ya_rand/
secure.rs

1use crate::rng::*;
2use chachacha::{BUF_LEN_U64, ChaCha8Djb, SEED_LEN_U8};
3use core::mem::MaybeUninit;
4use getrandom::fill;
5
6/// A cryptographically secure random number generator.
7///
8/// The current implementation uses ChaCha with 8 rounds and a 64-bit counter.
9/// This allows for 1 ZiB (2<sup>70</sup> bytes) of output before cycling.
10/// That's over 147 **quintillion** calls to [`SecureRng::u64`].
11pub struct SecureRng {
12    buf: [u64; BUF_LEN_U64],
13    index: usize,
14    internal: ChaCha8Djb,
15}
16
17impl SecureYARandGenerator for SecureRng {
18    #[inline]
19    fn fill_bytes(&mut self, dst: &mut [u8]) {
20        // The `chachacha` crate provides a thoroughly tested and
21        // extremely fast fill implementation.
22        self.internal.fill(dst);
23    }
24}
25
26impl YARandGenerator for SecureRng {
27    #[inline]
28    fn try_new() -> Result<Self, getrandom::Error> {
29        // We randomize **all** bits of the matrix, even the counter.
30        // If used as a cipher this approach is completely braindead,
31        // but since this is exclusively for use as a CRNG it's fine.
32        #[allow(invalid_value)]
33        let mut state = unsafe { MaybeUninit::<[u8; SEED_LEN_U8]>::uninit().assume_init() };
34        fill(&mut state)?;
35        let mut internal = ChaCha8Djb::from(state);
36        let buf = internal.get_block_u64();
37        let index = 0;
38        Ok(Self {
39            buf,
40            index,
41            internal,
42        })
43    }
44
45    #[cfg_attr(feature = "inline", inline)]
46    fn u64(&mut self) -> u64 {
47        // TODO: This is the cold path, occuring only once every
48        // 32 calls to `Self::u64`. If there is ever a cold/unlikely
49        // intrinsic moved to stable then test the performance impact
50        // of applying it to this branch.
51        if self.index >= self.buf.len() {
52            self.index = 0;
53            self.internal.fill_block_u64(&mut self.buf);
54        }
55        // Bounds check is elided thanks to above code.
56        let result = self.buf[self.index];
57        self.index += 1;
58        result
59    }
60}
ya_rand/secure.rs

ya_rand/
secure.rs
