Private Point-of-Sale (PPoS) Protocol
A private point-of-sale protocol (PPoS).
Note: this project is inspired by @abigger87's cloaks and a Hayden Adam's tweet about McDonald's equity being tokenized
Keeping orders private every time
Since menus generally have a limited number of items, we need to ensure that the hashed order inputs into the order() function are unique every time. That is, an order input value, i.e. one Chicken Pesto Parm, will return a unique hashed output for every new order of the same item. The intent of uniquely hashed order values for every individual order is to increase the level of privacy for Alice's order history.
We can achieve this by adding a salt value along with the hash of the order.
Attack vectors
1. Order contents
One potential attack vector is the publicly available price that is paid for the order. Since the same order, containing the exact same items, will have the same total price, one could deduce the list of items that were in the order.
2. Anticipating order schedules
With the information provided by the order contents that an account address makes, with a complete history of scheduled purchases (i.e. they know when the account usually makes their orders from public transaction history on-chain), a malicious actor could create and submit a volley of fake orders to drive up gas prices for their victims. The malicious actor could also buy out certain items from a vendors menu, preventing their target from being able to make their regularly order. Further protocol design and research could be done to further reduce these kinds of attacks.
Architecture
Critical features of the PPoS protocol include:
1. MEV minimization
Out-going transactions from the PPoS protocol are protected against MEV, i.e. against:
- frontrunning
- targeted attacks on order schedules (causes havoc for either the vendor or consumer)
- etc.
2. Privacy
In-going and out-going transactions to the PPoS protocol are kept private from external parties to maximize order confidentiality.
3. Fast confirmations/receipts
In traditional finance, consumer orders are typically processed instantly, along with a receipt that is sent to the buyer.
PPoS aims to maintain the same level of speed for order confirmations and receipts so that consumer purchases/sales feel just as familiar as in the tradfi world.
Appendix
i. Only stablecoins, initially
An obvious decision, yet it must be noted that users of the PPoS protocol can only use stablecoins, at least initially, to pay for items from vendors (sellers).
Although only stablecoins will be accepted initially by default, in the future, there could be other contracts/protocols that offer the feature to create escrow contracts between parties that enable purchases/sales with alternative tokens, e.g. ETH, WETH, WBTC, etc.