Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

8 files changed, 1657 insertions, 0 deletions

diff --git a/third_party/rust/subtle/.cargo-checksum.json b/third_party/rust/subtle/.cargo-checksum.json
new file mode 100644
index 0000000000..62db1587b3
--- /dev/null
+++ b/third_party/rust/subtle/.cargo-checksum.json
@@ -0,0 +1 @@
+{"files":{"CHANGELOG.md":"02f92a31269311c965b1dfa705f22f341dc9cce73af08a8c9840c91b8ceb79df","CONTRIBUTING.md":"2fbb44138ececdef7c0950fae6ed1dcad481fb2f368df0e3734c9902be791f3e","Cargo.toml":"72ff6f9d47061233fc938824f2adc126ba9e8f686df75dec4ab7a0f44327d5c6","LICENSE":"36c48715a280d334a995f26fc38103f21cb92425a20c8eeaa368b229b49b6d4d","README.md":"9a04bb0dee4e6c350d1728ec225f162081d31273dbae6580757aadb363c76cdf","src/lib.rs":"7e14a5d5f2351343e41ff0e085a348190178ebe19cf12ffce083ce75ae6fba9d","tests/mod.rs":"61e6540375c1ccf5a5f134336d5297ecbda6ef76dd3cd81c600b303d2572e7ee"},"package":"81cdd64d312baedb58e21336b31bc043b77e01cc99033ce76ef539f78e965ebc"}
\ No newline at end of file
diff --git a/third_party/rust/subtle/CHANGELOG.md b/third_party/rust/subtle/CHANGELOG.md
new file mode 100644
index 0000000000..e6a3863653
--- /dev/null
+++ b/third_party/rust/subtle/CHANGELOG.md
@@ -0,0 +1,74 @@
+# Changelog
+
+Entries are listed in reverse chronological order.
+
+## 2.5.0
+
+* Add constant-timedness note to the documentation for `CtOption::unwrap_or_else`.
+* Add `CtOption::expect`.
+* Add `ConstantTimeEq::ct_ne` with default implementation.
+* Add new `core_hint_black_box` feature from Diane Hosfelt and Amber
+  Sprenkels which utilises the original `black_box` functionality from
+  when subtle was first written, which has now found it's way into the
+  Rust standard library.
+* Add new `const-generics` feature from @survived which adds support
+  for subtle traits for generic arrays `[T; N]`.
+* Add new feature for supporting `core::cmp::Ordering` for types which
+  implement subtle traits, patch from @tarcieri.
+* Update `rand` dependency to 0.8.
+
+## 2.4.1
+
+* Fix a bug in how the README was included in the documentation builds
+  which caused nightly builds to break.
+
+## 2.4.0
+
+* Add new `ConstantTimeGreater` and `ConstantTimeLess` traits, as well
+  as implementations for unsigned integers, by @isislovecruft.
+
+## 2.3.0
+
+* Add `impl ConstantTimeEq for Choice` by @tarcieri.
+* Add `impl From<CtOption<T>> for Option<T>` by @CPerezz.  This is useful for
+  handling library code that produces `CtOption`s in contexts where timing
+  doesn't matter.
+* Introduce an MSRV policy.
+
+## 2.2.3
+
+* Remove the `nightly`-only asm-based `black_box` barrier in favor of the
+  volatile-based one, fixing compilation on current nightlies.
+
+## 2.2.2
+
+* Update README.md to clarify that 2.2 and above do not require the `nightly`
+  feature.
+
+## 2.2.1
+
+* Adds an `or_else` combinator for `CtOption`, by @ebfull.
+* Optimized `black_box` for `nightly`, by @jethrogb.
+* Optimized `black_box` for `stable`, by @dsprenkels.
+* Fixed CI for `no_std`, by @dsprenkels.
+* Fixed fuzz target compilation, by @3for.
+
+## 2.2.0
+
+* Error during `cargo publish`, yanked.
+
+## 2.1.1
+
+* Adds the "crypto" tag to crate metadata.
+* New shorter, more efficient ct_eq() for integers, contributed by Thomas Pornin.
+
+## 2.1.0
+
+* Adds a new `CtOption<T>` which acts as a constant-time `Option<T>`
+  (thanks to @ebfull for the implementation).
+* `Choice` now itself implements `ConditionallySelectable`.
+
+## 2.0.0
+
+* Stable version with traits reworked from 1.0.0 to interact better
+  with the orphan rules.
diff --git a/third_party/rust/subtle/CONTRIBUTING.md b/third_party/rust/subtle/CONTRIBUTING.md
new file mode 100644
index 0000000000..2d24605166
--- /dev/null
+++ b/third_party/rust/subtle/CONTRIBUTING.md
@@ -0,0 +1,33 @@
+# Contributing to subtle
+
+If you have questions or comments, please feel free to email the
+authors. 
+
+For feature requests, suggestions, and bug reports, please open an
+issue on [our Github](https://github.com/dalek-cryptography/subtle).  (Or,
+send us an email if you're opposed to using Github for whatever reason.)
+
+Patches are welcomed as pull requests on
+[our Github](https://github.com/dalek-cryptography/subtle), as well as by
+email (preferably sent to all of the authors listed in `Cargo.toml`).
+
+We're happy to take generalised utility code, provided the code is:
+
+1. constant time for all potential valid invocations, and
+2. applicable to implementations of several different protocols/primitives.
+
+All issues on subtle are mentored, if you want help with a bug just ask
+@isislovecruft or @hdevalence.
+
+Some issues are easier than others. The `easy` label can be used to find the
+easy issues. If you want to work on an issue, please leave a comment so that we
+can assign it to you!
+
+# Code of Conduct
+
+We follow the [Rust Code of Conduct](http://www.rust-lang.org/conduct.html),
+with the following additional clauses:
+
+* We respect the rights to privacy and anonymity for contributors and people in
+  the community.  If someone wishes to contribute under a pseudonym different to
+  their primary identity, that wish is to be respected by all contributors.
diff --git a/third_party/rust/subtle/Cargo.toml b/third_party/rust/subtle/Cargo.toml
new file mode 100644
index 0000000000..351989ace0
--- /dev/null
+++ b/third_party/rust/subtle/Cargo.toml
@@ -0,0 +1,38 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies.
+#
+# If you are reading this file be aware that the original Cargo.toml
+# will likely look very different (and much more reasonable).
+# See Cargo.toml.orig for the original contents.
+
+[package]
+edition = "2018"
+name = "subtle"
+version = "2.5.0"
+authors = ["Isis Lovecruft <isis@patternsinthevoid.net>", "Henry de Valence <hdevalence@hdevalence.ca>"]
+exclude = ["**/.gitignore", ".travis.yml"]
+description = "Pure-Rust traits and utilities for constant-time cryptographic implementations."
+homepage = "https://dalek.rs/"
+documentation = "https://docs.rs/subtle"
+readme = "README.md"
+keywords = ["cryptography", "crypto", "constant-time", "utilities"]
+categories = ["cryptography", "no-std"]
+license = "BSD-3-Clause"
+repository = "https://github.com/dalek-cryptography/subtle"
+[dev-dependencies.rand]
+version = "0.8"
+
+[features]
+const-generics = []
+core_hint_black_box = []
+default = ["std", "i128"]
+i128 = []
+nightly = []
+std = []
+[badges.travis-ci]
+branch = "master"
+repository = "dalek-cryptography/subtle"
diff --git a/third_party/rust/subtle/LICENSE b/third_party/rust/subtle/LICENSE
new file mode 100644
index 0000000000..927c02c80b
--- /dev/null
+++ b/third_party/rust/subtle/LICENSE
@@ -0,0 +1,28 @@
+Copyright (c) 2016-2017 Isis Agora Lovecruft, Henry de Valence. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+1. Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright
+notice, this list of conditions and the following disclaimer in the
+documentation and/or other materials provided with the distribution.
