A wrapper around any PRNG that implements BlockRngCore
, that adds the
ability to reseed it.
ReseedingRng
reseeds the underlying PRNG in the following cases:
- On a manual call to
reseed()
.
- After
clone()
, the clone will be reseeded on first use.
- After a process is forked, the RNG in the child process is reseeded within
the next few generated values, depending on the block size of the
underlying PRNG. For
ChaChaCore
and Hc128Core
this is a maximum of
15 u32
values before reseeding.
- After the PRNG has generated a configurable number of random bytes.
Reseeding after a fixed number of generated bytes is never strictly
necessary. Cryptographic PRNGs don't have a limited number of bytes they
can output, or at least not a limit reachable in any practical way. There is
no such thing as 'running out of entropy'.
Occasionally reseeding can be seen as some form of 'security in depth'. Even
if in the future a cryptographic weakness is found in the CSPRNG being used,
or a flaw in the implementation, occasionally reseeding should make
exploiting it much more difficult or even impossible.
Use ReseedingRng::new
with a threshold
of 0
to disable reseeding
after a fixed number of generated bytes.
Although unlikely, reseeding the wrapped PRNG can fail. ReseedingRng
will
never panic but try to handle the error intelligently through some
combination of retrying and delaying reseeding until later.
If handling the source error fails ReseedingRng
will continue generating
data from the wrapped PRNG without reseeding.
Manually calling reseed()
will not have this retry or delay logic, but
reports the error.
use rand::prelude::*;
use rand_chacha::ChaChaCore;
use rand::rngs::OsRng;
use rand::rngs::adapter::ReseedingRng;
let prng = ChaChaCore::from_entropy();
let reseeder = OsRng::new().unwrap();
let mut reseeding_rng = ReseedingRng::new(prng, 0, reseeder);
println!("{}", reseeding_rng.gen::<u64>());
let mut cloned_rng = reseeding_rng.clone();
assert!(reseeding_rng.gen::<u64>() != cloned_rng.gen::<u64>());
pub fn new(rng: R, threshold: u64, reseeder: Rsdr) -> Self | [src] |
Create a new ReseedingRng
from an existing PRNG, combined with a RNG
to use as reseeder.
threshold
sets the number of generated bytes after which to reseed the
PRNG. Set it to zero to never reseed based on the number of generated
values.
Reseed the internal PRNG.
Performs copy-assignment from source
. Read more
Formats the value using the given formatter. Read more
Fill dest
entirely with random data. Read more
Return a random value supporting the [Standard
] distribution. Read more
Generate a random value in the range [low
, high
), i.e. inclusive of low
and exclusive of high
. Read more
Sample a new value, using the given distribution. Read more
Important traits for DistIter<'a, D, R, T>
impl<'a, D, R, T> Iterator for DistIter<'a, D, R, T> where
D: Distribution<T>,
R: Rng + 'a, type Item = T;
Create an iterator that generates values using the given distribution. Read more
Fill dest
entirely with random bytes (uniform value distribution), where dest
is any type supporting AsByteSliceMut
, namely slices and arrays over primitive integer types (i8
, i16
, u32
, etc.). Read more
Fill dest
entirely with random bytes (uniform value distribution), where dest
is any type supporting AsByteSliceMut
, namely slices and arrays over primitive integer types (i8
, i16
, u32
, etc.). Read more
Return a bool with a probability p
of being true. Read more
Return a bool with a probability of numerator/denominator
of being true. I.e. gen_ratio(2, 3)
has chance of 2 in 3, or about 67%, of returning true. If numerator == denominator
, then the returned value is guaranteed to be true
. If numerator == 0
, then the returned value is guaranteed to be false
. Read more
Deprecated since 0.6.0:
use SliceRandom::choose instead
Return a random element from values
. Read more
Deprecated since 0.6.0:
use SliceRandom::choose_mut instead
Return a mutable pointer to a random element from values
. Read more
Deprecated since 0.6.0:
use SliceRandom::shuffle instead
Creates owned data from borrowed data, usually by cloning. Read more
🔬 This is a nightly-only experimental API. (toowned_clone_into
)
recently added
Uses borrowed data to replace owned data, usually by cloning. Read more
🔬 This is a nightly-only experimental API. (try_from
)
The type returned in the event of a conversion error.
🔬 This is a nightly-only experimental API. (try_from
)
Immutably borrows from an owned value. Read more
🔬 This is a nightly-only experimental API. (get_type_id
)
this method will likely be replaced by an associated static
🔬 This is a nightly-only experimental API. (try_from
)
The type returned in the event of a conversion error.
🔬 This is a nightly-only experimental API. (try_from
)
Mutably borrows from an owned value. Read more
Numeric cast from T
to Self
.
Numeric cast from self
to T
.
Safe lossless bitwise transmute from T
to Self
.
Safe lossless bitwise transmute from self
to T
.