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-rw-r--r--rand/rand_jitter/src/error.rs77
-rw-r--r--rand/rand_jitter/src/lib.rs750
-rw-r--r--rand/rand_jitter/src/platform.rs44
3 files changed, 871 insertions, 0 deletions
diff --git a/rand/rand_jitter/src/error.rs b/rand/rand_jitter/src/error.rs
new file mode 100644
index 0000000..b54fffa
--- /dev/null
+++ b/rand/rand_jitter/src/error.rs
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+// Copyright 2018 Developers of the Rand project.
+// Copyright 2013-2015 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.
+
+use rand_core::Error;
+use core::fmt;
+
+/// Base code for all `JitterRng` errors
+const ERROR_BASE: u32 = 0xAE53_0400;
+
+/// An error that can occur when [`JitterRng::test_timer`] fails.
+///
+/// All variants have a value of 0xAE530400 = 2924676096 plus a small
+/// increment (1 through 5).
+///
+/// [`JitterRng::test_timer`]: crate::JitterRng::test_timer
+#[derive(Debug, Clone, PartialEq, Eq)]
+#[repr(u32)]
+pub enum TimerError {
+ /// No timer available.
+ NoTimer = ERROR_BASE + 1,
+ /// Timer too coarse to use as an entropy source.
+ CoarseTimer = ERROR_BASE + 2,
+ /// Timer is not monotonically increasing.
+ NotMonotonic = ERROR_BASE + 3,
+ /// Variations of deltas of time too small.
+ TinyVariantions = ERROR_BASE + 4,
+ /// Too many stuck results (indicating no added entropy).
+ TooManyStuck = ERROR_BASE + 5,
+ #[doc(hidden)]
+ __Nonexhaustive,
+}
+
+impl TimerError {
+ fn description(&self) -> &'static str {
+ match *self {
+ TimerError::NoTimer => "no timer available",
+ TimerError::CoarseTimer => "coarse timer",
+ TimerError::NotMonotonic => "timer not monotonic",
+ TimerError::TinyVariantions => "time delta variations too small",
+ TimerError::TooManyStuck => "too many stuck results",
+ TimerError::__Nonexhaustive => unreachable!(),
+ }
+ }
+}
+
+impl fmt::Display for TimerError {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ write!(f, "{}", self.description())
+ }
+}
+
+#[cfg(feature = "std")]
+impl ::std::error::Error for TimerError {
+ fn description(&self) -> &str {
+ self.description()
+ }
+}
+
+impl From<TimerError> for Error {
+ fn from(err: TimerError) -> Error {
+ // Timer check is already quite permissive of failures so we don't
+ // expect false-positive failures, i.e. any error is irrecoverable.
+ #[cfg(feature = "std")] {
+ Error::new(err)
+ }
+ #[cfg(not(feature = "std"))] {
+ Error::from(core::num::NonZeroU32::new(err as u32).unwrap())
+ }
+ }
+}
+
diff --git a/rand/rand_jitter/src/lib.rs b/rand/rand_jitter/src/lib.rs
new file mode 100644
index 0000000..49c53e6
--- /dev/null
+++ b/rand/rand_jitter/src/lib.rs
@@ -0,0 +1,750 @@
+// Copyright 2018 Developers of the Rand project.
+//
+// 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.
+//
+// Based on jitterentropy-library, http://www.chronox.de/jent.html.
+// Copyright Stephan Mueller <smueller@chronox.de>, 2014 - 2017.
+//
+// With permission from Stephan Mueller to relicense the Rust translation under
+// the MIT license.
+
+//! Non-physical true random number generator based on timing jitter.
+//!
+//! Note that this RNG is not suited for use cases where cryptographic security is
+//! required (also see this [discussion]).
+//!
+//! This is a true random number generator, as opposed to pseudo-random
+//! generators. Random numbers generated by `JitterRng` can be seen as fresh
+//! entropy. A consequence is that it is orders of magnitude slower than `OsRng`
+//! and PRNGs (about 10<sup>3</sup>..10<sup>6</sup> slower).
+//!
+//! There are very few situations where using this RNG is appropriate. Only very
+//! few applications require true entropy. A normal PRNG can be statistically
+//! indistinguishable, and a cryptographic PRNG should also be as impossible to
+//! predict.
+//!
