Encrypted Compressed Air

In regular uncompressed air in a container, the position of all the air molecules within the container is fairly random. You can compress the air by pushing all the air molecules into, for example, the lower half of the container.

In encrypted compressed air, the container is divided into a huge number of cells, which contain an average of 1 air molecule each, but sometimes more or less. The distribution of all the air molecules between the cells appears fairly random, but it's actually generated by a cryptographic random number generator, from a secret seed/key.

Someone with the key can open all the cells with more air molecules than average (while leaving the empty cells closed), and get compressed air out. But if someone steals the containers as they are being shipped from the manufacturer to the buyer, without the key, it is effectively just full of regular air.

If it's too hard to exactly control the exact number of molecules in each cell, the manufacturer can just expose some cells (while open) to compressed air, and others to a vacuum. This will give an approximate distribution of the molecules, and still allow the receiver to extract compressed air.