Struct ring::rand::SystemRandom
[−]
[src]
pub struct SystemRandom;
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 non-Linux Unix-/Posix-ish platforms, fill()
is currently always
implemented by reading from /dev/urandom
. (This is something that should
be improved, at least for platforms that offer something better.)
On Linux, 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
. Library crates should avoid
explicitly enabling the dev_urandom_fallback
feature.
On Windows, fill
is implemented using the platform's API for secure
random number generation.
When /dev/urandom
is used, a file handle for /dev/urandom
won't be
opened until fill
is called. In particular, 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 instance of SystemRandom
will share a single file
handle.
On Linux, 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
.
Methods
impl SystemRandom
[src]
fn new() -> SystemRandom
Constructs a new SystemRandom
.
impl SystemRandom
[src]
fn fill(&self, dest: &mut [u8]) -> Result<(), Unspecified>
This is the same as calling fill
through the SecureRandom
trait,
but allows callers to avoid the annoying step of needing to
use rand::SecureRandom
just to call fill
on a SystemRandom
.