Merging upstream version 1.70.0+dfsg2.

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

1 files changed, 811 insertions, 0 deletions

diff --git a/vendor/zeroize/src/lib.rs b/vendor/zeroize/src/lib.rs
new file mode 100644
index 000000000..5ee0f2c96
--- /dev/null
+++ b/vendor/zeroize/src/lib.rs
@@ -0,0 +1,811 @@
+#![no_std]
+#![cfg_attr(docsrs, feature(doc_cfg))]
+#![doc(
+    html_logo_url = "https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg",
+    html_favicon_url = "https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg"
+)]
+#![warn(missing_docs, rust_2018_idioms, unused_qualifications)]
+
+//! Securely zero memory with a simple trait ([`Zeroize`]) built on stable Rust
+//! primitives which guarantee the operation will not be "optimized away".
+//!
+//! ## About
+//!
+//! [Zeroing memory securely is hard] - compilers optimize for performance, and
+//! in doing so they love to "optimize away" unnecessary zeroing calls. There are
+//! many documented "tricks" to attempt to avoid these optimizations and ensure
+//! that a zeroing routine is performed reliably.
+//!
+//! This crate isn't about tricks: it uses [`core::ptr::write_volatile`]
+//! and [`core::sync::atomic`] memory fences to provide easy-to-use, portable
+//! zeroing behavior which works on all of Rust's core number types and slices
+//! thereof, implemented in pure Rust with no usage of FFI or assembly.
+//!
+//! - No insecure fallbacks!
+//! - No dependencies!
+//! - No FFI or inline assembly! **WASM friendly** (and tested)!
+//! - `#![no_std]` i.e. **embedded-friendly**!
+//! - No functionality besides securely zeroing memory!
+//! - (Optional) Custom derive support for zeroing complex structures
+//!
+//! ## Minimum Supported Rust Version
+//!
+//! Requires Rust **1.51** or newer.
+//!
+//! In the future, we reserve the right to change MSRV (i.e. MSRV is out-of-scope
+//! for this crate's SemVer guarantees), however when we do it will be accompanied
+//! by a minor version bump.
+//!
+//! ## Usage
+//!
+//! ```
+//! use zeroize::Zeroize;
+//!
+//! fn main() {
+//!     // Protip: don't embed secrets in your source code.
+//!     // This is just an example.
+//!     let mut secret = b"Air shield password: 1,2,3,4,5".to_vec();
+//!     // [ ... ] open the air shield here
+//!
+//!     // Now that we're done using the secret, zero it out.
+//!     secret.zeroize();
+//! }
+//! ```
+//!
+//! The [`Zeroize`] trait is impl'd on all of Rust's core scalar types including
+//! integers, floats, `bool`, and `char`.
+//!
+//! Additionally, it's implemented on slices and `IterMut`s of the above types.
+//!
+//! When the `alloc` feature is enabled (which it is by default), it's also
+//! impl'd for `Vec<T>` for the above types as well as `String`, where it provides
+//! [`Vec::clear`] / [`String::clear`]-like behavior (truncating to zero-length)
+//! but ensures the backing memory is securely zeroed with some caveats.
+//!
+//! With the `std` feature enabled (which it is **not** by default), [`Zeroize`]
+//! is also implemented for [`CString`]. After calling `zeroize()` on a `CString`,
+//! it will its internal buffer will contain exactly one nul byte. The backing
+//! memory is zeroed by converting it to a `Vec<u8>` and back into a `CString`.
+//! (NOTE: see "Stack/Heap Zeroing Notes" for important `Vec`/`String`/`CString` details)
+//!
+//!
+//! The [`DefaultIsZeroes`] marker trait can be impl'd on types which also
+//! impl [`Default`], which implements [`Zeroize`] by overwriting a value with
+//! the default value.
+//!
+//! ## Custom Derive Support
+//!
+//! This crate has custom derive support for the `Zeroize` trait,
+//! gated under the `zeroize` crate's `zeroize_derive` Cargo feature,
+//! which automatically calls `zeroize()` on all members of a struct
+//! or tuple struct.
+//!
+//! Attributes supported for `Zeroize`:
+//!
+//! On the item level:
+//! - `#[zeroize(drop)]`: *deprecated* use `ZeroizeOnDrop` instead
+//! - `#[zeroize(bound = "T: MyTrait")]`: this replaces any trait bounds
+//!   inferred by zeroize
+//!
