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| </pre><pre class="rust"><code><span class="comment">// Copyright 2018 Developers of the Rand project. |
| // Copyright 2013 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 |
| // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| </span><span class="doccomment">//! A wrapper around another PRNG that reseeds it after it |
| //! generates a certain number of random bytes. |
| |
| </span><span class="kw">use </span>core::mem::size_of; |
| |
| <span class="kw">use </span>rand_core::block::{BlockRng, BlockRngCore}; |
| <span class="kw">use </span>rand_core::{CryptoRng, Error, RngCore, SeedableRng}; |
| |
| <span class="doccomment">/// A wrapper around any PRNG that implements [`BlockRngCore`], that adds the |
| /// ability to reseed it. |
| /// |
| /// `ReseedingRng` reseeds the underlying PRNG in the following cases: |
| /// |
| /// - On a manual call to [`reseed()`]. |
| /// - After `clone()`, the clone will be reseeded on first use. |
| /// - When a process is forked on UNIX, the RNGs in both the parent and child |
| /// processes will be reseeded just before the next call to |
| /// [`BlockRngCore::generate`], i.e. "soon". For ChaCha and Hc128 this is a |
| /// maximum of fifteen `u32` values before reseeding. |
| /// - After the PRNG has generated a configurable number of random bytes. |
| /// |
| /// # When should reseeding after a fixed number of generated bytes be used? |
| /// |
| /// Reseeding after a fixed number of generated bytes is never strictly |
| /// *necessary*. Cryptographic PRNGs don't have a limited number of bytes they |
| /// can output, or at least not a limit reachable in any practical way. There is |
| /// no such thing as 'running out of entropy'. |
| /// |
| /// Occasionally reseeding can be seen as some form of 'security in depth'. Even |
| /// if in the future a cryptographic weakness is found in the CSPRNG being used, |
| /// or a flaw in the implementation, occasionally reseeding should make |
| /// exploiting it much more difficult or even impossible. |
| /// |
| /// Use [`ReseedingRng::new`] with a `threshold` of `0` to disable reseeding |
| /// after a fixed number of generated bytes. |
| /// |
| /// # Limitations |
| /// |
| /// It is recommended that a `ReseedingRng` (including `ThreadRng`) not be used |
| /// from a fork handler. |
| /// Use `OsRng` or `getrandom`, or defer your use of the RNG until later. |
| /// |
| /// # Error handling |
| /// |
| /// Although unlikely, reseeding the wrapped PRNG can fail. `ReseedingRng` will |
| /// never panic but try to handle the error intelligently through some |
| /// combination of retrying and delaying reseeding until later. |
| /// If handling the source error fails `ReseedingRng` will continue generating |
| /// data from the wrapped PRNG without reseeding. |
| /// |
| /// Manually calling [`reseed()`] will not have this retry or delay logic, but |
| /// reports the error. |
| /// |
| /// # Example |
| /// |
| /// ``` |
| /// use rand::prelude::*; |
| /// use rand_chacha::ChaCha20Core; // Internal part of ChaChaRng that |
| /// // implements BlockRngCore |
| /// use rand::rngs::OsRng; |
| /// use rand::rngs::adapter::ReseedingRng; |
| /// |
| /// let prng = ChaCha20Core::from_entropy(); |
| /// let mut reseeding_rng = ReseedingRng::new(prng, 0, OsRng); |
| /// |
| /// println!("{}", reseeding_rng.gen::<u64>()); |
| /// |
| /// let mut cloned_rng = reseeding_rng.clone(); |
| /// assert!(reseeding_rng.gen::<u64>() != cloned_rng.gen::<u64>()); |
| /// ``` |
| /// |
| /// [`BlockRngCore`]: rand_core::block::BlockRngCore |
| /// [`ReseedingRng::new`]: ReseedingRng::new |
| /// [`reseed()`]: ReseedingRng::reseed |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub struct </span>ReseedingRng<R, Rsdr>(BlockRng<ReseedingCore<R, Rsdr>>) |
| <span class="kw">where |
