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<!DOCTYPE html>
<!--
SPDX-License-Identifier: BSD-2-Clause
SPDX-FileCopyrightText: Copyright (c) 2025 Runxi Yu <https://runxiyu.org>
-->
<html lang="en">
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<title>Proof-of-work challenge</title>
<link rel="stylesheet" href="/.powxy/static/style.css" />
<script>
/*
@licstart The following is the entire license notice for the
JavaScript code in this page.
Copyright (C) 2025 Runxi Yu
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.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS "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.
@licend The above is the entire license notice
for the JavaScript code in this page.
*/
</script>
</head>
<body>
<main>
<header>
<h1>Proof-of-work challenge</h1>
</header>
<section>
<p>This site is protected by <a href="{{ .Global.SourceURL }}">Powxy</a>{{ if .Global.Version }} {{ .Global.Version }}{{ end }}.</p>
<p>You must complete this proof-of-work challenge before you can access this site.</p>
</section>
<section>
<p>Select a nonce no longer than 32 bytes, such that when it is appended to the decoded form of the challenge identifier, and the entire result is hashed with SHA-256, the first {{ .Global.NeedBits }} bits of the SHA-256 hash are all zeros. Within one octet, higher bits are considered to come before lower bits.</p>
<p>In other words, find an nonce <math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>N</mi><annotation encoding="application/x-tex">N</annotation></semantics></math> with <math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo stretchy="false" form="prefix">|</mo><mi>N</mi><mo stretchy="false" form="postfix">|</mo><mo>≤</mo><mn>32</mn><mspace width="0.167em"></mspace><mi mathvariant="normal">B</mi></mrow><annotation encoding="application/x-tex">\lvert N\rvert \le 32\,\mathrm{B}</annotation></semantics></math>, such that <math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mrow><mi mathvariant="normal">S</mi><mi mathvariant="normal">H</mi><mi mathvariant="normal">A</mi><mn mathvariant="normal">256</mn></mrow><mrow><mo stretchy="true" form="prefix">(</mo><mi>I</mi><mspace width="0.167em"></mspace><mo stretchy="false" form="postfix">∥</mo><mspace width="0.167em"></mspace><mi>N</mi><mo stretchy="true" form="postfix">)</mo></mrow><mo><</mo><msup><mn>2</mn><mn>{{ .Global.NeedBitsReverse }}</mn></msup></mrow><annotation encoding="application/x-tex">\mathrm{SHA256}(I \,\|\, N) < 2^{{{ .Global.NeedBitsReverse }}}</annotation></semantics></math> in big endian, where <math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>I</mi><annotation encoding="application/x-tex">I</annotation></semantics></math> is the identifier provided below.</p>
<label for="identifier">Challenge identifier (read-only)</label>
<pre id="identifier">{{ .Identifier }}</pre>
</section>
<section>
<form method="POST">
<p>Encode your selected nonce in base64 and submit it below.</p>
<p>Please note that if your submission is successful, you will be given a cookie that will allow you to access this site for a period of time without having to complete the challenge again. By pressing the submit button, you agree to be given cookies for this purpose.</p>
<label for="nonce">Nonce</label>
<input id="nonce" name="powxy" type="text" />
<input type="submit" value="Submit" />
</form>
</section>
{{- if .Message }}
<section>
<p><strong>{{ .Message }}</strong></p>
</section>
{{- end }}
<section>
<p class="somewhat-transparent" id="solver_status">JavaScript seems to be disabled. You must solve the challenge externally.</p>
</section>
<section>
<p class="somewhat-transparent"><a href="/.powxy/static/solver.c">A C implementation of the challenge solver</a> is available.</p>
</section>
</main>
<script>
document.addEventListener("DOMContentLoaded", async function() {
let challenge_b64 = "{{ .Identifier }}";
let difficulty = {{ .Global.NeedBits }};
let form = document.querySelector("form");
let field = form.querySelector("input[name='powxy']");
let status_el = document.getElementById("solver_status");
let identifier_bytes = Uint8Array.from(
atob(challenge_b64),
ch => ch.charCodeAt(0)
);
status_el.textContent = "Starting WebAssembly solver as a worker...";
let worker = new Worker("/.powxy/static/solver.js");
worker.onmessage = function(e) {
let { nonce, nonce_bytes } = e.data;
let nonce_str = String.fromCharCode(...nonce_bytes);
field.value = btoa(nonce_str);
status_el.textContent = "Challenge solved automatically in " + nonce + " iterations";
};
worker.postMessage({ identifier_bytes, difficulty });
});
</script>
</body>
</html>
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