+//! On the field level:
+//! - `#[zeroize(skip)]`: skips this field or variant when calling `zeroize()`
+//!
+//! Attributes supported for `ZeroizeOnDrop`:
+//!
+//! On the field level:
+//! - `#[zeroize(skip)]`: skips this field or variant when calling `zeroize()`
+//!
+//! Example which derives `Drop`:
+//!
+//! ```
+//! # #[cfg(feature = "zeroize_derive")]
+//! # {
+//! use zeroize::{Zeroize, ZeroizeOnDrop};
+//!
+//! // This struct will be zeroized on drop
+//! #[derive(Zeroize, ZeroizeOnDrop)]
+//! struct MyStruct([u8; 32]);
+//! # }
+//! ```
+//!
+//! Example which does not derive `Drop` (useful for e.g. `Copy` types)
+//!
+//! ```
+//! #[cfg(feature = "zeroize_derive")]
+//! # {
+//! use zeroize::Zeroize;
+//!
+//! // This struct will *NOT* be zeroized on drop
+//! #[derive(Copy, Clone, Zeroize)]
+//! struct MyStruct([u8; 32]);
+//! # }
+//! ```
+//!
+//! Example which only derives `Drop`:
+//!
+//! ```
+//! # #[cfg(feature = "zeroize_derive")]
+//! # {
+//! use zeroize::ZeroizeOnDrop;
+//!
+//! // This struct will be zeroized on drop
+//! #[derive(ZeroizeOnDrop)]
+//! struct MyStruct([u8; 32]);
+//! # }
+//! ```
+//!
+//! ## `Zeroizing<Z>`: wrapper for zeroizing arbitrary values on drop
+//!
+//! `Zeroizing<Z: Zeroize>` is a generic wrapper type that impls `Deref`
+//! and `DerefMut`, allowing access to an inner value of type `Z`, and also
+//! impls a `Drop` handler which calls `zeroize()` on its contents:
+//!
+//! ```
+//! use zeroize::Zeroizing;
+//!
+//! fn main() {
+//!     let mut secret = Zeroizing::new([0u8; 5]);
+//!
+//!     // Set the air shield password
+//!     // Protip (again): don't embed secrets in your source code.
+//!     secret.copy_from_slice(&[1, 2, 3, 4, 5]);
+//!     assert_eq!(secret.as_ref(), &[1, 2, 3, 4, 5]);
+//!
+//!     // The contents of `secret` will be automatically zeroized on drop
+//! }
+//! ```
+//!
+//! ## What guarantees does this crate provide?
+//!
+//! This crate guarantees the following:
+//!
+//! 1. The zeroing operation can't be "optimized away" by the compiler.
+//! 2. All subsequent reads to memory will see "zeroized" values.
+//!
+//! LLVM's volatile semantics ensure #1 is true.
+//!
+//! Additionally, thanks to work by the [Unsafe Code Guidelines Working Group],
+//! we can now fairly confidently say #2 is true as well. Previously there were
+//! worries that the approach used by this crate (mixing volatile and
+//! non-volatile accesses) was undefined behavior due to language contained
+//! in the documentation for `write_volatile`, however after some discussion
+//! [these remarks have been removed] and the specific usage pattern in this
+//! crate is considered to be well-defined.
+//!
+//! Additionally this crate leverages [`core::sync::atomic::compiler_fence`]
+//! with the strictest ordering
+//! ([`Ordering::SeqCst`]) as a
+//! precaution to help ensure reads are not reordered before memory has been
+//! zeroed.
+//!
+//! All of that said, there is still potential for microarchitectural attacks
+//! (ala Spectre/Meltdown) to leak "zeroized" secrets through covert channels.
+//! This crate makes no guarantees that zeroized values cannot be leaked
+//! through such channels, as they represent flaws in the underlying hardware.
+//!
+//! ## Stack/Heap Zeroing Notes
+//!
+//! This crate can be used to zero values from either the stack or the heap.
+//!
+//! However, be aware several operations in Rust can unintentionally leave
+//! copies of data in memory. This includes but is not limited to:
+//!
+//! - Moves and [`Copy`]
+//! - Heap reallocation when using [`Vec`] and [`String`]
+//! - Borrowers of a reference making copies of the data
+//!
+//! [`Pin`][`core::pin::Pin`] can be leveraged in conjunction with this crate
+//! to ensure data kept on the stack isn't moved.
