Include ChaCha pseudorandom generator

Author: sneves

src/librand/chacha.rs

@@ -0,0 +1,285 @@
+// 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::prelude::*;
+
+use {Rng, SeedableRng, Rand};
+
+static KEY_WORDS    : uint =  8; // 8 words for the 256-bit key
+static STATE_WORDS  : uint = 16;
+static CHACHA_ROUNDS: uint = 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)
+
+pub struct ChaChaRng {
+    buffer:  [u32, ..STATE_WORDS], // Internal buffer of output
+    state:   [u32, ..STATE_WORDS], // Initial state
+    index:   uint,                 // Index into state
+}
+
+static EMPTY: ChaChaRng = ChaChaRng {
+    buffer:  [0, ..STATE_WORDS],
+    state:   [0, ..STATE_WORDS],
+    index:   STATE_WORDS
+};
+
+
+macro_rules! quarter_round{
+    ($a: expr, $b: expr, $c: expr, $d: expr) => {{
+        $a += $b; $d ^= $a; $d = $d.rotate_left(16);
+        $c += $d; $b ^= $c; $b = $b.rotate_left(12);
+        $a += $b; $d ^= $a; $d = $d.rotate_left( 8);
+        $c += $d; $b ^= $c; $b = $b.rotate_left( 7);
+    }}
+}
+
+macro_rules! double_round{
+    ($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 [u32, ..STATE_WORDS], input: &[u32, ..STATE_WORDS]) {
+    *output = *input;
+
+    for _ in range(0, CHACHA_ROUNDS / 2) {
+        double_round!(output);
+    }
+
+    for i in range(0, STATE_WORDS) {
+        output[i] += input[i];
+    }
+}
+
+impl ChaChaRng {
+
+    /// Create an ChaCha random number generator using the default
+    /// fixed key of 8 zero words.
+    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`.
+    pub fn set_counter(&mut self, counter_low: u64, counter_high: u64) {
+        self.state[12] = (counter_low >>  0) as u32;
+        self.state[13] = (counter_low >> 32) as u32;
+        self.state[14] = (counter_high >>  0) as u32;
+        self.state[15] = (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:
+    /// ```notrust
+    /// 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] = 0x61707865;
+        self.state[1] = 0x3320646E;
+        self.state[2] = 0x79622D32;
+        self.state[3] = 0x6B206574;
+
+        for i in range(0, KEY_WORDS) {
+            self.state[4+i] = key[i];
+        }
+
+        self.state[12] = 0;
+        self.state[13] = 0;
+        self.state[14] = 0;
+        self.state[15] = 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] += 1;
+        if self.state[12] != 0 { return };
+        self.state[13] += 1;
+        if self.state[13] != 0 { return };
+        self.state[14] += 1;
+        if self.state[14] != 0 { return };
+        self.state[15] += 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
+    }
+}
+
+impl<'a> SeedableRng<&'a [u32]> for ChaChaRng {
+
+    fn reseed(&mut self, seed: &'a [u32]) {
+        // reset state
+        self.init(&[0u32, ..KEY_WORDS]);
+        // set key inplace
+        let key = self.state.slice_mut(4, 4+KEY_WORDS);
+        for (k, s) in key.iter_mut().zip(seed.iter()) {
+            *k = *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.as_slice())
+    }
+}
+
+
+#[cfg(test)]
+mod test {
+    use std::prelude::*;
+
+    use core::iter::order;
+    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.as_slice());
+        let mut rb: ChaChaRng = SeedableRng::from_seed(s.as_slice());
+        assert!(order::equals(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!(order::equals(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.as_slice());
+        let string1: String = r.gen_ascii_chars().take(100).collect();
+
+        r.reseed(s.as_slice());
+
+        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 = Vec::from_fn(16, |_| ra.next_u32());
+        assert_eq!(v,
+                   vec!(0xade0b876, 0x903df1a0, 0xe56a5d40, 0x28bd8653,
+                        0xb819d2bd, 0x1aed8da0, 0xccef36a8, 0xc70d778b,
+                        0x7c5941da, 0x8d485751, 0x3fe02477, 0x374ad8b8,
+                        0xf4b8436a, 0x1ca11815, 0x69b687c3, 0x8665eeb2));
+
+        let v = Vec::from_fn(16, |_| ra.next_u32());
+        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 range(0u, 16) {
+            v.push(ra.next_u32());
+            for _ in range(0u, 16) {
+                ra.next_u32();
+            }
+        }
+
+        assert_eq!(v,
+                   vec!(0xf225c81a, 0x6ab1be57, 0x04d42951, 0x70858036,
+                        0x49884684, 0x64efec72, 0x4be2d186, 0x3615b384,
+                        0x11cfa18e, 0xd3c50049, 0x75c775f6, 0x434c6530,
+                        0x2c5bad8f, 0x898881dc, 0x5f1c86d9, 0xc1f8e7f4));
+    }
+}
+

src/librand/lib.rs

@@ -39,6 +39,7 @@ extern crate core;
 use core::prelude::*;
 
 pub use isaac::{IsaacRng, Isaac64Rng};
+pub use chacha::ChaChaRng;
 
 use distributions::{Range, IndependentSample};
 use distributions::range::SampleRange;
@@ -48,6 +49,7 @@ static RAND_BENCH_N: u64 = 100;
 
 pub mod distributions;
 pub mod isaac;
+pub mod chacha;
 pub mod reseeding;
 mod rand_impls;
 

src/libstd/rand/mod.rs

@@ -233,7 +233,7 @@ use core_rand::IsaacRng as IsaacWordRng;
 use core_rand::Isaac64Rng as IsaacWordRng;
 
 pub use core_rand::{Rand, Rng, SeedableRng, Open01, Closed01};
-pub use core_rand::{XorShiftRng, IsaacRng, Isaac64Rng};
+pub use core_rand::{XorShiftRng, IsaacRng, Isaac64Rng, ChaChaRng};
 pub use core_rand::{distributions, reseeding};
 pub use rand::os::OsRng;