From c77b4efed4107ab7a3fd756c1c6747567af84281 Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Fri, 3 Jul 2026 21:20:22 +0000
Subject: [PATCH] Fix timing attack in token authentication

The previous implementation of token authentication in `src/cli/commands/serve.ts` short-circuited constant-time comparison if the lengths of the provided token and expected token did not match. This allowed attackers to infer the length of a token via a timing side channel. This fix hashes both the provided and expected tokens to a fixed length using SHA-256 prior to calling `crypto.timingSafeEqual`, ensuring a true constant-time comparison.
---
 .jules/sentinel.md                         | 4 ++++
 src/cli/commands/serve.ts                  | 7 +++----
 tests/integration/prompt_templates.test.ts | 4 +++-
 3 files changed, 10 insertions(+), 5 deletions(-)
 create mode 100644 .jules/sentinel.md

diff --git a/.jules/sentinel.md b/.jules/sentinel.md
new file mode 100644
index 00000000..c8db18a4
--- /dev/null
+++ b/.jules/sentinel.md
@@ -0,0 +1,4 @@
+## 2025-02-14 - Fix Timing Attack in Authentication
+**Vulnerability:** Fast-path short-circuiting in token validation using buffer length comparisons before calling `crypto.timingSafeEqual` introduces a timing attack vulnerability.
+**Learning:** Evaluating the lengths of tokens before performing a constant-time comparison leaks the length of the secret auth token.
+**Prevention:** Always hash both the expected and provided secrets to a fixed length (e.g., using `crypto.createHash('sha256')`) before comparison to ensure true constant-time evaluation regardless of input length.
diff --git a/src/cli/commands/serve.ts b/src/cli/commands/serve.ts
index 2c37293e..09448b63 100644
--- a/src/cli/commands/serve.ts
+++ b/src/cli/commands/serve.ts
@@ -349,10 +349,9 @@ export async function handleServeCommand(_options: unknown, command: Command) {
             const tokenBuffer = Buffer.from(token);
             for (const authToken of authTokens) {
               const authTokenBuffer = Buffer.from(authToken);
-              if (
-                tokenBuffer.length === authTokenBuffer.length &&
-                crypto.timingSafeEqual(tokenBuffer, authTokenBuffer)
-              ) {
+              const tokenHash = crypto.createHash('sha256').update(tokenBuffer).digest();
+              const expectedHash = crypto.createHash('sha256').update(authTokenBuffer).digest();
+              if (crypto.timingSafeEqual(tokenHash, expectedHash)) {
                 isAuthenticated = true;
                 break;
               }
diff --git a/tests/integration/prompt_templates.test.ts b/tests/integration/prompt_templates.test.ts
index 21905259..f1360d78 100644
--- a/tests/integration/prompt_templates.test.ts
+++ b/tests/integration/prompt_templates.test.ts
@@ -36,7 +36,9 @@ describe('Prompt templates', () => {
 
     expect(planSystem).toContain('You are SalmonLoop.');
     expect(patchSystem).toContain('You are PATCH, a phase-native diff compiler.');
-    expect(autopilotSystem).toContain('You are a senior software engineer running in "autopilot" mode.');
+    expect(autopilotSystem).toContain(
+      'You are a senior software engineer running in "autopilot" mode.',
+    );
     expect(answerSystem).toContain('You are a coding assistant in "answer" mode.');
     expect(researchSystem).toContain('You are a research assistant.');
   });