Update nitrokey crate to 0.4.0

This change finally updates the version of the nitrokey crate that we
consume to 0.4.0. Along with that we update rand_core, one of its
dependencies, to 0.5.1. Further more we add cfg-if in version 0.1.10 and
getrandom in version 0.1.13, both of which are now new (non-development)
dependencies.

Import subrepo nitrokey/:nitrokey at e81057037e9b4f370b64c0a030a725bc6bdfb870
Import subrepo cfg-if/:cfg-if at 4484a6faf816ff8058088ad857b0c6bb2f4b02b2
Import subrepo getrandom/:getrandom at d661aa7e1b8cc80b47dabe3d2135b3b47d2858af
Import subrepo rand/:rand at d877ed528248b52d947e0484364a4e1ae59ca502

6 files changed, 318 insertions, 304 deletions

diff --git a/rand/rand_chacha/CHANGELOG.md b/rand/rand_chacha/CHANGELOG.md
index a1979f6..d242f97 100644
--- a/rand/rand_chacha/CHANGELOG.md
+++ b/rand/rand_chacha/CHANGELOG.md
@@ -4,6 +4,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.2.1] - 2019-07-22
+- Force enable the `simd` feature of `c2-chacha` (#845)
+
+## [0.2.0] - 2019-06-06
+- Rewrite based on the much faster `c2-chacha` crate (#789)
+
 ## [0.1.1] - 2019-01-04
 - Disable `i128` and `u128` if the `target_os` is `emscripten` (#671: work-around Emscripten limitation)
 - Update readme and doc links
diff --git a/rand/rand_chacha/Cargo.toml b/rand/rand_chacha/Cargo.toml
index 028428c..6a47b86 100644
--- a/rand/rand_chacha/Cargo.toml
+++ b/rand/rand_chacha/Cargo.toml
@@ -1,25 +1,28 @@
 [package]
 name = "rand_chacha"
-version = "0.1.1"
-authors = ["The Rand Project Developers", "The Rust Project Developers"]
-license = "MIT/Apache-2.0"
+version = "0.2.1"
+authors = ["The Rand Project Developers", "The Rust Project Developers", "The CryptoCorrosion Contributors"]
+license = "MIT OR Apache-2.0"
 readme = "README.md"
 repository = "https://github.com/rust-random/rand"
-documentation = "https://rust-random.github.io/rand/rand_chacha"
+documentation = "https://rust-random.github.io/rand/rand_chacha/"
 homepage = "https://crates.io/crates/rand_chacha"
 description = """
 ChaCha random number generator
 """
 keywords = ["random", "rng", "chacha"]
 categories = ["algorithms", "no-std"]
-build = "build.rs"
+edition = "2018"
 
 [badges]
 travis-ci = { repository = "rust-random/rand" }
 appveyor = { repository = "rust-random/rand" }
 
 [dependencies]
-rand_core = { path = "../rand_core", version = ">=0.2, <0.4", default-features=false }
+rand_core = { path = "../rand_core", version = "0.5" }
+c2-chacha = { version = "0.2.2", default-features = false, features = ["simd"] }
 
-[build-dependencies]
-autocfg = "0.1"
+[features]
+default = ["std", "simd"]
+std = ["c2-chacha/std"]
+simd = [] # deprecated
diff --git a/rand/rand_chacha/README.md b/rand/rand_chacha/README.md
index 5a1dbac..69a0ce7 100644
--- a/rand/rand_chacha/README.md
+++ b/rand/rand_chacha/README.md
@@ -6,7 +6,7 @@
 [![Book](https://img.shields.io/badge/book-master-yellow.svg)](https://rust-random.github.io/book/)
 [![API](https://img.shields.io/badge/api-master-yellow.svg)](https://rust-random.github.io/rand/rand_chacha)
 [![API](https://docs.rs/rand_chacha/badge.svg)](https://docs.rs/rand_chacha)
-[![Minimum rustc version](https://img.shields.io/badge/rustc-1.22+-lightgray.svg)](https://github.com/rust-random/rand#rust-version-requirements)
+[![Minimum rustc version](https://img.shields.io/badge/rustc-1.32+-lightgray.svg)](https://github.com/rust-random/rand#rust-version-requirements)
 
 A cryptographically secure random number generator that uses the ChaCha
 algorithm.
@@ -16,11 +16,14 @@ as an RNG. It is an improved variant of the Salsa20 cipher family, which was
 selected as one of the "stream ciphers suitable for widespread adoption" by
 eSTREAM[^2].
 