+//! `JitterRng` can be used without the standard library, but not conveniently,
+//! you must provide a high-precision timer and carefully have to follow the
+//! instructions of [`JitterRng::new_with_timer`].
+//!
+//! This implementation is based on [Jitterentropy] version 2.1.0.
+//!
+//! Note: There is no accurate timer available on WASM platforms, to help
+//! prevent fingerprinting or timing side-channel attacks. Therefore
+//! [`JitterRng::new()`] is not available on WASM. It is also unavailable
+//! with disabled `std` feature.
+//!
+//! [Jitterentropy]: http://www.chronox.de/jent.html
+//! [discussion]: https://github.com/rust-random/rand/issues/699
+
+#![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk.png",
+ html_favicon_url = "https://www.rust-lang.org/favicon.ico",
+ html_root_url = "https://rust-random.github.io/rand/")]
+
+#![deny(missing_docs)]
+#![deny(missing_debug_implementations)]
+#![doc(test(attr(allow(unused_variables), deny(warnings))))]
+
+// Note: the C implementation of `Jitterentropy` relies on being compiled
+// without optimizations. This implementation goes through lengths to make the
+// compiler not optimize out code which does influence timing jitter, but is
+// technically dead code.
+#![no_std]
+#[cfg(feature = "std")]
+extern crate std;
+
+pub use rand_core;
+
+// Coming from https://crates.io/crates/doc-comment
+#[cfg(test)]
+macro_rules! doc_comment {
+ ($x:expr) => {
+ #[doc = $x]
+ extern {}
+ };
+}
+
+#[cfg(test)]
+doc_comment!(include_str!("../README.md"));
+
+#[allow(unused)]
+macro_rules! trace { ($($x:tt)*) => (
+ #[cfg(feature = "log")] {
+ log::trace!($($x)*)
+ }
+) }
+#[allow(unused)]
+macro_rules! debug { ($($x:tt)*) => (
+ #[cfg(feature = "log")] {
+ log::debug!($($x)*)
+ }
+) }
+#[allow(unused)]
+macro_rules! info { ($($x:tt)*) => (
+ #[cfg(feature = "log")] {
+ log::info!($($x)*)
+ }
+) }
+#[allow(unused)]
+macro_rules! warn { ($($x:tt)*) => (
+ #[cfg(feature = "log")] {
+ log::warn!($($x)*)
+ }
+) }
+#[allow(unused)]
+macro_rules! error { ($($x:tt)*) => (
+ #[cfg(feature = "log")] {
+ log::error!($($x)*)
+ }
+) }
+
+#[cfg(feature = "std")]
+mod platform;
+mod error;
+
+use rand_core::{RngCore, Error, impls};
+pub use crate::error::TimerError;
+
+use core::{fmt, mem, ptr};
+#[cfg(feature = "std")]
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+const MEMORY_BLOCKS: usize = 64;
+const MEMORY_BLOCKSIZE: usize = 32;
+const MEMORY_SIZE: usize = MEMORY_BLOCKS * MEMORY_BLOCKSIZE;
+
+/// A true random number generator based on jitter in the CPU execution time,
+/// and jitter in memory access time.
+///
+/// Note that this RNG is not suitable for use cases where cryptographic
+/// security is required.
+pub struct JitterRng {
+ data: u64, // Actual random number
+ // Number of rounds to run the entropy collector per 64 bits
+ rounds: u8,
+ // Timer used by `measure_jitter`
+ timer: fn() -> u64,
+ // Memory for the Memory Access noise source
+ mem_prev_index: u16,
+ // Make `next_u32` not waste 32 bits
+ data_half_used: bool,
+}
+
+// Note: `JitterRng` maintains a small 64-bit entropy pool. With every
+// `generate` 64 new bits should be integrated in the pool. If a round of
+// `generate` were to collect less than the expected 64 bit, then the returned
+// value, and the new state of the entropy pool, would be in some way related to
+// the initial state. It is therefore better if the initial state of the entropy
+// pool is different on each call to `generate`. This has a few implications:
+// - `generate` should be called once before using `JitterRng` to produce the
+// first usable value (this is done by default in `new`);
+// - We do not zero the entropy pool after generating a result. The reference
+// implementation also does not support zeroing, but recommends generating a
+// new value without using it if you want to protect a previously generated
+// 'secret' value from someone inspecting the memory;
+// - Implementing `Clone` seems acceptable, as it would not cause the systematic
+// bias a constant might cause. Only instead of one value that could be
+// potentially related to the same initial state, there are now two.