+
+3. Neither the name of the copyright holder nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
+TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
diff --git a/third_party/rust/subtle/README.md b/third_party/rust/subtle/README.md
new file mode 100644
index 0000000000..de77575540
--- /dev/null
+++ b/third_party/rust/subtle/README.md
@@ -0,0 +1,82 @@
+# subtle [![](https://img.shields.io/crates/v/subtle.svg)](https://crates.io/crates/subtle) [![](https://img.shields.io/badge/dynamic/json.svg?label=docs&uri=https%3A%2F%2Fcrates.io%2Fapi%2Fv1%2Fcrates%2Fsubtle%2Fversions&query=%24.versions%5B0%5D.num&colorB=4F74A6)](https://doc.dalek.rs/subtle) [![](https://travis-ci.org/dalek-cryptography/subtle.svg?branch=master)](https://travis-ci.org/dalek-cryptography/subtle)
+
+**Pure-Rust traits and utilities for constant-time cryptographic implementations.**
+
+It consists of a `Choice` type, and a collection of traits using `Choice`
+instead of `bool` which are intended to execute in constant-time.  The `Choice`
+type is a wrapper around a `u8` that holds a `0` or `1`.
+
+```toml
+subtle = "2.5"
+```
+
+This crate represents a “best-effort” attempt, since side-channels
+are ultimately a property of a deployed cryptographic system
+including the hardware it runs on, not just of software.
+
+The traits are implemented using bitwise operations, and should execute in
+constant time provided that a) the bitwise operations are constant-time and
+b) the bitwise operations are not recognized as a conditional assignment and
+optimized back into a branch.
+
+For a compiler to recognize that bitwise operations represent a conditional
+assignment, it needs to know that the value used to generate the bitmasks is
+really a boolean `i1` rather than an `i8` byte value. In an attempt to
+prevent this refinement, the crate tries to hide the value of a `Choice`'s
+inner `u8` by passing it through a volatile read. For more information, see
+the _About_ section below.
+
+Rust versions from 1.66 or higher support a new best-effort optimization
+barrier ([`core::hint::black_box`]).  To use the new optimization barrier,
+enable the `core_hint_black_box` feature.
+
+Rust versions from 1.51 or higher have const generics support. You may enable
+`const-generics` feautre to have `subtle` traits implemented for arrays `[T; N]`.
+
+Versions prior to `2.2` recommended use of the `nightly` feature to enable an
+optimization barrier; this is not required in versions `2.2` and above.
+
+Note: the `subtle` crate contains `debug_assert`s to check invariants during
+debug builds. These invariant checks involve secret-dependent branches, and
+are not present when compiled in release mode. This crate is intended to be
+used in release mode.
+
+## Documentation
+
+Documentation is available [here][docs].
+
+## Minimum Supported Rust Version
+
+Rust **1.41** or higher.
+
+Minimum supported Rust version can be changed in the future, but it will be done with a minor version bump.
+
+## About
+
+This library aims to be the Rust equivalent of Go’s `crypto/subtle` module.
+
+Old versions of the optimization barrier in `impl From<u8> for Choice` were
+based on Tim Maclean's [work on `rust-timing-shield`][rust-timing-shield],
+which attempts to provide a more comprehensive approach for preventing
+software side-channels in Rust code.
+
+From version `2.2`, it was based on Diane Hosfelt and Amber Sprenkels' work on
+"Secret Types in Rust".  Version `2.5` adds the `core_hint_black_box` feature,
+which uses the original method through the [`core::hint::black_box`] function
+from the Rust standard library.
+
+`subtle` is authored by isis agora lovecruft and Henry de Valence.
+
+## Warning
+
+This code is a low-level library, intended for specific use-cases implementing
+cryptographic protocols.  It represents a best-effort attempt to protect
+against some software side-channels.  Because side-channel resistance is not a
+property of software alone, but of software together with hardware, any such
+effort is fundamentally limited.
+
+**USE AT YOUR OWN RISK**
+
+[docs]: https://docs.rs/subtle
+[`core::hint::black_box`]: https://doc.rust-lang.org/core/hint/fn.black_box.html
+[rust-timing-shield]: https://www.chosenplaintext.ca/open-source/rust-timing-shield/security
diff --git a/third_party/rust/subtle/src/lib.rs b/third_party/rust/subtle/src/lib.rs
new file mode 100644
index 0000000000..795eade44a
--- /dev/null
+++ b/third_party/rust/subtle/src/lib.rs
@@ -0,0 +1,976 @@
+// -*- mode: rust; -*-
+//
+// This file is part of subtle, part of the dalek cryptography project.
+// Copyright (c) 2016-2018 isis lovecruft, Henry de Valence
+// See LICENSE for licensing information.
+//
+// Authors:
+// - isis agora lovecruft <isis@patternsinthevoid.net>
+// - Henry de Valence <hdevalence@hdevalence.ca>
+
+#![no_std]
+#![deny(missing_docs)]
+#![doc(html_logo_url = "https://doc.dalek.rs/assets/dalek-logo-clear.png")]
+#![doc(html_root_url = "https://docs.rs/subtle/2.5.0")]
+
+//! # subtle [![](https://img.shields.io/crates/v/subtle.svg)](https://crates.io/crates/subtle) [![](https://img.shields.io/badge/dynamic/json.svg?label=docs&uri=https%3A%2F%2Fcrates.io%2Fapi%2Fv1%2Fcrates%2Fsubtle%2Fversions&query=%24.versions%5B0%5D.num&colorB=4F74A6)](https://doc.dalek.rs/subtle) [![](https://travis-ci.org/dalek-cryptography/subtle.svg?branch=master)](https://travis-ci.org/dalek-cryptography/subtle)
+//!
+//! **Pure-Rust traits and utilities for constant-time cryptographic implementations.**
+//!
+//! It consists of a `Choice` type, and a collection of traits using `Choice`
+//! instead of `bool` which are intended to execute in constant-time.  The `Choice`
+//! type is a wrapper around a `u8` that holds a `0` or `1`.
+//!
+//! ```toml
+//! subtle = "2.5"
+//! ```
+//!
+//! This crate represents a “best-effort” attempt, since side-channels
+//! are ultimately a property of a deployed cryptographic system
+//! including the hardware it runs on, not just of software.
+//!
+//! The traits are implemented using bitwise operations, and should execute in
+//! constant time provided that a) the bitwise operations are constant-time and
+//! b) the bitwise operations are not recognized as a conditional assignment and
+//! optimized back into a branch.
+//!
+//! For a compiler to recognize that bitwise operations represent a conditional
+//! assignment, it needs to know that the value used to generate the bitmasks is
+//! really a boolean `i1` rather than an `i8` byte value. In an attempt to
+//! prevent this refinement, the crate tries to hide the value of a `Choice`'s
+//! inner `u8` by passing it through a volatile read. For more information, see
+//! the _About_ section below.
+//!
+//! Rust versions from 1.66 or higher support a new best-effort optimization
+//! barrier ([`core::hint::black_box`]).  To use the new optimization barrier,
+//! enable the `core_hint_black_box` feature.
+//!
+//! Rust versions from 1.51 or higher have const generics support. You may enable
+//! `const-generics` feautre to have `subtle` traits implemented for arrays `[T; N]`.
+//!
+//! Versions prior to `2.2` recommended use of the `nightly` feature to enable an
+//! optimization barrier; this is not required in versions `2.2` and above.
+//!
+//! Note: the `subtle` crate contains `debug_assert`s to check invariants during
+//! debug builds. These invariant checks involve secret-dependent branches, and
+//! are not present when compiled in release mode. This crate is intended to be
+//! used in release mode.
+//!
+//! ## Documentation
+//!
+//! Documentation is available [here][docs].
+//!