| </span>R: BlockRngCore + SeedableRng, |
| Rsdr: RngCore; |
| |
| <span class="kw">impl</span><R, Rsdr> ReseedingRng<R, Rsdr> |
| <span class="kw">where |
| </span>R: BlockRngCore + SeedableRng, |
| Rsdr: RngCore, |
| { |
| <span class="doccomment">/// Create a new `ReseedingRng` from an existing PRNG, combined with a RNG |
| /// to use as reseeder. |
| /// |
| /// `threshold` sets the number of generated bytes after which to reseed the |
| /// PRNG. Set it to zero to never reseed based on the number of generated |
| /// values. |
| </span><span class="kw">pub fn </span>new(rng: R, threshold: u64, reseeder: Rsdr) -> <span class="self">Self </span>{ |
| ReseedingRng(BlockRng::new(ReseedingCore::new(rng, threshold, reseeder))) |
| } |
| |
| <span class="doccomment">/// Reseed the internal PRNG. |
| </span><span class="kw">pub fn </span>reseed(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="prelude-ty">Result</span><(), Error> { |
| <span class="self">self</span>.<span class="number">0</span>.core.reseed() |
| } |
| } |
| |
| <span class="comment">// TODO: this should be implemented for any type where the inner type |
| // implements RngCore, but we can't specify that because ReseedingCore is private |
| </span><span class="kw">impl</span><R, Rsdr: RngCore> RngCore <span class="kw">for </span>ReseedingRng<R, Rsdr> |
| <span class="kw">where |
| </span>R: BlockRngCore<Item = u32> + SeedableRng, |
| <R <span class="kw">as </span>BlockRngCore>::Results: AsRef<[u32]> + AsMut<[u32]>, |
| { |
| <span class="attribute">#[inline(always)] |
| </span><span class="kw">fn </span>next_u32(<span class="kw-2">&mut </span><span class="self">self</span>) -> u32 { |
| <span class="self">self</span>.<span class="number">0</span>.next_u32() |
| } |
| |
| <span class="attribute">#[inline(always)] |
| </span><span class="kw">fn </span>next_u64(<span class="kw-2">&mut </span><span class="self">self</span>) -> u64 { |
| <span class="self">self</span>.<span class="number">0</span>.next_u64() |
| } |
| |
| <span class="kw">fn </span>fill_bytes(<span class="kw-2">&mut </span><span class="self">self</span>, dest: <span class="kw-2">&mut </span>[u8]) { |
| <span class="self">self</span>.<span class="number">0</span>.fill_bytes(dest) |
| } |
| |
| <span class="kw">fn </span>try_fill_bytes(<span class="kw-2">&mut </span><span class="self">self</span>, dest: <span class="kw-2">&mut </span>[u8]) -> <span class="prelude-ty">Result</span><(), Error> { |
| <span class="self">self</span>.<span class="number">0</span>.try_fill_bytes(dest) |
| } |
| } |
| |
| <span class="kw">impl</span><R, Rsdr> Clone <span class="kw">for </span>ReseedingRng<R, Rsdr> |
| <span class="kw">where |
| </span>R: BlockRngCore + SeedableRng + Clone, |
| Rsdr: RngCore + Clone, |
| { |
| <span class="kw">fn </span>clone(<span class="kw-2">&</span><span class="self">self</span>) -> ReseedingRng<R, Rsdr> { |
| <span class="comment">// Recreating `BlockRng` seems easier than cloning it and resetting |
| // the index. |
| </span>ReseedingRng(BlockRng::new(<span class="self">self</span>.<span class="number">0</span>.core.clone())) |
| } |
| } |
| |
| <span class="kw">impl</span><R, Rsdr> CryptoRng <span class="kw">for </span>ReseedingRng<R, Rsdr> |
| <span class="kw">where |
| </span>R: BlockRngCore + SeedableRng + CryptoRng, |
| Rsdr: RngCore + CryptoRng, |
| { |
| } |
| |
| <span class="attribute">#[derive(Debug)] |
| </span><span class="kw">struct </span>ReseedingCore<R, Rsdr> { |
| inner: R, |
| reseeder: Rsdr, |
| threshold: i64, |
| bytes_until_reseed: i64, |
| fork_counter: usize, |
| } |
| |
| <span class="kw">impl</span><R, Rsdr> BlockRngCore <span class="kw">for </span>ReseedingCore<R, Rsdr> |
| <span class="kw">where |
| </span>R: BlockRngCore + SeedableRng, |
| Rsdr: RngCore, |
| { |
| <span class="kw">type </span>Item = <R <span class="kw">as </span>BlockRngCore>::Item; |