+
+// Entropy collector state.
+// These values are not necessary to preserve across runs.
+struct EcState {
+ // Previous time stamp to determine the timer delta
+ prev_time: u64,
+ // Deltas used for the stuck test
+ last_delta: i32,
+ last_delta2: i32,
+ // Memory for the Memory Access noise source
+ mem: [u8; MEMORY_SIZE],
+}
+
+impl EcState {
+ // Stuck test by checking the:
+ // - 1st derivation of the jitter measurement (time delta)
+ // - 2nd derivation of the jitter measurement (delta of time deltas)
+ // - 3rd derivation of the jitter measurement (delta of delta of time
+ // deltas)
+ //
+ // All values must always be non-zero.
+ // This test is a heuristic to see whether the last measurement holds
+ // entropy.
+ fn stuck(&mut self, current_delta: i32) -> bool {
+ let delta2 = self.last_delta - current_delta;
+ let delta3 = delta2 - self.last_delta2;
+
+ self.last_delta = current_delta;
+ self.last_delta2 = delta2;
+
+ current_delta == 0 || delta2 == 0 || delta3 == 0
+ }
+}
+
+// Custom Debug implementation that does not expose the internal state
+impl fmt::Debug for JitterRng {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ write!(f, "JitterRng {{}}")
+ }
+}
+
+impl Clone for JitterRng {
+ fn clone(&self) -> JitterRng {
+ JitterRng {
+ data: self.data,
+ rounds: self.rounds,
+ timer: self.timer,
+ mem_prev_index: self.mem_prev_index,
+ // The 32 bits that may still be unused from the previous round are
+ // for the original to use, not for the clone.
+ data_half_used: false,
+ }
+ }
+}
+
+// Initialise to zero; must be positive
+#[cfg(all(feature = "std", not(target_arch = "wasm32")))]
+static JITTER_ROUNDS: AtomicUsize = AtomicUsize::new(0);
+
+impl JitterRng {
+ /// Create a new `JitterRng`. Makes use of `std::time` for a timer, or a
+ /// platform-specific function with higher accuracy if necessary and
+ /// available.
+ ///
+ /// During initialization CPU execution timing jitter is measured a few
+ /// hundred times. If this does not pass basic quality tests, an error is
+ /// returned. The test result is cached to make subsequent calls faster.
+ #[cfg(all(feature = "std", not(target_arch = "wasm32")))]
+ pub fn new() -> Result<JitterRng, TimerError> {
+ if cfg!(target_arch = "wasm32") {
+ return Err(TimerError::NoTimer);
+ }
+ let mut state = JitterRng::new_with_timer(platform::get_nstime);
+ let mut rounds = JITTER_ROUNDS.load(Ordering::Relaxed) as u8;
+ if rounds == 0 {
+ // No result yet: run test.
+ // This allows the timer test to run multiple times; we don't care.
+ rounds = state.test_timer()?;
+ JITTER_ROUNDS.store(rounds as usize, Ordering::Relaxed);
+ info!("JitterRng: using {} rounds per u64 output", rounds);
+ }
+ state.set_rounds(rounds);
+
+ // Fill `data` with a non-zero value.
+ state.gen_entropy();
+ Ok(state)
+ }
+
+ /// Create a new `JitterRng`.
+ /// A custom timer can be supplied, making it possible to use `JitterRng` in
+ /// `no_std` environments.
+ ///
+ /// The timer must have nanosecond precision.
+ ///
+ /// This method is more low-level than `new()`. It is the responsibility of
+ /// the caller to run [`test_timer`] before using any numbers generated with
+ /// `JitterRng`, and optionally call [`set_rounds`]. Also it is important to
+ /// consume at least one `u64` before using the first result to initialize
+ /// the entropy collection pool.
+ ///
+ /// # Example
+ ///
+ /// ```
+ /// # use rand_jitter::rand_core::{RngCore, Error};
+ /// use rand_jitter::JitterRng;
+ ///
+ /// # fn try_inner() -> Result<(), Error> {
+ /// fn get_nstime() -> u64 {
+ /// use std::time::{SystemTime, UNIX_EPOCH};
+ ///
+ /// let dur = SystemTime::now().duration_since(UNIX_EPOCH).unwrap();
+ /// // The correct way to calculate the current time is
+ /// // `dur.as_secs() * 1_000_000_000 + dur.subsec_nanos() as u64`
+ /// // But this is faster, and the difference in terms of entropy is
+ /// // negligible (log2(10^9) == 29.9).