+//! ## Minimum Supported Rust Version
+//!
+//! Rust **1.41** or higher.
+//!
+//! Minimum supported Rust version can be changed in the future, but it will be done with a minor version bump.
+//!
+//! ## About
+//!
+//! This library aims to be the Rust equivalent of Go’s `crypto/subtle` module.
+//!
+//! Old versions of the optimization barrier in `impl From<u8> for Choice` were
+//! based on Tim Maclean's [work on `rust-timing-shield`][rust-timing-shield],
+//! which attempts to provide a more comprehensive approach for preventing
+//! software side-channels in Rust code.
+//!
+//! From version `2.2`, it was based on Diane Hosfelt and Amber Sprenkels' work on
+//! "Secret Types in Rust". Version `2.5` adds the `core_hint_black_box` feature,
+//! which uses the original method through the [`core::hint::black_box`] function
+//! from the Rust standard library.
+//!
+//! `subtle` is authored by isis agora lovecruft and Henry de Valence.
+//!
+//! ## Warning
+//!
+//! This code is a low-level library, intended for specific use-cases implementing
+//! cryptographic protocols.  It represents a best-effort attempt to protect
+//! against some software side-channels.  Because side-channel resistance is not a
+//! property of software alone, but of software together with hardware, any such
+//! effort is fundamentally limited.
+//!
+//! **USE AT YOUR OWN RISK**
+//!
+//! [docs]: https://docs.rs/subtle
+//! [`core::hint::black_box`]: https://doc.rust-lang.org/core/hint/fn.black_box.html
+//! [rust-timing-shield]: https://www.chosenplaintext.ca/open-source/rust-timing-shield/security
+
+#[cfg(feature = "std")]
+#[macro_use]
+extern crate std;
+
+use core::cmp;
+use core::ops::{BitAnd, BitAndAssign, BitOr, BitOrAssign, BitXor, BitXorAssign, Neg, Not};
+use core::option::Option;
+
+/// The `Choice` struct represents a choice for use in conditional assignment.
+///
+/// It is a wrapper around a `u8`, which should have the value either `1` (true)
+/// or `0` (false).
+///
+/// The conversion from `u8` to `Choice` passes the value through an optimization
+/// barrier, as a best-effort attempt to prevent the compiler from inferring that
+/// the `Choice` value is a boolean. This strategy is based on Tim Maclean's
+/// [work on `rust-timing-shield`][rust-timing-shield], which attempts to provide
+/// a more comprehensive approach for preventing software side-channels in Rust
+/// code.
+///
+/// The `Choice` struct implements operators for AND, OR, XOR, and NOT, to allow
+/// combining `Choice` values. These operations do not short-circuit.
+///
+/// [rust-timing-shield]:
+/// https://www.chosenplaintext.ca/open-source/rust-timing-shield/security
+#[derive(Copy, Clone, Debug)]
+pub struct Choice(u8);
+
+impl Choice {
+    /// Unwrap the `Choice` wrapper to reveal the underlying `u8`.
+    ///
+    /// # Note
+    ///
+    /// This function only exists as an **escape hatch** for the rare case
+    /// where it's not possible to use one of the `subtle`-provided
+    /// trait impls.
+    ///
+    /// **To convert a `Choice` to a `bool`, use the `From` implementation instead.**
+    #[inline]
+    pub fn unwrap_u8(&self) -> u8 {
+        self.0
+    }
+}
+
+impl From<Choice> for bool {
+    /// Convert the `Choice` wrapper into a `bool`, depending on whether
+    /// the underlying `u8` was a `0` or a `1`.
+    ///
+    /// # Note
+    ///
+    /// This function exists to avoid having higher-level cryptographic protocol
+    /// implementations duplicating this pattern.
+    ///
+    /// The intended use case for this conversion is at the _end_ of a
+    /// higher-level primitive implementation: for example, in checking a keyed
+    /// MAC, where the verification should happen in constant-time (and thus use
+    /// a `Choice`) but it is safe to return a `bool` at the end of the
+    /// verification.
+    #[inline]
+    fn from(source: Choice) -> bool {
+        debug_assert!((source.0 == 0u8) | (source.0 == 1u8));
+        source.0 != 0
+    }
+}
+
+impl BitAnd for Choice {
+    type Output = Choice;
+    #[inline]
+    fn bitand(self, rhs: Choice) -> Choice {
+        (self.0 & rhs.0).into()
+    }
+}
+
+impl BitAndAssign for Choice {
+    #[inline]
+    fn bitand_assign(&mut self, rhs: Choice) {
+        *self = *self & rhs;
+    }
+}
+
+impl BitOr for Choice {
+    type Output = Choice;
+    #[inline]
+    fn bitor(self, rhs: Choice) -> Choice {
+        (self.0 | rhs.0).into()
+    }
+}
+
+impl BitOrAssign for Choice {
+    #[inline]
+    fn bitor_assign(&mut self, rhs: Choice) {
+        *self = *self | rhs;
+    }
+}
+
+impl BitXor for Choice {
+    type Output = Choice;
+    #[inline]
+    fn bitxor(self, rhs: Choice) -> Choice {
+        (self.0 ^ rhs.0).into()
+    }
+}
+
+impl BitXorAssign for Choice {
+    #[inline]
+    fn bitxor_assign(&mut self, rhs: Choice) {
+        *self = *self ^ rhs;
+    }
+}
+
+impl Not for Choice {
+    type Output = Choice;
+    #[inline]
+    fn not(self) -> Choice {
+        (1u8 & (!self.0)).into()
+    }
+}
+
+/// This function is a best-effort attempt to prevent the compiler from knowing
+/// anything about the value of the returned `u8`, other than its type.
+///
+/// Because we want to support stable Rust, we don't have access to inline
+/// assembly or test::black_box, so we use the fact that volatile values will
+/// never be elided to register values.
+///
+/// Note: Rust's notion of "volatile" is subject to change over time. While this
+/// code may break in a non-destructive way in the future, “constant-time” code
+/// is a continually moving target, and this is better than doing nothing.
+#[cfg(not(feature = "core_hint_black_box"))]
+#[inline(never)]
+fn black_box(input: u8) -> u8 {
+    debug_assert!((input == 0u8) | (input == 1u8));
+
+    unsafe {
+        // Optimization barrier
+        //
+        // Unsafe is ok, because:
+        //   - &input is not NULL;
+        //   - size of input is not zero;
+        //   - u8 is neither Sync, nor Send;
+        //   - u8 is Copy, so input is always live;
+        //   - u8 type is always properly aligned.
+        core::ptr::read_volatile(&input as *const u8)
+    }
+}
+
+#[cfg(feature = "core_hint_black_box")]
+#[inline(never)]
+fn black_box(input: u8) -> u8 {
+    debug_assert!((input == 0u8) | (input == 1u8));
+    core::hint::black_box(input)
+}
+
+impl From<u8> for Choice {
+    #[inline]
+    fn from(input: u8) -> Choice {
+        // Our goal is to prevent the compiler from inferring that the value held inside the
+        // resulting `Choice` struct is really an `i1` instead of an `i8`.
+        Choice(black_box(input))
+    }
+}
+
+/// An `Eq`-like trait that produces a `Choice` instead of a `bool`.
+///
+/// # Example
+///
+/// ```
+/// use subtle::ConstantTimeEq;
+/// let x: u8 = 5;
+/// let y: u8 = 13;
+///
+/// assert_eq!(x.ct_eq(&y).unwrap_u8(), 0);
+/// assert_eq!(x.ct_eq(&x).unwrap_u8(), 1);
+/// ```
+pub trait ConstantTimeEq {
+    /// Determine if two items are equal.
+    ///
+    /// The `ct_eq` function should execute in constant time.
+    ///
+    /// # Returns
+    ///
+    /// * `Choice(1u8)` if `self == other`;
+    /// * `Choice(0u8)` if `self != other`.
