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.
16 use {Rng, SeedableRng, Rand};
18 const KEY_WORDS : uint = 8; // 8 words for the 256-bit key
19 const STATE_WORDS : uint = 16;
20 const CHACHA_ROUNDS: uint = 20; // Cryptographically secure from 8 upwards as of this writing
22 /// A random number generator that uses the ChaCha20 algorithm [1].
24 /// The ChaCha algorithm is widely accepted as suitable for
25 /// cryptographic purposes, but this implementation has not been
26 /// verified as such. Prefer a generator like `OsRng` that defers to
27 /// the operating system for cases that need high security.
29 /// [1]: D. J. Bernstein, [*ChaCha, a variant of
30 /// Salsa20*](http://cr.yp.to/chacha.html)
32 pub struct ChaChaRng {
33 buffer: [u32, ..STATE_WORDS], // Internal buffer of output
34 state: [u32, ..STATE_WORDS], // Initial state
35 index: uint, // Index into state
38 static EMPTY: ChaChaRng = ChaChaRng {
39 buffer: [0, ..STATE_WORDS],
40 state: [0, ..STATE_WORDS],
45 macro_rules! quarter_round{
46 ($a: expr, $b: expr, $c: expr, $d: expr) => {{
47 $a += $b; $d ^= $a; $d = $d.rotate_left(16);
48 $c += $d; $b ^= $c; $b = $b.rotate_left(12);
49 $a += $b; $d ^= $a; $d = $d.rotate_left( 8);
50 $c += $d; $b ^= $c; $b = $b.rotate_left( 7);
54 macro_rules! double_round{
57 quarter_round!($x[ 0], $x[ 4], $x[ 8], $x[12]);
58 quarter_round!($x[ 1], $x[ 5], $x[ 9], $x[13]);
59 quarter_round!($x[ 2], $x[ 6], $x[10], $x[14]);
60 quarter_round!($x[ 3], $x[ 7], $x[11], $x[15]);
62 quarter_round!($x[ 0], $x[ 5], $x[10], $x[15]);
63 quarter_round!($x[ 1], $x[ 6], $x[11], $x[12]);
64 quarter_round!($x[ 2], $x[ 7], $x[ 8], $x[13]);
65 quarter_round!($x[ 3], $x[ 4], $x[ 9], $x[14]);
70 fn core(output: &mut [u32, ..STATE_WORDS], input: &[u32, ..STATE_WORDS]) {
73 for _ in range(0, CHACHA_ROUNDS / 2) {
74 double_round!(output);
77 for i in range(0, STATE_WORDS) {
78 output[i] += input[i];
84 /// Create an ChaCha random number generator using the default
85 /// fixed key of 8 zero words.
86 pub fn new_unseeded() -> ChaChaRng {
88 rng.init(&[0, ..KEY_WORDS]);
92 /// Sets the internal 128-bit ChaCha counter to
93 /// a user-provided value. This permits jumping
94 /// arbitrarily ahead (or backwards) in the pseudorandom stream.
96 /// Since the nonce words are used to extend the counter to 128 bits,
97 /// users wishing to obtain the conventional ChaCha pseudorandom stream
98 /// associated with a particular nonce can call this function with
99 /// arguments `0, desired_nonce`.
100 pub fn set_counter(&mut self, counter_low: u64, counter_high: u64) {
101 self.state[12] = (counter_low >> 0) as u32;
102 self.state[13] = (counter_low >> 32) as u32;
103 self.state[14] = (counter_high >> 0) as u32;
104 self.state[15] = (counter_high >> 32) as u32;
105 self.index = STATE_WORDS; // force recomputation
108 /// Initializes `self.state` with the appropriate key and constants
110 /// We deviate slightly from the ChaCha specification regarding
111 /// the nonce, which is used to extend the counter to 128 bits.
112 /// This is provably as strong as the original cipher, though,
113 /// since any distinguishing attack on our variant also works
114 /// against ChaCha with a chosen-nonce. See the XSalsa20 [1]
115 /// security proof for a more involved example of this.