+The RNGs provided by this crate are implemented via the fast stream ciphers of
+the [`c2-chacha`](https://crates.io/crates/c2-chacha) crate.
+
 Links:
 
 -   [API documentation (master)](https://rust-random.github.io/rand/rand_chacha)
 -   [API documentation (docs.rs)](https://docs.rs/rand_chacha)
--   [Changelog](CHANGELOG.md)
+-   [Changelog](https://github.com/rust-random/rand/blob/master/rand_chacha/CHANGELOG.md)
 
 [rand]: https://crates.io/crates/rand
 [^1]: D. J. Bernstein, [*ChaCha, a variant of Salsa20*](
@@ -32,8 +35,9 @@ Links:
 
 ## Crate Features
 
-`rand_chacha` is `no_std` compatible. It does not require any functionality
-outside of the `core` lib, thus there are no features to configure.
+`rand_chacha` is `no_std` compatible when disabling default features; the `std`
+feature can be explicitly required to re-enable `std` support. Using `std`
+allows detection of CPU features and thus better optimisation.
 
 
 # License
diff --git a/rand/rand_chacha/build.rs b/rand/rand_chacha/build.rs
deleted file mode 100644
index 06e12a4..0000000
--- a/rand/rand_chacha/build.rs
+++ /dev/null
@@ -1,7 +0,0 @@
-extern crate autocfg;
-
-fn main() {
-    println!("cargo:rerun-if-changed=build.rs");
-    let ac = autocfg::new();
-    ac.emit_rustc_version(1, 26);
-}
diff --git a/rand/rand_chacha/src/chacha.rs b/rand/rand_chacha/src/chacha.rs
index 86f191e..b1b89e0 100644
--- a/rand/rand_chacha/src/chacha.rs
+++ b/rand/rand_chacha/src/chacha.rs
@@ -1,5 +1,4 @@
 // Copyright 2018 Developers of the Rand project.
-// Copyright 2014 The Rust Project Developers.
 //
 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
 // https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
@@ -9,274 +8,251 @@
 
 //! The ChaCha random number generator.
 
-use core::fmt;
-use rand_core::{CryptoRng, RngCore, SeedableRng, Error, le};
-use rand_core::block::{BlockRngCore, BlockRng};
-
-const SEED_WORDS: usize = 8; // 8 words for the 256-bit key
-const STATE_WORDS: usize = 16;
-
-/// A cryptographically secure random number generator that uses the ChaCha
-/// algorithm.
-///
-/// ChaCha is a stream cipher designed by Daniel J. Bernstein[^1], that we use
-/// as an RNG. It is an improved variant of the Salsa20 cipher family, which was
-/// selected as one of the "stream ciphers suitable for widespread adoption" by
-/// eSTREAM[^2].
-///
-/// ChaCha uses add-rotate-xor (ARX) operations as its basis. These are safe
-/// against timing attacks, although that is mostly a concern for ciphers and
-/// not for RNGs. Also it is very suitable for SIMD implementation.
-/// Here we do not provide a SIMD implementation yet, except for what is
-/// provided by auto-vectorisation.
-///
-/// With the ChaCha algorithm it is possible to choose the number of rounds the
-/// core algorithm should run. The number of rounds is a tradeoff between
-/// performance and security, where 8 rounds is the minimum potentially
-/// secure configuration, and 20 rounds is widely used as a conservative choice.
-/// We use 20 rounds in this implementation, but hope to allow type-level
-/// configuration in the future.
-///
-/// We use a 64-bit counter and 64-bit stream identifier as in Bernstein's
-/// implementation[^1] except that we use a stream identifier in place of a
-/// nonce. A 64-bit counter over 64-byte (16 word) blocks allows 1 ZiB of output
-/// before cycling, and the stream identifier allows 2<sup>64</sup> unique
-/// streams of output per seed. Both counter and stream are initialized to zero
-/// but may be set via [`set_word_pos`] and [`set_stream`].
-///
-/// The word layout is:
-///
-/// ```text
-/// constant  constant  constant  constant
-/// seed      seed      seed      seed
-/// seed      seed      seed      seed
-/// counter   counter   stream_id stream_id
-/// ```
-///
-/// This implementation uses an output buffer of sixteen `u32` words, and uses
-/// [`BlockRng`] to implement the [`RngCore`] methods.
-///
-/// [^1]: D. J. Bernstein, [*ChaCha, a variant of Salsa20*](
-///       https://cr.yp.to/chacha.html)
-///
-/// [^2]: [eSTREAM: the ECRYPT Stream Cipher Project](
-///       http://www.ecrypt.eu.org/stream/)
-///
-/// [`set_word_pos`]: #method.set_word_pos
-/// [`set_stream`]: #method.set_stream
-/// [`BlockRng`]: ../rand_core/block/struct.BlockRng.html
-/// [`RngCore`]: ../rand_core/trait.RngCore.html
-#[derive(Clone, Debug)]
-pub struct ChaChaRng(BlockRng<ChaChaCore>);
-
-impl RngCore for ChaChaRng {
-    #[inline]
-    fn next_u32(&mut self) -> u32 {
-        self.0.next_u32()
+#[cfg(feature = "std")]
+use std as core;
+#[cfg(not(feature = "std"))]
+use core;
+
+use c2_chacha::guts::ChaCha;
+use self::core::fmt;
+use rand_core::block::{BlockRng, BlockRngCore};
+use rand_core::{CryptoRng, Error, RngCore, SeedableRng};
+
+const STREAM_PARAM_NONCE: u32 = 1;
+const STREAM_PARAM_BLOCK: u32 = 0;
+
+pub struct Array64<T>([T; 64]);
+impl<T> Default for Array64<T> where T: Default {
+    fn default() -> Self {
+        Self([T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default(),
+              T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default(),
+              T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default(),
+              T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default(),
+              T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default(),
+              T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default(),
+              T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default(),
+              T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default(), T::default()])
     }
-
-    #[inline]
-    fn next_u64(&mut self) -> u64 {
-        self.0.next_u64()
-    }
-
-    #[inline]
-    fn fill_bytes(&mut self, dest: &mut [u8]) {
-        self.0.fill_bytes(dest)
+}
+impl<T> AsRef<[T]> for Array64<T> {
+    fn as_ref(&self) -> &[T] {
+        &self.0
     }
-
-    #[inline]
-    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-        self.0.try_fill_bytes(dest)
+}
+impl<T> AsMut<[T]> for Array64<T> {
+    fn as_mut(&mut self) -> &mut [T] {
+        &mut self.0
     }
 }
-
-impl SeedableRng for ChaChaRng {
-    type Seed = <ChaChaCore as SeedableRng>::Seed;
-
-    fn from_seed(seed: Self::Seed) -> Self {
-        ChaChaRng(BlockRng::<ChaChaCore>::from_seed(seed))
+impl<T> Clone for Array64<T> where T: Copy + Default {
+    fn clone(&self) -> Self {
+        let mut new = Self::default();
+        new.0.copy_from_slice(&self.0);
+        new
     }
-
-    fn from_rng<R: RngCore>(rng: R) -> Result<Self, Error> {
-        BlockRng::<ChaChaCore>::from_rng(rng).map(ChaChaRng)
+}
+impl<T> fmt::Debug for Array64<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "Array64 {{}}")
     }
 }
 