+    #[inline]
+    fn ct_eq(&self, other: &Self) -> Choice;
+
+    /// Determine if two items are NOT equal.
+    ///
+    /// The `ct_ne` function should execute in constant time.
+    ///
+    /// # Returns
+    ///
+    /// * `Choice(0u8)` if `self == other`;
+    /// * `Choice(1u8)` if `self != other`.
+    #[inline]
+    fn ct_ne(&self, other: &Self) -> Choice {
+        !self.ct_eq(other)
+    }
+}
+
+impl<T: ConstantTimeEq> ConstantTimeEq for [T] {
+    /// Check whether two slices of `ConstantTimeEq` types are equal.
+    ///
+    /// # Note
+    ///
+    /// This function short-circuits if the lengths of the input slices
+    /// are different.  Otherwise, it should execute in time independent
+    /// of the slice contents.
+    ///
+    /// Since arrays coerce to slices, this function works with fixed-size arrays:
+    ///
+    /// ```
+    /// # use subtle::ConstantTimeEq;
+    /// #
+    /// let a: [u8; 8] = [0,1,2,3,4,5,6,7];
+    /// let b: [u8; 8] = [0,1,2,3,0,1,2,3];
+    ///
+    /// let a_eq_a = a.ct_eq(&a);
+    /// let a_eq_b = a.ct_eq(&b);
+    ///
+    /// assert_eq!(a_eq_a.unwrap_u8(), 1);
+    /// assert_eq!(a_eq_b.unwrap_u8(), 0);
+    /// ```
+    #[inline]
+    fn ct_eq(&self, _rhs: &[T]) -> Choice {
+        let len = self.len();
+
+        // Short-circuit on the *lengths* of the slices, not their
+        // contents.
+        if len != _rhs.len() {
+            return Choice::from(0);
+        }
+
+        // This loop shouldn't be shortcircuitable, since the compiler
+        // shouldn't be able to reason about the value of the `u8`
+        // unwrapped from the `ct_eq` result.
+        let mut x = 1u8;
+        for (ai, bi) in self.iter().zip(_rhs.iter()) {
+            x &= ai.ct_eq(bi).unwrap_u8();
+        }
+
+        x.into()
+    }
+}
+
+impl ConstantTimeEq for Choice {
+    #[inline]
+    fn ct_eq(&self, rhs: &Choice) -> Choice {
+        !(*self ^ *rhs)
+    }
+}
+
+/// Given the bit-width `$bit_width` and the corresponding primitive
+/// unsigned and signed types `$t_u` and `$t_i` respectively, generate
+/// an `ConstantTimeEq` implementation.
+macro_rules! generate_integer_equal {
+    ($t_u:ty, $t_i:ty, $bit_width:expr) => {
+        impl ConstantTimeEq for $t_u {
+            #[inline]
+            fn ct_eq(&self, other: &$t_u) -> Choice {
+                // x == 0 if and only if self == other
+                let x: $t_u = self ^ other;
+
+                // If x == 0, then x and -x are both equal to zero;
+                // otherwise, one or both will have its high bit set.
+                let y: $t_u = (x | x.wrapping_neg()) >> ($bit_width - 1);
+
+                // Result is the opposite of the high bit (now shifted to low).
+                ((y ^ (1 as $t_u)) as u8).into()
+            }
+        }
+        impl ConstantTimeEq for $t_i {
+            #[inline]
+            fn ct_eq(&self, other: &$t_i) -> Choice {
+                // Bitcast to unsigned and call that implementation.
+                (*self as $t_u).ct_eq(&(*other as $t_u))
+            }
+        }
+    };
+}
+
+generate_integer_equal!(u8, i8, 8);
+generate_integer_equal!(u16, i16, 16);
+generate_integer_equal!(u32, i32, 32);
+generate_integer_equal!(u64, i64, 64);
+#[cfg(feature = "i128")]
+generate_integer_equal!(u128, i128, 128);
+generate_integer_equal!(usize, isize, ::core::mem::size_of::<usize>() * 8);
+
+/// `Ordering` is `#[repr(i8)]` making it possible to leverage `i8::ct_eq`.
+impl ConstantTimeEq for cmp::Ordering {
+    #[inline]
+    fn ct_eq(&self, other: &Self) -> Choice {
+        (*self as i8).ct_eq(&(*other as i8))
+    }
+}
+
+/// A type which can be conditionally selected in constant time.
+///
+/// This trait also provides generic implementations of conditional
+/// assignment and conditional swaps.
+pub trait ConditionallySelectable: Copy {
+    /// Select `a` or `b` according to `choice`.
+    ///
+    /// # Returns
+    ///
+    /// * `a` if `choice == Choice(0)`;
+    /// * `b` if `choice == Choice(1)`.
+    ///
+    /// This function should execute in constant time.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use subtle::ConditionallySelectable;
+    /// #
+    /// # fn main() {
+    /// let x: u8 = 13;
+    /// let y: u8 = 42;
+    ///
+    /// let z = u8::conditional_select(&x, &y, 0.into());
+    /// assert_eq!(z, x);
+    /// let z = u8::conditional_select(&x, &y, 1.into());
+    /// assert_eq!(z, y);
+    /// # }
+    /// ```
+    #[inline]
+    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self;
+
+    /// Conditionally assign `other` to `self`, according to `choice`.
+    ///
+    /// This function should execute in constant time.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use subtle::ConditionallySelectable;
+    /// #
+    /// # fn main() {
+    /// let mut x: u8 = 13;
+    /// let mut y: u8 = 42;
+    ///
+    /// x.conditional_assign(&y, 0.into());
+    /// assert_eq!(x, 13);
+    /// x.conditional_assign(&y, 1.into());
+    /// assert_eq!(x, 42);
+    /// # }
+    /// ```
+    #[inline]
+    fn conditional_assign(&mut self, other: &Self, choice: Choice) {
+        *self = Self::conditional_select(self, other, choice);
+    }
+
+    /// Conditionally swap `self` and `other` if `choice == 1`; otherwise,
+    /// reassign both unto themselves.
+    ///
+    /// This function should execute in constant time.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use subtle::ConditionallySelectable;
+    /// #
+    /// # fn main() {
+    /// let mut x: u8 = 13;
+    /// let mut y: u8 = 42;
+    ///
+    /// u8::conditional_swap(&mut x, &mut y, 0.into());
+    /// assert_eq!(x, 13);
+    /// assert_eq!(y, 42);
+    /// u8::conditional_swap(&mut x, &mut y, 1.into());
+    /// assert_eq!(x, 42);
+    /// assert_eq!(y, 13);
+    /// # }
+    /// ```
+    #[inline]
+    fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice) {
+        let t: Self = *a;
+        a.conditional_assign(&b, choice);
+        b.conditional_assign(&t, choice);
+    }
+}
+
+macro_rules! to_signed_int {
+    (u8) => {
+        i8
+    };
+    (u16) => {
+        i16
+    };
+    (u32) => {
+        i32
+    };
+    (u64) => {
+        i64
+    };
+    (u128) => {
+        i128
+    };
+    (i8) => {
+        i8
+    };
+    (i16) => {
+        i16
+    };
+    (i32) => {
+        i32
+    };
+    (i64) => {
+        i64
+    };
+    (i128) => {
+        i128
+    };
+}
+
+macro_rules! generate_integer_conditional_select {
+    ($($t:tt)*) => ($(
+        impl ConditionallySelectable for $t {
+            #[inline]
+            fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
+                // if choice = 0, mask = (-0) = 0000...0000
+                // if choice = 1, mask = (-1) = 1111...1111
+                let mask = -(choice.unwrap_u8() as to_signed_int!($t)) as $t;
+                a ^ (mask & (a ^ b))
+            }
+
+            #[inline]
+            fn conditional_assign(&mut self, other: &Self, choice: Choice) {
+                // if choice = 0, mask = (-0) = 0000...0000
+                // if choice = 1, mask = (-1) = 1111...1111
+                let mask = -(choice.unwrap_u8() as to_signed_int!($t)) as $t;
+                *self ^= mask & (*self ^ *other);
+            }
+
+            #[inline]
+            fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice) {
+                // if choice = 0, mask = (-0) = 0000...0000
+                // if choice = 1, mask = (-1) = 1111...1111
+                let mask = -(choice.unwrap_u8() as to_signed_int!($t)) as $t;
+                let t = mask & (*a ^ *b);
+                *a ^= t;
+                *b ^= t;
+            }
+         }
+    )*)
+}
+
+generate_integer_conditional_select!(  u8   i8);
+generate_integer_conditional_select!( u16  i16);
+generate_integer_conditional_select!( u32  i32);
+generate_integer_conditional_select!( u64  i64);
+#[cfg(feature = "i128")]
+generate_integer_conditional_select!(u128 i128);
+
+/// `Ordering` is `#[repr(i8)]` where:
+///
+/// - `Less` => -1
+/// - `Equal` => 0
+/// - `Greater` => 1
+///
+/// Given this, it's possible to operate on orderings as if they're integers,
+/// which allows leveraging conditional masking for predication.