117 /// The modified word layout is:
119 /// constant constant constant constant
122 /// counter counter counter counter
124 /// [1]: Daniel J. Bernstein. [*Extending the Salsa20
125 /// nonce.*](http://cr.yp.to/papers.html#xsalsa)
126 fn init(&mut self, key: &[u32, ..KEY_WORDS]) {
127 self.state[0] = 0x61707865;
128 self.state[1] = 0x3320646E;
129 self.state[2] = 0x79622D32;
130 self.state[3] = 0x6B206574;
132 for i in range(0, KEY_WORDS) {
133 self.state[4+i] = key[i];
141 self.index = STATE_WORDS;
144 /// Refill the internal output buffer (`self.buffer`)
145 fn update(&mut self) {
146 core(&mut self.buffer, &self.state);
148 // update 128-bit counter
150 if self.state[12] != 0 { return };
152 if self.state[13] != 0 { return };
154 if self.state[14] != 0 { return };
159 impl Rng for ChaChaRng {
161 fn next_u32(&mut self) -> u32 {
162 if self.index == STATE_WORDS {
166 let value = self.buffer[self.index % STATE_WORDS];
172 impl<'a> SeedableRng<&'a [u32]> for ChaChaRng {
174 fn reseed(&mut self, seed: &'a [u32]) {
176 self.init(&[0u32, ..KEY_WORDS]);
178 let key = self.state.slice_mut(4, 4+KEY_WORDS);
179 for (k, s) in key.iter_mut().zip(seed.iter()) {
184 /// Create a ChaCha generator from a seed,
185 /// obtained from a variable-length u32 array.
186 /// Only up to 8 words are used; if less than 8
187 /// words are used, the remaining are set to zero.
188 fn from_seed(seed: &'a [u32]) -> ChaChaRng {
195 impl Rand for ChaChaRng {
196 fn rand<R: Rng>(other: &mut R) -> ChaChaRng {
197 let mut key : [u32, ..KEY_WORDS] = [0, ..KEY_WORDS];
198 for word in key.iter_mut() {
201 SeedableRng::from_seed(key.as_slice())
210 use core::iter::order;
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.as_slice());
218 let mut rb: ChaChaRng = SeedableRng::from_seed(s.as_slice());
219 assert!(order::equals(ra.gen_ascii_chars().take(100),
220 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!(order::equals(ra.gen_ascii_chars().take(100),
229 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.as_slice());
236 let string1: String = r.gen_ascii_chars().take(100).collect();
238 r.reseed(s.as_slice());
240 let string2: String = r.gen_ascii_chars().take(100).collect();
241 assert_eq!(string1, string2);
245 fn test_rng_true_values() {
246 // Test vectors 1 and 2 from
247 // http://tools.ietf.org/html/draft-nir-cfrg-chacha20-poly1305-04
248 let seed : &[_] = &[0u32, ..8];
249 let mut ra: ChaChaRng = SeedableRng::from_seed(seed);
251 let v = Vec::from_fn(16, |_| ra.next_u32());
253 vec!(0xade0b876, 0x903df1a0, 0xe56a5d40, 0x28bd8653,
254 0xb819d2bd, 0x1aed8da0, 0xccef36a8, 0xc70d778b,
255 0x7c5941da, 0x8d485751, 0x3fe02477, 0x374ad8b8,
256 0xf4b8436a, 0x1ca11815, 0x69b687c3, 0x8665eeb2));
258 let v = Vec::from_fn(16, |_| ra.next_u32());
260 vec!(0xbee7079f, 0x7a385155, 0x7c97ba98, 0x0d082d73,
261 0xa0290fcb, 0x6965e348, 0x3e53c612, 0xed7aee32,
262 0x7621b729, 0x434ee69c, 0xb03371d5, 0xd539d874,
263 0x281fed31, 0x45fb0a51, 0x1f0ae1ac, 0x6f4d794b));
266 let seed : &[_] = &[0,1,2,3,4,5,6,7];
267 let mut ra: ChaChaRng = SeedableRng::from_seed(seed);
269 // Store the 17*i-th 32-bit word,
270 // i.e., the i-th word of the i-th 16-word block
271 let mut v : Vec<u32> = Vec::new();
272 for _ in range(0u, 16) {
273 v.push(ra.next_u32());
274 for _ in range(0u, 16) {
280 vec!(0xf225c81a, 0x6ab1be57, 0x04d42951, 0x70858036,
281 0x49884684, 0x64efec72, 0x4be2d186, 0x3615b384,
282 0x11cfa18e, 0xd3c50049, 0x75c775f6, 0x434c6530,
283 0x2c5bad8f, 0x898881dc, 0x5f1c86d9, 0xc1f8e7f4));