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

1 files changed, 37 insertions, 54 deletions

diff --git a/rand/src/rngs/thread.rs b/rand/src/rngs/thread.rs
index 7977d85..2006f41 100644
--- a/rand/src/rngs/thread.rs
+++ b/rand/src/rngs/thread.rs
@@ -9,11 +9,12 @@
 //! Thread-local random number generator
 
 use std::cell::UnsafeCell;
+use std::ptr::NonNull;
 
-use {RngCore, CryptoRng, SeedableRng, Error};
-use rngs::adapter::ReseedingRng;
-use rngs::EntropyRng;
-use rand_hc::Hc128Core;
+use crate::{RngCore, CryptoRng, SeedableRng, Error};
+use crate::rngs::adapter::ReseedingRng;
+use crate::rngs::OsRng;
+use super::std::Core;
 
 // Rationale for using `UnsafeCell` in `ThreadRng`:
 //
@@ -28,61 +29,43 @@ use rand_hc::Hc128Core;
 // completely under our control. We just have to ensure none of them use
 // `ThreadRng` internally, which is nonsensical anyway. We should also never run
 // `ThreadRng` in destructors of its implementation, which is also nonsensical.
-//
-// The additional `Rc` is not strictly neccesary, and could be removed. For now
-// it ensures `ThreadRng` stays `!Send` and `!Sync`, and implements `Clone`.
 
 
-// Number of generated bytes after which to reseed `TreadRng`.
-//
-// The time it takes to reseed HC-128 is roughly equivalent to generating 7 KiB.
-// We pick a treshold here that is large enough to not reduce the average
-// performance too much, but also small enough to not make reseeding something
-// that basically never happens.
-const THREAD_RNG_RESEED_THRESHOLD: u64 = 32*1024*1024; // 32 MiB
+// Number of generated bytes after which to reseed `ThreadRng`.
+// According to benchmarks, reseeding has a noticable impact with thresholds
+// of 32 kB and less. We choose 64 kB to avoid significant overhead.
+const THREAD_RNG_RESEED_THRESHOLD: u64 = 1024 * 64;
 
 /// The type returned by [`thread_rng`], essentially just a reference to the
 /// PRNG in thread-local memory.
 ///
-/// `ThreadRng` uses [`ReseedingRng`] wrapping the same PRNG as [`StdRng`],
-/// which is reseeded after generating 32 MiB of random data. A single instance
-/// is cached per thread and the returned `ThreadRng` is a reference to this
-/// instance — hence `ThreadRng` is neither `Send` nor `Sync` but is safe to use
-/// within a single thread. This RNG is seeded and reseeded via [`EntropyRng`]
-/// as required.
+/// `ThreadRng` uses the same PRNG as [`StdRng`] for security and performance.
+/// As hinted by the name, the generator is thread-local. `ThreadRng` is a
+/// handle to this generator and thus supports `Copy`, but not `Send` or `Sync`.
 ///
-/// Note that the reseeding is done as an extra precaution against entropy
-/// leaks and is in theory unnecessary — to predict `ThreadRng`'s output, an
-/// attacker would have to either determine most of the RNG's seed or internal
-/// state, or crack the algorithm used.
+/// Unlike `StdRng`, `ThreadRng` uses the  [`ReseedingRng`] wrapper to reseed
+/// the PRNG from fresh entropy every 64 kiB of random data.
+/// [`OsRng`] is used to provide seed data.
 ///
-/// Like [`StdRng`], `ThreadRng` is a cryptographically secure PRNG. The current
-/// algorithm used is [HC-128], which is an array-based PRNG that trades memory
-/// usage for better performance. This makes it similar to ISAAC, the algorithm
-/// used in `ThreadRng` before rand 0.5.
+/// Note that the reseeding is done as an extra precaution against side-channel
+/// attacks and mis-use (e.g. if somehow weak entropy were supplied initially).
+/// The PRNG algorithms used are assumed to be secure.
 ///
-/// Cloning this handle just produces a new reference to the same thread-local
-/// generator.
-/// 
-/// [`thread_rng`]: ../fn.thread_rng.html
-/// [`ReseedingRng`]: adapter/struct.ReseedingRng.html
-/// [`StdRng`]: struct.StdRng.html
-/// [`EntropyRng`]: struct.EntropyRng.html
-/// [HC-128]: ../../rand_hc/struct.Hc128Rng.html
-#[derive(Clone, Debug)]
+/// [`ReseedingRng`]: crate::rngs::adapter::ReseedingRng
+/// [`StdRng`]: crate::rngs::StdRng
+#[derive(Copy, Clone, Debug)]
 pub struct ThreadRng {
-    // use of raw pointer implies type is neither Send nor Sync
-    rng: *mut ReseedingRng<Hc128Core, EntropyRng>,
+    // inner raw pointer implies type is neither Send nor Sync
+    rng: NonNull<ReseedingRng<Core, OsRng>>,
 }
 
