// 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());
}
}
}