fix: harden authentication and file access security

back/shared/password.ts

@@ -0,0 +1,30 @@
+import { randomBytes, scrypt, timingSafeEqual } from 'crypto';
+import { promisify } from 'util';
+
+const deriveKey = promisify(scrypt);
+const HASH_PREFIX = 'scrypt$';
+
+export async function hashPassword(password: string): Promise<string> {
+  const salt = randomBytes(16).toString('hex');
+  const key = (await deriveKey(password, salt, 64)) as Buffer;
+  return `${HASH_PREFIX}${salt}$${key.toString('hex')}`;
+}
+
+export function isPasswordHash(password: string): boolean {
+  return /^scrypt\$[a-f0-9]{32}\$[a-f0-9]{128}$/.test(password);
+}
+
+export async function verifyPassword(
+  password: string,
+  stored: string,
+): Promise<boolean> {
+  if (!isPasswordHash(stored)) {
+    // Existing installations migrate after a successful password check.
+    const input = Buffer.from(password);
+    const expected = Buffer.from(stored);
+    return input.length === expected.length && timingSafeEqual(input, expected);
+  }
+  const [, salt, hash] = stored.split('$');
+  const key = (await deriveKey(password, salt, 64)) as Buffer;
+  return timingSafeEqual(key, Buffer.from(hash, 'hex'));
+}