Struct ring::rand::SystemRandom
source · pub struct SystemRandom(/* private fields */);
Expand description
A secure random number generator where the random values come directly from the operating system.
A single SystemRandom
may be shared across multiple threads safely.
new()
is guaranteed to always succeed and to have low latency; it won’t
try to open or read from a file or do similar things. The first call to
fill()
may block a substantial amount of time since any and all
initialization is deferred to it. Therefore, it may be a good idea to call
fill()
once at a non-latency-sensitive time to minimize latency for
future calls.
On Linux (including Android), fill()
will use the getrandom
syscall.
If the kernel is too old to support getrandom
then by default fill()
falls back to reading from /dev/urandom
. This decision is made the first
time fill
succeeds. The fallback to /dev/urandom
can be disabled by
disabling the dev_urandom_fallback
default feature; this should be done
whenever the target system is known to support getrandom
. When
/dev/urandom
is used, a file handle for /dev/urandom
won’t be opened
until fill
is called; SystemRandom::new()
will not open /dev/urandom
or do other potentially-high-latency things. The file handle will never be
closed, until the operating system closes it at process shutdown. All
instances of SystemRandom
will share a single file handle. To properly
implement seccomp filtering when the dev_urandom_fallback
default feature
is disabled, allow getrandom
through. When the fallback is enabled, allow
file opening, getrandom
, and read
up until the first call to fill()
succeeds; after that, allow getrandom
and read
.
On macOS and iOS, fill()
is implemented using SecRandomCopyBytes
.
On wasm32-unknown-unknown (non-WASI), fill()
is implemented using
window.crypto.getRandomValues()
. It must be used in a context where the
global object is a Window
; i.e. it must not be used in a Worker or a
non-browser context.
On Windows, fill
is implemented using the platform’s API for secure
random number generation.
Implementations§
source§impl SystemRandom
impl SystemRandom
Trait Implementations§
source§impl Clone for SystemRandom
impl Clone for SystemRandom
source§fn clone(&self) -> SystemRandom
fn clone(&self) -> SystemRandom
1.0.0 · source§fn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read moreAuto Trait Implementations§
impl Freeze for SystemRandom
impl RefUnwindSafe for SystemRandom
impl Send for SystemRandom
impl Sync for SystemRandom
impl Unpin for SystemRandom
impl UnwindSafe for SystemRandom
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
source§impl<T> CloneToUninit for Twhere
T: Clone,
impl<T> CloneToUninit for Twhere
T: Clone,
source§default unsafe fn clone_to_uninit(&self, dst: *mut T)
default unsafe fn clone_to_uninit(&self, dst: *mut T)
clone_to_uninit
)