| layout | short_title | title |
|---|---|---|
page |
Checker |
Client-Side Answer Checker |
Answers are considered as a string of letters A–Z by changing lowercase letters to uppercase and stripping any other characters. Uses scrypt-js. What is this?
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Text to reveal after a correct answer (optional):<textarea id="gen-solution"></textarea>
Generate URL <script type="text/javascript" src="/js/scrypt.js"></script> <script type="text/javascript"> const encoder = new TextEncoder(); const decoder = new TextDecoder(); function b64OfArray(arr) { const carr = []; arr.forEach((u8) => { carr.push(String.fromCharCode(u8)); }); return btoa(carr.join("")); } function unb64(s) { const bs = atob(s); const uarr = new Uint8Array(bs.length); for (let i = 0; i < bs.length; i++) { uarr[i] = bs.charCodeAt(i); } return uarr; } function canonicalize(rawGuess) { rawGuess = rawGuess.toUpperCase(); let canon = ""; for (var i = 0; i < rawGuess.length; i++) { if (/[A-Z]/.test(rawGuess[i])) { canon += rawGuess[i]; } } return canon; } // These security parameters are weaker than what most settings would need, to // keep things reasonably fast, since our pure JavaScript library is slower // than other options, and URLs reasonably compact. A brute-forcer who ran // scrypt elsewhere with these parameters could go much faster, but this // setting really isn't high-stakes. // Don't copy my parameters into "actual crypto code" (why would you do that. // just. why) function generateLocalSalt() { let saltArr = new Uint8Array(12); if (window.crypto && window.crypto.getRandomValues) { window.crypto.getRandomValues(saltArr); } else { // Not secure, but like I said, I think cryptographic guarantees just // aren't worth breaking over. for (let i = 0; i < saltArr.length; i++) { saltArr[i] = Math.floor(Math.random()*256); } } return b64OfArray(saltArr); } function generateHash(label, answer, solution, callback) { const version = '1'; // The caller should canonicalize the answer! const salt = generateLocalSalt(); let ciphertextPromise = null; if (solution === "") { ciphertextPromise = new Promise(resolve => resolve(null)); } else { // "-encrypt" for domain separation const encryptionSalt = encoder.encode("puzzlehunt.net/checker#" + version + '-encrypt#' + salt + '#' + label); let encodedSolution = encoder.encode(solution); // very lazy xor cipher ciphertextPromise = scrypt.scrypt(encoder.encode(answer), encryptionSalt, 4096, 8, 1, encodedSolution.length, function (progress) { callback({ 'progress': progress, 'encrypting': true }); }).then(function (key) { for (let i = 0; i < encodedSolution.length; i++) { encodedSolution[i] ^= key[i]; } return encodedSolution; }); } ciphertextPromise.then(function (ciphertext) { const encodedCiphertext = ciphertext ? b64OfArray(ciphertext) : null; // Note: add the label even if it's empty. Also assume the label is ASCII // (by being v0 URI-encoded or v1 base64ed) already. const fullSalt = encoder.encode("puzzlehunt.net/checker#" + version + '#' + salt + '#' + label + (encodedCiphertext ? "#" + encodedCiphertext : "")); // N = 4096 = 2^12 = memory cost factor (a normal lower bound, // e.g. libsodium's crypto_pwhash_scryptsalsa208sha256_OPSLIMIT_MIN, is // 2^15; so you can see how skimpy on computation we are. It's because // we're using a pure-JavaScript implementation, which automatically makes // the constant factors huge.) // r = 8 = block size factor // p = 1 = parallelization parameter // dkLen = 24 = desired key length scrypt.scrypt(encoder.encode(answer), fullSalt, 4096, 8, 1, 24, function (progress) { callback({ 'progress': progress }); }).then(function (key) { let ret = { 'version': version, 'salt': salt, 'hash': b64OfArray(key), }; if (encodedCiphertext) { ret.ciphertext = encodedCiphertext; } callback(ret); }); }); } function checkHash(version, label, salt, hash, answer, ciphertext, callback) { // Weirdly, the version doesn't yet affect this part of the code. if (version !== '0' && version !