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-// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-//! The ChaCha random number generator.
-
-use core::num::Wrapping as w;
-use {Rng, SeedableRng, Rand};
-
-#[allow(bad_style)]
-type w32 = w<u32>;
-
-const KEY_WORDS : usize = 8; // 8 words for the 256-bit key
-const STATE_WORDS : usize = 16;
-const CHACHA_ROUNDS: u32 = 20; // Cryptographically secure from 8 upwards as of this writing
-
-/// A random number generator that uses the ChaCha20 algorithm [1].
-///
-/// The ChaCha algorithm is widely accepted as suitable for
-/// cryptographic purposes, but this implementation has not been
-/// verified as such. Prefer a generator like `OsRng` that defers to
-/// the operating system for cases that need high security.
-///
-/// [1]: D. J. Bernstein, [*ChaCha, a variant of
-/// Salsa20*](http://cr.yp.to/chacha.html)
-#[derive(Copy, Clone, Debug)]
-pub struct ChaChaRng {
- buffer: [w32; STATE_WORDS], // Internal buffer of output
- state: [w32; STATE_WORDS], // Initial state
- index: usize, // Index into state
-}
-
-static EMPTY: ChaChaRng = ChaChaRng {
- buffer: [w(0); STATE_WORDS],
- state: [w(0); STATE_WORDS],
- index: STATE_WORDS
-};
-
-
-macro_rules! quarter_round{
- ($a: expr, $b: expr, $c: expr, $d: expr) => {{
- $a = $a + $b; $d = $d ^ $a; $d = w($d.0.rotate_left(16));
- $c = $c + $d; $b = $b ^ $c; $b = w($b.0.rotate_left(12));
- $a = $a + $b; $d = $d ^ $a; $d = w($d.0.rotate_left( 8));
- $c = $c + $d; $b = $b ^ $c; $b = w($b.0.rotate_left( 7));
- }}
-}
-
-macro_rules! double_round{
- ($x: expr) => {{
- // Column round
- quarter_round!($x[ 0], $x[ 4], $x[ 8], $x[12]);
- quarter_round!($x[ 1], $x[ 5], $x[ 9], $x[13]);
- quarter_round!($x[ 2], $x[ 6], $x[10], $x[14]);
- quarter_round!($x[ 3], $x[ 7], $x[11], $x[15]);
- // Diagonal round
- quarter_round!($x[ 0], $x[ 5], $x[10], $x[15]);
- quarter_round!($x[ 1], $x[ 6], $x[11], $x[12]);
- quarter_round!($x[ 2], $x[ 7], $x[ 8], $x[13]);
- quarter_round!($x[ 3], $x[ 4], $x[ 9], $x[14]);
- }}
-}
-
-#[inline]
-fn core(output: &mut [w32; STATE_WORDS], input: &[w32; STATE_WORDS]) {
- *output = *input;
-
- for _ in 0..CHACHA_ROUNDS / 2 {
- double_round!(output);
- }
-
- for i in 0..STATE_WORDS {
- output[i] = output[i] + input[i];
- }
-}
-
-impl ChaChaRng {
-
- /// Create an ChaCha random number generator using the default
- /// fixed key of 8 zero words.
- ///
- /// # Examples
- ///
- /// ```rust
- /// use rand::{Rng, ChaChaRng};
- ///
- /// let mut ra = ChaChaRng::new_unseeded();
- /// println!("{:?}", ra.next_u32());
- /// println!("{:?}", ra.next_u32());
- /// ```
- ///
- /// Since this equivalent to a RNG with a fixed seed, repeated executions
- /// of an unseeded RNG will produce the same result. This code sample will
- /// consistently produce:
- ///
- /// - 2917185654
- /// - 2419978656
- pub fn new_unseeded() -> ChaChaRng {
- let mut rng = EMPTY;
- rng.init(&[0; KEY_WORDS]);
- rng
- }
-
- /// Sets the internal 128-bit ChaCha counter to
- /// a user-provided value. This permits jumping
- /// arbitrarily ahead (or backwards) in the pseudorandom stream.
