linux-crng-ioctl

Rust wrappers for the ioctls of the Linux kernel CRNG and for its /proc/sys/kernel/random/* interface. Linux only.

ioctl

The ioctl module operates on /dev/random:

use linux_crng_ioctl::ioctl::{add_randomness_to_kernel, get_ent_cnt};

let entropy = [0u8; 32];
add_randomness_to_kernel(&entropy, (entropy.len() * 8) as u32)?;

println!("entropy count: {}", get_ent_cnt()?);

Only credit entropy which really is entropy: the amount of bits passed to add_randomness_to_kernel is what the kernel adds to its entropy count. It is rejected if it exceeds entropy.len() * 8, and one call writes at most 2 kB.

proc

The proc module reads the read-only files below /proc/sys/kernel/random/: boot_id(), uuid(), entropy_avail(), poolsize(), urandom_min_reseed_secs() and write_wakeup_threshold().

use linux_crng_ioctl::proc::{entropy_avail, poolsize};

println!("{} of {} bits available", entropy_avail()?, poolsize()?);

Tests

The test suite skips the cases which need CAP_SYS_ADMIN when it does not have them, so cargo test works as an ordinary user.