diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 9c9d083b..fb5e5642 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -1,3 +1,7 @@
+## 2026-08-30 - [Sentinel: Unhandled ValueError in API Key Middleware]
+**Vulnerability:** Unhandled TypeError when processing non-ASCII API keys in `X-API-Key` header.
+**Learning:** Python's `hmac.compare_digest` raises a `TypeError` when comparing non-ASCII string arguments. If user input like an API key is passed directly to `compare_digest` without ensuring it is ASCII or encoding it to bytes, an attacker can crash the request process with a 500 server error by providing Unicode characters.
+**Prevention:** Always encode user-provided secrets and configured secrets to bytes (e.g., `.encode('utf-8')`) before passing them to `hmac.compare_digest`.
 ## 2026-07-25 - [Cross-platform upload basename normalization]
 **Behavior:** Upload metadata now interprets both forward slashes and backslashes as path separators before extracting a basename.
 **Learning:** On POSIX systems, `pathlib.Path(filename).name` retains backslashes because they are ordinary characters there. That caused inconsistent manifest and converter filenames for Windows-style client paths. The upload itself is still written inside a trusted temporary workspace, and batch archive entry names are generated outputs; this change does not establish a filesystem traversal or archive-entry escape.
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9313538b..84f7b42f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,5 +10,6 @@
 - 순수 영숫자 토큰은 정규식 호출을 건너뛰되 다국어·문장부호 토큰화 결과는 기존 의미와 동일하게 유지합니다. 근거, 한계, APA 7 참고문헌은 [`docs/doctoring/token-fast-path-equivalence.md`](docs/doctoring/token-fast-path-equivalence.md)에 기록했습니다.
 
 ### Fixed
+- 비 ASCII 문자가 포함된 `X-API-Key` 헤더를 처리할 때 `hmac.compare_digest`에서 발생하는 `TypeError`를 해결하기 위해, 비교 전 두 값을 UTF-8로 인코딩하도록 수정했습니다.
 - 단일·일괄 대상 크기 입력을 비웠을 때 이전 custom validity와 `aria-invalid` 상태를 즉시 초기화해 현재 필수 입력 상태를 정확히 전달합니다.
 - 업로드 파일명의 경로 구분자를 정규화하여 POSIX에서도 Windows 형식의 클라이언트 경로가 일관된 basename으로 기록되도록 수정했습니다.
diff --git a/saas_web.py b/saas_web.py
index 63265e94..071b1419 100644
--- a/saas_web.py
+++ b/saas_web.py
@@ -114,7 +114,7 @@ async def require_api_key(request: Request, call_next):
     if configured_keys and not (request.method == "GET" and request.url.path == "/"):
         provided_key = request.headers.get("x-api-key", "")
         if not any(
-            hmac.compare_digest(provided_key, key) for key in configured_keys
+            hmac.compare_digest(provided_key.encode("utf-8"), key.encode("utf-8")) for key in configured_keys
         ):
             return JSONResponse(
                 status_code=401,
diff --git a/tests/test_saas_web.py b/tests/test_saas_web.py
index 3b57e033..9701b8e2 100644
--- a/tests/test_saas_web.py
+++ b/tests/test_saas_web.py
@@ -1222,6 +1222,27 @@ def test_video_content_type_accepted_by_validator(self):
             )
         )
 
+    def test_unicode_api_key_handled_safely(self):
+        import asyncio
+        from fastapi import Request
+        from fastapi.responses import JSONResponse
+
+        class MockCallNext:
+            async def __call__(self, request):
+                return JSONResponse({"status": "ok"})
+
+        scope = {
+            "type": "http",
+            "method": "POST",
+            "url": "/shrink",
+            "headers": [(b"x-api-key", "안녕".encode("utf-8"))],
+        }
+
+        request = Request(scope)
+        with patch("saas_web.get_configured_api_keys", return_value=["secret1"]):
+            res = asyncio.run(saas_web.require_api_key(request, MockCallNext()))
+            self.assertEqual(res.status_code, 401)
+
 
 if __name__ == "__main__":
     unittest.main()