// SPDX-License-Identifier: BSD-2-Clause
// SPDX-FileCopyrightText: Copyright (c) 2025 Runxi Yu <https://runxiyu.org>
package main
import (
"html"
"log"
"text/template"
)
var tmpl *template.Template
func init() {
var err error
tmpl, err = template.New("powxy").Parse(`<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<title>Proof of Work Challenge</title>
<style>
html {
font-family: sans-serif;
background-color: var(--background-color);
color: var(--text-color);
--radius-1: 0.32rem;
--background-color: hsl(0, 0%, 100%);
--text-color: hsl(0, 0%, 0%);
--link-color: hsl(320, 50%, 36%);
--light-text-color: hsl(0, 0%, 45%);
--darker-border-color: hsl(0, 0%, 72%);
--lighter-border-color: hsl(0, 0%, 85%);
--text-decoration-color: hsl(0, 0%, 72%);
--darker-box-background-color: hsl(0, 0%, 92%);
--lighter-box-background-color: hsl(0, 0%, 95%);
--primary-color: hsl(320, 50%, 36%);
--primary-color-contrast: hsl(320, 0%, 100%);
--danger-color: #ff0000;
--danger-color-contrast: #ffffff;
}
@media (prefers-color-scheme: dark) {
html {
--background-color: hsl(0, 0%, 0%);
--text-color: hsl(0, 0%, 100%);
--link-color: hsl(320, 50%, 76%);
--light-text-color: hsl(0, 0%, 78%);
--darker-border-color: hsl(0, 0%, 35%);
--lighter-border-color: hsl(0, 0%, 25%);
--text-decoration-color: hsl(0, 0%, 30%);
--darker-box-background-color: hsl(0, 0%, 20%);
--lighter-box-background-color: hsl(0, 0%, 15%);
}
}
body {
margin: 0;
padding: 1rem;
}
main {
max-width: 720px;
margin: 0 auto;
}
*:focus-visible {
outline: 1.5px var(--primary-color) solid;
}
section {
margin: 0;
}
label {
display: block;
font-style: italic;
margin-top: 1rem;
margin-bottom: 0.5rem;
}
h1 {
margin-top: 0;
color: var(--primary-color);
}
p, summary {
line-height: 1.2;
}
a {
color: var(--link-color);
text-decoration-color: var(--text-decoration-color);
}
input[type="text"] {
background-color: var(--lighter-box-background-color);
width: 100%;
padding: 0.5rem;
border-radius: var(--radius-1);
border: none;
box-shadow: inset 0 1px 4px rgba(0, 0, 0, 0.15);
margin-bottom: 1rem;
box-sizing: border-box;
}
input[type="submit"] {
padding: 0.5rem 1rem;
background-color: var(--primary-color);
color: var(--primary-color-contrast);
border: none;
border-radius: var(--radius-1);
cursor: pointer;
}
input[readonly] {
background-color: var(--lighter-box-background-color);
color: var(--text-color);
cursor: text;
}
details {
margin-top: 2rem;
background-color: var(--lighter-box-background-color);
padding: 0.5rem;
border-radius: var(--radius-1);
box-shadow: inset 0 1px 4px rgba(0, 0, 0, 0.15);
}
pre {
overflow-x: auto;
white-space: pre-wrap;
word-break: break-word;
}
#solver_status {
font-size: 0.9rem;
color: var(--light-text-color);
margin-top: 1rem;
}
</style>
<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 }}, version {{ .Global.Version }}{{ end }}.</p>
<p>You must complete this proof of work challenge before you can access this site.</p>
</section>
{{- if .Message }}
<section>
<p><strong>{{ .Message }}</strong></p>
</section>
{{- end }}
<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>
<label for="unsigned-identifier">Challenge identifier (read-only)</label>
<input id="unsigned-identifier" type="text" readonly disabled tabindex="-1" value="{{ .Identifier }}" />
</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>
<section>
<p id="solver_status">JavaScript seems to be disabled. You must solve the challenge externally.</p>
</section>
<details>
<summary>Offline solver program</summary>
<pre>` + html.EscapeString(solverProgram) + `</pre>
</details>
</main>
<script>
document.addEventListener("DOMContentLoaded", 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");
if (!window.crypto || !window.crypto.subtle) {
status_el.textContent = "SubtleCrypto not available. You must solve the challenge externally.";
return;
}
status_el.textContent = "SubtleCrypto detected. Attempting to solve the challenge automatically...";
let solver_active = true;
form.addEventListener("submit", function() {
solver_active = false;
});
async function solve_pow() {
let identifier_bytes = Uint8Array.from(
atob(challenge_b64),
ch => ch.charCodeAt(0)
);
let nonce = 0n;
let buf = new ArrayBuffer(8);
let view = new DataView(buf);
while (solver_active) {
view.setBigUint64(0, nonce, true);
let candidate = new Uint8Array(identifier_bytes.length + 8);
candidate.set(identifier_bytes, 0);
candidate.set(new Uint8Array(buf), identifier_bytes.length);
let digest_buffer = await crypto.subtle.digest("SHA-256", candidate);
let digest = new Uint8Array(digest_buffer);
if (has_leading_zero_bits(digest, difficulty)) {
let nonce_str = String.fromCharCode(...new Uint8Array(buf));
field.value = btoa(nonce_str);
status_el.textContent = "A solution has been found automatically in " + nonce + " iterations.";
return;
}
nonce++;
if ((nonce & 0x00FFn) === 0n) {
status_el.textContent = "Attempting to solve automatically. Tried " + nonce + " candidates so far...";
await new Promise(r => setTimeout(r, 0));
}
}
}
function has_leading_zero_bits(digest, bits) {
let full_bytes = bits >>> 3;
for (let i = 0; i < full_bytes; i++) {
if (digest[i] !== 0) {
return false;
}
}
let remainder = bits & 7;
if (remainder !== 0) {
let mask = 0xFF << (8 - remainder);
if ((digest[full_bytes] & mask) !== 0) {
return false;
}
}
return true;
}
solve_pow();
});
</script>
</body>
</html>`)
if err != nil {
log.Fatal(err)
}
}