+impl ConditionallySelectable for cmp::Ordering {
+    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
+        let a = *a as i8;
+        let b = *b as i8;
+        let ret = i8::conditional_select(&a, &b, choice);
+
+        // SAFETY: `Ordering` is `#[repr(i8)]` and `ret` has been assigned to
+        // a value which was originally a valid `Ordering` then cast to `i8`
+        unsafe { *((&ret as *const _) as *const cmp::Ordering) }
+    }
+}
+
+impl ConditionallySelectable for Choice {
+    #[inline]
+    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
+        Choice(u8::conditional_select(&a.0, &b.0, choice))
+    }
+}
+
+#[cfg(feature = "const-generics")]
+impl<T, const N: usize> ConditionallySelectable for [T; N]
+where
+    T: ConditionallySelectable,
+{
+    #[inline]
+    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
+        let mut output = *a;
+        output.conditional_assign(b, choice);
+        output
+    }
+
+    fn conditional_assign(&mut self, other: &Self, choice: Choice) {
+        for (a_i, b_i) in self.iter_mut().zip(other) {
+            a_i.conditional_assign(b_i, choice)
+        }
+    }
+}
+
+/// A type which can be conditionally negated in constant time.
+///
+/// # Note
+///
+/// A generic implementation of `ConditionallyNegatable` is provided
+/// for types `T` which are `ConditionallySelectable` and have `Neg`
+/// implemented on `&T`.
+pub trait ConditionallyNegatable {
+    /// Negate `self` if `choice == Choice(1)`; otherwise, leave it
+    /// unchanged.
+    ///
+    /// This function should execute in constant time.
+    #[inline]
+    fn conditional_negate(&mut self, choice: Choice);
+}
+
+impl<T> ConditionallyNegatable for T
+where
+    T: ConditionallySelectable,
+    for<'a> &'a T: Neg<Output = T>,
+{
+    #[inline]
+    fn conditional_negate(&mut self, choice: Choice) {
+        // Need to cast to eliminate mutability
+        let self_neg: T = -(self as &T);
+        self.conditional_assign(&self_neg, choice);
+    }
+}
+
+/// The `CtOption<T>` type represents an optional value similar to the
+/// [`Option<T>`](core::option::Option) type but is intended for
+/// use in constant time APIs.
+///
+/// Any given `CtOption<T>` is either `Some` or `None`, but unlike
+/// `Option<T>` these variants are not exposed. The
+/// [`is_some()`](CtOption::is_some) method is used to determine if
+/// the value is `Some`, and [`unwrap_or()`](CtOption::unwrap_or) and
+/// [`unwrap_or_else()`](CtOption::unwrap_or_else) methods are
+/// provided to access the underlying value. The value can also be
+/// obtained with [`unwrap()`](CtOption::unwrap) but this will panic
+/// if it is `None`.
+///
+/// Functions that are intended to be constant time may not produce
+/// valid results for all inputs, such as square root and inversion
+/// operations in finite field arithmetic. Returning an `Option<T>`
+/// from these functions makes it difficult for the caller to reason
+/// about the result in constant time, and returning an incorrect
+/// value burdens the caller and increases the chance of bugs.
+#[derive(Clone, Copy, Debug)]
+pub struct CtOption<T> {
+    value: T,
+    is_some: Choice,
+}
+
+impl<T> From<CtOption<T>> for Option<T> {
+    /// Convert the `CtOption<T>` wrapper into an `Option<T>`, depending on whether
+    /// the underlying `is_some` `Choice` was a `0` or a `1` once unwrapped.
+    ///
+    /// # Note
+    ///
+    /// This function exists to avoid ending up with ugly, verbose and/or bad handled
+    /// conversions from the `CtOption<T>` wraps to an `Option<T>` or `Result<T, E>`.
+    /// This implementation doesn't intend to be constant-time nor try to protect the
+    /// leakage of the `T` since the `Option<T>` will do it anyways.
+    fn from(source: CtOption<T>) -> Option<T> {
+        if source.is_some().unwrap_u8() == 1u8 {
+            Option::Some(source.value)
+        } else {
+            None
+        }
+    }
+}
+
+impl<T> CtOption<T> {
+    /// This method is used to construct a new `CtOption<T>` and takes
+    /// a value of type `T`, and a `Choice` that determines whether
+    /// the optional value should be `Some` or not. If `is_some` is
+    /// false, the value will still be stored but its value is never
+    /// exposed.
+    #[inline]
+    pub fn new(value: T, is_some: Choice) -> CtOption<T> {
+        CtOption {
+            value: value,
+            is_some: is_some,
+        }
+    }
+
+    /// Returns the contained value, consuming the `self` value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the value is none with a custom panic message provided by
+    /// `msg`.
+    pub fn expect(self, msg: &str) -> T {
+        assert_eq!(self.is_some.unwrap_u8(), 1, "{}", msg);
+
+        self.value
+    }
+
+    /// This returns the underlying value but panics if it
+    /// is not `Some`.
+    #[inline]
+    pub fn unwrap(self) -> T {
+        assert_eq!(self.is_some.unwrap_u8(), 1);
+
+        self.value
+    }
+
+    /// This returns the underlying value if it is `Some`
+    /// or the provided value otherwise.
+    #[inline]
+    pub fn unwrap_or(self, def: T) -> T
+    where
+        T: ConditionallySelectable,
+    {
+        T::conditional_select(&def, &self.value, self.is_some)
+    }
+
+    /// This returns the underlying value if it is `Some`
+    /// or the value produced by the provided closure otherwise.
+    ///
+    /// This operates in constant time, because the provided closure
+    /// is always called.
+    #[inline]
+    pub fn unwrap_or_else<F>(self, f: F) -> T
+    where
+        T: ConditionallySelectable,
+        F: FnOnce() -> T,
+    {
+        T::conditional_select(&f(), &self.value, self.is_some)
+    }
+
+    /// Returns a true `Choice` if this value is `Some`.
+    #[inline]
+    pub fn is_some(&self) -> Choice {
+        self.is_some
+    }
+
+    /// Returns a true `Choice` if this value is `None`.
+    #[inline]
+    pub fn is_none(&self) -> Choice {
+        !self.is_some
+    }
+
+    /// Returns a `None` value if the option is `None`, otherwise
+    /// returns a `CtOption` enclosing the value of the provided closure.
+    /// The closure is given the enclosed value or, if the option is
+    /// `None`, it is provided a dummy value computed using
+    /// `Default::default()`.
+    ///
+    /// This operates in constant time, because the provided closure
+    /// is always called.
