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<meta name="description" content="n bytes from the OS CSPRNG, as a 2n-character hex string.">
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<div class="crumbs"><a href="api.html">API Reference</a> <span>›</span> <a href="ns-crypto.html">Crypto</a> <span>›</span> <span class="here">Crypto.random_bytes</span></div>
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<span class="kind-badge kind-method">method</span>
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<h1 id="top">Crypto.random_bytes</h1>
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<code class="sig">Crypto.random_bytes(n) -> string</code>
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<div class="desc"><p>Draws <code>n</code> bytes from the operating system's cryptographically-secure random number generator and returns them as a <code>2n</code>-character lowercase hex string. Use it for unguessable tokens, nonces, and session secrets — anything whose whole value is that an attacker cannot predict it. The result is hex rather than raw bytes for the same reason digests are: a <code>str</code> is null-terminated and raw random bytes can contain a zero byte, so hex is the form you can safely store and compare.</p><p>This is deliberately **non-deterministic** — it must never seed the lockstep simulation RNG (<a href="ns-Random"><code>Random</code></a>). Two calls return different values. On a platform without an OS CSPRNG (for example a bare wasm target) the draw degrades to zeroes rather than faulting; treat a real CSPRNG there as a platform-layer responsibility.</p></div>
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<div class="params"><h2>Parameters</h2><div class="param" id="param-n"><code class="pname">n</code><span class="pdesc">the number of secure random bytes to draw</span></div></div>
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<div class="examples"><h2>Example</h2><pre data-lang="ludic">program Token {
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entry {
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let session = Crypto.random_bytes(16) # 32 hex chars, unguessable
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print(len(session)) # 32
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}
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}</pre></div>
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