Key backup from Settings works for every login; 4-digit PINs behind a server-side lockout (0.5.0)

package.json

@@ -1,7 +1,7 @@
 {
   "name": "qryptchat-web",
   "private": true,
-  "version": "0.4.0",
+  "version": "0.5.0",
   "type": "module",
   "bin": {
     "qc": "./bin/qc.js",

src/app/anon/page.jsx

@@ -115,8 +115,8 @@ function AnonRegister() {
 
 	async function setBackupPinFn(e) {
 		e?.preventDefault();
-		if (!backupPin || !/^\d+$/.test(backupPin) || backupPin.length < 6 || backupPin.length > 12) {
-			msgStore.error('PIN must be 6-12 digits');
+		if (!backupPin || !/^\d{4,12}$/.test(backupPin)) {
+			msgStore.error('PIN must be 4-12 digits');
 			return;
 		}
 		if (backupPin !== confirmBackupPin) {
@@ -140,7 +140,7 @@ function AnonRegister() {
 			const backupRes = await fetch('/api/auth/key-backup', {
 				method: 'PUT',
 				headers,
-				body: JSON.stringify({ encrypted_keys: encryptedData })
+				body: JSON.stringify({ encrypted_keys: encryptedData, pin: backupPin })
 			});
 			if (!backupRes.ok) {
 				const err = await backupRes.json().catch(() => ({}));
@@ -262,14 +262,14 @@ function AnonRegister() {
 						</div>
 						<form onSubmit={setBackupPinFn}>
 							<div className="input-group">
-								<label>Backup PIN (6-12 digits) *</label>
+								<label>Backup PIN (4-12 digits) *</label>
 								<div className="password-input">
 									<input
 										type={showBackupPin ? 'text' : 'password'}
 										inputMode="numeric"
 										value={backupPin}
 										onChange={(e) => setBackupPin(e.target.value.replace(/\D/g, '').slice(0, 12))}
-										placeholder="Enter 6-12 digit PIN"
+										placeholder="Enter 4-12 digit PIN"
 										required
 										disabled={submitting}
 										className="code-input"

src/app/api/auth/backup-pin/route.js

@@ -2,17 +2,14 @@
 // Handles setting and checking the user's backup PIN hash
 
 import { NextResponse } from 'next/server';
-import { randomBytes, scrypt as scryptCallback } from 'node:crypto';
-import { promisify } from 'node:util';
 import { createClient } from '@supabase/supabase-js';
 import { supabaseAuthCookieName } from '@/lib/supabase/auth-cookie.js';
 import { createServiceRoleClient } from '@/lib/supabase/service-role.js';
+import { checkPin, hashPin, PIN_ALGORITHM, PIN_PATTERN, PIN_RULE, resolveInternalUserId as resolveUserId } from '@/lib/auth/backup-pin.js';
 
 // node:crypto is required for scrypt, so pin this route to the Node runtime.
 export const runtime = 'nodejs';
 
-const scrypt = promisify(scryptCallback);
-
 let supabaseServiceRole = null;
 function getServiceRoleClient() {
 	if (!supabaseServiceRole) {
@@ -102,60 +99,10 @@ async function authenticateUser(request) {
 	}
 }
 
-// scrypt work factors. N=2^17/r=8/p=1 is OWASP's recommended minimum; the previous
-// N=16384 (Node's default) cost only ~16MB per derivation, which left the 6-12 digit
-// PIN keyspace within reach of an offline GPU sweep. The per-user salt means there is
-// no shared work across users on top of that.
-const SCRYPT_N = 131072;
-const SCRYPT_R = 8;
-const SCRYPT_P = 1;
-// scrypt needs roughly 128 * N * r bytes; Node's default 32MB cap would reject N=2^17.
-const SCRYPT_MAXMEM = 192 * 1024 * 1024;
-const SCRYPT_KEYLEN = 64;
-const SCRYPT_SALT_BYTES = 16;
-export const PIN_ALGORITHM = `scrypt-n${SCRYPT_N}-r${SCRYPT_R}-p${SCRYPT_P}`;
-
-/**
- * Derive a PIN hash using scrypt and a per-user random salt.
- *
- * Replaces the previous unsalted `crypto.subtle.digest('SHA-256', pin)`, which
- * a rainbow table over the numeric PIN keyspace reversed instantly once the
- * hash column was readable (GHSA-jpfm-vrpc-p6rr).
- *
- * @param {string} pin
- * @param {string} [saltHex] existing salt, hex-encoded; a new one is generated when omitted
- * @returns {Promise<{hash: string, salt: string, algorithm: string}>}
- */
-async function hashPin(pin, saltHex) {
-	const salt = saltHex ?? randomBytes(SCRYPT_SALT_BYTES).toString('hex');
-	const derived = /** @type {Buffer} */ (
-		await scrypt(pin, salt, SCRYPT_KEYLEN, {
-			N: SCRYPT_N,
-			r: SCRYPT_R,
-			p: SCRYPT_P,
-			maxmem: SCRYPT_MAXMEM
-		})
-	);
-	return { hash: derived.toString('hex'), salt, algorithm: PIN_ALGORITHM };
-}
+export { PIN_ALGORITHM };
 