+ /// dur.as_secs() << 30 | dur.subsec_nanos() as u64
+ /// }
+ ///
+ /// let mut rng = JitterRng::new_with_timer(get_nstime);
+ /// let rounds = rng.test_timer()?;
+ /// rng.set_rounds(rounds); // optional
+ /// let _ = rng.next_u64();
+ ///
+ /// // Ready for use
+ /// let v: u64 = rng.next_u64();
+ /// # Ok(())
+ /// # }
+ ///
+ /// # let _ = try_inner();
+ /// ```
+ ///
+ /// [`test_timer`]: JitterRng::test_timer
+ /// [`set_rounds`]: JitterRng::set_rounds
+ pub fn new_with_timer(timer: fn() -> u64) -> JitterRng {
+ JitterRng {
+ data: 0,
+ rounds: 64,
+ timer,
+ mem_prev_index: 0,
+ data_half_used: false,
+ }
+ }
+
+ /// Configures how many rounds are used to generate each 64-bit value.
+ /// This must be greater than zero, and has a big impact on performance
+ /// and output quality.
+ ///
+ /// [`new_with_timer`] conservatively uses 64 rounds, but often less rounds
+ /// can be used. The `test_timer()` function returns the minimum number of
+ /// rounds required for full strength (platform dependent), so one may use
+ /// `rng.set_rounds(rng.test_timer()?);` or cache the value.
+ ///
+ /// [`new_with_timer`]: JitterRng::new_with_timer
+ pub fn set_rounds(&mut self, rounds: u8) {
+ assert!(rounds > 0);
+ self.rounds = rounds;
+ }
+
+ // Calculate a random loop count used for the next round of an entropy
+ // collection, based on bits from a fresh value from the timer.
+ //
+ // The timer is folded to produce a number that contains at most `n_bits`
+ // bits.
+ //
+ // Note: A constant should be added to the resulting random loop count to
+ // prevent loops that run 0 times.
+ #[inline(never)]
+ fn random_loop_cnt(&mut self, n_bits: u32) -> u32 {
+ let mut rounds = 0;
+
+ let mut time = (self.timer)();
+ // Mix with the current state of the random number balance the random
+ // loop counter a bit more.
+ time ^= self.data;
+
+ // We fold the time value as much as possible to ensure that as many
+ // bits of the time stamp are included as possible.
+ let folds = (64 + n_bits - 1) / n_bits;
+ let mask = (1 << n_bits) - 1;
+ for _ in 0..folds {
+ rounds ^= time & mask;
+ time >>= n_bits;
+ }
+
+ rounds as u32
+ }
+
+ // CPU jitter noise source
+ // Noise source based on the CPU execution time jitter
+ //
+ // This function injects the individual bits of the time value into the
+ // entropy pool using an LFSR.
+ //
+ // The code is deliberately inefficient with respect to the bit shifting.
+ // This function not only acts as folding operation, but this function's
+ // execution is used to measure the CPU execution time jitter. Any change to
+ // the loop in this function implies that careful retesting must be done.
+ #[inline(never)]
+ fn lfsr_time(&mut self, time: u64, var_rounds: bool) {
+ fn lfsr(mut data: u64, time: u64) -> u64{
+ for i in 1..65 {
+ let mut tmp = time << (64 - i);
+ tmp >>= 64 - 1;
+
+ // Fibonacci LSFR with polynomial of
+ // x^64 + x^61 + x^56 + x^31 + x^28 + x^23 + 1 which is
+ // primitive according to
+ // http://poincare.matf.bg.ac.rs/~ezivkovm/publications/primpol1.pdf
+ // (the shift values are the polynomial values minus one
+ // due to counting bits from 0 to 63). As the current
+ // position is always the LSB, the polynomial only needs
+ // to shift data in from the left without wrap.
