If the
bytestring is of sufficent length the call should always succeed.
Length of input entropy necessary to instantiate or reseed a generator
genBytes len g generates a random ByteString of length
len and new generator.
The MonadCryptoRandom package has routines useful for converting the ByteString
to commonly needed values (but cereal or other deserialization libraries would also work).
This routine can fail if the generator has gone too long without a reseed (usually this
is in the ball-park of 2^48 requests). Suggested error in this cases is
genBytesWithEntropy g i entropy generates
i random bytes and use the
entropy in the generation of the requested data to
increase the confidence our generated data is a secure random stream.
Some generators use
entropy to perturb the state of the generator, meaning:
(_,g2') <- genBytesWithEntropy len g1 ent (_,g2 ) <- genBytes len g1 g2 /= g2'
But this is not required.
genBytesWithEntropy g bytes entropy = xor entropy (genBytes g bytes)
If the generator has produced too many random bytes on its existing seed
it will throw
NeedReseed. In that case, reseed the generator using this function and
a new high-entropy seed of length >=
genSeedLength. Using bytestrings that are too short
can result in an error (
many generators have these error conditions in common
Requested more bytes than a single pass can generate (The maximum request is generator dependent)
Some generators cease operation after too high a count without a reseed (ex: NIST SP 800-90)
For instantiating new generators (or reseeding)
This generator can not be instantiated or reseeded with a finite seed (ex:
Helper functions and expanded interface
Not that it is technically correct as an instance of
CryptoRandomGen, but simply because
it's a reasonable engineering choice here is a CryptoRandomGen which streams the system randoms. Take note: