The secure key fob

It can hold secret keys, even hiding a key from the owner. Yje fob can generate a secret key, hiding it from everyone. But from that secret key the fob generates public keys with the power to verify your signature. In the simple  swap, I can issue a public key to my notary bot with the power to revoke within timeout.  We can see this action repeated over more complex swaps. The key fob need not have pipeline control, (no double spend except by counterfeit processor).  The double spend problem managed by notaries over the ledgers. Not everything need be a pipeline controlled, handheld.