+ data ^= tmp;
+ data ^= (data >> 63) & 1;
+ data ^= (data >> 60) & 1;
+ data ^= (data >> 55) & 1;
+ data ^= (data >> 30) & 1;
+ data ^= (data >> 27) & 1;
+ data ^= (data >> 22) & 1;
+ data = data.rotate_left(1);
+ }
+ data
+ }
+
+ // Note: in the reference implementation only the last round effects
+ // `self.data`, all the other results are ignored. To make sure the
+ // other rounds are not optimised out, we first run all but the last
+ // round on a throw-away value instead of the real `self.data`.
+ let mut lfsr_loop_cnt = 0;
+ if var_rounds { lfsr_loop_cnt = self.random_loop_cnt(4) };
+
+ let mut throw_away: u64 = 0;
+ for _ in 0..lfsr_loop_cnt {
+ throw_away = lfsr(throw_away, time);
+ }
+ black_box(throw_away);
+
+ self.data = lfsr(self.data, time);
+ }
+
+ // Memory Access noise source
+ // This is a noise source based on variations in memory access times
+ //
+ // This function performs memory accesses which will add to the timing
+ // variations due to an unknown amount of CPU wait states that need to be
+ // added when accessing memory. The memory size should be larger than the L1
+ // caches as outlined in the documentation and the associated testing.
+ //
+ // The L1 cache has a very high bandwidth, albeit its access rate is usually
+ // slower than accessing CPU registers. Therefore, L1 accesses only add
+ // minimal variations as the CPU has hardly to wait. Starting with L2,
+ // significant variations are added because L2 typically does not belong to
+ // the CPU any more and therefore a wider range of CPU wait states is
+ // necessary for accesses. L3 and real memory accesses have even a wider
+ // range of wait states. However, to reliably access either L3 or memory,
+ // the `self.mem` memory must be quite large which is usually not desirable.
+ #[inline(never)]
+ fn memaccess(&mut self, mem: &mut [u8; MEMORY_SIZE], var_rounds: bool) {
+ let mut acc_loop_cnt = 128;
+ if var_rounds { acc_loop_cnt += self.random_loop_cnt(4) };
+
+ let mut index = self.mem_prev_index as usize;
+ for _ in 0..acc_loop_cnt {
+ // Addition of memblocksize - 1 to index with wrap around logic to
+ // ensure that every memory location is hit evenly.
+ // The modulus also allows the compiler to remove the indexing
+ // bounds check.
+ index = (index + MEMORY_BLOCKSIZE - 1) % MEMORY_SIZE;
+
+ // memory access: just add 1 to one byte
+ // memory access implies read from and write to memory location
+ mem[index] = mem[index].wrapping_add(1);
+ }
+ self.mem_prev_index = index as u16;
+ }
+
+ // This is the heart of the entropy generation: calculate time deltas and
+ // use the CPU jitter in the time deltas. The jitter is injected into the
+ // entropy pool.
+ //
+ // Ensure that `ec.prev_time` is primed before using the output of this
+ // function. This can be done by calling this function and not using its
+ // result.
+ fn measure_jitter(&mut self, ec: &mut EcState) -> Option<()> {
+ // Invoke one noise source before time measurement to add variations
+ self.memaccess(&mut ec.mem, true);
+
+ // Get time stamp and calculate time delta to previous
+ // invocation to measure the timing variations
+ let time = (self.timer)();
+ // Note: wrapping_sub combined with a cast to `i64` generates a correct
+ // delta, even in the unlikely case this is a timer that is not strictly
+ // monotonic.
+ let current_delta = time.wrapping_sub(ec.prev_time) as i64 as i32;
+ ec.prev_time = time;
+
+ // Call the next noise source which also injects the data
+ self.lfsr_time(current_delta as u64, true);
+
+ // Check whether we have a stuck measurement (i.e. does the last
+ // measurement holds entropy?).
+ if ec.stuck(current_delta) { return None };
+
+ // Rotate the data buffer by a prime number (any odd number would
+ // do) to ensure that every bit position of the input time stamp
+ // has an even chance of being merged with a bit position in the
+ // entropy pool. We do not use one here as the adjacent bits in
+ // successive time deltas may have some form of dependency. The
+ // chosen value of 7 implies that the low 7 bits of the next
+ // time delta value is concatenated with the current time delta.
+ self.data = self.data.rotate_left(7);
+
+ Some(())
+ }
+
+ // Shuffle the pool a bit by mixing some value with a bijective function
+ // (XOR) into the pool.
