diff --git a/keyserver/src/session/cookies.js b/keyserver/src/session/cookies.js
--- a/keyserver/src/session/cookies.js
+++ b/keyserver/src/session/cookies.js
@@ -807,6 +807,22 @@
   await dbQuery(query);
 }
 
+// Returns `true` if row with `id = cookieID` exists AND
+// `signed_identity_keys` is `NULL`. Otherwise, returns `false`.
+async function isCookieMissingSignedIdentityKeysBlob(
+  cookieID: string,
+): Promise<boolean> {
+  const query = SQL`
+    SELECT signed_identity_keys
+    FROM cookies 
+    WHERE id = ${cookieID}
+  `;
+  const [queryResult] = await dbQuery(query);
+  return (
+    queryResult.length === 1 && queryResult[0].signed_identity_keys === null
+  );
+}
+
 async function setCookiePlatform(
   viewer: Viewer,
   platform: Platform,
@@ -855,6 +871,7 @@
   addCookieToJSONResponse,
   addCookieToHomeResponse,
   setCookieSignedIdentityKeysBlob,
+  isCookieMissingSignedIdentityKeysBlob,
   setCookiePlatform,
   setCookiePlatformDetails,
 };