== '1') { callback({ 'error': 'Unsupported version: ' + version, }); } // The caller should canonicalize the answer! // Note: add the label even if it's empty. Also assume the label is ASCII // (by being v0 URI-encoded or v1 base64ed) already. const fullSalt = encoder.encode("puzzlehunt.net/checker#" + version + '#' + salt + '#' + label + (ciphertext ? "#" + ciphertext : "")); scrypt.scrypt(encoder.encode(answer), fullSalt, 4096, 8, 1, 24, function (progress) { callback({ 'progress': progress }); }).then(function (key) { if (b64OfArray(key) === hash) { if (ciphertext === "") { callback({ 'correct': true }); } else { const encryptionSalt = encoder.encode("puzzlehunt.net/checker#" + version + '-encrypt#' + salt + '#' + label); const encodedSolution = unb64(ciphertext); scrypt.scrypt(encoder.encode(answer), encryptionSalt, 4096, 8, 1, encodedSolution.length, function (progress) { callback({ 'correct': true, 'progress': progress }); }).then(function (key) { for (let i = 0; i < encodedSolution.length; i++) { encodedSolution[i] ^= key[i]; } callback({ 'correct': true, 'solution': decoder.decode(encodedSolution), }); }); } } else { callback({ 'correct': false }); } }); } document.addEventListener('DOMContentLoaded', function() { const checkForm = document.getElementById('check'); const checkInput = document.getElementById('check-input'); const checkLabel = document.getElementById('check-label'); const checkOut = document.getElementById('check-out'); const checkSolution = document.getElementById('check-solution'); const genForm = document.getElementById('gen'); const genOuter = document.getElementById('gen-outer'); const genOut = document.getElementById('gen-out'); const genInput = document.getElementById('gen-input'); const genSolution = document.getElementById('gen-solution'); const genLink = document.getElementById('gen-link'); // Always strings. let version = ""; let salt = ""; let hash = ""; let label = ""; let ciphertext = ""; function updateFromHash() { const params = location.hash.substr(1).split('#'); version = params[0] || ""; salt = params[1] || ""; hash = params[2] || ""; label = params[3] || ""; ciphertext = params[4] || ""; if (version && salt && hash) { checkForm.style.display = "block"; if (version === "0" && label) { checkLabel.textContent = "Check your answer for " + decodeURIComponent(label) + ":"; } else if (version === "1" && label) { checkLabel.textContent = "Check your answer for " + decoder.decode(unb64(label)) + ":"; } else { checkLabel.textContent = "Check your answer:"; } genForm.style.display = "none"; checkOut.style.display = 'none'; checkSolution.style.display = 'none'; } else { checkForm.style.display = "none"; genForm.style.display = "block"; } }; checkForm.addEventListener('submit', function (event) { event.preventDefault(); checkInput.select(); const answer = canonicalize(checkInput.value); checkOut.style.display = 'block'; checkOut.textContent = 'Checking...'; checkOut.className = 'padded-callout'; checkSolution.style.display = 'none'; checkHash(version, label, salt, hash, answer, ciphertext, function (v) { if ('error' in v) { checkOut.className = 'padded-callout error'; checkOut.textContent = 'Error: ' + v.error; } else if ('correct' in v) { checkOut.className = v.correct ? 'padded-callout success' : 'padded-callout error'; checkOut.textContent = answer + ' is ' + (v.correct ? 'correct!' : 'incorrect.'); if ('progress' in v) { checkOut.textContent += ' Decrypting (' + Math.floor(v.progress * 100) + '%)...'; } if ('solution' in v) { checkSolution.style.display = 'block'; checkSolution.className = 'padded-callout'; checkSolution.textContent = v.solution; } } else if ('progress' in v) { checkOut.textContent = 'Checking (' + Math.floor(v.progress * 100) + '%)...'; } }); }); updateFromHash(); window.addEventListener('hashchange', updateFromHash); genForm.addEventListener('submit', function (event) { event.preventDefault(); const answer = canonicalize(genInput.value); const solution = genSolution.value; genOuter.className = 'padded-callout'; genOut.textContent = 'Generating...'; genLink.textContent = ''; genLink.href = '#'; // this part is version 1 instead of version 0... const genLabel = b64OfArray(encoder.encode(document.getElementById('gen-label').value)); generateHash(genLabel, answer, solution, function (v) { if ('error' in v) { genOuter.className = 'padded-callout error'; genOut.textContent = 'Error: ' + v.error; genLink.textContent = ''; genLink.href = '#'; } else if ('version' in v && 'salt' in v && 'hash' in v) { genOuter.className = 'padded-callout success'; genOut.textContent = 'Answer checker URL for ' + answer + ': '; let url = location.protocol + '//' + location.host + location.pathname + '#' + [v.version, v.salt, v.hash, genLabel].join('#'); if ('ciphertext' in v) { url += '#' + v.ciphertext; } genLink.textContent = url; genLink.href = url; } else if ('progress' in v) { if (v.encrypting) { genOut.textContent = 'Encrypting (' + Math.floor(v.progress * 100) + '%)...'; } else { genOut.textContent = 'Generating (' + Math.floor(v.progress * 100) + '%)...'; } genLink.textContent = ''; genLink.href = '#'; } }); }); document.getElementById('loading').style.display = "none"; }); </script>