nanorand/rand/
chacha.rs

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1use crate::{
2	crypto::chacha,
3	rand::{Rng, SeedableRng},
4};
5use core::fmt::{self, Debug, Display, Formatter};
6#[cfg(feature = "zeroize")]
7use zeroize::Zeroize;
8
9/// The ChaCha CSPRNG, with 8 rounds.
10pub type ChaCha8 = ChaCha<8>;
11
12/// The ChaCha CSPRNG, with 12 rounds.
13pub type ChaCha12 = ChaCha<12>;
14
15/// The ChaCha CSPRNG, with 20 rounds.
16pub type ChaCha20 = ChaCha<20>;
17
18/// An instance of the ChaCha random number generator.
19/// Seeded from the system entropy generator when available.
20/// **This generator _is theoretically_ cryptographically secure.**
21#[cfg_attr(feature = "zeroize", derive(Zeroize))]
22#[cfg_attr(feature = "zeroize", zeroize(drop))]
23pub struct ChaCha<const ROUNDS: u8> {
24	state: [u32; 16],
25}
26
27impl<const ROUNDS: u8> ChaCha<ROUNDS> {
28	/// Create a new [`ChaCha`] instance, seeding from the system's default source of entropy.
29	#[must_use]
30	pub fn new() -> Self {
31		let mut key: [u8; 32] = Default::default();
32		crate::entropy::system(&mut key);
33		let mut nonce: [u8; 8] = Default::default();
34		crate::entropy::system(&mut nonce);
35		let state = chacha::chacha_init(key, nonce);
36		Self { state }
37	}
38
39	/// Create a new [`ChaCha`] instance, using the provided key and nonce.
40	#[must_use]
41	pub const fn new_key(key: [u8; 32], nonce: [u8; 8]) -> Self {
42		let state = chacha::chacha_init(key, nonce);
43		Self { state }
44	}
45}
46
47impl<const ROUNDS: u8> Default for ChaCha<ROUNDS> {
48	fn default() -> Self {
49		let mut key: [u8; 32] = Default::default();
50		crate::entropy::system(&mut key);
51		let mut nonce: [u8; 8] = Default::default();
52		crate::entropy::system(&mut nonce);
53		let state = chacha::chacha_init(key, nonce);
54		Self { state }
55	}
56}
57
58impl<const ROUNDS: u8> Rng<64> for ChaCha<ROUNDS> {
59	fn rand(&mut self) -> [u8; 64] {
60		let block = chacha::chacha_block::<ROUNDS>(self.state);
61		let mut ret = [0_u8; 64];
62		block.iter().enumerate().for_each(|(idx, num)| {
63			let x = num.to_ne_bytes();
64			let n = idx * 4;
65			ret[n] = x[0];
66			ret[n + 1] = x[1];
67			ret[n + 2] = x[2];
68			ret[n + 3] = x[3];
69		});
70		// Now, we're going to just increment our counter so we get an entirely new output next time.
71		// If the counter overflows, we just reseed entirely instead.
72		if !chacha::chacha_increment_counter(&mut self.state) {
73			let mut new_seed: [u8; 40] = [42_u8; 40];
74			crate::entropy::system(&mut new_seed);
75			self.reseed(new_seed);
76		}
77		ret
78	}
79}
80
81impl<const ROUNDS: u8> Clone for ChaCha<ROUNDS> {
82	fn clone(&self) -> Self {
83		Self { state: self.state }
84	}
85}
86
87impl<const ROUNDS: u8> Display for ChaCha<ROUNDS> {
88	fn fmt(&self, f: &mut Formatter) -> fmt::Result {
89		write!(f, "ChaCha ({:p}, {} rounds)", self, ROUNDS)
90	}
91}
92
93impl<const ROUNDS: u8> SeedableRng<40, 64> for ChaCha<ROUNDS> {
94	fn reseed(&mut self, seed: [u8; 40]) {
95		let mut key = [0_u8; 32];
96		let mut nonce = [0_u8; 8];
97		key.copy_from_slice(&seed[..32]);
98		nonce.copy_from_slice(&seed[32..]);
99		self.state = chacha::chacha_init(key, nonce);
100	}
101}
102
103impl<const ROUNDS: u8> Debug for ChaCha<ROUNDS> {
104	fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
105		let counter = ((self.state[13] as u64) << 32) | (self.state[12] as u64);
106		f.debug_struct("ChaCha20")
107			.field("rounds", &ROUNDS)
108			.field("counter", &counter)
109			.finish()
110	}
111}
nanorand/rand/chacha.rs

nanorand/rand/
chacha.rs