+//!
+//! The `Zeroize` impls for `Vec`, `String` and `CString` zeroize the entire
+//! capacity of their backing buffer, but cannot guarantee copies of the data
+//! were not previously made by buffer reallocation. It's therefore important
+//! when attempting to zeroize such buffers to initialize them to the correct
+//! capacity, and take care to prevent subsequent reallocation.
+//!
+//! The `secrecy` crate provides higher-level abstractions for eliminating
+//! usage patterns which can cause reallocations:
+//!
+//! <https://crates.io/crates/secrecy>
+//!
+//! ## What about: clearing registers, mlock, mprotect, etc?
+//!
+//! This crate is focused on providing simple, unobtrusive support for reliably
+//! zeroing memory using the best approach possible on stable Rust.
+//!
+//! Clearing registers is a difficult problem that can't easily be solved by
+//! something like a crate, and requires either inline ASM or rustc support.
+//! See <https://github.com/rust-lang/rust/issues/17046> for background on
+//! this particular problem.
+//!
+//! Other memory protection mechanisms are interesting and useful, but often
+//! overkill (e.g. defending against RAM scraping or attackers with swap access).
+//! In as much as there may be merit to these approaches, there are also many
+//! other crates that already implement more sophisticated memory protections.
+//! Such protections are explicitly out-of-scope for this crate.
+//!
+//! Zeroing memory is [good cryptographic hygiene] and this crate seeks to promote
+//! it in the most unobtrusive manner possible. This includes omitting complex
+//! `unsafe` memory protection systems and just trying to make the best memory
+//! zeroing crate available.
+//!
+//! [Zeroing memory securely is hard]: http://www.daemonology.net/blog/2014-09-04-how-to-zero-a-buffer.html
+//! [Unsafe Code Guidelines Working Group]: https://github.com/rust-lang/unsafe-code-guidelines
+//! [these remarks have been removed]: https://github.com/rust-lang/rust/pull/60972
+//! [good cryptographic hygiene]: https://github.com/veorq/cryptocoding#clean-memory-of-secret-data
+//! [`Ordering::SeqCst`]: core::sync::atomic::Ordering::SeqCst
+
+#[cfg(feature = "alloc")]
+extern crate alloc;
+
+#[cfg(feature = "std")]
+extern crate std;
+
+#[cfg(feature = "zeroize_derive")]
+#[cfg_attr(docsrs, doc(cfg(feature = "zeroize_derive")))]
+pub use zeroize_derive::{Zeroize, ZeroizeOnDrop};
+
+#[cfg(all(feature = "aarch64", target_arch = "aarch64"))]
+mod aarch64;
+#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+mod x86;
+
+use core::{
+    marker::{PhantomData, PhantomPinned},
+    mem::{self, MaybeUninit},
+    num::{
+        NonZeroI128, NonZeroI16, NonZeroI32, NonZeroI64, NonZeroI8, NonZeroIsize, NonZeroU128,
+        NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU8, NonZeroUsize,
+    },
+    ops, ptr,
+    slice::IterMut,
+    sync::atomic,
+};
+
+#[cfg(feature = "alloc")]
+use {
+    alloc::{boxed::Box, string::String, vec::Vec},
+    core::slice,
+};
+
+#[cfg(feature = "std")]
+use std::ffi::CString;
+
+/// Trait for securely erasing values from memory.
+pub trait Zeroize {
+    /// Zero out this object from memory using Rust intrinsics which ensure the
+    /// zeroization operation is not "optimized away" by the compiler.
+    fn zeroize(&mut self);
+}
+
+/// Marker trait signifying that this type will [`Zeroize::zeroize`] itself on [`Drop`].
+pub trait ZeroizeOnDrop {}
+
+/// Marker trait for types whose [`Default`] is the desired zeroization result
+pub trait DefaultIsZeroes: Copy + Default + Sized {}
+
+/// Fallible trait for representing cases where zeroization may or may not be
+/// possible.
+///
+/// This is primarily useful for scenarios like reference counted data, where
+/// zeroization is only possible when the last reference is dropped.
+pub trait TryZeroize {
+    /// Try to zero out this object from memory using Rust intrinsics which
+    /// ensure the zeroization operation is not "optimized away" by the
+    /// compiler.
