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/*
* proof-of-work.js -- Alternative captcha based on SHA-256 proof-of-work.
* Copyright © 2022 - 2023 Jakob L. Kreuze <zerodaysfordays@sdf.org>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see
* <http://www.gnu.org/licenses/>.
*/
function makeid(length) {
let result = '';
let alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
for (let i = 0; i < length; i++) {
result += alphabet.charAt(Math.floor(Math.random() * alphabet.length));
}
return result;
}
async function digestMessage(message) {
const msgUtf8 = new TextEncoder().encode(message);
const hashBuffer = await crypto.subtle.digest('SHA-256', msgUtf8);
const hashArray = Array.from(new Uint8Array(hashBuffer));
const hashHex = hashArray.map((b) => b.toString(16).padStart(2, '0')).join('');
return hashHex;
}
async function findPrefix(hardness, nonce) {
while (true) {
let prefix = makeid(32);
let digestHex = await digestMessage(prefix + nonce);
if (digestHex.startsWith("0".repeat(hardness))) {
return prefix;
}
}
}
function makeRequest (method, url) {
return new Promise(function (resolve, reject) {
var xhr = new XMLHttpRequest();
xhr.open(method, url);
xhr.onload = function () {
if (xhr.status >= 200 && xhr.status < 300) {
resolve(xhr.response);
} else {
reject({
status: xhr.status,
statusText: xhr.statusText
});
}
};
xhr.onerror = function () {
reject({
status: xhr.status,
statusText: xhr.statusText
});
};
xhr.send();
});
}
function raceEndpoint() {
return new Promise(function (resolve, reject) {
makeRequest("GET", "/api/challenge/proof-of-work")
.then(function (data) {
let challengeData = JSON.parse(data);
findPrefix(challengeData.hardness, challengeData.nonce)
.then((prefix) => { resolve([prefix, challengeData["challenge-id"]]) } );
})
.catch(reject);
});
}
window.addEventListener("load", () => {
let trigger = document.getElementById("pow-trigger");
trigger.removeAttribute("hidden");
trigger.addEventListener("click", (e) => {
trigger.innerHTML = "Please wait...";
trigger.disabled = true;
raceEndpoint()
.then((result) => {
let resultField = document.getElementById("captcha-alt");
let challengeIdField = document.getElementById("captcha-alt-id");
resultField.value = result[0];
challengeIdField.value = result[1];
trigger.innerHTML = "Proof-of-Work completed successfully!";
trigger.disabled = true;
// Hide the primary captcha, too, to make it clear that it isn't necessary to complete.
let primaryChallenge = document.getElementById("captcha-challenge-primary");
primaryChallenge.hidden = true;
})
.catch((err) => {
console.log(err);
trigger.innerHTML = "Proof-of-Work failed!";
trigger.disabled = true;
});
e.preventDefault();
})
});
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