What security forbids

What can no combination of access control, protection and privacy give you, and what position is left to choose?

What this mechanism forbids, in total

These are the impossibility statements of this whole mechanism. Each is a limit, not a lack of effort.

• You cannot enforce above the narrowest waist.
• You cannot have stateless verification with immediate revocation (a self-contained token cannot be recalled before it expires).
• You cannot preserve authorization context across an asynchronous boundary (a queue, a job, a cache).
• You cannot list the effective access under an expressive policy language.
• You cannot protect data from its own legitimate processing path, because the key must be available where the data is used.
• You cannot compress ciphertext, and compressing a secret alongside attacker-controlled input leaks it through length.
• You cannot encrypt a column and keep pruning on it, and any relation you keep to avoid that is a relation you have published.
• You cannot anonymize with any deterministic transform.
• You cannot bound inference with cell-level access control.
• You cannot compose syntactic privacy guarantees.
• You cannot delete from a trained model cheaply.
• You cannot combine key custody with server-side computation.
• You cannot go beyond the jurisdiction of whoever holds the enforcement point.