Portability | portable |
---|---|

Stability | beta |

Maintainer | Thomas.DuBuisson@gmail.com |

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 `newGen`

directly

entropy <- getEntropy nrBytes let generator = newGen entropy

- class CryptoRandomGen g where
- newGen :: ByteString -> Either GenError g
- genSeedLength :: Tagged g ByteLength
- genBytes :: ByteLength -> g -> Either GenError (ByteString, g)
- genBytesWithEntropy :: ByteLength -> ByteString -> g -> Either GenError (ByteString, g)
- reseed :: ByteString -> g -> Either GenError g
- newGenIO :: IO g

- data GenError
- splitGen :: CryptoRandomGen g => g -> Either GenError (g, g)
- data SystemRandom

# Basic Interface

class CryptoRandomGen g whereSource

A class of random bit generators that allows for the possibility of failure, reseeding, providing entropy at the same time as requesting bytes

Minimum complete definition: `newGen`

, `genSeedLength`

, `genBytes`

, `reseed`

.

newGen :: ByteString -> Either GenError gSource

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.

genSeedLength :: Tagged g ByteLengthSource

Length of input entropy necessary to instantiate or reseed a generator

genBytes :: ByteLength -> g -> Either GenError (ByteString, g)Source

`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 `NeedReseed`

genBytesWithEntropy :: ByteLength -> ByteString -> g -> Either GenError (ByteString, g)Source

`genBytesWithEntropy g i entropy`

generates `i`

random bytes and use the
additional input `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.

Default:

genBytesWithEntropy g bytes entropy = xor entropy (genBytes g bytes)

reseed :: ByteString -> g -> Either GenError gSource

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 (`NotEnoughEntropy`

).

By default this uses System.Crypto.Random to obtain entropy for `newGen`

.

many generators have these error conditions in common

GenErrorOther String | Misc |

RequestedTooManyBytes | Requested more bytes than a single pass can generate (The maximum request is generator dependent) |

RangeInvalid | When using |

NeedReseed | Some generators cease operation after too high a count without a reseed (ex: NIST SP 800-90) |

NotEnoughEntropy | For instantiating new generators (or reseeding) |

NeedsInfiniteSeed | This generator can not be instantiated or reseeded with a finite seed (ex: |

# Helper functions and expanded interface

splitGen :: CryptoRandomGen g => g -> Either GenError (g, g)Source

# Instances

data SystemRandom Source

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: