| <!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="Random number generators and adapters"><meta name="keywords" content="rust, rustlang, rust-lang, rngs"><title>rand::rngs - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../ayu.css" disabled><link rel="stylesheet" type="text/css" href="../../dark.css" disabled><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../storage.js"></script><script src="../../crates.js"></script><script defer src="../../main.js"></script> |
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| </a><h2 class="location">Module rngs</h2><div class="sidebar-elems"><div class="block items"><ul><li><a href="#modules">Modules</a></li><li><a href="#structs">Structs</a></li></ul></div><div id="sidebar-vars" data-name="rngs" data-ty="mod" data-relpath="./"></div><script defer src="./sidebar-items.js"></script></div></nav><main><div class="width-limiter"><div class="sub-container"><a class="sub-logo-container" href="../../rand/index.html"><img src="https://www.rust-lang.org/logos/rust-logo-128x128-blk.png" alt="logo"></a><nav class="sub"><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!" aria-haspopup="menu" title="themes"><img width="18" height="18" alt="Pick another theme!" src="../../brush.svg"></button><div id="theme-choices" role="menu"></div></div><form class="search-form"><div class="search-container"><div> |
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| <details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Random number generators and adapters</p> |
| <h3 id="background-random-number-generators-rngs" class="section-header"><a href="#background-random-number-generators-rngs">Background: Random number generators (RNGs)</a></h3> |
| <p>Computers cannot produce random numbers from nowhere. We classify |
| random number generators as follows:</p> |
| <ul> |
| <li>“True” random number generators (TRNGs) use hard-to-predict data sources |
| (e.g. the high-resolution parts of event timings and sensor jitter) to |
| harvest random bit-sequences, apply algorithms to remove bias and |
| estimate available entropy, then combine these bits into a byte-sequence |
| or an entropy pool. This job is usually done by the operating system or |
| a hardware generator (HRNG).</li> |
| <li>“Pseudo”-random number generators (PRNGs) use algorithms to transform a |
| seed into a sequence of pseudo-random numbers. These generators can be |
| fast and produce well-distributed unpredictable random numbers (or not). |
| They are usually deterministic: given algorithm and seed, the output |
| sequence can be reproduced. They have finite period and eventually loop; |
| with many algorithms this period is fixed and can be proven sufficiently |
| long, while others are chaotic and the period depends on the seed.</li> |
| <li>“Cryptographically secure” pseudo-random number generators (CSPRNGs) |
| are the sub-set of PRNGs which are secure. Security of the generator |
| relies both on hiding the internal state and using a strong algorithm.</li> |
| </ul> |
| <h3 id="traits-and-functionality" class="section-header"><a href="#traits-and-functionality">Traits and functionality</a></h3> |
| <p>All RNGs implement the <a href="../trait.RngCore.html"><code>RngCore</code></a> trait, as a consequence of which the |
| <a href="../trait.Rng.html"><code>Rng</code></a> extension trait is automatically implemented. Secure RNGs may |
| additionally implement the <a href="../trait.CryptoRng.html"><code>CryptoRng</code></a> trait.</p> |
| <p>All PRNGs require a seed to produce their random number sequence. The |
| <a href="../trait.SeedableRng.html"><code>SeedableRng</code></a> trait provides three ways of constructing PRNGs:</p> |
| <ul> |
| <li><code>from_seed</code> accepts a type specific to the PRNG</li> |
| <li><code>from_rng</code> allows a PRNG to be seeded from any other RNG</li> |
| <li><code>seed_from_u64</code> allows any PRNG to be seeded from a <code>u64</code> insecurely</li> |
| <li><code>from_entropy</code> securely seeds a PRNG from fresh entropy</li> |
| </ul> |
| <p>Use the <a href="../../rand_core/index.html" title="rand_core"><code>rand_core</code></a> crate when implementing your own RNGs.</p> |
| <h3 id="our-generators" class="section-header"><a href="#our-generators">Our generators</a></h3> |
| <p>This crate provides several random number generators:</p> |
| <ul> |
| <li><a href="struct.OsRng.html" title="OsRng"><code>OsRng</code></a> is an interface to the operating system’s random number |
| source. Typically the operating system uses a CSPRNG with entropy |
| provided by a TRNG and some type of on-going re-seeding.</li> |
| <li><a href="struct.ThreadRng.html" title="ThreadRng"><code>ThreadRng</code></a>, provided by the <a href="../fn.thread_rng.html"><code>thread_rng</code></a> function, is a handle to a |
| thread-local CSPRNG with periodic seeding from <a href="struct.OsRng.html" title="OsRng"><code>OsRng</code></a>. Because this |
| is local, it is typically much faster than <a href="struct.OsRng.html" title="OsRng"><code>OsRng</code></a>. It should be |
| secure, though the paranoid may prefer <a href="struct.OsRng.html" title="OsRng"><code>OsRng</code></a>.</li> |
| <li><a href="struct.StdRng.html" title="StdRng"><code>StdRng</code></a> is a CSPRNG chosen for good performance and trust of security |
| (based on reviews, maturity and usage). The current algorithm is ChaCha12, |
| which is well established and rigorously analysed. |
| <a href="struct.StdRng.html" title="StdRng"><code>StdRng</code></a> provides the algorithm used by <a href="struct.ThreadRng.html" title="ThreadRng"><code>ThreadRng</code></a> but without |
| periodic reseeding.</li> |
| <li><a href="struct.SmallRng.html" title="SmallRng"><code>SmallRng</code></a> is an <strong>insecure</strong> PRNG designed to be fast, simple, require |
| little memory, and have good output quality.</li> |
| </ul> |
| <p>The algorithms selected for <a href="struct.StdRng.html" title="StdRng"><code>StdRng</code></a> and <a href="struct.SmallRng.html" title="SmallRng"><code>SmallRng</code></a> may change in any |
| release and may be platform-dependent, therefore they should be considered |
| <strong>not reproducible</strong>.</p> |
| <h3 id="additional-generators" class="section-header"><a href="#additional-generators">Additional generators</a></h3> |
| <p><strong>TRNGs</strong>: The <a href="https://crates.io/crates/rdrand"><code>rdrand</code></a> crate provides an interface to the RDRAND and |
| RDSEED instructions available in modern Intel and AMD CPUs. |
| The <a href="https://crates.io/crates/rand_jitter"><code>rand_jitter</code></a> crate provides a user-space implementation of |
| entropy harvesting from CPU timer jitter, but is very slow and has |
| <a href="https://github.com/rust-random/rand/issues/699">security issues</a>.</p> |
| <p><strong>PRNGs</strong>: Several companion crates are available, providing individual or |
| families of PRNG algorithms. These provide the implementations behind |
| <a href="struct.StdRng.html" title="StdRng"><code>StdRng</code></a> and <a href="struct.SmallRng.html" title="SmallRng"><code>SmallRng</code></a> but can also be used directly, indeed <em>should</em> |
| be used directly when <strong>reproducibility</strong> matters. |
| Some suggestions are: <a href="https://crates.io/crates/rand_chacha"><code>rand_chacha</code></a>, <a href="https://crates.io/crates/rand_pcg"><code>rand_pcg</code></a>, <a href="https://crates.io/crates/rand_xoshiro"><code>rand_xoshiro</code></a>. |
| A full list can be found by searching for crates with the <a href="https://crates.io/keywords/rng"><code>rng</code> tag</a>.</p> |
| </div></details><h2 id="modules" class="small-section-header"><a href="#modules">Modules</a></h2> |
| <div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="mod" href="adapter/index.html" title="rand::rngs::adapter mod">adapter</a><span class="stab portability" title="This is supported on crate feature `std` only"><code>std</code></span></div><div class="item-right docblock-short"><p>Wrappers / adapters forming RNGs</p> |
| </div></div><div class="item-row"><div class="item-left module-item"><a class="mod" href="mock/index.html" title="rand::rngs::mock mod">mock</a></div><div class="item-right docblock-short"><p>Mock random number generator</p> |
| </div></div></div><h2 id="structs" class="small-section-header"><a href="#structs">Structs</a></h2> |
| <div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.OsRng.html" title="rand::rngs::OsRng struct">OsRng</a><span class="stab portability" title="This is supported on crate feature `getrandom` only"><code>getrandom</code></span></div><div class="item-right docblock-short"><p>A random number generator that retrieves randomness from the |
| operating system.</p> |
| </div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.SmallRng.html" title="rand::rngs::SmallRng struct">SmallRng</a><span class="stab portability" title="This is supported on crate feature `small_rng` only"><code>small_rng</code></span></div><div class="item-right docblock-short"><p>A small-state, fast non-crypto PRNG</p> |
| </div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.StdRng.html" title="rand::rngs::StdRng struct">StdRng</a><span class="stab portability" title="This is supported on crate feature `std_rng` only"><code>std_rng</code></span></div><div class="item-right docblock-short"><p>The standard RNG. The PRNG algorithm in <code>StdRng</code> is chosen to be efficient |
| on the current platform, to be statistically strong and unpredictable |
| (meaning a cryptographically secure PRNG).</p> |
| </div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.ThreadRng.html" title="rand::rngs::ThreadRng struct">ThreadRng</a><span class="stab portability" title="This is supported on crate features `std` and `std_rng` only"><code>std</code> and <code>std_rng</code></span></div><div class="item-right docblock-short"><p>A reference to the thread-local generator</p> |
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