A deterministic random bit generator (DRBG).

Create a DRBG with new, and then use and reuse it to generate bytes as needed.

>>> drbg <- new entropy nonce personalization_string
>>> bytes0 <- gen drbg mempty 10
>>> bytes1 <- gen drbg mempty 10
>>> drbg
"<drbg>"

A DRBG error.

Create a HMAC-SHA256 DRBG from the supplied entropy, nonce, and personalization string.

The DRBG is returned in any PrimMonad, e.g. 'ST s' or IO.

>>> new entropy nonce personalization_string
"<drbg>"

Generate bytes from a DRBG, optionally injecting additional bytes per SP 800-90A.

Per SP 800-90A, the maximum number of bytes that can be requested on any invocation is 65536. Larger requests will return MaxBytesExceeded.

>>> import qualified Data.ByteString.Base16 as B16
>>> drbg <- new entropy nonce personalization_string
>>> Right bytes0 <- gen drbg addl_bytes 16
>>> Right bytes1 <- gen drbg addl_bytes 16
>>> B16.encode bytes0
"938d6ca6d0b797f7b3c653349d6e3135"
>>> B16.encode bytes1
"5f379d16de6f2c6f8a35c56f13f9e5a5"

Reseed a DRBG.

Each DRBG has an internal reseed counter that tracks the number of requests made to the generator (note requests made, not bytes generated). SP 800-90A specifies that a HMAC-DRBG should support 2 ^ 48 requests before requiring a reseed, so in practice you're unlikely to ever need to use this to actually reset the counter.

Note however that reseed can be used to implement "explicit" prediction resistance, per SP 800-90A, by injecting entropy generated elsewhere into the DRBG.

>>> import qualified System.Entropy as E
>>> entropy <- E.getEntropy 32
>>> reseed entropy addl_bytes drbg
"<reseeded drbg>"

Wipe the state of a DRBG.

You should call this when you're finished with a DRBG to ensure that its state is wiped from memory.

>>> drbg <- new mempty mempty mempty
>>> Right bytes <- gen drbg addl_bytes 16
>>> wipe drbg
>>> -- do something with bytes