Today’s invention is a private key encryption device which relies on fluid dynamics.
Highly viscous flow at low velocity is, near-as-dammit, reversible.
Today’s invention is to use an apparatus such as that in the film linked to above. A message (or an image) would be printed into the body of a gel-like material using eg laser-based rapid prototyping techniques.
This would then be subject to a pattern of low speed rotational shear flow, using a rotary system as shown, to obscure the content. This rotation would however be undertaken by an inner cylinder which could move both circumferentially and axially (as controlled by the user’s choice from a large number of screw cam ‘keys’). The gel could then be transported physically anywhere without the message being decipherable.
It might even be possible to send only images of the gel electronically (ie its local contrast distribution). On receipt of the message, it could be decoded by reversing the action of the original key.