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