-impl CryptoRng for ChaChaRng {}
-
-impl ChaChaRng {
-    /// Get the offset from the start of the stream, in 32-bit words.
-    ///
-    /// Since the generated blocks are 16 words (2<sup>4</sup>) long and the
-    /// counter is 64-bits, the offset is a 68-bit number. Sub-word offsets are
-    /// not supported, hence the result can simply be multiplied by 4 to get a
-    /// byte-offset.
-    ///
-    /// Note: this function is currently only available with Rust 1.26 or later.
-    #[cfg(all(rustc_1_26, not(target_os = "emscripten")))]
-    pub fn get_word_pos(&self) -> u128 {
-        let mut c = (self.0.core.state[13] as u64) << 32
-                  | (self.0.core.state[12] as u64);
-        let mut index = self.0.index();
-        // c is the end of the last block generated, unless index is at end
-        if index >= STATE_WORDS {
-            index = 0;
-        } else {
-            c = c.wrapping_sub(1);
+macro_rules! chacha_impl {
+    ($ChaChaXCore:ident, $ChaChaXRng:ident, $rounds:expr, $doc:expr) => {
+        #[doc=$doc]
+        #[derive(Clone)]
+        pub struct $ChaChaXCore {
+            state: ChaCha,
         }
-        ((c as u128) << 4) | (index as u128)
-    }
 
-    /// Set the offset from the start of the stream, in 32-bit words.
-    ///
-    /// As with `get_word_pos`, we use a 68-bit number. Since the generator
-    /// simply cycles at the end of its period (1 ZiB), we ignore the upper
-    /// 60 bits.
-    ///
-    /// Note: this function is currently only available with Rust 1.26 or later.
-    #[cfg(all(rustc_1_26, not(target_os = "emscripten")))]
-    pub fn set_word_pos(&mut self, word_offset: u128) {
-        let index = (word_offset as usize) & 0xF;
-        let counter = (word_offset >> 4) as u64;
-        self.0.core.state[12] = counter as u32;
-        self.0.core.state[13] = (counter >> 32) as u32;
-        if index != 0 {
-            self.0.generate_and_set(index); // also increments counter
-        } else {
-            self.0.reset();
+        // Custom Debug implementation that does not expose the internal state
+        impl fmt::Debug for $ChaChaXCore {
+            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                write!(f, "ChaChaXCore {{}}")
+            }
         }
-    }
 
