| Maintainer | Thomas.DuBuisson@gmail.com |
|---|---|
| Stability | beta |
| Portability | portable |
| Safe Haskell | None |
| Language | Haskell98 |
Crypto.Random
Description
This module is for instantiating cryptographicly strong
determinitic random bit generators (DRBGs, aka PRNGs) For the simple
use case of using the system random number generator
(Entropy) 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
- data GenError
- data ReseedInfo
- splitGen :: CryptoRandomGen g => g -> Either GenError (g, g)
- throwLeft :: Exception e => Either e a -> a
- data SystemRandom
Basic Interface
class CryptoRandomGen g where Source #
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, reseedInfo, reseedPeriod.
Minimal complete definition
newGen, genSeedLength, genBytes, reseedInfo, reseedPeriod, reseed
Methods
newGen :: ByteString -> Either GenError g Source #
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 ByteLength Source #
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
reseedInfo :: g -> ReseedInfo Source #
Indicates how soon a reseed is needed
reseedPeriod :: g -> ReseedInfo Source #
Indicates the period between reseeds (constant for most generators).
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 g Source #
If the generator has produced too many random bytes on its
existing seed it will return 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.Entropy to obtain
entropy for newGen.
WARNING: The default implementation opens a file handle which will never be closed!
Instances
Generator failures should always return the appropriate GenError.
Note GenError in an instance of exception but wether or not an
exception is thrown depends on if the selected generator (read:
if you don't want execptions from code that uses throw then
pass in a generator that never has an error for the used functions)
Constructors
| 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: |
data ReseedInfo Source #
Constructors
| InXBytes !Word64 | Generator needs reseeded in X bytes |
| InXCalls !Word64 | Generator needs reseeded in X calls |
| NotSoon | The bound is over 2^64 bytes or calls |
| Never | This generator never reseeds (ex: |
Instances
Helper functions and expanded interface
splitGen :: CryptoRandomGen g => g -> Either GenError (g, g) Source #
While the safety and wisdom of a splitting function depends on the
properties of the generator being split, several arguments from
informed people indicate such a function is safe for NIST SP 800-90
generators. (see libraries@haskell.org discussion around Sept, Oct
2010). You can find implementations of such generators in the DRBG
package.
throwLeft :: Exception e => Either e a -> a Source #
Useful utility to extract the result of a generator operation and translate error results to exceptions.
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:
Instances