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fix: fix instrumentation challenges expiration (standalone@2.2.1)

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This commit is contained in:
tiago
2026-03-01 15:41:09 +00:00
parent e0d97298fb
commit 338a01b40d
3 changed files with 3 additions and 59 deletions
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standalone/package.json
+1 -1
View File
@@ -1,6 +1,6 @@
{
"name": "cap-standalone",
"version": "2.2.0",
"version": "2.2.1",
"keywords": [
"algorithm",
"anti-abuse",
standalone/public/login.html
Vendored
+1 -1
View File
@@ -334,7 +334,7 @@
"cap_auth",
JSON.stringify({
token: session_token,
expires: expires,
expires,
hash: hashed_token,
}),
);
standalone/src/cap.js
+1 -57
View File
@@ -14,8 +14,6 @@ import { ratelimitGenerator } from "./ratelimit.js";
const CHALLENGE_TTL_MS = 15 * 60 * 1000; // 15min
const TOKEN_TTL_MS = 2 * 60 * 60 * 1000; // 2h
// ── JWT helpers (HMAC-SHA256, compact JWS) ──────────────────────────────
const b64url = (buf) =>
(buf instanceof Uint8Array ? Buffer.from(buf) : Buffer.from(buf, "utf8")).toString("base64url");
@@ -41,7 +39,6 @@ function jwtVerify(token, secret) {
if (actual.length !== expected.length) return null;
// Constant-time comparison
const a = new Uint8Array(expected);
const b = new Uint8Array(actual);
let diff = 0;
@@ -55,31 +52,16 @@ function jwtVerify(token, secret) {
}
}
/** Return the raw signature bytes (last segment) for blocklisting */
function jwtSigHex(token) {
const lastDot = token.lastIndexOf(".");
if (lastDot === -1) return null;
return b64urlDecode(token.slice(lastDot + 1)).toString("hex");
}
// ── AES-256-GCM helpers ─────────────────────────────────────────────────
// Used to encrypt instrumentation metadata inside the JWT so that the
// expected answers are completely opaque to the client.
/**
* Derive a 32-byte encryption key from the site's jwtSecret.
* We HMAC the secret with a fixed context label so the signing key
* and the encryption key are always distinct even though they share
* the same root secret.
*/
function deriveEncKey(jwtSecret) {
return createHmac("sha256", jwtSecret).update("cap:instr-enc-v1").digest();
}
/**
* Encrypt arbitrary JSON-serialisable data with AES-256-GCM.
* Returns a base64url string: iv (12 B) || authTag (16 B) || ciphertext
*/
function encrypt(data, jwtSecret) {
const key = deriveEncKey(jwtSecret);
const iv = randomBytes(12);
@@ -90,10 +72,6 @@ function encrypt(data, jwtSecret) {
return Buffer.concat([iv, tag, encrypted]).toString("base64url");
}
/**
* Decrypt a blob produced by encrypt(). Returns the parsed object, or
* null if decryption / authentication fails.
*/
function decrypt(blob, jwtSecret) {
try {
const buf = Buffer.from(blob, "base64url");
@@ -111,8 +89,6 @@ function decrypt(blob, jwtSecret) {
}
}
// ── prng (must match @cap.js/server and the widget) ─────────────────────
function prng(seed, length) {
function fnv1a(str) {
let hash = 2166136261;
@@ -141,14 +117,10 @@ function prng(seed, length) {
return result.substring(0, length);
}
// ── sha256 ──────────────────────────────────────────────────────────────
async function sha256(str) {
return new Bun.CryptoHasher("sha256").update(str).digest("hex");
}
// ── Route definitions ───────────────────────────────────────────────────
export const capServer = new Elysia({
detail: {
tags: ["Challenges"],
@@ -169,11 +141,6 @@ export const capServer = new Elysia({
}),
)
// ── POST /:siteKey/challenge ────────────────────────────────────────
// No DB writes — the challenge token IS a JWT signed with the site's
// jwtSecret. The JWT payload carries all data needed by /redeem.
// Instrumentation metadata is AES-256-GCM encrypted so the expected
// answers are never visible to the client.
