fuchsia_cprng/
lib.rs

1// Copyright 2019 The Fuchsia Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5//! Type-safe bindings for the Zircon kernel's CPRNG.
6//!
7//! This is intended to be a minimal dependency for out-of-tree callers. In-tree
8//! callers should use `zx` instead.
9
10#![no_std]
11
12/// Draw random bytes from the kernel's CPRNG to fill the given buffer.
13///
14/// Wraps the
15/// [zx_cprng_draw](https://fuchsia.dev/fuchsia-src/reference/syscalls/cprng_draw.md)
16/// syscall.
17pub fn cprng_draw(buffer: &mut [u8]) {
18    unsafe { zx_cprng_draw(buffer.as_mut_ptr(), buffer.len()) };
19}
20
21// From libzircon.so
22extern "C" {
23    fn zx_cprng_draw(buffer: *mut u8, length: usize);
24}
25
26#[cfg(test)]
27mod tests {
28    use super::*;
29
30    #[test]
31    fn cprng() {
32        let mut buffer = [0; 20];
33        cprng_draw(&mut buffer);
34        let mut first_zero = 0;
35        let mut last_zero = 0;
36        for _ in 0..30 {
37            let mut buffer = [0; 20];
38            cprng_draw(&mut buffer);
39            if buffer[0] == 0 {
40                first_zero += 1;
41            }
42            if buffer[19] == 0 {
43                last_zero += 1;
44            }
45        }
46        assert_ne!(first_zero, 30);
47        assert_ne!(last_zero, 30);
48    }
49
50    #[test]
51    fn cprng_large() {
52        let mut buffer = [0; 1024];
53        cprng_draw(&mut buffer);
54
55        for mut s in buffer.chunks_mut(256) {
56            cprng_draw(&mut s);
57        }
58    }
59}