+    #[must_use]
+    fn try_zeroize(&mut self) -> bool;
+}
+
+impl<Z> Zeroize for Z
+where
+    Z: DefaultIsZeroes,
+{
+    fn zeroize(&mut self) {
+        volatile_write(self, Z::default());
+        atomic_fence();
+    }
+}
+
+macro_rules! impl_zeroize_with_default {
+    ($($type:ty),+) => {
+        $(impl DefaultIsZeroes for $type {})+
+    };
+}
+
+#[rustfmt::skip]
+impl_zeroize_with_default! {
+    bool, char,
+    f32, f64,
+    i8, i16, i32, i64, i128, isize,
+    u8, u16, u32, u64, u128, usize
+}
+
+macro_rules! impl_zeroize_for_non_zero {
+    ($($type:ty),+) => {
+        $(
+            impl Zeroize for $type {
+                fn zeroize(&mut self) {
+                    volatile_write(self, unsafe { <$type>::new_unchecked(1) });
+                    atomic_fence();
+                }
+            }
+        )+
+    };
+}
+
+impl_zeroize_for_non_zero!(
+    NonZeroI8,
+    NonZeroI16,
+    NonZeroI32,
+    NonZeroI64,
+    NonZeroI128,
+    NonZeroIsize,
+    NonZeroU8,
+    NonZeroU16,
+    NonZeroU32,
+    NonZeroU64,
+    NonZeroU128,
+    NonZeroUsize
+);
+
+/// Impl [`Zeroize`] on arrays of types that impl [`Zeroize`].
+impl<Z, const N: usize> Zeroize for [Z; N]
+where
+    Z: Zeroize,
+{
+    fn zeroize(&mut self) {
+        self.iter_mut().zeroize();
+    }
+}
+
+/// Impl [`ZeroizeOnDrop`] on arrays of types that impl [`ZeroizeOnDrop`].
+impl<Z, const N: usize> ZeroizeOnDrop for [Z; N] where Z: ZeroizeOnDrop {}
+
+impl<'a, Z> Zeroize for IterMut<'a, Z>
+where
+    Z: Zeroize,
+{
+    fn zeroize(&mut self) {
+        for elem in self {
+            elem.zeroize();
+        }
+    }
+}
+
+impl<Z> Zeroize for Option<Z>
+where
+    Z: Zeroize,
+{
+    fn zeroize(&mut self) {
+        if let Some(value) = self {
+            value.zeroize();
+
+            // Ensures self is None and that the value was dropped. Without the take, the drop
+            // of the (zeroized) value isn't called, which might lead to a leak or other
+            // unexpected behavior. For example, if this were Option<Vec<T>>, the above call to
+            // zeroize would not free the allocated memory, but the the `take` call will.
+            self.take();
+        }
+
+        // Ensure that if the `Option` were previously `Some` but a value was copied/moved out
+        // that the remaining space in the `Option` is zeroized.
+        //
+        // Safety:
+        //
+        // The memory pointed to by `self` is valid for `mem::size_of::<Self>()` bytes.
+        // It is also properly aligned, because `u8` has an alignment of `1`.
+        unsafe {
+            volatile_set(self as *mut _ as *mut u8, 0, mem::size_of::<Self>());
+        }
+
+        // Ensures self is overwritten with the default bit pattern. volatile_write can't be
+        // used because Option<Z> is not copy.
+        //
+        // Safety:
+        //
+        // self is safe to replace with the default, which the take() call above should have
+        // already done semantically. Any value which needed to be dropped will have been
+        // done so by take().
+        unsafe { ptr::write_volatile(self, Option::default()) }
+
+        atomic_fence();
+    }
+}
+
+impl<Z> ZeroizeOnDrop for Option<Z> where Z: ZeroizeOnDrop {}
+
+/// Impl [`Zeroize`] on slices of [`MaybeUninit`] types.
+///
+/// This impl can eventually be optimized using an memset intrinsic,
+/// such as [`core::intrinsics::volatile_set_memory`].
+///
+/// This fills the slice with zeroes.
+///
+/// Note that this ignore invariants that `Z` might have, because
+/// [`MaybeUninit`] removes all invariants.
+impl<Z> Zeroize for [MaybeUninit<Z>] {
+    fn zeroize(&mut self) {
+        let ptr = self.as_mut_ptr() as *mut MaybeUninit<u8>;
+        let size = self.len().checked_mul(mem::size_of::<Z>()).unwrap();
+        assert!(size <= isize::MAX as usize);
+
+        // Safety:
+        //
+        // This is safe, because every valid pointer is well aligned for u8
+        // and it is backed by a single allocated object for at least `self.len() * size_pf::<Z>()` bytes.
