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171 lines
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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Securely zero memory with a simple trait (`Zeroize`) built on stable Rust primitives which guarantee the operation will not be “optimized away”."><title>zeroize - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-6b053e98.ttf.woff2,FiraSans-Italic-81dc35de.woff2,FiraSans-Regular-0fe48ade.woff2,FiraSans-MediumItalic-ccf7e434.woff2,FiraSans-Medium-e1aa3f0a.woff2,SourceCodePro-Regular-8badfe75.ttf.woff2,SourceCodePro-Semibold-aa29a496.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2"href="../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../static.files/normalize-9960930a.css"><link rel="stylesheet" href="../static.files/rustdoc-ca0dd0c4.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="zeroize" data-themes="" data-resource-suffix="" data-rustdoc-version="1.93.1 (01f6ddf75 2026-02-11) (Arch Linux rust 1:1.93.1-1)" data-channel="1.93.1" data-search-js="search-9e2438ea.js" data-stringdex-js="stringdex-a3946164.js" data-settings-js="settings-c38705f0.js" ><script src="../static.files/storage-e2aeef58.js"></script><script defer src="../crates.js"></script><script defer src="../static.files/main-a410ff4d.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-263c88ec.css"></noscript><link rel="icon" href="https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg"></head><body class="rustdoc mod crate"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><rustdoc-topbar><h2><a href="#">Crate zeroize</a></h2></rustdoc-topbar><nav class="sidebar"><div class="sidebar-crate"><a class="logo-container" href="../zeroize/index.html"><img src="https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg" alt="logo"></a><h2><a href="../zeroize/index.html">zeroize</a><span class="version">1.8.2</span></h2></div><div class="sidebar-elems"><ul class="block"><li><a id="all-types" href="all.html">All Items</a></li></ul><section id="rustdoc-toc"><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#about" title="About">About</a></li><li><a href="#minimum-supported-rust-version" title="Minimum Supported Rust Version">Minimum Supported Rust Version</a></li><li><a href="#usage" title="Usage">Usage</a></li><li><a href="#custom-derive-support" title="Custom Derive Support">Custom Derive Support</a></li><li><a href="#zeroizingz-wrapper-for-zeroizing-arbitrary-values-on-drop" title="`Zeroizing<Z>`: wrapper for zeroizing arbitrary values on drop"><code>Zeroizing<Z></code>: wrapper for zeroizing arbitrary values on drop</a></li><li><a href="#what-guarantees-does-this-crate-provide" title="What guarantees does this crate provide?">What guarantees does this crate provide?</a></li><li><a href="#stackheap-zeroing-notes" title="Stack/Heap Zeroing Notes">Stack/Heap Zeroing Notes</a></li><li><a href="#what-about-clearing-registers-mlock-mprotect-etc" title="What about: clearing registers, mlock, mprotect, etc?">What about: clearing registers, mlock, mprotect, etc?</a></li></ul><h3><a href="#structs">Crate Items</a></h3><ul class="block"><li><a href="#structs" title="Structs">Structs</a></li><li><a href="#traits" title="Traits">Traits</a></li><li><a href="#functions" title="Functions">Functions</a></li></ul></section><div id="rustdoc-modnav"></div></div></nav><div class="sidebar-resizer" title="Drag to resize sidebar"></div><main><div class="width-limiter"><section id="main-content" class="content"><div class="main-heading"><h1>Crate <span>zeroize</span> <button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><rustdoc-toolbar></rustdoc-toolbar><span class="sub-heading"><a class="src" href="../src/zeroize/lib.rs.html#1-875">Source</a> </span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Securely zero memory with a simple trait (<a href="trait.Zeroize.html" title="trait zeroize::Zeroize"><code>Zeroize</code></a>) built on stable Rust
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primitives which guarantee the operation will not be “optimized away”.</p>
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<h3 id="about"><a class="doc-anchor" href="#about">§</a>About</h3>
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<p><a href="http://www.daemonology.net/blog/2014-09-04-how-to-zero-a-buffer.html">Zeroing memory securely is hard</a> - compilers optimize for performance, and
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in doing so they love to “optimize away” unnecessary zeroing calls. There are
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many documented “tricks” to attempt to avoid these optimizations and ensure
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that a zeroing routine is performed reliably.</p>
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<p>This crate isn’t about tricks: it uses <a href="https://doc.rust-lang.org/1.93.1/core/ptr/fn.write_volatile.html" title="fn core::ptr::write_volatile"><code>core::ptr::write_volatile</code></a>