| <span class="kw">type </span>Results = <R <span class="kw">as </span>BlockRngCore>::Results; |
| |
| <span class="kw">fn </span>generate(<span class="kw-2">&mut </span><span class="self">self</span>, results: <span class="kw-2">&mut </span><span class="self">Self</span>::Results) { |
| <span class="kw">let </span>global_fork_counter = fork::get_fork_counter(); |
| <span class="kw">if </span><span class="self">self</span>.bytes_until_reseed <= <span class="number">0 </span>|| <span class="self">self</span>.is_forked(global_fork_counter) { |
| <span class="comment">// We get better performance by not calling only `reseed` here |
| // and continuing with the rest of the function, but by directly |
| // returning from a non-inlined function. |
| </span><span class="kw">return </span><span class="self">self</span>.reseed_and_generate(results, global_fork_counter); |
| } |
| <span class="kw">let </span>num_bytes = results.as_ref().len() * size_of::<<span class="self">Self</span>::Item>(); |
| <span class="self">self</span>.bytes_until_reseed -= num_bytes <span class="kw">as </span>i64; |
| <span class="self">self</span>.inner.generate(results); |
| } |
| } |
| |
| <span class="kw">impl</span><R, Rsdr> ReseedingCore<R, Rsdr> |
| <span class="kw">where |
| </span>R: BlockRngCore + SeedableRng, |
| Rsdr: RngCore, |
| { |
| <span class="doccomment">/// Create a new `ReseedingCore`. |
| </span><span class="kw">fn </span>new(rng: R, threshold: u64, reseeder: Rsdr) -> <span class="self">Self </span>{ |
| <span class="kw">use </span>::core::i64::MAX; |
| fork::register_fork_handler(); |
| |
| <span class="comment">// Because generating more values than `i64::MAX` takes centuries on |
| // current hardware, we just clamp to that value. |
| // Also we set a threshold of 0, which indicates no limit, to that |
| // value. |
| </span><span class="kw">let </span>threshold = <span class="kw">if </span>threshold == <span class="number">0 </span>{ |
| MAX |
| } <span class="kw">else if </span>threshold <= MAX <span class="kw">as </span>u64 { |
| threshold <span class="kw">as </span>i64 |
| } <span class="kw">else </span>{ |
| MAX |
| }; |
| |
| ReseedingCore { |
| inner: rng, |
| reseeder, |
| threshold: threshold <span class="kw">as </span>i64, |
| bytes_until_reseed: threshold <span class="kw">as </span>i64, |
| fork_counter: <span class="number">0</span>, |
| } |
| } |
| |
| <span class="doccomment">/// Reseed the internal PRNG. |
| </span><span class="kw">fn </span>reseed(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="prelude-ty">Result</span><(), Error> { |
| R::from_rng(<span class="kw-2">&mut </span><span class="self">self</span>.reseeder).map(|result| { |
| <span class="self">self</span>.bytes_until_reseed = <span class="self">self</span>.threshold; |
| <span class="self">self</span>.inner = result |
| }) |
| } |
| |
| <span class="kw">fn </span>is_forked(<span class="kw-2">&</span><span class="self">self</span>, global_fork_counter: usize) -> bool { |
| <span class="comment">// In theory, on 32-bit platforms, it is possible for |
| // `global_fork_counter` to wrap around after ~4e9 forks. |
| // |
| // This check will detect a fork in the normal case where |
| // `fork_counter < global_fork_counter`, and also when the difference |
| // between both is greater than `isize::MAX` (wrapped around). |
| // |
| // It will still fail to detect a fork if there have been more than |
| // `isize::MAX` forks, without any reseed in between. Seems unlikely |
| // enough. |
| </span>(<span class="self">self</span>.fork_counter.wrapping_sub(global_fork_counter) <span class="kw">as </span>isize) < <span class="number">0 |
| </span>} |
| |
| <span class="attribute">#[inline(never)] |
| </span><span class="kw">fn </span>reseed_and_generate( |