+        // and 0 is a valid value for `MaybeUninit<Z>`
+        // The memory of the slice should not wrap around the address space.
+        unsafe { volatile_set(ptr, MaybeUninit::new(0), size) }
+        atomic_fence();
+    }
+}
+
+/// Impl [`Zeroize`] on slices of types that can be zeroized with [`Default`].
+///
+/// This impl can eventually be optimized using an memset intrinsic,
+/// such as [`core::intrinsics::volatile_set_memory`]. For that reason the
+/// blanket impl on slices is bounded by [`DefaultIsZeroes`].
+///
+/// To zeroize a mut slice of `Z: Zeroize` which does not impl
+/// [`DefaultIsZeroes`], call `iter_mut().zeroize()`.
+impl<Z> Zeroize for [Z]
+where
+    Z: DefaultIsZeroes,
+{
+    fn zeroize(&mut self) {
+        assert!(self.len() <= isize::MAX as usize);
+
+        // Safety:
+        //
+        // This is safe, because the slice is well aligned and is backed by a single allocated
+        // object for at least `self.len()` elements of type `Z`.
+        // `self.len()` is also not larger than an `isize`, because of the assertion above.
+        // The memory of the slice should not wrap around the address space.
+        unsafe { volatile_set(self.as_mut_ptr(), Z::default(), self.len()) };
+        atomic_fence();
+    }
+}
+
+/// [`PhantomData`] is always zero sized so provide a [`Zeroize`] implementation.
+impl<Z> Zeroize for PhantomData<Z> {
+    fn zeroize(&mut self) {}
+}
+
+/// [`PhantomData` is always zero sized so provide a ZeroizeOnDrop implementation.
+impl<Z> ZeroizeOnDrop for PhantomData<Z> {}
+
+/// `PhantomPinned` is zero sized so provide a Zeroize implementation.
+impl Zeroize for PhantomPinned {
+    fn zeroize(&mut self) {}
+}
+
+/// `PhantomPinned` is zero sized so provide a ZeroizeOnDrop implementation.
+impl ZeroizeOnDrop for PhantomPinned {}
+
+/// `()` is zero sized so provide a Zeroize implementation.
+impl Zeroize for () {
+    fn zeroize(&mut self) {}
+}
+
+/// `()` is zero sized so provide a ZeroizeOnDrop implementation.
+impl ZeroizeOnDrop for () {}
+
+/// Generic implementation of Zeroize for tuples up to 10 parameters.
+impl<A: Zeroize> Zeroize for (A,) {
+    fn zeroize(&mut self) {
+        self.0.zeroize();
+    }
+}
+
+/// Generic implementation of ZeroizeOnDrop for tuples up to 10 parameters.
+impl<A: ZeroizeOnDrop> ZeroizeOnDrop for (A,) {}
+
+macro_rules! impl_zeroize_tuple {
+    ( $( $type_name:ident ),+ ) => {
+        impl<$($type_name: Zeroize),+> Zeroize for ($($type_name),+) {
+            fn zeroize(&mut self) {
+                #[allow(non_snake_case)]
+                let ($($type_name),+) = self;
+                $($type_name.zeroize());+
+            }
+        }
+
+        impl<$($type_name: ZeroizeOnDrop),+> ZeroizeOnDrop for ($($type_name),+) { }
+    }
+}
+
+// Generic implementations for tuples up to 10 parameters.
+impl_zeroize_tuple!(A, B);
+impl_zeroize_tuple!(A, B, C);
+impl_zeroize_tuple!(A, B, C, D);
+impl_zeroize_tuple!(A, B, C, D, E);
+impl_zeroize_tuple!(A, B, C, D, E, F);
+impl_zeroize_tuple!(A, B, C, D, E, F, G);
+impl_zeroize_tuple!(A, B, C, D, E, F, G, H);
+impl_zeroize_tuple!(A, B, C, D, E, F, G, H, I);
+impl_zeroize_tuple!(A, B, C, D, E, F, G, H, I, J);
+
+#[cfg(feature = "alloc")]
+#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
+impl<Z> Zeroize for Vec<Z>
+where
+    Z: Zeroize,
+{
+    /// "Best effort" zeroization for `Vec`.
