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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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