- ///
- /// Since the nonce words are used to extend the counter to 128 bits,
- /// users wishing to obtain the conventional ChaCha pseudorandom stream
- /// associated with a particular nonce can call this function with
- /// arguments `0, desired_nonce`.
- ///
- /// # Examples
- ///
- /// ```rust
- /// use rand::{Rng, ChaChaRng};
- ///
- /// let mut ra = ChaChaRng::new_unseeded();
- /// ra.set_counter(0u64, 1234567890u64);
- /// println!("{:?}", ra.next_u32());
- /// println!("{:?}", ra.next_u32());
- /// ```
- pub fn set_counter(&mut self, counter_low: u64, counter_high: u64) {
- self.state[12] = w((counter_low >> 0) as u32);
- self.state[13] = w((counter_low >> 32) as u32);
- self.state[14] = w((counter_high >> 0) as u32);
- self.state[15] = w((counter_high >> 32) as u32);
- self.index = STATE_WORDS; // force recomputation
- }
-
- /// Initializes `self.state` with the appropriate key and constants
- ///
- /// We deviate slightly from the ChaCha specification regarding
- /// the nonce, which is used to extend the counter to 128 bits.
- /// This is provably as strong as the original cipher, though,
- /// since any distinguishing attack on our variant also works
- /// against ChaCha with a chosen-nonce. See the XSalsa20 [1]
- /// security proof for a more involved example of this.
- ///
- /// The modified word layout is:
- /// ```text
- /// constant constant constant constant
- /// key key key key
- /// key key key key
- /// counter counter counter counter
- /// ```
- /// [1]: Daniel J. Bernstein. [*Extending the Salsa20
- /// nonce.*](http://cr.yp.to/papers.html#xsalsa)
- fn init(&mut self, key: &[u32; KEY_WORDS]) {
- self.state[0] = w(0x61707865);
- self.state[1] = w(0x3320646E);
- self.state[2] = w(0x79622D32);
- self.state[3] = w(0x6B206574);
-
- for i in 0..KEY_WORDS {
- self.state[4+i] = w(key[i]);
- }
-
- self.state[12] = w(0);
- self.state[13] = w(0);
- self.state[14] = w(0);
- self.state[15] = w(0);
-
- self.index = STATE_WORDS;
- }
-
- /// Refill the internal output buffer (`self.buffer`)
- fn update(&mut self) {
- core(&mut self.buffer, &self.state);
- self.index = 0;
- // update 128-bit counter
- self.state[12] = self.state[12] + w(1);
- if self.state[12] != w(0) { return };
- self.state[13] = self.state[13] + w(1);
- if self.state[13] != w(0) { return };
- self.state[14] = self.state[14] + w(1);
- if self.state[14] != w(0) { return };
- self.state[15] = self.state[15] + w(1);
- }
-}
-
-impl Rng for ChaChaRng {
- #[inline]
- fn next_u32(&mut self) -> u32 {
- if self.index == STATE_WORDS {
- self.update();
- }
-
- let value = self.buffer[self.index % STATE_WORDS];
- self.index += 1;
- value.0
- }
-}
-
-impl<'a> SeedableRng<&'a [u32]> for ChaChaRng {
-
- fn reseed(&mut self, seed: &'a [u32]) {
- // reset state
- self.init(&[0u32; KEY_WORDS]);
- // set key in place
- let key = &mut self.state[4 .. 4+KEY_WORDS];
- for (k, s) in key.iter_mut().zip(seed.iter()) {
- *k = w(*s);
- }
- }
-
- /// Create a ChaCha generator from a seed,
- /// obtained from a variable-length u32 array.
- /// Only up to 8 words are used; if less than 8
- /// words are used, the remaining are set to zero.
- fn from_seed(seed: &'a [u32]) -> ChaChaRng {
- let mut rng = EMPTY;
- rng.reseed(seed);
- rng
- }
-}
-
-impl Rand for ChaChaRng {
- fn rand<R: Rng>(other: &mut R) -> ChaChaRng {
- let mut key : [u32; KEY_WORDS] = [0; KEY_WORDS];
- for word in key.iter_mut() {
- *word = other.gen();
- }
- SeedableRng::from_seed(&key[..])