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and <a href="https://doc.rust-lang.org/1.93.1/core/sync/atomic/index.html" title="mod core::sync::atomic"><code>core::sync::atomic</code></a> memory fences to provide easy-to-use, portable
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zeroing behavior which works on all of Rust’s core number types and slices
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thereof, implemented in pure Rust with no usage of FFI or assembly.</p>
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<ul>
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<li>No insecure fallbacks!</li>
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<li>No dependencies!</li>
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<li>No FFI or inline assembly! <strong>WASM friendly</strong> (and tested)!</li>
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<li><code>#![no_std]</code> i.e. <strong>embedded-friendly</strong>!</li>
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<li>No functionality besides securely zeroing memory!</li>
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<li>(Optional) Custom derive support for zeroing complex structures</li>
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</ul>
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<h3 id="minimum-supported-rust-version"><a class="doc-anchor" href="#minimum-supported-rust-version">§</a>Minimum Supported Rust Version</h3>
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<p>Requires Rust <strong>1.72</strong> or newer.</p>
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<p>In the future, we reserve the right to change MSRV (i.e. MSRV is out-of-scope
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for this crate’s SemVer guarantees), however when we do it will be accompanied
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by a minor version bump.</p>
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<h3 id="usage"><a class="doc-anchor" href="#usage">§</a>Usage</h3>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>zeroize::Zeroize;
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<span class="comment">// Protip: don't embed secrets in your source code.
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// This is just an example.
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</span><span class="kw">let </span><span class="kw-2">mut </span>secret = <span class="string">b"Air shield password: 1,2,3,4,5"</span>.to_vec();
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<span class="comment">// [ ... ] open the air shield here
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// Now that we're done using the secret, zero it out.
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</span>secret.zeroize();</code></pre></div>
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<p>The <a href="trait.Zeroize.html" title="trait zeroize::Zeroize"><code>Zeroize</code></a> trait is impl’d on all of Rust’s core scalar types including
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integers, floats, <code>bool</code>, and <code>char</code>.</p>
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<p>Additionally, it’s implemented on slices and <code>IterMut</code>s of the above types.</p>
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<p>When the <code>alloc</code> feature is enabled (which it is by default), it’s also
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impl’d for <code>Vec<T></code> for the above types as well as <code>String</code>, where it provides
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<a href="https://doc.rust-lang.org/1.93.1/alloc/vec/struct.Vec.html#method.clear" title="method alloc::vec::Vec::clear"><code>Vec::clear</code></a> / <a href="https://doc.rust-lang.org/1.93.1/alloc/string/struct.String.html#method.clear" title="method alloc::string::String::clear"><code>String::clear</code></a>-like behavior (truncating to zero-length)
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but ensures the backing memory is securely zeroed with some caveats.</p>
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<p>With the <code>std</code> feature enabled (which it is <strong>not</strong> by default), <a href="trait.Zeroize.html" title="trait zeroize::Zeroize"><code>Zeroize</code></a>
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is also implemented for <a href="https://doc.rust-lang.org/std/ffi/struct.CString.html"><code>CString</code></a>. After calling <code>zeroize()</code> on a <code>CString</code>,
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its internal buffer will contain exactly one nul byte. The backing
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memory is zeroed by converting it to a <code>Vec<u8></code> and back into a <code>CString</code>.
