      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203
    204
    205
    206
    207
    208
    209
    210
    211
    212
    213
    214
    215
    216
    217
    218
    219
    220
    221
    222
    223
    224
    225
    226
    227
    228
    229
    230
    231
    232
    233
    234
    235
    236
    237
    238
    239
    240
    241
    242
    243
    244
    245
    246
    247
    248
    249
    250
    251
    252
    253
    254
    255
    256
    257
    258
    259
    260
    261
    262
    263
    264
    265
    266
    267
    268
    269
    270
    271
    272
    273
    274
    275
    276
    277
    278
    279
    280
    281
    282
    283
    284
    285
    286
    287
    288
    289
    290
    291
    292
    293
    294
    295
    296
    297
    298
    299
    300
    301
    302
    303
    304
    305
    306
    307
    308
    309
    310
    311
    312
    313
    314
    315
    316
    317
    318

    // 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)]
    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());
            }
        }
    }

# Help

## Keyboard Shortcuts

?
  Show this help dialog
S
  Focus the search field
⇤
  Move up in search results
⇥
  Move down in search results
⏎
  Go to active search result
+
  Collapse/expand all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)