1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! The ChaCha random number generator.
13 use {Rng, SeedableRng, Rand};
15 const KEY_WORDS: usize = 8; // 8 words for the 256-bit key
16 const STATE_WORDS: usize = 16;
17 const CHACHA_ROUNDS: usize = 20; // Cryptographically secure from 8 upwards as of this writing
19 /// A random number generator that uses the ChaCha20 algorithm [1].
21 /// The ChaCha algorithm is widely accepted as suitable for
22 /// cryptographic purposes, but this implementation has not been
23 /// verified as such. Prefer a generator like `OsRng` that defers to
24 /// the operating system for cases that need high security.
26 /// [1]: D. J. Bernstein, [*ChaCha, a variant of
27 /// Salsa20*](http://cr.yp.to/chacha.html)
28 #[derive(Copy, Clone)]
29 pub struct ChaChaRng {
30 buffer: [u32; STATE_WORDS], // Internal buffer of output
31 state: [u32; STATE_WORDS], // Initial state
32 index: usize, // Index into state
35 static EMPTY: ChaChaRng = ChaChaRng {
36 buffer: [0; STATE_WORDS],
37 state: [0; STATE_WORDS],
42 macro_rules! quarter_round{
43 ($a: expr, $b: expr, $c: expr, $d: expr) => {{
44 $a = $a.wrapping_add($b); $d = $d ^ $a; $d = $d.rotate_left(16);
45 $c = $c.wrapping_add($d); $b = $b ^ $c; $b = $b.rotate_left(12);
46 $a = $a.wrapping_add($b); $d = $d ^ $a; $d = $d.rotate_left( 8);
47 $c = $c.wrapping_add($d); $b = $b ^ $c; $b = $b.rotate_left( 7);
51 macro_rules! double_round{
54 quarter_round!($x[ 0], $x[ 4], $x[ 8], $x[12]);
55 quarter_round!($x[ 1], $x[ 5], $x[ 9], $x[13]);
56 quarter_round!($x[ 2], $x[ 6], $x[10], $x[14]);
57 quarter_round!($x[ 3], $x[ 7], $x[11], $x[15]);
59 quarter_round!($x[ 0], $x[ 5], $x[10], $x[15]);
60 quarter_round!($x[ 1], $x[ 6], $x[11], $x[12]);
61 quarter_round!($x[ 2], $x[ 7], $x[ 8], $x[13]);
62 quarter_round!($x[ 3], $x[ 4], $x[ 9], $x[14]);
67 fn core(output: &mut [u32; STATE_WORDS], input: &[u32; STATE_WORDS]) {
70 for _ in 0..CHACHA_ROUNDS / 2 {
71 double_round!(output);
74 for i in 0..STATE_WORDS {
75 output[i] = output[i].wrapping_add(input[i]);
80 /// Create an ChaCha random number generator using the default
81 /// fixed key of 8 zero words.
82 pub fn new_unseeded() -> ChaChaRng {
84 rng.init(&[0; KEY_WORDS]);
88 /// Sets the internal 128-bit ChaCha counter to
89 /// a user-provided value. This permits jumping
90 /// arbitrarily ahead (or backwards) in the pseudorandom stream.
92 /// Since the nonce words are used to extend the counter to 128 bits,
93 /// users wishing to obtain the conventional ChaCha pseudorandom stream
94 /// associated with a particular nonce can call this function with
95 /// arguments `0, desired_nonce`.
96 pub fn set_counter(&mut self, counter_low: u64, counter_high: u64) {
97 self.state[12] = (counter_low >> 0) as u32;
98 self.state[13] = (counter_low >> 32) as u32;
99 self.state[14] = (counter_high >> 0) as u32;
100 self.state[15] = (counter_high >> 32) as u32;
101 self.index = STATE_WORDS; // force recomputation
104 /// Initializes `self.state` with the appropriate key and constants
106 /// We deviate slightly from the ChaCha specification regarding
107 /// the nonce, which is used to extend the counter to 128 bits.
108 /// This is provably as strong as the original cipher, though,
109 /// since any distinguishing attack on our variant also works
110 /// against ChaCha with a chosen-nonce. See the XSalsa20 [1]
111 /// security proof for a more involved example of this.