-    /// Set the stream number.
-    ///
-    /// This is initialized to zero; 2<sup>64</sup> unique streams of output
-    /// are available per seed/key.
-    ///
-    /// Note that in order to reproduce ChaCha output with a specific 64-bit
-    /// nonce, one can convert that nonce to a `u64` in little-endian fashion
-    /// and pass to this function. In theory a 96-bit nonce can be used by
-    /// passing the last 64-bits to this function and using the first 32-bits as
-    /// the most significant half of the 64-bit counter (which may be set
-    /// indirectly via `set_word_pos`), but this is not directly supported.
-    pub fn set_stream(&mut self, stream: u64) {
-        let index = self.0.index();
-        self.0.core.state[14] = stream as u32;
-        self.0.core.state[15] = (stream >> 32) as u32;
-        if index < STATE_WORDS {
-            // we need to regenerate a partial result buffer
-            {
-                // reverse of counter adjustment in generate()
-                if self.0.core.state[12] == 0 {
-                    self.0.core.state[13] = self.0.core.state[13].wrapping_sub(1);
+        impl BlockRngCore for $ChaChaXCore {
+            type Item = u32;
+            type Results = Array64<u32>;
+            #[inline]
+            fn generate(&mut self, r: &mut Self::Results) {
+                // Fill slice of words by writing to equivalent slice of bytes, then fixing endianness.
+                self.state.refill4($rounds, unsafe {
+                    &mut *(&mut *r as *mut Array64<u32> as *mut [u8; 256])
+                });
+                for x in r.as_mut() {
+                    *x = x.to_le();
                 }
-                self.0.core.state[12] = self.0.core.state[12].wrapping_sub(1);
             }
-            self.0.generate_and_set(index);
         }
-    }
-}
 
-/// The core of `ChaChaRng`, used with `BlockRng`.
-#[derive(Clone)]
-pub struct ChaChaCore {
-    state: [u32; STATE_WORDS],
-}
-
-// Custom Debug implementation that does not expose the internal state
-impl fmt::Debug for ChaChaCore {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "ChaChaCore {{}}")
-    }
-}
+        impl SeedableRng for $ChaChaXCore {
+            type Seed = [u8; 32];
+            #[inline]
+            fn from_seed(seed: Self::Seed) -> Self {
+                $ChaChaXCore { state: ChaCha::new(&seed, &[0u8; 8]) }
+            }
+        }
 
-macro_rules! quarter_round{
-    ($a: expr, $b: expr, $c: expr, $d: expr) => {{
-        $a = $a.wrapping_add($b); $d ^= $a; $d = $d.rotate_left(16);
-        $c = $c.wrapping_add($d); $b ^= $c; $b = $b.rotate_left(12);
-        $a = $a.wrapping_add($b); $d ^= $a; $d = $d.rotate_left( 8);
-        $c = $c.wrapping_add($d); $b ^= $c; $b = $b.rotate_left( 7);
-    }}
-}
+        /// A cryptographically secure random number generator that uses the ChaCha algorithm.
+        ///
+        /// ChaCha is a stream cipher designed by Daniel J. Bernstein[^1], that we use as an RNG. It is
+        /// an improved variant of the Salsa20 cipher family, which was selected as one of the "stream
+        /// ciphers suitable for widespread adoption" by eSTREAM[^2].
+        ///
+        /// ChaCha uses add-rotate-xor (ARX) operations as its basis. These are safe against timing
+        /// attacks, although that is mostly a concern for ciphers and not for RNGs. We provide a SIMD
+        /// implementation to support high throughput on a variety of common hardware platforms.
+        ///
+        /// With the ChaCha algorithm it is possible to choose the number of rounds the core algorithm
+        /// should run. The number of rounds is a tradeoff between performance and security, where 8
+        /// rounds is the minimum potentially secure configuration, and 20 rounds is widely used as a
+        /// conservative choice.
+        ///
+        /// We use a 64-bit counter and 64-bit stream identifier as in Bernstein's implementation[^1]
+        /// except that we use a stream identifier in place of a nonce. A 64-bit counter over 64-byte
+        /// (16 word) blocks allows 1 ZiB of output before cycling, and the stream identifier allows
+        /// 2<sup>64</sup> unique streams of output per seed. Both counter and stream are initialized
+        /// to zero but may be set via the `set_word_pos` and `set_stream` methods.
+        ///
+        /// The word layout is:
+        ///
+        /// ```text
+        /// constant  constant  constant  constant
+        /// seed      seed      seed      seed
+        /// seed      seed      seed      seed
+        /// counter   counter   stream_id stream_id
+        /// ```
+        ///
+        /// This implementation uses an output buffer of sixteen `u32` words, and uses
+        /// [`BlockRng`] to implement the [`RngCore`] methods.
+        ///
+        /// [^1]: D. J. Bernstein, [*ChaCha, a variant of Salsa20*](
+        ///       https://cr.yp.to/chacha.html)
+        ///
+        /// [^2]: [eSTREAM: the ECRYPT Stream Cipher Project](
+        ///       http://www.ecrypt.eu.org/stream/)
+        #[derive(Clone, Debug)]
+        pub struct $ChaChaXRng {
+            rng: BlockRng<$ChaChaXCore>,
+        }
 