+    #[inline]
+    pub fn map<U, F>(self, f: F) -> CtOption<U>
+    where
+        T: Default + ConditionallySelectable,
+        F: FnOnce(T) -> U,
+    {
+        CtOption::new(
+            f(T::conditional_select(
+                &T::default(),
+                &self.value,
+                self.is_some,
+            )),
+            self.is_some,
+        )
+    }
+
+    /// Returns a `None` value if the option is `None`, otherwise
+    /// returns the result of the provided closure. The closure is
+    /// given the enclosed value or, if the option is `None`, it
+    /// is provided a dummy value computed using `Default::default()`.
+    ///
+    /// This operates in constant time, because the provided closure
+    /// is always called.
+    #[inline]
+    pub fn and_then<U, F>(self, f: F) -> CtOption<U>
+    where
+        T: Default + ConditionallySelectable,
+        F: FnOnce(T) -> CtOption<U>,
+    {
+        let mut tmp = f(T::conditional_select(
+            &T::default(),
+            &self.value,
+            self.is_some,
+        ));
+        tmp.is_some &= self.is_some;
+
+        tmp
+    }
+
+    /// Returns `self` if it contains a value, and otherwise returns the result of
+    /// calling `f`. The provided function `f` is always called.
+    #[inline]
+    pub fn or_else<F>(self, f: F) -> CtOption<T>
+    where
+        T: ConditionallySelectable,
+        F: FnOnce() -> CtOption<T>,
+    {
+        let is_none = self.is_none();
+        let f = f();
+
+        Self::conditional_select(&self, &f, is_none)
+    }
+}
+
+impl<T: ConditionallySelectable> ConditionallySelectable for CtOption<T> {
+    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
+        CtOption::new(
+            T::conditional_select(&a.value, &b.value, choice),
+            Choice::conditional_select(&a.is_some, &b.is_some, choice),
+        )
+    }
+}
+
+impl<T: ConstantTimeEq> ConstantTimeEq for CtOption<T> {
+    /// Two `CtOption<T>`s are equal if they are both `Some` and
+    /// their values are equal, or both `None`.
+    #[inline]
+    fn ct_eq(&self, rhs: &CtOption<T>) -> Choice {
+        let a = self.is_some();
+        let b = rhs.is_some();
+
+        (a & b & self.value.ct_eq(&rhs.value)) | (!a & !b)
+    }
+}
+
+/// A type which can be compared in some manner and be determined to be greater
+/// than another of the same type.
+pub trait ConstantTimeGreater {
+    /// Determine whether `self > other`.
+    ///
+    /// The bitwise-NOT of the return value of this function should be usable to
+    /// determine if `self <= other`.
+    ///
+    /// This function should execute in constant time.
+    ///
+    /// # Returns
+    ///
+    /// A `Choice` with a set bit if `self > other`, and with no set bits
+    /// otherwise.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use subtle::ConstantTimeGreater;
+    ///
+    /// let x: u8 = 13;
+    /// let y: u8 = 42;
+    ///
+    /// let x_gt_y = x.ct_gt(&y);
+    ///
+    /// assert_eq!(x_gt_y.unwrap_u8(), 0);
+    ///
+    /// let y_gt_x = y.ct_gt(&x);
+    ///
+    /// assert_eq!(y_gt_x.unwrap_u8(), 1);
+    ///
+    /// let x_gt_x = x.ct_gt(&x);
+    ///
+    /// assert_eq!(x_gt_x.unwrap_u8(), 0);
+    /// ```
+    fn ct_gt(&self, other: &Self) -> Choice;
+}
+
+macro_rules! generate_unsigned_integer_greater {
+    ($t_u: ty, $bit_width: expr) => {
+        impl ConstantTimeGreater for $t_u {
+            /// Returns Choice::from(1) iff x > y, and Choice::from(0) iff x <= y.
+            ///
+            /// # Note
+            ///
+            /// This algoritm would also work for signed integers if we first
+            /// flip the top bit, e.g. `let x: u8 = x ^ 0x80`, etc.
+            #[inline]
+            fn ct_gt(&self, other: &$t_u) -> Choice {
+                let gtb = self & !other; // All the bits in self that are greater than their corresponding bits in other.
+                let mut ltb = !self & other; // All the bits in self that are less than their corresponding bits in other.
+                let mut pow = 1;
+
+                // Less-than operator is okay here because it's dependent on the bit-width.
+                while pow < $bit_width {
+                    ltb |= ltb >> pow; // Bit-smear the highest set bit to the right.
+                    pow += pow;
+                }
+                let mut bit = gtb & !ltb; // Select the highest set bit.
+                let mut pow = 1;
+
+                while pow < $bit_width {
+                    bit |= bit >> pow; // Shift it to the right until we end up with either 0 or 1.
+                    pow += pow;
+                }
+                // XXX We should possibly do the above flattening to 0 or 1 in the
+                //     Choice constructor rather than making it a debug error?
+                Choice::from((bit & 1) as u8)
+            }
+        }
+    };
+}
+
+generate_unsigned_integer_greater!(u8, 8);
+generate_unsigned_integer_greater!(u16, 16);
+generate_unsigned_integer_greater!(u32, 32);
+generate_unsigned_integer_greater!(u64, 64);
+#[cfg(feature = "i128")]
+generate_unsigned_integer_greater!(u128, 128);
+
+impl ConstantTimeGreater for cmp::Ordering {
+    #[inline]
+    fn ct_gt(&self, other: &Self) -> Choice {
+        // No impl of `ConstantTimeGreater` for `i8`, so use `u8`
+        let a = (*self as i8) + 1;
+        let b = (*other as i8) + 1;
+        (a as u8).ct_gt(&(b as u8))
+    }
+}
+
+/// A type which can be compared in some manner and be determined to be less
+/// than another of the same type.
+pub trait ConstantTimeLess: ConstantTimeEq + ConstantTimeGreater {
+    /// Determine whether `self < other`.
+    ///
+    /// The bitwise-NOT of the return value of this function should be usable to
+    /// determine if `self >= other`.
+    ///
+    /// A default implementation is provided and implemented for the unsigned
+    /// integer types.
+    ///
+    /// This function should execute in constant time.