113 /// The modified word layout is:
115 /// constant constant constant constant
118 /// counter counter counter counter
120 /// [1]: Daniel J. Bernstein. [*Extending the Salsa20
121 /// nonce.*](http://cr.yp.to/papers.html#xsalsa)
122 fn init(&mut self, key: &[u32; KEY_WORDS]) {
123 self.state[0] = 0x61707865;
124 self.state[1] = 0x3320646E;
125 self.state[2] = 0x79622D32;
126 self.state[3] = 0x6B206574;
128 for i in 0..KEY_WORDS {
129 self.state[4 + i] = key[i];
137 self.index = STATE_WORDS;
140 /// Refill the internal output buffer (`self.buffer`)
141 fn update(&mut self) {
142 core(&mut self.buffer, &self.state);
144 // update 128-bit counter
146 if self.state[12] != 0 {
150 if self.state[13] != 0 {
154 if self.state[14] != 0 {
161 impl Rng for ChaChaRng {
163 fn next_u32(&mut self) -> u32 {
164 if self.index == STATE_WORDS {
168 let value = self.buffer[self.index % STATE_WORDS];
174 impl<'a> SeedableRng<&'a [u32]> for ChaChaRng {
175 fn reseed(&mut self, seed: &'a [u32]) {
177 self.init(&[0; KEY_WORDS]);
179 let key = &mut self.state[4..4 + KEY_WORDS];
180 for (k, s) in key.iter_mut().zip(seed) {
185 /// Create a ChaCha generator from a seed,
186 /// obtained from a variable-length u32 array.
187 /// Only up to 8 words are used; if less than 8
188 /// words are used, the remaining are set to zero.
189 fn from_seed(seed: &'a [u32]) -> ChaChaRng {
196 impl Rand for ChaChaRng {
197 fn rand<R: Rng>(other: &mut R) -> ChaChaRng {
198 let mut key: [u32; KEY_WORDS] = [0; KEY_WORDS];
199 for word in &mut key {
202 SeedableRng::from_seed(&key[..])
209 use std::prelude::v1::*;
211 use {Rng, SeedableRng};
212 use super::ChaChaRng;
215 fn test_rng_rand_seeded() {
216 let s = ::test::rng().gen_iter::<u32>().take(8).collect::<Vec<u32>>();
217 let mut ra: ChaChaRng = SeedableRng::from_seed(&*s);
218 let mut rb: ChaChaRng = SeedableRng::from_seed(&*s);
219 assert!(ra.gen_ascii_chars().take(100)
220 .eq(rb.gen_ascii_chars().take(100)));
224 fn test_rng_seeded() {
225 let seed: &[_] = &[0, 1, 2, 3, 4, 5, 6, 7];
226 let mut ra: ChaChaRng = SeedableRng::from_seed(seed);
227 let mut rb: ChaChaRng = SeedableRng::from_seed(seed);
228 assert!(ra.gen_ascii_chars().take(100)
229 .eq(rb.gen_ascii_chars().take(100)));
233 fn test_rng_reseed() {
234 let s = ::test::rng().gen_iter::<u32>().take(8).collect::<Vec<u32>>();
235 let mut r: ChaChaRng = SeedableRng::from_seed(&*s);
236 let string1: String = r.gen_ascii_chars().take(100).collect();
240 let string2: String = r.gen_ascii_chars().take(100).collect();
241 assert_eq!(string1, string2);
246 fn test_rng_true_values() {
247 // Test vectors 1 and 2 from
248 // http://tools.ietf.org/html/draft-nir-cfrg-chacha20-poly1305-04
249 let seed: &[_] = &[0; 8];
250 let mut ra: ChaChaRng = SeedableRng::from_seed(seed);
252 let v = (0..16).map(|_| ra.next_u32()).collect::<Vec<_>>();
254 vec!(0xade0b876, 0x903df1a0, 0xe56a5d40, 0x28bd8653,
255 0xb819d2bd, 0x1aed8da0, 0xccef36a8, 0xc70d778b,
256 0x7c5941da, 0x8d485751, 0x3fe02477, 0x374ad8b8,
257 0xf4b8436a, 0x1ca11815, 0x69b687c3, 0x8665eeb2));
259 let v = (0..16).map(|_| ra.next_u32()).collect::<Vec<_>>();
261 vec!(0xbee7079f, 0x7a385155, 0x7c97ba98, 0x0d082d73,
262 0xa0290fcb, 0x6965e348, 0x3e53c612, 0xed7aee32,
263 0x7621b729, 0x434ee69c, 0xb03371d5, 0xd539d874,
264 0x281fed31, 0x45fb0a51, 0x1f0ae1ac, 0x6f4d794b));
267 let seed: &[_] = &[0, 1, 2, 3, 4, 5, 6, 7];
268 let mut ra: ChaChaRng = SeedableRng::from_seed(seed);
270 // Store the 17*i-th 32-bit word,
271 // i.e., the i-th word of the i-th 16-word block
272 let mut v: Vec<u32> = Vec::new();
274 v.push(ra.next_u32());
281 vec!(0xf225c81a, 0x6ab1be57, 0x04d42951, 0x70858036,
282 0x49884684, 0x64efec72, 0x4be2d186, 0x3615b384,
283 0x11cfa18e, 0xd3c50049, 0x75c775f6, 0x434c6530,
284 0x2c5bad8f, 0x898881dc, 0x5f1c86d9, 0xc1f8e7f4));
288 fn test_rng_clone() {
289 let seed: &[_] = &[0; 8];
290 let mut rng: ChaChaRng = SeedableRng::from_seed(seed);
291 let mut clone = rng.clone();
293 assert_eq!(rng.next_u64(), clone.next_u64());