---
id: security-2fa-totp-webauthn
title: 2FA — TOTP / WebAuthn / Passkey
category: Coding
status: draft
source_trust_level: B
verification_status: conceptual
created_at: 2026-05-09
updated_at: 2026-05-09
tags: [security, 2fa, totp, webauthn, passkey, vibe-coding]
tech_stack: { language: "TS / WebAuthn", applicable_to: ["Backend", "Frontend"] }
applied_in: []
aliases: [2FA, TOTP, Google Authenticator, WebAuthn, passkey, FIDO2]
---

# 2FA / Passkeys

> SMS 2FA = SIM swap 위험. **TOTP (Authenticator) = 무료 + 안전**, **WebAuthn / Passkey = 진짜 phishing-resistant**. iOS/Android Passkey 가 미래.

## 📖 핵심 개념
- TOTP: 6자리 30초 코드 (RFC 6238). HMAC + 시간.
- WebAuthn: 공개키 인증. 서버 = 비밀 X.
- Passkey: WebAuthn 의 동기화 + UX 개선 — Apple/Google 계정에 sync.
- Recovery codes: 백업 — 1회용.

## 💻 코드 패턴

### TOTP (otplib)
```ts
import { authenticator } from 'otplib';

// Setup
const secret = authenticator.generateSecret(); // base32
const otpauth = authenticator.keyuri(user.email, 'Acme', secret);
// QR: otpauth → qrcode 라이브러리

await db.user2fa.upsert({ userId: user.id, secret, enabled: false });

// Verify (활성화)
function verify(code: string, secret: string) {
  return authenticator.check(code, secret);
}

// 정상 검증 후
await db.user2fa.update(userId, { enabled: true });
```

### Login flow with TOTP
```ts
// Step 1: password
const u = await verifyPassword(email, password);
if (!u) return 401;

if (u.twoFactorEnabled) {
  // 임시 token (TOTP 만 검증 가능, 30초 유효)
  return { needs2FA: true, partialToken: signPartial({ userId: u.id }) };
}
return loginSuccess(u);

// Step 2: TOTP
app.post('/login/2fa', async (req, res) => {
  const partial = verifyPartial(req.body.partialToken);
  const { secret } = await db.user2fa.find(partial.userId);
  if (!authenticator.check(req.body.code, secret)) return res.status(401).end();
  return loginSuccess({ id: partial.userId });
});
```

### Recovery codes
```ts
import { randomBytes } from 'node:crypto';

function generateRecoveryCodes(n = 10): string[] {
  return Array.from({ length: n }, () => randomBytes(8).toString('hex'));
}

const codes = generateRecoveryCodes();
const hashed = await Promise.all(codes.map(c => argon2.hash(c)));
await db.recoveryCodes.insertMany(userId, hashed);
// codes 한 번만 사용자에게 표시
```

### WebAuthn / Passkey (server side)
```ts
import { generateRegistrationOptions, verifyRegistrationResponse,
         generateAuthenticationOptions, verifyAuthenticationResponse }
  from '@simplewebauthn/server';

// Registration
app.post('/webauthn/register/options', authRequired, async (req, res) => {
  const opts = await generateRegistrationOptions({
    rpName: 'Acme',
    rpID: 'acme.com',
    userID: Buffer.from(req.user.id),
    userName: req.user.email,
    attestationType: 'none',
    authenticatorSelection: {
      residentKey: 'preferred', // passkey 만들기
      userVerification: 'preferred',
    },
  });
  await redis.set(`webauthn:reg:${req.user.id}`, opts.challenge, 'EX', 300);
  res.json(opts);
});

app.post('/webauthn/register/verify', authRequired, async (req, res) => {
  const expectedChallenge = await redis.get(`webauthn:reg:${req.user.id}`);
  const v = await verifyRegistrationResponse({
    response: req.body, expectedChallenge: expectedChallenge!,
    expectedOrigin: 'https://acme.com', expectedRPID: 'acme.com',
  });
  if (!v.verified) return res.status(400).end();

  await db.passkeys.insert({
    userId: req.user.id,
    credentialId: v.registrationInfo!.credentialID,
    publicKey: v.registrationInfo!.credentialPublicKey,
    counter: v.registrationInfo!.counter,
  });
  res.json({ ok: true });
});
```

```ts
// Authentication
app.post('/webauthn/login/options', async (req, res) => {
  const opts = await generateAuthenticationOptions({
    rpID: 'acme.com',
    userVerification: 'preferred',
  });
  await redis.set(`webauthn:auth:${opts.challenge}`, '1', 'EX', 300);
  res.json(opts);
});

app.post('/webauthn/login/verify', async (req, res) => {
  // ... credentialId 로 passkey lookup
  const passkey = await db.passkeys.findByCredentialId(req.body.id);
  const v = await verifyAuthenticationResponse({
    response: req.body,
    expectedChallenge: ..., expectedOrigin, expectedRPID,
    authenticator: { credentialID: passkey.credentialId, credentialPublicKey: passkey.publicKey, counter: passkey.counter },
  });
  if (!v.verified) return res.status(401).end();
  await db.passkeys.update(passkey.id, { counter: v.authenticationInfo.newCounter });
  res.json(loginSuccess(passkey.userId));
});
```

### Client (browser)
```ts
import { startRegistration, startAuthentication } from '@simplewebauthn/browser';

const opts = await fetch('/webauthn/register/options').then(r => r.json());
const att = await startRegistration(opts); // 시스템 dialog
await fetch('/webauthn/register/verify', { method: 'POST', body: JSON.stringify(att) });
```

### Conditional UI (auto-fill passkey)
```html
<input type="text" name="username" autocomplete="username webauthn" />
```

```ts
const att = await startAuthentication({ ...opts, useBrowserAutofill: true });
```

## 🤔 의사결정 기준
| 사용자 / 환경 | 추천 |
|---|---|
| 일반 사용자 | TOTP + recovery codes |
| 보안 강 | TOTP + WebAuthn |
| 미래 / UX 최고 | Passkey (Apple/Google) |
| Enterprise SSO | SAML / OIDC + MFA on IdP |
| SMS | 비추 (SIM swap) — 다른 방법 없을 때만 |
| Hardware token | YubiKey + WebAuthn |

## ❌ 안티패턴
- **SMS only**: SIM swap.
- **TOTP secret 평문 저장**: 암호화 저장 또는 KMS.
- **Recovery codes 무제한 사용**: 1회용 필수.
- **Passkey 만 — fallback X**: device 잃으면 lock-out. recovery 같이.
- **Counter 검증 안 함 (WebAuthn)**: clone 방어 못 함.
- **Challenge 재사용**: replay 가능.
- **TOTP window 큼 (5+)**: 30초 코드 무의미.
- **2FA 우회 endpoint**: 모두 enforce.

## 🤖 LLM 활용 힌트
- TOTP = otplib + recovery codes.
- Passkey = @simplewebauthn (server + browser).
- 두 개 모두 지원 + recovery.

## 🔗 관련 문서
- [[Security_OWASP_Top_10_Practical]]
- [[Security_OAuth_Flows]]
- [[Security_Auth_Authz_Patterns]]
