Industry standards on cash protocol

 It is up to the industry. I have n idea!

Any cash signature can be arrange in a square and the public currency ledger is displayed. And that pack of digits can be validated by the hand held, it is fab compliant in the shared secret keys.  The hand held can scan through the cash accounts for various currency regimes fairly fast, sy, to validate a visa, just flip until the visa is visible and show that to the clerk. Your grandma can actually issue a semi liquid contract to wash your house, and you can see her signature quite visibly on the contract. It is a pre paid cash contract, you bought her a sack of potatoes last week.  The visible verification could be a thumbprint, and ultimately is. You hold the bag up from your pleading grandma until she prints the contract.

Fab manager and cash protocol.  The fab proves cash when the Fab defines the native security coin, the chip metric that proves cash up to a published limit. It is another linked contract, no cash protocol can be safer than the hand held security coin. The fab buries that protocol in protected kernel code, and is an integral part of spectre compliance. It really is the kernel making sure another currency protocol doesn't sniff out you cash levels from cache traces.

Scroll down and read the series on analog logic keys, this is complete and provable, all these contract links bounded and stable.