-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]);
-    }}
-}
+        impl SeedableRng for $ChaChaXRng {
+            type Seed = [u8; 32];
+            #[inline]
+            fn from_seed(seed: Self::Seed) -> Self {
+                let core = $ChaChaXCore::from_seed(seed);
+                Self {
+                    rng: BlockRng::new(core),
+                }
+            }
+        }
 
-impl BlockRngCore for ChaChaCore {
-    type Item = u32;
-    type Results = [u32; STATE_WORDS];
-
-    fn generate(&mut self, results: &mut Self::Results) {
-        // For some reason extracting this part into a separate function
-        // improves performance by 50%.
-        fn core(results: &mut [u32; STATE_WORDS],
-                state: &[u32; STATE_WORDS])
-        {
-            let mut tmp = *state;
-            let rounds = 20;
-            for _ in 0..rounds / 2 {
-                double_round!(tmp);
+        impl RngCore for $ChaChaXRng {
+            #[inline]
+            fn next_u32(&mut self) -> u32 {
+                self.rng.next_u32()
+            }
+            #[inline]
+            fn next_u64(&mut self) -> u64 {
+                self.rng.next_u64()
             }
-            for i in 0..STATE_WORDS {
-                results[i] = tmp[i].wrapping_add(state[i]);
+            #[inline]
+            fn fill_bytes(&mut self, bytes: &mut [u8]) {
+                self.rng.fill_bytes(bytes)
+            }
+            #[inline]
+            fn try_fill_bytes(&mut self, bytes: &mut [u8]) -> Result<(), Error> {
+                self.rng.try_fill_bytes(bytes)
             }
         }
 
-        core(results, &self.state);
+        impl $ChaChaXRng {
+            // The buffer is a 4-block window, i.e. it is always at a block-aligned position in the
+            // stream but if the stream has been seeked it may not be self-aligned.
+
+            /// Get the offset from the start of the stream, in 32-bit words.
+            ///
+            /// Since the generated blocks are 16 words (2<sup>4</sup>) long and the
+            /// counter is 64-bits, the offset is a 68-bit number. Sub-word offsets are
+            /// not supported, hence the result can simply be multiplied by 4 to get a
+            /// byte-offset.
+            #[inline]
+            pub fn get_word_pos(&self) -> u128 {
+                let mut block = u128::from(self.rng.core.state.get_stream_param(STREAM_PARAM_BLOCK));
+                // counter is incremented *after* filling buffer
+                block -= 4;
+                (block << 4) + self.rng.index() as u128
+            }
 
-        // update 64-bit counter
-        self.state[12] = self.state[12].wrapping_add(1);
-        if self.state[12] != 0 { return; };
-        self.state[13] = self.state[13].wrapping_add(1);
-    }
-}
+            /// Set the offset from the start of the stream, in 32-bit words.
+            ///
+            /// As with `get_word_pos`, we use a 68-bit number. Since the generator
+            /// simply cycles at the end of its period (1 ZiB), we ignore the upper
+            /// 60 bits.
+            #[inline]
+            pub fn set_word_pos(&mut self, word_offset: u128) {
+                let block = (word_offset >> 4) as u64;
+                self.rng
+                    .core
+                    .state
+                    .set_stream_param(STREAM_PARAM_BLOCK, block);
+                self.rng.generate_and_set((word_offset & 15) as usize);
+            }
 
-impl SeedableRng for ChaChaCore {
-    type Seed = [u8; SEED_WORDS*4];
-
-    fn from_seed(seed: Self::Seed) -> Self {
-        let mut seed_le = [0u32; SEED_WORDS];
-        le::read_u32_into(&seed, &mut seed_le);
-        Self {
-            state: [0x61707865, 0x3320646E, 0x79622D32, 0x6B206574, // constants
-                    seed_le[0], seed_le[1], seed_le[2], seed_le[3], // seed
-                    seed_le[4], seed_le[5], seed_le[6], seed_le[7], // seed
-                    0, 0, 0, 0], // counter
-         }
-    }
-}
+            /// Set the stream number.
+            ///
+            /// This is initialized to zero; 2<sup>64</sup> unique streams of output
+            /// are available per seed/key.
+            ///
+            /// Note that in order to reproduce ChaCha output with a specific 64-bit
+            /// nonce, one can convert that nonce to a `u64` in little-endian fashion
+            /// and pass to this function. In theory a 96-bit nonce can be used by
+            /// passing the last 64-bits to this function and using the first 32-bits as
+            /// the most significant half of the 64-bit counter (which may be set
+            /// indirectly via `set_word_pos`), but this is not directly supported.
+            #[inline]
+            pub fn set_stream(&mut self, stream: u64) {
+                self.rng
+                    .core
+                    .state
+                    .set_stream_param(STREAM_PARAM_NONCE, stream);
+                if self.rng.index() != 64 {
+                    let wp = self.get_word_pos();
+                    self.set_word_pos(wp);
+                }
+            }
+        }
 