| <span class="kw-2">&mut </span><span class="self">self</span>, results: <span class="kw-2">&mut </span><<span class="self">Self </span><span class="kw">as </span>BlockRngCore>::Results, global_fork_counter: usize, |
| ) { |
| <span class="attribute">#![allow(clippy::if_same_then_else)] </span><span class="comment">// false positive |
| </span><span class="kw">if </span><span class="self">self</span>.is_forked(global_fork_counter) { |
| <span class="macro">info!</span>(<span class="string">"Fork detected, reseeding RNG"</span>); |
| } <span class="kw">else </span>{ |
| <span class="macro">trace!</span>(<span class="string">"Reseeding RNG (periodic reseed)"</span>); |
| } |
| |
| <span class="kw">let </span>num_bytes = results.as_ref().len() * size_of::<<R <span class="kw">as </span>BlockRngCore>::Item>(); |
| |
| <span class="kw">if let </span><span class="prelude-val">Err</span>(e) = <span class="self">self</span>.reseed() { |
| <span class="macro">warn!</span>(<span class="string">"Reseeding RNG failed: {}"</span>, e); |
| <span class="kw">let _ </span>= e; |
| } |
| <span class="self">self</span>.fork_counter = global_fork_counter; |
| |
| <span class="self">self</span>.bytes_until_reseed = <span class="self">self</span>.threshold - num_bytes <span class="kw">as </span>i64; |
| <span class="self">self</span>.inner.generate(results); |
| } |
| } |
| |
| <span class="kw">impl</span><R, Rsdr> Clone <span class="kw">for </span>ReseedingCore<R, Rsdr> |
| <span class="kw">where |
| </span>R: BlockRngCore + SeedableRng + Clone, |
| Rsdr: RngCore + Clone, |
| { |
| <span class="kw">fn </span>clone(<span class="kw-2">&</span><span class="self">self</span>) -> ReseedingCore<R, Rsdr> { |
| ReseedingCore { |
| inner: <span class="self">self</span>.inner.clone(), |
| reseeder: <span class="self">self</span>.reseeder.clone(), |
| threshold: <span class="self">self</span>.threshold, |
| bytes_until_reseed: <span class="number">0</span>, <span class="comment">// reseed clone on first use |
| </span>fork_counter: <span class="self">self</span>.fork_counter, |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><R, Rsdr> CryptoRng <span class="kw">for </span>ReseedingCore<R, Rsdr> |
| <span class="kw">where |
| </span>R: BlockRngCore + SeedableRng + CryptoRng, |
| Rsdr: RngCore + CryptoRng, |
| { |
| } |
| |
| |
| <span class="attribute">#[cfg(all(unix, not(target_os = <span class="string">"emscripten"</span>)))] |
| </span><span class="kw">mod </span>fork { |
| <span class="kw">use </span>core::sync::atomic::{AtomicUsize, Ordering}; |
| <span class="kw">use </span>std::sync::Once; |
| |
| <span class="comment">// Fork protection |
| // |
| // We implement fork protection on Unix using `pthread_atfork`. |
| // When the process is forked, we increment `RESEEDING_RNG_FORK_COUNTER`. |
| // Every `ReseedingRng` stores the last known value of the static in |
| // `fork_counter`. If the cached `fork_counter` is less than |
| // `RESEEDING_RNG_FORK_COUNTER`, it is time to reseed this RNG. |
| // |
| // If reseeding fails, we don't deal with this by setting a delay, but just |
| // don't update `fork_counter`, so a reseed is attempted as soon as |
| // possible. |
| |
| </span><span class="kw">static </span>RESEEDING_RNG_FORK_COUNTER: AtomicUsize = AtomicUsize::new(<span class="number">0</span>); |
| |
| <span class="kw">pub fn </span>get_fork_counter() -> usize { |
| RESEEDING_RNG_FORK_COUNTER.load(Ordering::Relaxed) |
| } |
| |
| <span class="kw">extern </span><span class="string">"C" </span><span class="kw">fn </span>fork_handler() { |
| <span class="comment">// Note: fetch_add is defined to wrap on overflow |
| // (which is what we want). |
| </span>RESEEDING_RNG_FORK_COUNTER.fetch_add(<span class="number">1</span>, Ordering::Relaxed); |
| } |
| |
| <span class="kw">pub fn </span>register_fork_handler() { |
| <span class="kw">static </span>REGISTER: Once = Once::new(); |
| REGISTER.call_once(|| { |
