diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 9c9d083b..9040d758 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -65,3 +65,8 @@
 **Vulnerability:** Path traversal in `media_shrinker.py` via unresolved `..` segments or symlink escapes before deriving conversion output paths.
 **Learning:** `Path.relative_to()` is only a lexical containment check unless both the source and root have first been resolved into canonical absolute paths. Relative paths and symlinks can otherwise bypass root-boundary assumptions.
 **Prevention:** Resolve both source and root once, reject sources outside the resolved root with a sanitized `MediaShrinkerError`, and derive `rel_source` from the resolved paths before planning outputs.
+
+## 2024-05-31 - [Sentinel: Unhandled UnicodeError in hmac.compare_digest]
+**취약점:** `hmac.compare_digest()` 사용 시 비 ASCII 문자가 입력으로 들어올 때 발생하는 `TypeError`를 통한 500 서버 에러 (DoS 취약점).
+**학습:** Python의 `hmac.compare_digest()`는 비 ASCII 문자가 포함된 문자열(`str`) 인스턴스를 비교할 때 예외(`TypeError`)를 발생시킵니다. 웹 프레임워크 미들웨어에서 인증 헤더와 같이 사용자 제어가 가능한 입력을 이 함수로 직접 비교하면 악의적인 사용자가 비 ASCII 문자(예: 이모지)를 전송하여 서비스 거부 상태를 유발할 수 있습니다.
+**예방:** `hmac.compare_digest()`에 전달되는 모든 문자열 인수는 명시적으로 바이트(`.encode('utf-8')`)로 인코딩하여 비교해야 합니다.
diff --git a/saas_web.py b/saas_web.py
index 63265e94..7a1b8900 100644
--- a/saas_web.py
+++ b/saas_web.py
@@ -113,8 +113,9 @@ async def require_api_key(request: Request, call_next):
     configured_keys = get_configured_api_keys()
     if configured_keys and not (request.method == "GET" and request.url.path == "/"):
         provided_key = request.headers.get("x-api-key", "")
+        provided_key_bytes = provided_key.encode('utf-8')
         if not any(
-            hmac.compare_digest(provided_key, key) for key in configured_keys
+            hmac.compare_digest(provided_key_bytes, 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..c3c8468f 100644
--- a/tests/test_saas_web.py
+++ b/tests/test_saas_web.py
@@ -32,6 +32,36 @@
     _HAS_FASTAPI, "fastapi not installed (optional integration dependency)"
 )
 class TestSaasWeb(unittest.TestCase):
+    def test_require_api_key_non_ascii_header(self):
+        from starlette.requests import Request
+        from starlette.responses import JSONResponse
+        import asyncio
+
+        scope = {
+            'type': 'http',
+            'method': 'POST',
+            'path': '/jobs',
+            'headers': [(b'x-api-key', b'test\xf0\x9f\x98\x80')]  # 'test😀' in utf-8
+        }
+        request = Request(scope)
+
+        async def mock_call_next(req):
+            return JSONResponse(status_code=200, content={"status": "ok"})
+
+        import os
+        import saas_web
+
+        original_keys = os.environ.get("CODEC_CARVER_API_KEYS")
+        os.environ["CODEC_CARVER_API_KEYS"] = "testkey"
+        try:
+            response = asyncio.run(saas_web.require_api_key(request, mock_call_next))
+            self.assertEqual(response.status_code, 401)
+        finally:
+            if original_keys is not None:
+                os.environ["CODEC_CARVER_API_KEYS"] = original_keys
+            else:
+                del os.environ["CODEC_CARVER_API_KEYS"]
+
     def test_get_ui(self):
         response = client.get("/")
         self.assertEqual(response.status_code, 200)