Struct rand::rngs::EntropyRng

pub struct EntropyRng { /* fields omitted */ }

An interface returning random data from external source(s), provided specifically for securely seeding algorithmic generators (PRNGs).

Where possible, EntropyRng retrieves random data from the operating system's interface for random numbers (OsRng); if that fails it will fall back to the JitterRng entropy collector. In the latter case it will still try to use OsRng on the next usage.

If no secure source of entropy is available EntropyRng will panic on use; i.e. it should never output predictable data.

This is either a little slow (OsRng requires a system call) or extremely slow (JitterRng must use significant CPU time to generate sufficient jitter); for better performance it is common to seed a local PRNG from external entropy then primarily use the local PRNG (thread_rng is provided as a convenient, local, automatically-seeded CSPRNG).

Panics

On most systems, like Windows, Linux, macOS and *BSD on common hardware, it is highly unlikely for both OsRng and JitterRng to fail. But on combinations like webassembly without Emscripten or stdweb both sources are unavailable. If both sources fail, only try_fill_bytes is able to report the error, and only the one from OsRng. The other RngCore methods will panic in case of an error.

Methods

impl EntropyRng

pub fn new() -> Self

Create a new EntropyRng.

This method will do no system calls or other initialization routines, those are done on first use. This is done to make new infallible, and try_fill_bytes the only place to report errors.

Trait Implementations

impl Debug for EntropyRng

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Default for EntropyRng

fn default() -> Self

Returns the "default value" for a type.

impl RngCore for EntropyRng

fn next_u32(&mut self) -> u32

Return the next random u32.

fn next_u64(&mut self) -> u64

Return the next random u64.

fn fill_bytes(&mut self, dest: &mut [u8])

Fill dest with random data.

fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error>

Fill dest entirely with random data.

impl CryptoRng for EntropyRng