My lips are sealed ---------- 守口如瓶（成语）

英文释义
（IDIOM）An interjection assuring the listener that you will reveal no secrets.

例句
When my brother told me his secret plan for a new business, I told him "my lips are sealed" and he knew he could trust me.
当我的兄弟把他的新商业秘密计划告诉我时，我对他说：“我会守口如瓶。”他知道，他可以信任我。