+    ///
+    /// # Returns
+    ///
+    /// A `Choice` with a set bit if `self < other`, and with no set bits
+    /// otherwise.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use subtle::ConstantTimeLess;
+    ///
+    /// let x: u8 = 13;
+    /// let y: u8 = 42;
+    ///
+    /// let x_lt_y = x.ct_lt(&y);
+    ///
+    /// assert_eq!(x_lt_y.unwrap_u8(), 1);
+    ///
+    /// let y_lt_x = y.ct_lt(&x);
+    ///
+    /// assert_eq!(y_lt_x.unwrap_u8(), 0);
+    ///
+    /// let x_lt_x = x.ct_lt(&x);
+    ///
+    /// assert_eq!(x_lt_x.unwrap_u8(), 0);
+    /// ```
+    #[inline]
+    fn ct_lt(&self, other: &Self) -> Choice {
+        !self.ct_gt(other) & !self.ct_eq(other)
+    }
+}
+
+impl ConstantTimeLess for u8 {}
+impl ConstantTimeLess for u16 {}
+impl ConstantTimeLess for u32 {}
+impl ConstantTimeLess for u64 {}
+#[cfg(feature = "i128")]
+impl ConstantTimeLess for u128 {}
+
+impl ConstantTimeLess for cmp::Ordering {
+    #[inline]
+    fn ct_lt(&self, other: &Self) -> Choice {
+        // No impl of `ConstantTimeLess` for `i8`, so use `u8`
+        let a = (*self as i8) + 1;
+        let b = (*other as i8) + 1;
+        (a as u8).ct_lt(&(b as u8))
+    }
+}
diff --git a/third_party/rust/subtle/tests/mod.rs b/third_party/rust/subtle/tests/mod.rs
new file mode 100644
index 0000000000..f6b3982e02
--- /dev/null
+++ b/third_party/rust/subtle/tests/mod.rs
@@ -0,0 +1,425 @@
+use std::cmp;
+
+use rand::rngs::OsRng;
+use rand::RngCore;
+
+use subtle::*;
+
+#[test]
+#[should_panic]
+fn slices_equal_different_lengths() {
+    let a: [u8; 3] = [0, 0, 0];
+    let b: [u8; 4] = [0, 0, 0, 0];
+
+    assert_eq!((&a).ct_eq(&b).unwrap_u8(), 1);
+}
+
+#[test]
+fn slices_equal() {
+    let a: [u8; 8] = [1, 2, 3, 4, 5, 6, 7, 8];
+    let b: [u8; 8] = [1, 2, 3, 4, 4, 3, 2, 1];
+
+    let a_eq_a = (&a).ct_eq(&a);
+    let a_eq_b = (&a).ct_eq(&b);
+
+    assert_eq!(a_eq_a.unwrap_u8(), 1);
+    assert_eq!(a_eq_b.unwrap_u8(), 0);
+
+    let c: [u8; 16] = [0u8; 16];
+
+    let a_eq_c = (&a).ct_eq(&c);
+    assert_eq!(a_eq_c.unwrap_u8(), 0);
+}
+
+#[test]
+fn conditional_assign_i32() {
+    let mut a: i32 = 5;
+    let b: i32 = 13;
+
+    a.conditional_assign(&b, 0.into());
+    assert_eq!(a, 5);
+    a.conditional_assign(&b, 1.into());
+    assert_eq!(a, 13);
+}
+
+#[test]
+fn conditional_assign_i64() {
+    let mut c: i64 = 2343249123;
+    let d: i64 = 8723884895;
+
+    c.conditional_assign(&d, 0.into());
+    assert_eq!(c, 2343249123);
+    c.conditional_assign(&d, 1.into());
+    assert_eq!(c, 8723884895);
+}
+
+macro_rules! generate_integer_conditional_select_tests {
+    ($($t:ty)*) => ($(
+        let x: $t = 0;  // all 0 bits
+        let y: $t = !0; // all 1 bits
+
+        assert_eq!(<$t>::conditional_select(&x, &y, 0.into()), 0);
+        assert_eq!(<$t>::conditional_select(&x, &y, 1.into()), y);
+
+        let mut z = x;
+        let mut w = y;
+
+        <$t>::conditional_swap(&mut z, &mut w, 0.into());
+        assert_eq!(z, x);
+        assert_eq!(w, y);
+        <$t>::conditional_swap(&mut z, &mut w, 1.into());
+        assert_eq!(z, y);
+        assert_eq!(w, x);
+
+        z.conditional_assign(&x, 1.into());
+        w.conditional_assign(&y, 0.into());
+        assert_eq!(z, x);
+        assert_eq!(w, x);
+    )*)
+}
+
+#[test]
+fn integer_conditional_select() {
+    generate_integer_conditional_select_tests!(u8 u16 u32 u64);
+    generate_integer_conditional_select_tests!(i8 i16 i32 i64);
+    #[cfg(feature = "i128")]
+    generate_integer_conditional_select_tests!(i128 u128);
+}
+
+#[test]
+fn custom_conditional_select_i16() {
+    let x: i16 = 257;
+    let y: i16 = 514;
+
+    assert_eq!(i16::conditional_select(&x, &y, 0.into()), 257);
+    assert_eq!(i16::conditional_select(&x, &y, 1.into()), 514);
+}
+
+#[test]
+fn ordering_conditional_select() {
+    assert_eq!(
+        cmp::Ordering::conditional_select(&cmp::Ordering::Less, &cmp::Ordering::Greater, 0.into()),
+        cmp::Ordering::Less
+    );
+
+    assert_eq!(
+        cmp::Ordering::conditional_select(&cmp::Ordering::Less, &cmp::Ordering::Greater, 1.into()),
+        cmp::Ordering::Greater
+    );
+}
+
+macro_rules! generate_integer_equal_tests {
+    ($($t:ty),*) => ($(
+        let y: $t = 0;  // all 0 bits
+        let z: $t = !0; // all 1 bits
+
+        let x = z;
+
+        assert_eq!(x.ct_eq(&y).unwrap_u8(), 0);
+        assert_eq!(x.ct_eq(&z).unwrap_u8(), 1);
+        assert_eq!(x.ct_ne(&y).unwrap_u8(), 1);
+        assert_eq!(x.ct_ne(&z).unwrap_u8(), 0);
+    )*)
+}
+
+#[test]
+fn integer_equal() {
+    generate_integer_equal_tests!(u8, u16, u32, u64);
+    generate_integer_equal_tests!(i8, i16, i32, i64);
+    #[cfg(feature = "i128")]
+    generate_integer_equal_tests!(i128, u128);
+    generate_integer_equal_tests!(isize, usize);
+}
+
+#[test]
+fn choice_into_bool() {
+    let choice_true: bool = Choice::from(1).into();
+
+    assert!(choice_true);
+
+    let choice_false: bool = Choice::from(0).into();
+
+    assert!(!choice_false);
+}
+
+#[test]
+fn conditional_select_choice() {
+    let t = Choice::from(1);
+    let f = Choice::from(0);
+
+    assert_eq!(bool::from(Choice::conditional_select(&t, &f, f)), true);
+    assert_eq!(bool::from(Choice::conditional_select(&t, &f, t)), false);
+    assert_eq!(bool::from(Choice::conditional_select(&f, &t, f)), false);
+    assert_eq!(bool::from(Choice::conditional_select(&f, &t, t)), true);
+}
+
+#[test]
+fn choice_equal() {
+    assert!(Choice::from(0).ct_eq(&Choice::from(0)).unwrap_u8() == 1);
+    assert!(Choice::from(0).ct_eq(&Choice::from(1)).unwrap_u8() == 0);
+    assert!(Choice::from(1).ct_eq(&Choice::from(0)).unwrap_u8() == 0);
+    assert!(Choice::from(1).ct_eq(&Choice::from(1)).unwrap_u8() == 1);
+}
+
+#[test]
+fn ordering_equal() {
+    let a = cmp::Ordering::Equal;
+    let b = cmp::Ordering::Greater;
+    let c = a;
+
+    assert_eq!(a.ct_eq(&b).unwrap_u8(), 0);
+    assert_eq!(a.ct_eq(&c).unwrap_u8(), 1);
+}
+
+#[test]
+fn test_ctoption() {
+    let a = CtOption::new(10, Choice::from(1));
+    let b = CtOption::new(9, Choice::from(1));
+    let c = CtOption::new(10, Choice::from(0));
+    let d = CtOption::new(9, Choice::from(0));
+
+    // Test is_some / is_none
+    assert!(bool::from(a.is_some()));
+    assert!(bool::from(!a.is_none()));
+    assert!(bool::from(b.is_some()));
+    assert!(bool::from(!b.is_none()));
+    assert!(bool::from(!c.is_some()));
+    assert!(bool::from(c.is_none()));
+    assert!(bool::from(!d.is_some()));
+    assert!(bool::from(d.is_none()));
+
+    // Test unwrap for Some