-/**
- * Resolve the internal users.id for a Supabase Auth user.
- * @param {{id: string}} user
- * @returns {Promise<{userId?: string, error?: string}>}
- */
 async function resolveInternalUserId(user) {
-	const { data, error } = await getServiceRoleClient()
-		.from('users')
-		.select('id')
-		.eq('auth_user_id', user.id)
-		.single();
-
-	if (error || !data?.id) {
-		return { error: error?.message ?? 'User record not found' };
-	}
-
-	return { userId: data.id };
+	return resolveUserId(getServiceRoleClient(), user);
 }
 
 /**
@@ -214,13 +161,13 @@ export async function POST(request) {
 			return NextResponse.json({ error: 'Invalid JSON body' }, { status: 400 });
 		}
 
-		const { pin } = body;
+		const { pin, currentPin } = body;
 
-		if (!pin || typeof pin !== 'string' || pin.length < 6 || pin.length > 12) {
-			return NextResponse.json({ error: 'PIN must be 6-12 digits' }, { status: 400 });
+		if (!pin || typeof pin !== 'string' || pin.length < 4 || pin.length > 12) {
+			return NextResponse.json({ error: PIN_RULE }, { status: 400 });
 		}
 
-		if (!/^\d+$/.test(pin)) {
+		if (!PIN_PATTERN.test(pin)) {
 			return NextResponse.json({ error: 'PIN must contain only digits' }, { status: 400 });
 		}
 
@@ -230,6 +177,27 @@ export async function POST(request) {
 			return NextResponse.json({ error: 'Failed to set backup PIN' }, { status: 500 });
 		}
 
+		// Replacing a PIN the server can verify takes the current one. Otherwise a
+		// stolen session could set its own PIN and walk through the restore gate.
+		const current = await checkPin(getServiceRoleClient(), userId, typeof currentPin === 'string' ? currentPin : '');
+		if (current.status === 'error') {
+			console.error('Error checking backup PIN:', current.error);
+			return NextResponse.json({ error: 'Failed to set backup PIN' }, { status: 500 });
+		}
+		if (current.status === 'locked' || (current.status === 'wrong' && current.retryAfter)) {
+			const retryAfter = current.retryAfter;
+			return NextResponse.json(
+				{ error: 'Too many wrong PINs. Try again later.', code: 'PIN_LOCKED', retryAfter },
+				{ status: 429, headers: { 'Retry-After': String(retryAfter) } }
+			);
+		}
+		if (current.status === 'required') {
+			return NextResponse.json({ error: 'Enter your current PIN to change it', code: 'PIN_REQUIRED' }, { status: 403 });
+		}
+		if (current.status === 'wrong') {
+			return NextResponse.json({ error: 'Current PIN is wrong', code: 'PIN_WRONG', remaining: current.remaining }, { status: 403 });
+		}
+
 		const { hash, salt, algorithm } = await hashPin(pin);
 
 		const { error } = await getServiceRoleClient()

src/app/api/auth/backup-pin/route.test.js

@@ -205,4 +205,40 @@ describe('backup PIN cookie authentication', () => {
 		expect(body.error).toBe('Invalid JSON body');
 		expect(mocks.serviceFrom).not.toHaveBeenCalled();
 	});
+
+	it('accepts a 4-digit PIN', async () => {
+		const { POST } = await import('./route.js');
+		const response = await POST({
+			headers: new Headers({ authorization: 'Bearer access-token' }),
+			json: vi.fn().mockResolvedValue({ pin: '4821' })
+		});
+		expect(response.status).toBe(200);
+	});
+
+	it('will not replace a verifiable PIN without the current one', async () => {
+		const { hashPin } = await import('@/lib/auth/backup-pin.js');
+		const existing = await hashPin('4821');
+		mocks.serviceFrom.mockImplementation((table) => {
+			if (table === 'users') return createUsersQuery();
+			if (table === 'user_backup_pins') {
+				const query = createBackupPinsQuery();
+				query.maybeSingle = vi.fn(() =>
+					Promise.resolve({
+						data: { user_id: 'internal-user-id', pin_hash: existing.hash, pin_salt: existing.salt, algorithm: existing.algorithm, failed_attempts: 0 },
+						error: null
+					})
+				);
+				return query;
+			}
+			throw new Error(`Unexpected table: ${table}`);
+		});
+		const { POST } = await import('./route.js');
+		const response = await POST({
+			headers: new Headers({ authorization: 'Bearer access-token' }),
+			json: vi.fn().mockResolvedValue({ pin: '1111' })
+		});
+		expect(response.status).toBe(403);
+		expect((await response.json()).code).toBe('PIN_REQUIRED');
+		expect(mocks.pinUpsert).not.toHaveBeenCalled();
+	});
 });