+ //
+ // The function generates a mixer value that depends on the bits set and
+ // the location of the set bits in the random number generated by the
+ // entropy source. Therefore, based on the generated random number, this
+ // mixer value can have 2^64 different values. That mixer value is
+ // initialized with the first two SHA-1 constants. After obtaining the
+ // mixer value, it is XORed into the random number.
+ //
+ // The mixer value is not assumed to contain any entropy. But due to the
+ // XOR operation, it can also not destroy any entropy present in the
+ // entropy pool.
+ #[inline(never)]
+ fn stir_pool(&mut self) {
+ // This constant is derived from the first two 32 bit initialization
+ // vectors of SHA-1 as defined in FIPS 180-4 section 5.3.1
+ // The order does not really matter as we do not rely on the specific
+ // numbers. We just pick the SHA-1 constants as they have a good mix of
+ // bit set and unset.
+ const CONSTANT: u64 = 0x67452301efcdab89;
+
+ // The start value of the mixer variable is derived from the third
+ // and fourth 32 bit initialization vector of SHA-1 as defined in
+ // FIPS 180-4 section 5.3.1
+ let mut mixer = 0x98badcfe10325476;
+
+ // This is a constant time function to prevent leaking timing
+ // information about the random number.
+ // The normal code is:
+ // ```
+ // for i in 0..64 {
+ // if ((self.data >> i) & 1) == 1 { mixer ^= CONSTANT; }
+ // }
+ // ```
+ // This is a bit fragile, as LLVM really wants to use branches here, and
+ // we rely on it to not recognise the opportunity.
+ for i in 0..64 {
+ let apply = (self.data >> i) & 1;
+ let mask = !apply.wrapping_sub(1);
+ mixer ^= CONSTANT & mask;
+ mixer = mixer.rotate_left(1);
+ }
+
+ self.data ^= mixer;
+ }
+
+ fn gen_entropy(&mut self) -> u64 {
+ trace!("JitterRng: collecting entropy");
+
+ // Prime `ec.prev_time`, and run the noice sources to make sure the
+ // first loop round collects the expected entropy.
+ let mut ec = EcState {
+ prev_time: (self.timer)(),
+ last_delta: 0,
+ last_delta2: 0,
+ mem: [0; MEMORY_SIZE],
+ };
+ let _ = self.measure_jitter(&mut ec);
+
+ for _ in 0..self.rounds {
+ // If a stuck measurement is received, repeat measurement
+ // Note: we do not guard against an infinite loop, that would mean
+ // the timer suddenly became broken.
+ while self.measure_jitter(&mut ec).is_none() {}
+ }
+
+ // Do a single read from `self.mem` to make sure the Memory Access noise
+ // source is not optimised out.
+ black_box(ec.mem[0]);
+
+ self.stir_pool();
+ self.data
+ }
+
+ /// Basic quality tests on the timer, by measuring CPU timing jitter a few
+ /// hundred times.
+ ///
+ /// If successful, this will return the estimated number of rounds necessary
+ /// to collect 64 bits of entropy. Otherwise a [`TimerError`] with the cause
+ /// of the failure will be returned.
+ pub fn test_timer(&mut self) -> Result<u8, TimerError> {
+ debug!("JitterRng: testing timer ...");
+ // We could add a check for system capabilities such as `clock_getres`
+ // or check for `CONFIG_X86_TSC`, but it does not make much sense as the
+ // following sanity checks verify that we have a high-resolution timer.
+
+ let mut delta_sum = 0;
+ let mut old_delta = 0;
+
+ let mut time_backwards = 0;
+ let mut count_mod = 0;
+ let mut count_stuck = 0;
+
+ let mut ec = EcState {
+ prev_time: (self.timer)(),
+ last_delta: 0,
+ last_delta2: 0,
+ mem: [0; MEMORY_SIZE],
+ };
+
+ // TESTLOOPCOUNT needs some loops to identify edge systems.
+ // 100 is definitely too little.
