To keep under wraps

To keep under wraps - to keep something concealed until some future time.

Example - "We kept the plan under wraps until after the election"

Image - http://media3.popsugar-assets.com/files/2014/05/26/063/n/24155406/92bff4ca62d91e67_2628431835_669ef923c3_o.xxxlarge/i/Keep-Under-Wraps.jpg