-impl CryptoRng for ChaChaCore {}
+        impl CryptoRng for $ChaChaXRng {}
 
-impl From<ChaChaCore> for ChaChaRng {
-    fn from(core: ChaChaCore) -> Self {
-        ChaChaRng(BlockRng::new(core))
+        impl From<$ChaChaXCore> for $ChaChaXRng {
+            fn from(core: $ChaChaXCore) -> Self {
+                $ChaChaXRng {
+                    rng: BlockRng::new(core),
+                }
+            }
+        }
     }
 }
 
+chacha_impl!(ChaCha20Core, ChaCha20Rng, 10, "ChaCha with 20 rounds");
+chacha_impl!(ChaCha12Core, ChaCha12Rng, 6, "ChaCha with 12 rounds");
+chacha_impl!(ChaCha8Core, ChaCha8Rng, 4, "ChaCha with 8 rounds");
+
 #[cfg(test)]
 mod test {
-    use ::rand_core::{RngCore, SeedableRng};
-    use super::ChaChaRng;
+    use rand_core::{RngCore, SeedableRng};
+
+    type ChaChaRng = super::ChaCha20Rng;
 
     #[test]
     fn test_chacha_construction() {
-        let seed = [0,0,0,0,0,0,0,0,
-            1,0,0,0,0,0,0,0,
-            2,0,0,0,0,0,0,0,
-            3,0,0,0,0,0,0,0];
+        let seed = [
+            0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 0, 0,
+            0, 0, 0,
+        ];
         let mut rng1 = ChaChaRng::from_seed(seed);
         assert_eq!(rng1.next_u32(), 137206642);
 
@@ -292,18 +268,24 @@ mod test {
         let mut rng = ChaChaRng::from_seed(seed);
 
         let mut results = [0u32; 16];
-        for i in results.iter_mut() { *i = rng.next_u32(); }
-        let expected = [0xade0b876, 0x903df1a0, 0xe56a5d40, 0x28bd8653,
-                        0xb819d2bd, 0x1aed8da0, 0xccef36a8, 0xc70d778b,
-                        0x7c5941da, 0x8d485751, 0x3fe02477, 0x374ad8b8,
-                        0xf4b8436a, 0x1ca11815, 0x69b687c3, 0x8665eeb2];
+        for i in results.iter_mut() {
+            *i = rng.next_u32();
+        }
+        let expected = [
+            0xade0b876, 0x903df1a0, 0xe56a5d40, 0x28bd8653, 0xb819d2bd, 0x1aed8da0, 0xccef36a8,
+            0xc70d778b, 0x7c5941da, 0x8d485751, 0x3fe02477, 0x374ad8b8, 0xf4b8436a, 0x1ca11815,
+            0x69b687c3, 0x8665eeb2,
+        ];
         assert_eq!(results, expected);
 
-        for i in results.iter_mut() { *i = rng.next_u32(); }
-        let expected = [0xbee7079f, 0x7a385155, 0x7c97ba98, 0x0d082d73,
-                        0xa0290fcb, 0x6965e348, 0x3e53c612, 0xed7aee32,
-                        0x7621b729, 0x434ee69c, 0xb03371d5, 0xd539d874,
-                        0x281fed31, 0x45fb0a51, 0x1f0ae1ac, 0x6f4d794b];
+        for i in results.iter_mut() {
+            *i = rng.next_u32();
+        }
+        let expected = [
+            0xbee7079f, 0x7a385155, 0x7c97ba98, 0x0d082d73, 0xa0290fcb, 0x6965e348, 0x3e53c612,
+            0xed7aee32, 0x7621b729, 0x434ee69c, 0xb03371d5, 0xd539d874, 0x281fed31, 0x45fb0a51,
+            0x1f0ae1ac, 0x6f4d794b,
+        ];
         assert_eq!(results, expected);
     }
 
@@ -311,51 +293,62 @@ mod test {
     fn test_chacha_true_values_b() {
         // Test vector 3 from
         // https://tools.ietf.org/html/draft-nir-cfrg-chacha20-poly1305-04
-        let seed = [0, 0, 0, 0, 0, 0, 0, 0,
-                    0, 0, 0, 0, 0, 0, 0, 0,
-                    0, 0, 0, 0, 0, 0, 0, 0,
-                    0, 0, 0, 0, 0, 0, 0, 1];
+        let seed = [
+            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            0, 0, 1,
+        ];
         let mut rng = ChaChaRng::from_seed(seed);
 
