In Shufflecake, each hidden volume is encrypted with a different secret key, scrambled across the empty space of an underlying existing storage medium, and indistinguishable from random noise when not decrypted. Even if the presence of the Shufflecake software itself cannot be hidden - and hence the presence of secret volumes is suspected - the number of volumes is also hidden. This allows a user to create a hierarchy of plausible deniability, where "most hidden" secret volumes are buried under "less hidden" decoy volumes, whose passwords can be surrendered under pressure. In other words, a user can plausibly "lie" to a coercive adversary about the existence of hidden data, by providing a password that unlocks "decoy" data. Every volume can be managed independently as a virtual block device, i.e. partitioned, formatted with any filesystem of choice, and mounted and dismounted like a normal disc. The whole system is very fast, with I/O performance surpassing the most popular disk encryption tools under many scenarios, and with negligible waste of memory and disc space.

dang

I think most data need to be ephemeral but some needs to be hidden.