+    ///
+    /// Ensures the entire capacity of the `Vec` is zeroed. Cannot ensure that
+    /// previous reallocations did not leave values on the heap.
+    fn zeroize(&mut self) {
+        // Zeroize all the initialized elements.
+        self.iter_mut().zeroize();
+
+        // Set the Vec's length to 0 and drop all the elements.
+        self.clear();
+
+        // Zero the full capacity of `Vec`.
+        // Safety:
+        //
+        // This is safe, because `Vec` never allocates more than `isize::MAX` bytes.
+        // This exact use case is even mentioned in the documentation of `pointer::add`.
+        // This is safe because MaybeUninit ignores all invariants,
+        // so we can create a slice of MaybeUninit<Z> using the full capacity of the Vec
+        let uninit_slice = unsafe {
+            slice::from_raw_parts_mut(self.as_mut_ptr() as *mut MaybeUninit<Z>, self.capacity())
+        };
+
+        uninit_slice.zeroize();
+    }
+}
+
+#[cfg(feature = "alloc")]
+#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
+impl<Z> ZeroizeOnDrop for Vec<Z> where Z: ZeroizeOnDrop {}
+
+#[cfg(feature = "alloc")]
+#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
+impl<Z> Zeroize for Box<[Z]>
+where
+    Z: Zeroize,
+{
+    /// Unlike `Vec`, `Box<[Z]>` cannot reallocate, so we can be sure that we are not leaving
+    /// values on the heap.
+    fn zeroize(&mut self) {
+        self.iter_mut().zeroize();
+    }
+}
+
+#[cfg(feature = "alloc")]
+#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
+impl<Z> ZeroizeOnDrop for Box<[Z]> where Z: ZeroizeOnDrop {}
+
+#[cfg(feature = "alloc")]
+#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
+impl Zeroize for String {
+    fn zeroize(&mut self) {
+        unsafe { self.as_mut_vec() }.zeroize();
+    }
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+impl Zeroize for CString {
+    fn zeroize(&mut self) {
+        // mem::take uses replace internally to swap the pointer
+        // Unfortunately this results in an allocation for a Box::new(&[0]) as CString must
+        // contain a trailing zero byte
+        let this = mem::take(self);
+
+        // - CString::into_bytes calls ::into_vec which takes ownership of the heap pointer
+        // as a Vec<u8>
+        // - Calling .zeroize() on the resulting vector clears out the bytes
+        // From: https://github.com/RustCrypto/utils/pull/759#issuecomment-1087976570
+        let mut buf = this.into_bytes();
+        buf.zeroize();
+
+        // expect() should never fail, because zeroize() truncates the Vec
+        let zeroed = CString::new(buf).expect("buf not truncated");
+
+        // Replace self by the zeroed CString to maintain the original ptr of the buffer
+        let _ = mem::replace(self, zeroed);
+    }
+}
+
+/// `Zeroizing` is a a wrapper for any `Z: Zeroize` type which implements a
+/// `Drop` handler which zeroizes dropped values.
+#[derive(Debug, Default, Eq, PartialEq)]
+pub struct Zeroizing<Z: Zeroize>(Z);
+
+impl<Z> Zeroizing<Z>
+where
+    Z: Zeroize,
+{
+    /// Move value inside a `Zeroizing` wrapper which ensures it will be
+    /// zeroized when it's dropped.