+ const TESTLOOPCOUNT: u64 = 300;
+ const CLEARCACHE: u64 = 100;
+
+ for i in 0..(CLEARCACHE + TESTLOOPCOUNT) {
+ // Measure time delta of core entropy collection logic
+ let time = (self.timer)();
+ self.memaccess(&mut ec.mem, true);
+ self.lfsr_time(time, true);
+ let time2 = (self.timer)();
+
+ // Test whether timer works
+ if time == 0 || time2 == 0 {
+ return Err(TimerError::NoTimer);
+ }
+ let delta = time2.wrapping_sub(time) as i64 as i32;
+
+ // Test whether timer is fine grained enough to provide delta even
+ // when called shortly after each other -- this implies that we also
+ // have a high resolution timer
+ if delta == 0 {
+ return Err(TimerError::CoarseTimer);
+ }
+
+ // Up to here we did not modify any variable that will be
+ // evaluated later, but we already performed some work. Thus we
+ // already have had an impact on the caches, branch prediction,
+ // etc. with the goal to clear it to get the worst case
+ // measurements.
+ if i < CLEARCACHE { continue; }
+
+ if ec.stuck(delta) { count_stuck += 1; }
+
+ // Test whether we have an increasing timer.
+ if !(time2 > time) { time_backwards += 1; }
+
+ // Count the number of times the counter increases in steps of 100ns
+ // or greater.
+ if (delta % 100) == 0 { count_mod += 1; }
+
+ // Ensure that we have a varying delta timer which is necessary for
+ // the calculation of entropy -- perform this check only after the
+ // first loop is executed as we need to prime the old_delta value
+ delta_sum += (delta - old_delta).abs() as u64;
+ old_delta = delta;
+ }
+
+ // Do a single read from `self.mem` to make sure the Memory Access noise
+ // source is not optimised out.
+ black_box(ec.mem[0]);
+
+ // We allow the time to run backwards for up to three times.
+ // This can happen if the clock is being adjusted by NTP operations.
+ // If such an operation just happens to interfere with our test, it
+ // should not fail. The value of 3 should cover the NTP case being
+ // performed during our test run.
+ if time_backwards > 3 {
+ return Err(TimerError::NotMonotonic);
+ }
+
+ // Test that the available amount of entropy per round does not get to
+ // low. We expect 1 bit of entropy per round as a reasonable minimum
+ // (although less is possible, it means the collector loop has to run
+ // much more often).
+ // `assert!(delta_average >= log2(1))`
+ // `assert!(delta_sum / TESTLOOPCOUNT >= 1)`
+ // `assert!(delta_sum >= TESTLOOPCOUNT)`
+ if delta_sum < TESTLOOPCOUNT {
+ return Err(TimerError::TinyVariantions);
+ }
+
+ // Ensure that we have variations in the time stamp below 100 for at
+ // least 10% of all checks -- on some platforms, the counter increments
+ // in multiples of 100, but not always
+ if count_mod > (TESTLOOPCOUNT * 9 / 10) {
+ return Err(TimerError::CoarseTimer);
+ }
+
+ // If we have more than 90% stuck results, then this Jitter RNG is
+ // likely to not work well.
+ if count_stuck > (TESTLOOPCOUNT * 9 / 10) {
+ return Err(TimerError::TooManyStuck);
+ }
+
+ // Estimate the number of `measure_jitter` rounds necessary for 64 bits
+ // of entropy.
+ //
+ // We don't try very hard to come up with a good estimate of the
+ // available bits of entropy per round here for two reasons:
+ // 1. Simple estimates of the available bits (like Shannon entropy) are
+ // too optimistic.
+ // 2. Unless we want to waste a lot of time during intialization, there
+ // only a small number of samples are available.
+ //
+ // Therefore we use a very simple and conservative estimate:
+ // `let bits_of_entropy = log2(delta_average) / 2`.
+ //
+ // The number of rounds `measure_jitter` should run to collect 64 bits
+ // of entropy is `64 / bits_of_entropy`.
+ let delta_average = delta_sum / TESTLOOPCOUNT;
+
+ if delta_average >= 16 {
+ let log2 = 64 - delta_average.leading_zeros();
+ // Do something similar to roundup(64/(log2/2)):
+ Ok( ((64u32 * 2 + log2 - 1) / log2) as u8)
+ } else {
+ // For values < 16 the rounding error becomes too large, use a
+ // lookup table.
+ // Values 0 and 1 are invalid, and filtered out by the
+ // `delta_sum < TESTLOOPCOUNT` test above.
