From ZmnSCPxj at protonmail.com  Wed Nov 28 05:51:37 2018
From: ZmnSCPxj at protonmail.com (ZmnSCPxj)
Date: Wed, 28 Nov 2018 05:51:37 +0000
Subject: [Lightning-dev] Offline Lightning-enabled Vending Machines
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Good morning list,

Since I have not spammed the list enough with pointless ideas, I consider now an extension of this idea, the meta-vending machine.

A vending machine contains products and dispenses them for proof that the owner of the machine has been paid.
A meta-vending machine contains vending machines and dispenses them for proof-of-payment.

In actuality, a meta-vending machine contains several machine-lockable boxes.
Each box is initially empty.
The contents of each box is visible.

Suppose I have a product I wish to sell.
I "rent" one of these boxes by paying the meta-vending machine owner (using the same technique already discussed below).
Then the box requests for my invoice.

Later, someone passes by the meta-vending machine, and sees my product and decides to purchase it.
The meta-vending machine provides the invoice, and in exchange for the preimage to the hash in the invoice, opens the bos and lets the buyer get th product.
The box can then be reused by another seller.

Suppose the product is not sold.
Since I know the preimage, I can also provide the preimage and get my product back.
I could then replace the product, or sell another product, or refresh the invoice.

Such an automated system would be useful for selling small items.
Depending on the security of the machine itself, the value of the item may be large.
It can also be used as a somewhat-anonymous rendezvous point for transferring small items in exchange for money, such as valuable collectible cards.

In essence, such a meta-vending machine provides an HTLC-like behavior in the real world, and allows us to extend the ZKCP by one hop into real-world items.

Of course, trust is now needed in the meta-vending machine owner.
Presumably the meta-vending machine owner can simply unlock any arbitrary box and take the item inside.
Thus the practical maximum value of the items sold via such a machine may be limited by the trustworthiness of the meta-vending machine owner.

Regards,
ZmnSCPxj