I've uploaded "Box Short.stl" and "Lid Short.stl" which are 62.5% of the original height of the box for those not requiring the size of the original box. These components also include a minor improvement in the design of the hidden corners for assisting in holding the box closed. I test printed both components and they printed fine.
END OF UPDATE.
I've seen many of these over the years, the latest I found a few years ago made of wood. This 3D printed version is a very simple, yet pretty effective "secret" box.
Even with pretty close examination, it appears as if there is no way to open the box. Only by gripping the correct opposite corners on the correct end and pulling, will the box open.
Designed using Sketchup Make 2015, and printed in PLA on a Makerbot Replicator 2 using Makerware 22.214.171.124 "Standard" Settings (.2mm layer height, 2 shells, 10% infill).