chacha.rs.html -- source
Description: Source to the Rust file `C:\Users\Gray\.cargo\registry\src\github.com-1ecc6299db9ec823\rand-0.3.18\src\chacha.rs`.
Keywords: rust, rustlang, rust-lang

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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 std::num::Wrapping as w;
    use {Rng, SeedableRng, Rand, w32};

    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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