fix:Harden authentication and sensitive file handling

src/utils/totp.ts

@@ -70,17 +70,22 @@ function normalizeToken(token: string): string {
   return token.replace(/\s+/g, '');
 }
 
-export async function verifyTotpToken(secretRaw: string, tokenRaw: string, nowMs: number = Date.now()): Promise<boolean> {
+export async function findMatchingTotpCounter(
+  secretRaw: string,
+  tokenRaw: string,
+  nowMs: number = Date.now()
+): Promise<number | null> {
   const token = normalizeToken(tokenRaw);
-  if (!/^\d{6}$/.test(token)) return false;
+  if (!/^\d{6}$/.test(token)) return null;
 
   const secret = base32Decode(secretRaw);
-  if (!secret) return false;
+  if (!secret) return null;
 
   const currentCounter = Math.floor(nowMs / 1000 / TOTP_STEP_SECONDS);
-  let matched = false;
+  let matchedCounter: number | null = null;
   for (let delta = -TOTP_WINDOW; delta <= TOTP_WINDOW; delta++) {
-    const expected = await hotp(secret, currentCounter + delta);
+    const candidateCounter = currentCounter + delta;
+    const expected = await hotp(secret, candidateCounter);
     // Constant-time comparison: always check all windows, never short-circuit.
     const a = new TextEncoder().encode(expected);
     const b = new TextEncoder().encode(token);
@@ -88,9 +93,13 @@ export async function verifyTotpToken(secretRaw: string, tokenRaw: string, nowMs
     for (let i = 0; i < a.length && i < b.length; i++) {
       diff |= a[i] ^ b[i];
     }
-    if (diff === 0) matched = true;
+    if (diff === 0 && matchedCounter == null) matchedCounter = candidateCounter;
   }
-  return matched;
+  return matchedCounter;
+}
+
+export async function verifyTotpToken(secretRaw: string, tokenRaw: string, nowMs: number = Date.now()): Promise<boolean> {
+  return (await findMatchingTotpCounter(secretRaw, tokenRaw, nowMs)) != null;
 }
 
 export function isTotpEnabled(secretRaw: string | undefined | null): boolean {