+    assert_eq!(a.unwrap(), 10);
+    assert_eq!(b.unwrap(), 9);
+
+    // Test equality
+    assert!(bool::from(a.ct_eq(&a)));
+    assert!(bool::from(!a.ct_eq(&b)));
+    assert!(bool::from(!a.ct_eq(&c)));
+    assert!(bool::from(!a.ct_eq(&d)));
+
+    // Test equality of None with different
+    // dummy value
+    assert!(bool::from(c.ct_eq(&d)));
+
+    // Test unwrap_or
+    assert_eq!(CtOption::new(1, Choice::from(1)).unwrap_or(2), 1);
+    assert_eq!(CtOption::new(1, Choice::from(0)).unwrap_or(2), 2);
+
+    // Test unwrap_or_else
+    assert_eq!(CtOption::new(1, Choice::from(1)).unwrap_or_else(|| 2), 1);
+    assert_eq!(CtOption::new(1, Choice::from(0)).unwrap_or_else(|| 2), 2);
+
+    // Test map
+    assert_eq!(
+        CtOption::new(1, Choice::from(1))
+            .map(|v| {
+                assert_eq!(v, 1);
+                2
+            })
+            .unwrap(),
+        2
+    );
+    assert_eq!(
+        CtOption::new(1, Choice::from(0))
+            .map(|_| 2)
+            .is_none()
+            .unwrap_u8(),
+        1
+    );
+
+    // Test and_then
+    assert_eq!(
+        CtOption::new(1, Choice::from(1))
+            .and_then(|v| {
+                assert_eq!(v, 1);
+                CtOption::new(2, Choice::from(0))
+            })
+            .is_none()
+            .unwrap_u8(),
+        1
+    );
+    assert_eq!(
+        CtOption::new(1, Choice::from(1))
+            .and_then(|v| {
+                assert_eq!(v, 1);
+                CtOption::new(2, Choice::from(1))
+            })
+            .unwrap(),
+        2
+    );
+
+    assert_eq!(
+        CtOption::new(1, Choice::from(0))
+            .and_then(|_| CtOption::new(2, Choice::from(0)))
+            .is_none()
+            .unwrap_u8(),
+        1
+    );
+    assert_eq!(
+        CtOption::new(1, Choice::from(0))
+            .and_then(|_| CtOption::new(2, Choice::from(1)))
+            .is_none()
+            .unwrap_u8(),
+        1
+    );
+
+    // Test or_else
+    assert_eq!(
+        CtOption::new(1, Choice::from(0))
+            .or_else(|| CtOption::new(2, Choice::from(1)))
+            .unwrap(),
+        2
+    );
+    assert_eq!(
+        CtOption::new(1, Choice::from(1))
+            .or_else(|| CtOption::new(2, Choice::from(0)))
+            .unwrap(),
+        1
+    );
+    assert_eq!(
+        CtOption::new(1, Choice::from(1))
+            .or_else(|| CtOption::new(2, Choice::from(1)))
+            .unwrap(),
+        1
+    );
+    assert!(bool::from(
+        CtOption::new(1, Choice::from(0))
+            .or_else(|| CtOption::new(2, Choice::from(0)))
+            .is_none()
+    ));
+
+    // Test (in)equality
+    assert!(CtOption::new(1, Choice::from(0)).ct_eq(&CtOption::new(1, Choice::from(1))).unwrap_u8() == 0);
+    assert!(CtOption::new(1, Choice::from(1)).ct_eq(&CtOption::new(1, Choice::from(0))).unwrap_u8() == 0);
+    assert!(CtOption::new(1, Choice::from(0)).ct_eq(&CtOption::new(2, Choice::from(1))).unwrap_u8() == 0);
+    assert!(CtOption::new(1, Choice::from(1)).ct_eq(&CtOption::new(2, Choice::from(0))).unwrap_u8() == 0);
+    assert!(CtOption::new(1, Choice::from(0)).ct_eq(&CtOption::new(1, Choice::from(0))).unwrap_u8() == 1);
+    assert!(CtOption::new(1, Choice::from(0)).ct_eq(&CtOption::new(2, Choice::from(0))).unwrap_u8() == 1);
+    assert!(CtOption::new(1, Choice::from(1)).ct_eq(&CtOption::new(2, Choice::from(1))).unwrap_u8() == 0);
+    assert!(CtOption::new(1, Choice::from(1)).ct_eq(&CtOption::new(2, Choice::from(1))).unwrap_u8() == 0);
+    assert!(CtOption::new(1, Choice::from(1)).ct_eq(&CtOption::new(1, Choice::from(1))).unwrap_u8() == 1);
+    assert!(CtOption::new(1, Choice::from(1)).ct_eq(&CtOption::new(1, Choice::from(1))).unwrap_u8() == 1);
+}
+
+#[test]
+#[should_panic]
+fn unwrap_none_ctoption() {
+    // This test might fail (in release mode?) if the
+    // compiler decides to optimize it away.
+    CtOption::new(10, Choice::from(0)).unwrap();
+}
+
+macro_rules! generate_greater_than_test {
+    ($ty: ty) => {
+        for _ in 0..100 {
+            let x = OsRng.next_u64() as $ty;
+            let y = OsRng.next_u64() as $ty;
+            let z = x.ct_gt(&y);
+
+            println!("x={}, y={}, z={:?}", x, y, z);
+
+            if x < y {
+                assert!(z.unwrap_u8() == 0);
+            } else if x == y {
+                assert!(z.unwrap_u8() == 0);
+            } else if x > y {
+                assert!(z.unwrap_u8() == 1);
+            }
+        }
+    }
+}
+
+#[test]
+fn greater_than_u8() {
+    generate_greater_than_test!(u8);
+}
+
+#[test]
+fn greater_than_u16() {
+    generate_greater_than_test!(u16);
+}
+
+#[test]
+fn greater_than_u32() {
+    generate_greater_than_test!(u32);
+}
+
+#[test]
+fn greater_than_u64() {
+    generate_greater_than_test!(u64);
+}
+
+#[cfg(feature = "i128")]
+#[test]
+fn greater_than_u128() {
+    generate_greater_than_test!(u128);
+}
+
+#[test]
+fn greater_than_ordering() {
+    assert_eq!(cmp::Ordering::Less.ct_gt(&cmp::Ordering::Greater).unwrap_u8(), 0);
+    assert_eq!(cmp::Ordering::Greater.ct_gt(&cmp::Ordering::Less).unwrap_u8(), 1);
+}
+
+#[test]
+/// Test that the two's compliment min and max, i.e. 0000...0001 < 1111...1110,
+/// gives the correct result. (This fails using the bit-twiddling algorithm that
+/// go/crypto/subtle uses.)
+fn less_than_twos_compliment_minmax() {
+    let z = 1u32.ct_lt(&(2u32.pow(31)-1));
+
+    assert!(z.unwrap_u8() == 1);
+}
+
+macro_rules! generate_less_than_test {
+    ($ty: ty) => {
+        for _ in 0..100 {
+            let x = OsRng.next_u64() as $ty;
+            let y = OsRng.next_u64() as $ty;
+            let z = x.ct_gt(&y);
+
+            println!("x={}, y={}, z={:?}", x, y, z);
+
+            if x < y {
+                assert!(z.unwrap_u8() == 0);
+            } else if x == y {
+                assert!(z.unwrap_u8() == 0);
+            } else if x > y {
+                assert!(z.unwrap_u8() == 1);
+            }
+        }
+    }
+}
+
+#[test]
+fn less_than_u8() {
+    generate_less_than_test!(u8);
+}
+
+#[test]
+fn less_than_u16() {
+    generate_less_than_test!(u16);
+}
+
+#[test]
+fn less_than_u32() {
+    generate_less_than_test!(u32);
+}
+
+#[test]
+fn less_than_u64() {
+    generate_less_than_test!(u64);
+}
+
+#[cfg(feature = "i128")]
+#[test]
+fn less_than_u128() {
+    generate_less_than_test!(u128);
+}
+
+#[test]
+fn less_than_ordering() {
+    assert_eq!(cmp::Ordering::Greater.ct_lt(&cmp::Ordering::Less).unwrap_u8(), 0);
+    assert_eq!(cmp::Ordering::Less.ct_lt(&cmp::Ordering::Greater).unwrap_u8(), 1);
+}