keep (something) close to (one's) chest
To keep one's plans, intentions, or tactics secret from everyone else. Refers to holding one's playing cards close to one's chest in a card game, so as not to allow other players to see one's hand. We're all curious about what the boss has been discussing in those meetings with the lawyers, but she's keeping it close to her chest. Sorry for not being more straightforward about my plans, but I'm keeping this one close to the chest for the time being.