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(NOTE: see “Stack/Heap Zeroing Notes” for important <code>Vec</code>/<code>String</code>/<code>CString</code> details)</p>
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<p>The <a href="trait.DefaultIsZeroes.html" title="trait zeroize::DefaultIsZeroes"><code>DefaultIsZeroes</code></a> marker trait can be impl’d on types which also
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impl <a href="https://doc.rust-lang.org/1.93.1/core/default/trait.Default.html" title="trait core::default::Default"><code>Default</code></a>, which implements <a href="trait.Zeroize.html" title="trait zeroize::Zeroize"><code>Zeroize</code></a> by overwriting a value with
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the default value.</p>
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<h3 id="custom-derive-support"><a class="doc-anchor" href="#custom-derive-support">§</a>Custom Derive Support</h3>
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<p>This crate has custom derive support for the <code>Zeroize</code> trait,
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gated under the <code>zeroize</code> crate’s <code>zeroize_derive</code> Cargo feature,
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which automatically calls <code>zeroize()</code> on all members of a struct
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or tuple struct.</p>
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<p>Attributes supported for <code>Zeroize</code>:</p>
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<p>On the item level:</p>
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<ul>
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<li><code>#[zeroize(drop)]</code>: <em>deprecated</em> use <code>ZeroizeOnDrop</code> instead</li>
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<li><code>#[zeroize(bound = "T: MyTrait")]</code>: this replaces any trait bounds
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inferred by zeroize</li>
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</ul>
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<p>On the field level:</p>
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<ul>
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<li><code>#[zeroize(skip)]</code>: skips this field or variant when calling <code>zeroize()</code></li>
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</ul>
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<p>Attributes supported for <code>ZeroizeOnDrop</code>:</p>
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<p>On the field level:</p>
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<ul>
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<li><code>#[zeroize(skip)]</code>: skips this field or variant when calling <code>zeroize()</code></li>
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</ul>
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<p>Example which derives <code>Drop</code>:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>zeroize::{Zeroize, ZeroizeOnDrop};
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<span class="comment">// This struct will be zeroized on drop
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</span><span class="attr">#[derive(Zeroize, ZeroizeOnDrop)]
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</span><span class="kw">struct </span>MyStruct([u8; <span class="number">32</span>]);</code></pre></div>
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<p>Example which does not derive <code>Drop</code> (useful for e.g. <code>Copy</code> types)</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[cfg(feature = <span class="string">"zeroize_derive"</span>)]
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</span><span class="kw">use </span>zeroize::Zeroize;
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<span class="comment">// This struct will *NOT* be zeroized on drop
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</span><span class="attr">#[derive(Copy, Clone, Zeroize)]
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</span><span class="kw">struct </span>MyStruct([u8; <span class="number">32</span>]);</code></pre></div>
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<p>Example which only derives <code>Drop</code>:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>zeroize::ZeroizeOnDrop;
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<span class="comment">// This struct will be zeroized on drop
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</span><span class="attr">#[derive(ZeroizeOnDrop)]
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</span><span class="kw">struct </span>MyStruct([u8; <span class="number">32</span>]);</code></pre></div><h3 id="zeroizingz-wrapper-for-zeroizing-arbitrary-values-on-drop"><a class="doc-anchor" href="#zeroizingz-wrapper-for-zeroizing-arbitrary-values-on-drop">§</a><code>Zeroizing<Z></code>: wrapper for zeroizing arbitrary values on drop</h3>
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<p><code>Zeroizing<Z: Zeroize></code> is a generic wrapper type that impls <code>Deref</code>
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and <code>DerefMut</code>, allowing access to an inner value of type <code>Z</code>, and also
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impls a <code>Drop</code> handler which calls <code>zeroize()</code> on its contents:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>zeroize::Zeroizing;
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<span class="kw">fn </span>use_secret() {
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<span class="kw">let </span><span class="kw-2">mut </span>secret = Zeroizing::new([<span class="number">0u8</span>; <span class="number">5</span>]);
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<span class="comment">// Set the air shield password
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// Protip (again): don't embed secrets in your source code.