+    #[inline(always)]
+    pub fn new(value: Z) -> Self {
+        Self(value)
+    }
+}
+
+impl<Z: Zeroize + Clone> Clone for Zeroizing<Z> {
+    #[inline(always)]
+    fn clone(&self) -> Self {
+        Self(self.0.clone())
+    }
+
+    #[inline(always)]
+    fn clone_from(&mut self, source: &Self) {
+        self.0.zeroize();
+        self.0.clone_from(&source.0);
+    }
+}
+
+impl<Z> From<Z> for Zeroizing<Z>
+where
+    Z: Zeroize,
+{
+    #[inline(always)]
+    fn from(value: Z) -> Zeroizing<Z> {
+        Zeroizing(value)
+    }
+}
+
+impl<Z> ops::Deref for Zeroizing<Z>
+where
+    Z: Zeroize,
+{
+    type Target = Z;
+
+    #[inline(always)]
+    fn deref(&self) -> &Z {
+        &self.0
+    }
+}
+
+impl<Z> ops::DerefMut for Zeroizing<Z>
+where
+    Z: Zeroize,
+{
+    #[inline(always)]
+    fn deref_mut(&mut self) -> &mut Z {
+        &mut self.0
+    }
+}
+
+impl<T, Z> AsRef<T> for Zeroizing<Z>
+where
+    T: ?Sized,
+    Z: AsRef<T> + Zeroize,
+{
+    #[inline(always)]
+    fn as_ref(&self) -> &T {
+        self.0.as_ref()
+    }
+}
+
+impl<T, Z> AsMut<T> for Zeroizing<Z>
+where
+    T: ?Sized,
+    Z: AsMut<T> + Zeroize,
+{
+    #[inline(always)]
+    fn as_mut(&mut self) -> &mut T {
+        self.0.as_mut()
+    }
+}
+
+impl<Z> Zeroize for Zeroizing<Z>
+where
+    Z: Zeroize,
+{
+    fn zeroize(&mut self) {
+        self.0.zeroize();
+    }
+}
+
+impl<Z> ZeroizeOnDrop for Zeroizing<Z> where Z: Zeroize {}
+
+impl<Z> Drop for Zeroizing<Z>
+where
+    Z: Zeroize,
+{
+    fn drop(&mut self) {
+        self.0.zeroize()
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<Z> serde::Serialize for Zeroizing<Z>
+where
+    Z: Zeroize + serde::Serialize,
+{
+    #[inline(always)]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        self.0.serialize(serializer)
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<'de, Z> serde::Deserialize<'de> for Zeroizing<Z>
+where
+    Z: Zeroize + serde::Deserialize<'de>,
+{
+    #[inline(always)]
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        Ok(Self(Z::deserialize(deserializer)?))
+    }
+}
+
+/// Use fences to prevent accesses from being reordered before this
+/// point, which should hopefully help ensure that all accessors
+/// see zeroes after this point.
+#[inline(always)]
+fn atomic_fence() {
+    atomic::compiler_fence(atomic::Ordering::SeqCst);
+}
+
+/// Perform a volatile write to the destination
+#[inline(always)]
+fn volatile_write<T: Copy + Sized>(dst: &mut T, src: T) {
+    unsafe { ptr::write_volatile(dst, src) }
+}
+
+/// Perform a volatile `memset` operation which fills a slice with a value
+///
+/// Safety:
+/// The memory pointed to by `dst` must be a single allocated object that is valid for `count`
+/// contiguous elements of `T`.
+/// `count` must not be larger than an `isize`.
+/// `dst` being offset by `mem::size_of::<T> * count` bytes must not wrap around the address space.
+/// Also `dst` must be properly aligned.
+#[inline(always)]
+unsafe fn volatile_set<T: Copy + Sized>(dst: *mut T, src: T, count: usize) {
+    // TODO(tarcieri): use `volatile_set_memory` when stabilized
+    for i in 0..count {
+        // Safety:
+        //
+        // This is safe because there is room for at least `count` objects of type `T` in the
+        // allocation pointed to by `dst`, because `count <= isize::MAX` and because
+        // `dst.add(count)` must not wrap around the address space.
+        let ptr = dst.add(i);
+
+        // Safety:
+        //
+        // This is safe, because the pointer is valid and because `dst` is well aligned for `T` and
+        // `ptr` is an offset of `dst` by a multiple of `mem::size_of::<T>()` bytes.
+        ptr::write_volatile(ptr, src);
+    }
+}
+
+/// Internal module used as support for `AssertZeroizeOnDrop`.
+#[doc(hidden)]
+pub mod __internal {
+    use super::*;
+
+    /// Auto-deref workaround for deriving `ZeroizeOnDrop`.
+    pub trait AssertZeroizeOnDrop {
+        fn zeroize_or_on_drop(self);
+    }
+
+    impl<T: ZeroizeOnDrop + ?Sized> AssertZeroizeOnDrop for &&mut T {
+        fn zeroize_or_on_drop(self) {}
+    }
+
+    /// Auto-deref workaround for deriving `ZeroizeOnDrop`.
+    pub trait AssertZeroize {
+        fn zeroize_or_on_drop(&mut self);
+    }
+
+    impl<T: Zeroize + ?Sized> AssertZeroize for T {
+        fn zeroize_or_on_drop(&mut self) {
+            self.zeroize()
+        }
+    }
+}