diff --git a/.jules/sentinel.md b/.jules/sentinel.md
new file mode 100644
index 0000000..0c850a3
--- /dev/null
+++ b/.jules/sentinel.md
@@ -0,0 +1,4 @@
+## 2024-04-08 - [TOCTOU in SSH Key Generation]
+**Vulnerability:** SSH private keys were temporarily written to disk with default permissions before `chmod 600` was applied, creating a Time-of-Check to Time-of-Use (TOCTOU) vulnerability where other users could theoretically read the key in the brief window between creation and permission change.
+**Learning:** Shell redirection (`>`) creates files with default umask permissions. Applying `chmod` immediately after still leaves a race condition.
+**Prevention:** Shell scripts handling sensitive data must enforce strict access control using `umask 077` (globally or in a subshell) before file creation to prevent TOCTOU vulnerabilities.
diff --git a/tools/setup-ssh-keys.sh b/tools/setup-ssh-keys.sh
index bde52fd..f7db0c9 100755
--- a/tools/setup-ssh-keys.sh
+++ b/tools/setup-ssh-keys.sh
@@ -152,13 +152,17 @@ cmd_restore() {
     mkdir -p "$SSH_DIR"
     chmod 700 "$SSH_DIR"
 
-    # Read private key from 1Password and save locally
-    op read "op://$VAULT/$KEY_NAME/private_key" > "$PRIVATE_KEY_FILE"
-    chmod 600 "$PRIVATE_KEY_FILE"
+    # Read private key from 1Password and save locally (prevent TOCTOU)
+    (
+        umask 077
+        op read "op://$VAULT/$KEY_NAME/private_key" > "$PRIVATE_KEY_FILE"
+    )
 
     # Read public key from 1Password and save locally
-    op read "op://$VAULT/$KEY_NAME/public_key" > "$PUBLIC_KEY_FILE"
-    chmod 644 "$PUBLIC_KEY_FILE"
+    (
+        umask 022
+        op read "op://$VAULT/$KEY_NAME/public_key" > "$PUBLIC_KEY_FILE"
+    )
 
     say "SSH key restored to $SSH_DIR"
     echo ""