| <span class="comment">// Bump the counter before and after forking (see #1169): |
| </span><span class="kw">let </span>ret = <span class="kw">unsafe </span>{ libc::pthread_atfork( |
| <span class="prelude-val">Some</span>(fork_handler), |
| <span class="prelude-val">Some</span>(fork_handler), |
| <span class="prelude-val">Some</span>(fork_handler), |
| ) }; |
| <span class="kw">if </span>ret != <span class="number">0 </span>{ |
| <span class="macro">panic!</span>(<span class="string">"libc::pthread_atfork failed with code {}"</span>, ret); |
| } |
| }); |
| } |
| } |
| |
| <span class="attribute">#[cfg(not(all(unix, not(target_os = <span class="string">"emscripten"</span>))))] |
| </span><span class="kw">mod </span>fork { |
| <span class="kw">pub fn </span>get_fork_counter() -> usize { |
| <span class="number">0 |
| </span>} |
| <span class="kw">pub fn </span>register_fork_handler() {} |
| } |
| |
| |
| <span class="attribute">#[cfg(feature = <span class="string">"std_rng"</span>)] |
| #[cfg(test)] |
| </span><span class="kw">mod </span>test { |
| <span class="kw">use </span><span class="kw">super</span>::ReseedingRng; |
| <span class="kw">use </span><span class="kw">crate</span>::rngs::mock::StepRng; |
| <span class="kw">use </span><span class="kw">crate</span>::rngs::std::Core; |
| <span class="kw">use crate</span>::{Rng, SeedableRng}; |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_reseeding() { |
| <span class="kw">let </span><span class="kw-2">mut </span>zero = StepRng::new(<span class="number">0</span>, <span class="number">0</span>); |
| <span class="kw">let </span>rng = Core::from_rng(<span class="kw-2">&mut </span>zero).unwrap(); |
| <span class="kw">let </span>thresh = <span class="number">1</span>; <span class="comment">// reseed every time the buffer is exhausted |
| </span><span class="kw">let </span><span class="kw-2">mut </span>reseeding = ReseedingRng::new(rng, thresh, zero); |
| |
| <span class="comment">// RNG buffer size is [u32; 64] |
| // Debug is only implemented up to length 32 so use two arrays |
| </span><span class="kw">let </span><span class="kw-2">mut </span>buf = ([<span class="number">0u32</span>; <span class="number">32</span>], [<span class="number">0u32</span>; <span class="number">32</span>]); |
| reseeding.fill(<span class="kw-2">&mut </span>buf.<span class="number">0</span>); |
| reseeding.fill(<span class="kw-2">&mut </span>buf.<span class="number">1</span>); |
| <span class="kw">let </span>seq = buf; |
| <span class="kw">for _ in </span><span class="number">0</span>..<span class="number">10 </span>{ |
| reseeding.fill(<span class="kw-2">&mut </span>buf.<span class="number">0</span>); |
| reseeding.fill(<span class="kw-2">&mut </span>buf.<span class="number">1</span>); |
| <span class="macro">assert_eq!</span>(buf, seq); |
| } |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_clone_reseeding() { |
| <span class="attribute">#![allow(clippy::redundant_clone)] |
| |
| </span><span class="kw">let </span><span class="kw-2">mut </span>zero = StepRng::new(<span class="number">0</span>, <span class="number">0</span>); |
| <span class="kw">let </span>rng = Core::from_rng(<span class="kw-2">&mut </span>zero).unwrap(); |
| <span class="kw">let </span><span class="kw-2">mut </span>rng1 = ReseedingRng::new(rng, <span class="number">32 </span>* <span class="number">4</span>, zero); |
| |
| <span class="kw">let </span>first: u32 = rng1.gen(); |
| <span class="kw">for _ in </span><span class="number">0</span>..<span class="number">10 </span>{ |
| <span class="kw">let _ </span>= rng1.gen::<u32>(); |
| } |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>rng2 = rng1.clone(); |
| <span class="macro">assert_eq!</span>(first, rng2.gen::<u32>()); |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../../" data-current-crate="rand" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