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</span>secret.copy_from_slice(<span class="kw-2">&</span>[<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>]);
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<span class="macro">assert_eq!</span>(secret.as_ref(), <span class="kw-2">&</span>[<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>]);
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<span class="comment">// The contents of `secret` will be automatically zeroized on drop
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</span>}
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</code></pre></div><h3 id="what-guarantees-does-this-crate-provide"><a class="doc-anchor" href="#what-guarantees-does-this-crate-provide">§</a>What guarantees does this crate provide?</h3>
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<p>This crate guarantees the following:</p>
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<ol>
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<li>The zeroing operation can’t be “optimized away” by the compiler.</li>
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<li>All subsequent reads to memory will see “zeroized” values.</li>
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</ol>
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<p>LLVM’s volatile semantics ensure #1 is true.</p>
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<p>Additionally, thanks to work by the <a href="https://github.com/rust-lang/unsafe-code-guidelines">Unsafe Code Guidelines Working Group</a>,
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we can now fairly confidently say #2 is true as well. Previously there were
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worries that the approach used by this crate (mixing volatile and
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non-volatile accesses) was undefined behavior due to language contained
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in the documentation for <code>write_volatile</code>, however after some discussion
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<a href="https://github.com/rust-lang/rust/pull/60972">these remarks have been removed</a> and the specific usage pattern in this
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crate is considered to be well-defined.</p>
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<p>Additionally this crate leverages <a href="https://doc.rust-lang.org/1.93.1/core/sync/atomic/fn.compiler_fence.html" title="fn core::sync::atomic::compiler_fence"><code>core::sync::atomic::compiler_fence</code></a>
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with the strictest ordering
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(<a href="https://doc.rust-lang.org/1.93.1/core/sync/atomic/enum.Ordering.html#variant.SeqCst" title="variant core::sync::atomic::Ordering::SeqCst"><code>Ordering::SeqCst</code></a>) as a
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precaution to help ensure reads are not reordered before memory has been
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zeroed.</p>
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<p>All of that said, there is still potential for microarchitectural attacks
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(ala Spectre/Meltdown) to leak “zeroized” secrets through covert channels.
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This crate makes no guarantees that zeroized values cannot be leaked
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through such channels, as they represent flaws in the underlying hardware.</p>
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<h3 id="stackheap-zeroing-notes"><a class="doc-anchor" href="#stackheap-zeroing-notes">§</a>Stack/Heap Zeroing Notes</h3>
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<p>This crate can be used to zero values from either the stack or the heap.</p>
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<p>However, be aware several operations in Rust can unintentionally leave
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copies of data in memory. This includes but is not limited to:</p>
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<ul>
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<li>Moves and <a href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Copy.html" title="trait core::marker::Copy"><code>Copy</code></a></li>
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<li>Heap reallocation when using <a href="https://doc.rust-lang.org/1.93.1/alloc/vec/struct.Vec.html" title="struct alloc::vec::Vec"><code>Vec</code></a> and <a href="https://doc.rust-lang.org/1.93.1/alloc/string/struct.String.html" title="struct alloc::string::String"><code>String</code></a></li>
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<li>Borrowers of a reference making copies of the data</li>
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</ul>
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<p><a href="https://doc.rust-lang.org/1.93.1/core/pin/struct.Pin.html" title="struct core::pin::Pin"><code>Pin</code></a> can be leveraged in conjunction with this crate
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to ensure data kept on the stack isn’t moved.</p>
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<p>The <code>Zeroize</code> impls for <code>Vec</code>, <code>String</code> and <code>CString</code> zeroize the entire
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capacity of their backing buffer, but cannot guarantee copies of the data
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were not previously made by buffer reallocation. It’s therefore important
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when attempting to zeroize such buffers to initialize them to the correct
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capacity, and take care to prevent subsequent reallocation.</p>
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<p>The <code>secrecy</code> crate provides higher-level abstractions for eliminating
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usage patterns which can cause reallocations:</p>
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<p><a href="https://crates.io/crates/secrecy">https://crates.io/crates/secrecy</a></p>
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<h3 id="what-about-clearing-registers-mlock-mprotect-etc"><a class="doc-anchor" href="#what-about-clearing-registers-mlock-mprotect-etc">§</a>What about: clearing registers, mlock, mprotect, etc?</h3>
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<p>This crate is focused on providing simple, unobtrusive support for reliably
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zeroing memory using the best approach possible on stable Rust.</p>
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<p>Clearing registers is a difficult problem that can’t easily be solved by
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something like a crate, and requires either inline ASM or rustc support.