.post("/:siteKey/challenge", async ({ set, params }) => {
const [keyRow] = await db`SELECT config, jwtSecret FROM keys WHERE siteKey = ${params.siteKey}`;
@@ -195,7 +162,6 @@ export const capServer = new Elysia({
const d = keyConfig.difficulty ?? 4;
const expires = Date.now() + CHALLENGE_TTL_MS;
// A random nonce for JWT uniqueness
const nonce = randomBytes(25).toString("hex");
const jwtPayload = {
@@ -207,30 +173,23 @@ export const capServer = new Elysia({
exp: expires,
};
// If instrumentation is enabled, encrypt its verification metadata
// and embed the opaque ciphertext in the JWT. The cleartext
// instrumentation script (what the browser executes) is returned
// separately — outside the JWT — so the widget can run it.
let instrBytes = null;
if (keyConfig.instrumentation) {
const instr = await generateInstrumentationChallenge(keyConfig);
// This is the sensitive part: expected states, variable names, etc.
// Encrypt it so the JWT payload doesn't leak the answers.
jwtPayload.ei = encrypt(
{
id: instr.id,
validStates: instr.validStates,
vars: instr.vars,
blockAutomatedBrowsers: instr.blockAutomatedBrowsers,
expires: instr.expires,
expires,
},
jwtSecret,
);
instrBytes = instr.instrumentation;
// Keep the cache hot
warmForConfigs([keyConfig]);
}
@@ -249,16 +208,12 @@ export const capServer = new Elysia({
return response;
})
// ── POST /:siteKey/redeem ──────────────────────────────────────────
// Verifies the JWT, checks PoW solutions, blocklists the JWT sig,
// then generates a redemption token and inserts it into the DB.
.post("/:siteKey/redeem", async ({ body, set, params }) => {
if (!body || !body.token || !body.solutions) {
set.status = 400;
return { error: "Missing required fields" };
}
// ── look up site key & jwt secret ───────────────────────────────
const [keyRow] = await db`SELECT jwtSecret FROM keys WHERE siteKey = ${params.siteKey}`;
if (!keyRow) {
@@ -273,7 +228,6 @@ export const capServer = new Elysia({
return { error: "Site key is not configured for JWT challenges" };
}
// ── verify JWT ──────────────────────────────────────────────────
const payload = jwtVerify(body.token, jwtSecret);
if (!payload) {
@@ -291,7 +245,6 @@ export const capServer = new Elysia({
return { error: "Challenge expired" };
}
// ── replay protection: check blocklist ──────────────────────────
const sig = jwtSigHex(body.token);
if (!sig) {
set.status = 403;
@@ -304,7 +257,6 @@ export const capServer = new Elysia({
return { error: "Challenge already redeemed" };
}
// ── verify PoW solutions ────────────────────────────────────────
const { c, s: size, d: difficulty } = payload;
const solutions = body.solutions;
@@ -317,8 +269,6 @@ export const capServer = new Elysia({
return { error: "Invalid solutions" };
}
// The widget uses the full token string (the JWT) as the PRNG seed,
// so the server must do the same to regenerate identical challenges.
const prngSeed = body.token;
let idx = 0;
@@ -338,9 +288,6 @@ export const capServer = new Elysia({
return { error: "Invalid solution" };
}
// ── instrumentation verification ────────────────────────────────
// The `ei` field in the JWT is AES-256-GCM encrypted; decrypt it
// to recover the expected instrumentation state.
let instrMeta = null;
if (payload.ei) {
instrMeta = decrypt(payload.ei, jwtSecret);
@@ -364,7 +311,6 @@ export const capServer = new Elysia({
reason: "automated_browser_detected",
};
}
// blockAutomatedBrowsers is disabled — allow through
} else if (body.instr) {
let instrResult;
if (instrMeta.expires && Date.now() > instrMeta.expires) {
@@ -394,13 +340,11 @@ export const capServer = new Elysia({
}
}
// ── blocklist the JWT signature so it cannot be replayed ─────────
await db`
INSERT INTO challenge_blocklist (sig, expires)
VALUES (${sig}, ${payload.exp})
`;
// ── generate redemption token (NOT a JWT — opaque, DB-backed) ───
const redeemId = randomBytes(8).toString("hex");
const redeemSecret = randomBytes(15).toString("hex");
const redeemToken = `${redeemId}:${redeemSecret}`;