+ let log2_lookup = [0, 0, 128, 81, 64, 56, 50, 46,
+ 43, 41, 39, 38, 36, 35, 34, 33];
+ Ok(log2_lookup[delta_average as usize])
+ }
+ }
+
+ /// Statistical test: return the timer delta of one normal run of the
+ /// `JitterRng` entropy collector.
+ ///
+ /// Setting `var_rounds` to `true` will execute the memory access and the
+ /// CPU jitter noice sources a variable amount of times (just like a real
+ /// `JitterRng` round).
+ ///
+ /// Setting `var_rounds` to `false` will execute the noice sources the
+ /// minimal number of times. This can be used to measure the minimum amount
+ /// of entropy one round of the entropy collector can collect in the worst
+ /// case.
+ ///
+ /// See this crate's README on how to use `timer_stats` to test the quality
+ /// of `JitterRng`.
+ pub fn timer_stats(&mut self, var_rounds: bool) -> i64 {
+ let mut mem = [0; MEMORY_SIZE];
+
+ let time = (self.timer)();
+ self.memaccess(&mut mem, var_rounds);
+ self.lfsr_time(time, var_rounds);
+ let time2 = (self.timer)();
+ time2.wrapping_sub(time) as i64
+ }
+}
+
+// A function that is opaque to the optimizer to assist in avoiding dead-code
+// elimination. Taken from `bencher`.
+fn black_box<T>(dummy: T) -> T {
+ unsafe {
+ let ret = ptr::read_volatile(&dummy);
+ mem::forget(dummy);
+ ret
+ }
+}
+
+impl RngCore for JitterRng {
+ fn next_u32(&mut self) -> u32 {
+ // We want to use both parts of the generated entropy
+ if self.data_half_used {
+ self.data_half_used = false;
+ (self.data >> 32) as u32
+ } else {
+ self.data = self.next_u64();
+ self.data_half_used = true;
+ self.data as u32
+ }
+ }
+
+ fn next_u64(&mut self) -> u64 {
+ self.data_half_used = false;
+ self.gen_entropy()
+ }
+
+ fn fill_bytes(&mut self, dest: &mut [u8]) {
+ // Fill using `next_u32`. This is faster for filling small slices (four
+ // bytes or less), while the overhead is negligible.
+ //
+ // This is done especially for wrappers that implement `next_u32`
+ // themselves via `fill_bytes`.
+ impls::fill_bytes_via_next(self, dest)
+ }
+
+ fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
+ Ok(self.fill_bytes(dest))
+ }
+}
diff --git a/rand/rand_jitter/src/platform.rs b/rand/rand_jitter/src/platform.rs
new file mode 100644
index 0000000..8e3d0fb
--- /dev/null
+++ b/rand/rand_jitter/src/platform.rs
@@ -0,0 +1,44 @@
+// Copyright 2018 Developers of the Rand project.
+// Copyright 2013-2015 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.
+
+#[cfg(not(any(target_os = "macos", target_os = "ios", target_os = "windows")))]
+pub fn get_nstime() -> u64 {
+ use std::time::{SystemTime, UNIX_EPOCH};
+
+ let dur = SystemTime::now().duration_since(UNIX_EPOCH).unwrap();
+ // The correct way to calculate the current time is
+ // `dur.as_secs() * 1_000_000_000 + dur.subsec_nanos() as u64`
+ // But this is faster, and the difference in terms of entropy is
+ // negligible (log2(10^9) == 29.9).
+ dur.as_secs() << 30 | dur.subsec_nanos() as u64
+}
+
+#[cfg(any(target_os = "macos", target_os = "ios"))]
+pub fn get_nstime() -> u64 {
+ use libc;
+
+ // On Mac OS and iOS std::time::SystemTime only has 1000ns resolution.
+ // We use `mach_absolute_time` instead. This provides a CPU dependent
+ // unit, to get real nanoseconds the result should by multiplied by
+ // numer/denom from `mach_timebase_info`.
+ // But we are not interested in the exact nanoseconds, just entropy. So
+ // we use the raw result.
+ unsafe { libc::mach_absolute_time() }
+}
+
+#[cfg(target_os = "windows")]
+pub fn get_nstime() -> u64 {
+ use winapi;
+
+ unsafe {
+ let mut t = super::mem::zeroed();
+ winapi::um::profileapi::QueryPerformanceCounter(&mut t);
+ *t.QuadPart() as u64
+ }
+}