ZIP request: UX standard for specifying where fees come from.

[nathan-at-least]

Every time I ever use any cryptocurrency wallet, I am never quite sure which amount or balance the miner's fee will come out of. Let's fix that in the Zcash ecosystem with a ZIP that specifies a standardized usability behavior for all conforming wallets.

My Preference:

To get the ball rolling, in my opinion, when a user requests that an amount X of ZEC is to be transferred to a recipient address, then the associated transaction(s) should result in precisely X ZEC arriving at the recipient address. This implies that any fees come from the sender's balance in addition to all requested ZEC transfers.

To clarify with an example:

• Alice requests sending 1.234567 ZEC to Bob and 0.042 ZEC to Celia.
• Everybody involved uses Sapling addresses, because they're all down with the kids these days and in the know.
• Alice's wallet chooses to fulfill the request with a single transaction, which has the standard fully shielded fee of 0.0001, so Alice's user interface presents her with a confirmation display with the transaction plan.
• The transaction plan displays the recipient addresses receiving the amounts above, and includes an obvious separate line item saying "Transaction Miner Fee" of 0.0001.
• It also displays a delta to Alice's balance, should she accept this transaction plan, and that delta sums to -1.276667 = - (1.234567 + 0.042 + 0.0001)
• Alice accepts the plan, and the wallet (eventually) generates the transaction, safely emits it to the network privately, then notifies Alice when the result has been finalized.

Note: I tried to write this to account for wallets that might do fancy things like issue multiple transactions to meet a user's request for privacy or performance reasons, or any other reason. I think that basically boils down to focusing on a "transaction plan" to fulfill the user's request on the Zcash ledger over time. Is that general enough, while still obviously applicable to most present day wallets that have a very simplistic planning behavior?

Requests for Feedback:

• Do secure UX experts agree that this proposal is relatively sensible?
• Do secure UX experts agree that this proposal is the best approach, or is another approach better?
• Do cryptography or privacy tech experts have any thoughts here?

Requests for Help:

It's likely I won't have time within the next several months to flesh out this ZIP. Is anyone else available to chip in? I can probably pop in on occasion to do reviews / edits or help in other ways.

[defuse]

A related problem I've had: When I'm trying to send all my ZEC somewhere, I copy-paste the same z_sendmany command I normally use for sending ZEC, and I usually screw up by subtracting 0.01 or 0.001 instead of 0.0001.

I really like the idea of having UX standard ZIPs!

[adityapk00]

This makes sense to me, and is the current behaviour of Zecwallet. The fees are always paid by the sender, and the amount requested/shown in the UI is what is sent to the destination, with the additional ZEC 0.0001 coming from the sender.

[daira]

I support the proposed sender-pays-fee standard.