my lips are sealed 守口如瓶；我把嘴封住；我绝口不提

【例句】
As for anything told to me in confidence, well, my lips are sealed.
至于私底下告诉我的任何事情，我会守口如瓶的。

You can count on me, my lips are sealed.
你可以信得过我，我的嘴很严。