- }
-}
-
-
-#[cfg(test)]
-mod test {
- use {Rng, SeedableRng};
- use super::ChaChaRng;
-
- #[test]
- fn test_rng_rand_seeded() {
- let s = ::test::rng().gen_iter::<u32>().take(8).collect::<Vec<u32>>();
- let mut ra: ChaChaRng = SeedableRng::from_seed(&s[..]);
- let mut rb: ChaChaRng = SeedableRng::from_seed(&s[..]);
- assert!(::test::iter_eq(ra.gen_ascii_chars().take(100),
- rb.gen_ascii_chars().take(100)));
- }
-
- #[test]
- fn test_rng_seeded() {
- let seed : &[_] = &[0,1,2,3,4,5,6,7];
- let mut ra: ChaChaRng = SeedableRng::from_seed(seed);
- let mut rb: ChaChaRng = SeedableRng::from_seed(seed);
- assert!(::test::iter_eq(ra.gen_ascii_chars().take(100),
- rb.gen_ascii_chars().take(100)));
- }
-
- #[test]
- fn test_rng_reseed() {
- let s = ::test::rng().gen_iter::<u32>().take(8).collect::<Vec<u32>>();
- let mut r: ChaChaRng = SeedableRng::from_seed(&s[..]);
- let string1: String = r.gen_ascii_chars().take(100).collect();
-
- r.reseed(&s);
-
- let string2: String = r.gen_ascii_chars().take(100).collect();
- assert_eq!(string1, string2);
- }
-
- #[test]
- fn test_rng_true_values() {
- // Test vectors 1 and 2 from
- // http://tools.ietf.org/html/draft-nir-cfrg-chacha20-poly1305-04
- let seed : &[_] = &[0u32; 8];
- let mut ra: ChaChaRng = SeedableRng::from_seed(seed);
-
- let v = (0..16).map(|_| ra.next_u32()).collect::<Vec<_>>();
- assert_eq!(v,
- vec!(0xade0b876, 0x903df1a0, 0xe56a5d40, 0x28bd8653,
- 0xb819d2bd, 0x1aed8da0, 0xccef36a8, 0xc70d778b,
- 0x7c5941da, 0x8d485751, 0x3fe02477, 0x374ad8b8,
- 0xf4b8436a, 0x1ca11815, 0x69b687c3, 0x8665eeb2));
-
- let v = (0..16).map(|_| ra.next_u32()).collect::<Vec<_>>();
- assert_eq!(v,
- vec!(0xbee7079f, 0x7a385155, 0x7c97ba98, 0x0d082d73,
- 0xa0290fcb, 0x6965e348, 0x3e53c612, 0xed7aee32,
- 0x7621b729, 0x434ee69c, 0xb03371d5, 0xd539d874,
- 0x281fed31, 0x45fb0a51, 0x1f0ae1ac, 0x6f4d794b));
-
-
- let seed : &[_] = &[0,1,2,3,4,5,6,7];
- let mut ra: ChaChaRng = SeedableRng::from_seed(seed);
-
- // Store the 17*i-th 32-bit word,
- // i.e., the i-th word of the i-th 16-word block
- let mut v : Vec<u32> = Vec::new();
- for _ in 0..16 {
- v.push(ra.next_u32());
- for _ in 0..16 {
- ra.next_u32();
- }
- }
-
- assert_eq!(v,
- vec!(0xf225c81a, 0x6ab1be57, 0x04d42951, 0x70858036,
- 0x49884684, 0x64efec72, 0x4be2d186, 0x3615b384,
- 0x11cfa18e, 0xd3c50049, 0x75c775f6, 0x434c6530,
- 0x2c5bad8f, 0x898881dc, 0x5f1c86d9, 0xc1f8e7f4));
- }
-
- #[test]
- fn test_rng_clone() {
- let seed : &[_] = &[0u32; 8];
- let mut rng: ChaChaRng = SeedableRng::from_seed(seed);
- let mut clone = rng.clone();
- for _ in 0..16 {
- assert_eq!(rng.next_u64(), clone.next_u64());
- }
- }
-}
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