 thread_local!(
-    static THREAD_RNG_KEY: UnsafeCell<ReseedingRng<Hc128Core, EntropyRng>> = {
-        let mut entropy_source = EntropyRng::new();
-        let r = Hc128Core::from_rng(&mut entropy_source).unwrap_or_else(|err|
+    static THREAD_RNG_KEY: UnsafeCell<ReseedingRng<Core, OsRng>> = {
+        let r = Core::from_rng(OsRng).unwrap_or_else(|err|
                 panic!("could not initialize thread_rng: {}", err));
         let rng = ReseedingRng::new(r,
                                     THREAD_RNG_RESEED_THRESHOLD,
-                                    entropy_source);
+                                    OsRng);
         UnsafeCell::new(rng)
     }
 );
@@ -91,38 +74,38 @@ thread_local!(
 /// seeded by the system. Intended to be used in method chaining style,
 /// e.g. `thread_rng().gen::<i32>()`, or cached locally, e.g.
 /// `let mut rng = thread_rng();`.  Invoked by the `Default` trait, making
-/// `ThreadRng::default()` equivelent.
+/// `ThreadRng::default()` equivalent.
 ///
 /// For more information see [`ThreadRng`].
-///
-/// [`ThreadRng`]: rngs/struct.ThreadRng.html
 pub fn thread_rng() -> ThreadRng {
-    ThreadRng { rng: THREAD_RNG_KEY.with(|t| t.get()) }
+    let raw = THREAD_RNG_KEY.with(|t| t.get());
+    let nn = NonNull::new(raw).unwrap();
+    ThreadRng { rng: nn }
 }
 
 impl Default for ThreadRng {
     fn default() -> ThreadRng {
-        ::prelude::thread_rng()
+        crate::prelude::thread_rng()
     }
 }
 
 impl RngCore for ThreadRng {
     #[inline(always)]
     fn next_u32(&mut self) -> u32 {
-        unsafe { (*self.rng).next_u32() }
+        unsafe { self.rng.as_mut().next_u32() }
     }
 
     #[inline(always)]
     fn next_u64(&mut self) -> u64 {
-        unsafe { (*self.rng).next_u64() }
+        unsafe { self.rng.as_mut().next_u64() }
     }
 
     fn fill_bytes(&mut self, dest: &mut [u8]) {
-        unsafe { (*self.rng).fill_bytes(dest) }
+        unsafe { self.rng.as_mut().fill_bytes(dest) }
     }
 
     fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-        unsafe { (*self.rng).try_fill_bytes(dest) }
+        unsafe { self.rng.as_mut().try_fill_bytes(dest) }
     }
 }
 
@@ -133,8 +116,8 @@ impl CryptoRng for ThreadRng {}
 mod test {
     #[test]
     fn test_thread_rng() {
-        use Rng;
-        let mut r = ::thread_rng();
+        use crate::Rng;
+        let mut r = crate::thread_rng();
         r.gen::<i32>();
         assert_eq!(r.gen_range(0, 1), 0);
     }