         // Skip block 0
-        for _ in 0..16 { rng.next_u32(); }
+        for _ in 0..16 {
+            rng.next_u32();
+        }
 
         let mut results = [0u32; 16];
-        for i in results.iter_mut() { *i = rng.next_u32(); }
-        let expected = [0x2452eb3a, 0x9249f8ec, 0x8d829d9b, 0xddd4ceb1,
-                        0xe8252083, 0x60818b01, 0xf38422b8, 0x5aaa49c9,
-                        0xbb00ca8e, 0xda3ba7b4, 0xc4b592d1, 0xfdf2732f,
-                        0x4436274e, 0x2561b3c8, 0xebdd4aa6, 0xa0136c00];
+        for i in results.iter_mut() {
+            *i = rng.next_u32();
+        }
+        let expected = [
+            0x2452eb3a, 0x9249f8ec, 0x8d829d9b, 0xddd4ceb1, 0xe8252083, 0x60818b01, 0xf38422b8,
+            0x5aaa49c9, 0xbb00ca8e, 0xda3ba7b4, 0xc4b592d1, 0xfdf2732f, 0x4436274e, 0x2561b3c8,
+            0xebdd4aa6, 0xa0136c00,
+        ];
         assert_eq!(results, expected);
     }
 
     #[test]
-    #[cfg(all(rustc_1_26, not(target_os = "emscripten")))]
     fn test_chacha_true_values_c() {
         // Test vector 4 from
         // https://tools.ietf.org/html/draft-nir-cfrg-chacha20-poly1305-04
-        let seed = [0, 0xff, 0, 0, 0, 0, 0, 0,
-                    0, 0, 0, 0, 0, 0, 0, 0,
-                    0, 0, 0, 0, 0, 0, 0, 0,
-                    0, 0, 0, 0, 0, 0, 0, 0];
-        let expected = [0xfb4dd572, 0x4bc42ef1, 0xdf922636, 0x327f1394,
-                        0xa78dea8f, 0x5e269039, 0xa1bebbc1, 0xcaf09aae,
-                        0xa25ab213, 0x48a6b46c, 0x1b9d9bcb, 0x092c5be6,
-                        0x546ca624, 0x1bec45d5, 0x87f47473, 0x96f0992e];
+        let seed = [
+            0, 0xff, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            0, 0, 0, 0,
+        ];
+        let expected = [
+            0xfb4dd572, 0x4bc42ef1, 0xdf922636, 0x327f1394, 0xa78dea8f, 0x5e269039, 0xa1bebbc1,
+            0xcaf09aae, 0xa25ab213, 0x48a6b46c, 0x1b9d9bcb, 0x092c5be6, 0x546ca624, 0x1bec45d5,
+            0x87f47473, 0x96f0992e,
+        ];
         let expected_end = 3 * 16;
         let mut results = [0u32; 16];
 
         // Test block 2 by skipping block 0 and 1
         let mut rng1 = ChaChaRng::from_seed(seed);
-        for _ in 0..32 { rng1.next_u32(); }
-        for i in results.iter_mut() { *i = rng1.next_u32(); }
+        for _ in 0..32 {
+            rng1.next_u32();
+        }
+        for i in results.iter_mut() {
+            *i = rng1.next_u32();
+        }
         assert_eq!(results, expected);
         assert_eq!(rng1.get_word_pos(), expected_end);
 
         // Test block 2 by using `set_word_pos`
         let mut rng2 = ChaChaRng::from_seed(seed);
         rng2.set_word_pos(2 * 16);
-        for i in results.iter_mut() { *i = rng2.next_u32(); }
+        for i in results.iter_mut() {
+            *i = rng2.next_u32();
+        }
         assert_eq!(results, expected);
         assert_eq!(rng2.get_word_pos(), expected_end);
 
@@ -376,7 +369,10 @@ mod test {
 
     #[test]
     fn test_chacha_multiple_blocks() {
-        let seed = [0,0,0,0, 1,0,0,0, 2,0,0,0, 3,0,0,0, 4,0,0,0, 5,0,0,0, 6,0,0,0, 7,0,0,0];
+        let seed = [
+            0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0, 5, 0, 0, 0, 6, 0, 0, 0, 7,
+            0, 0, 0,
+        ];
         let mut rng = ChaChaRng::from_seed(seed);
 