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See <a href="https://github.com/rust-lang/rust/issues/17046">https://github.com/rust-lang/rust/issues/17046</a> for background on
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this particular problem.</p>
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<p>Other memory protection mechanisms are interesting and useful, but often
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overkill (e.g. defending against RAM scraping or attackers with swap access).
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In as much as there may be merit to these approaches, there are also many
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other crates that already implement more sophisticated memory protections.
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Such protections are explicitly out-of-scope for this crate.</p>
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<p>Zeroing memory is <a href="https://github.com/veorq/cryptocoding#clean-memory-of-secret-data">good cryptographic hygiene</a> and this crate seeks to promote
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it in the most unobtrusive manner possible. This includes omitting complex
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<code>unsafe</code> memory protection systems and just trying to make the best memory
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zeroing crate available.</p>
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</div></details><h2 id="structs" class="section-header">Structs<a href="#structs" class="anchor">§</a></h2><dl class="item-table"><dt><a class="struct" href="struct.Zeroizing.html" title="struct zeroize::Zeroizing">Zeroizing</a></dt><dd><code>Zeroizing</code> is a a wrapper for any <code>Z: Zeroize</code> type which implements a
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<code>Drop</code> handler which zeroizes dropped values.</dd></dl><h2 id="traits" class="section-header">Traits<a href="#traits" class="anchor">§</a></h2><dl class="item-table"><dt><a class="trait" href="trait.DefaultIsZeroes.html" title="trait zeroize::DefaultIsZeroes">Default<wbr>IsZeroes</a></dt><dd>Marker trait for types whose <a href="https://doc.rust-lang.org/1.93.1/core/default/trait.Default.html" title="trait core::default::Default"><code>Default</code></a> is the desired zeroization result</dd><dt><a class="trait" href="trait.TryZeroize.html" title="trait zeroize::TryZeroize">TryZeroize</a></dt><dd>Fallible trait for representing cases where zeroization may or may not be
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possible.</dd><dt><a class="trait" href="trait.Zeroize.html" title="trait zeroize::Zeroize">Zeroize</a></dt><dd>Trait for securely erasing values from memory.</dd><dt><a class="trait" href="trait.ZeroizeOnDrop.html" title="trait zeroize::ZeroizeOnDrop">Zeroize<wbr>OnDrop</a></dt><dd>Marker trait signifying that this type will <a href="trait.Zeroize.html#tymethod.zeroize" title="method zeroize::Zeroize::zeroize"><code>Zeroize::zeroize</code></a> itself on <a href="https://doc.rust-lang.org/1.93.1/core/ops/drop/trait.Drop.html" title="trait core::ops::drop::Drop"><code>Drop</code></a>.</dd></dl><h2 id="functions" class="section-header">Functions<a href="#functions" class="anchor">§</a></h2><dl class="item-table"><dt><a class="fn" href="fn.zeroize_flat_type.html" title="fn zeroize::zeroize_flat_type">zeroize_<wbr>flat_<wbr>type</a><sup title="unsafe function">⚠</sup></dt><dd>Zeroizes a flat type/struct. Only zeroizes the values that it owns, and it does not work on
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dynamically sized values or trait objects. It would be inefficient to use this function on a
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type that already implements <code>ZeroizeOnDrop</code>.</dd></dl></section></div></main></body></html> |