```Python hl_lines="1  11-13"
{!../../../docs_src/security/tutorial007.py!}
```

这段代码确保 `credentials.username` 是 `"stanleyjobson"`，且 `credentials.password` 是`"swordfish"`。与以下代码类似：

```Python
if not (credentials.username == "stanleyjobson") or not (credentials.password == "swordfish"):
    # Return some error
    ...
```

但使用 `secrets.compare_digest()`，可以防御**时差攻击**，更加安全。

### 时差攻击

什么是**时差攻击**？

#### Die Zeit zum Antworten hilft den Angreifern

Wenn die Angreifer zu diesem Zeitpunkt feststellen, dass der Server einige Mikrosekunden länger braucht, um die Antwort „Incorrect username or password“ zu senden, wissen sie, dass sie _etwas_ richtig gemacht haben, einige der Anfangsbuchstaben waren richtig.

If it doesn't receive it, it returns an HTTP 401 "Unauthorized" error.

And returns a header `WWW-Authenticate` with a value of `Basic`, and an optional `realm` parameter.

That tells the browser to show the integrated prompt for a username and password.

Then, when you type that username and password, the browser sends them in the header automatically.

🍵 👈, 👥 🥇 🗜 `username` & `password` `bytes` 🔢 👫 ⏮️ 🔠-8️⃣.

⤴️ 👥 💪 ⚙️ `secrets.compare_digest()` 🚚 👈 `credentials.username` `"stanleyjobson"`, & 👈 `credentials.password` `"swordfish"`.

```Python hl_lines="1  11-21"
{!../../../docs_src/security/tutorial007.py!}
```

👉 🔜 🎏:

```Python
if not (credentials.username == "stanleyjobson") or not (credentials.password == "swordfish"):
    # Return some error