         // Store the 17*i-th 32-bit word,
@@ -388,10 +384,11 @@ mod test {
                 rng.next_u32();
             }
         }
-        let expected = [0xf225c81a, 0x6ab1be57, 0x04d42951, 0x70858036,
-                        0x49884684, 0x64efec72, 0x4be2d186, 0x3615b384,
-                        0x11cfa18e, 0xd3c50049, 0x75c775f6, 0x434c6530,
-                        0x2c5bad8f, 0x898881dc, 0x5f1c86d9, 0xc1f8e7f4];
+        let expected = [
+            0xf225c81a, 0x6ab1be57, 0x04d42951, 0x70858036, 0x49884684, 0x64efec72, 0x4be2d186,
+            0x3615b384, 0x11cfa18e, 0xd3c50049, 0x75c775f6, 0x434c6530, 0x2c5bad8f, 0x898881dc,
+            0x5f1c86d9, 0xc1f8e7f4,
+        ];
         assert_eq!(results, expected);
     }
 
@@ -401,10 +398,10 @@ mod test {
         let mut rng = ChaChaRng::from_seed(seed);
         let mut results = [0u8; 32];
         rng.fill_bytes(&mut results);
-        let expected = [118, 184, 224, 173, 160, 241, 61, 144,
-                        64, 93, 106, 229, 83, 134, 189, 40,
-                        189, 210, 25, 184, 160, 141, 237, 26,
-                        168, 54, 239, 204, 139, 119, 13, 199];
+        let expected = [
+            118, 184, 224, 173, 160, 241, 61, 144, 64, 93, 106, 229, 83, 134, 189, 40, 189, 210,
+            25, 184, 160, 141, 237, 26, 168, 54, 239, 204, 139, 119, 13, 199,
+        ];
         assert_eq!(results, expected);
     }
 
@@ -420,17 +417,23 @@ mod test {
         rng.set_stream(2u64 << (24 + 32));
 
         let mut results = [0u32; 16];
-        for i in results.iter_mut() { *i = rng.next_u32(); }
-        let expected = [0x374dc6c2, 0x3736d58c, 0xb904e24a, 0xcd3f93ef,
-                        0x88228b1a, 0x96a4dfb3, 0x5b76ab72, 0xc727ee54,
-                        0x0e0e978a, 0xf3145c95, 0x1b748ea8, 0xf786c297,
-                        0x99c28f5f, 0x628314e8, 0x398a19fa, 0x6ded1b53];
+        for i in results.iter_mut() {
+            *i = rng.next_u32();
+        }
+        let expected = [
+            0x374dc6c2, 0x3736d58c, 0xb904e24a, 0xcd3f93ef, 0x88228b1a, 0x96a4dfb3, 0x5b76ab72,
+            0xc727ee54, 0x0e0e978a, 0xf3145c95, 0x1b748ea8, 0xf786c297, 0x99c28f5f, 0x628314e8,
+            0x398a19fa, 0x6ded1b53,
+        ];
         assert_eq!(results, expected);
     }
 
     #[test]
     fn test_chacha_clone_streams() {
-        let seed = [0,0,0,0, 1,0,0,0, 2,0,0,0, 3,0,0,0, 4,0,0,0, 5,0,0,0, 6,0,0,0, 7,0,0,0];
+        let seed = [
+            0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0, 5, 0, 0, 0, 6, 0, 0, 0, 7,
+            0, 0, 0,
+        ];
         let mut rng = ChaChaRng::from_seed(seed);
         let mut clone = rng.clone();
         for _ in 0..16 {
@@ -441,7 +444,7 @@ mod test {
         for _ in 0..7 {
             assert!(rng.next_u32() != clone.next_u32());
         }
-        clone.set_stream(51);   // switch part way through block
+        clone.set_stream(51); // switch part way through block
         for _ in 7..16 {
             assert_eq!(rng.next_u32(), clone.next_u32());
         }
diff --git a/rand/rand_chacha/src/lib.rs b/rand/rand_chacha/src/lib.rs
index 74ad466..e374bdd 100644
--- a/rand/rand_chacha/src/lib.rs
+++ b/rand/rand_chacha/src/lib.rs
@@ -16,10 +16,15 @@
 #![deny(missing_debug_implementations)]
 #![doc(test(attr(allow(unused_variables), deny(warnings))))]
 
-#![no_std]
+#![cfg_attr(not(feature = "std"), no_std)]
 
-pub extern crate rand_core;
+pub use rand_core;
 
 mod chacha;
 
-pub use chacha::{ChaChaRng, ChaChaCore};
+pub use crate::chacha::{ChaCha12Core, ChaCha12Rng, ChaCha20Core, ChaCha20Rng, ChaCha8Core, ChaCha8Rng};
+
+/// ChaCha with 20 rounds
+pub type ChaChaRng = ChaCha20Rng;
+/// ChaCha with 20 rounds, low-level interface
+pub type ChaChaCore = ChaCha20Core;