Half-offline capability
The combination of ownership and publicly verifiable mint signatures allows for transactions in which the recipient can do a check against double-spends without having to communicate with the mint. The recipient only has to keep record of the DBCs sent to it that have a specific owner. If a DBC is presented twice a double spend is detected, if the DBC is unique and carries a valid signature by the mint the recipient can be sure that the DBC will be accepted by the mint for reissue at a later point in time. Since DBCs can include two owners that are exclusive to each other and cover two defined time spans, it is also possible to pre-generate DBCs to be used in an offline manner at a later point in time. The user simply generates DBCs for the intended recipient that after a certain time fall back to be reissue-able by the user’s key. This allows transactions between two parties in which both can be offline for a defined, possibly very long, time span without needing to interact with the mint. This makes the system very usable for scenarios of mobile point of sales transactions and simple hardware implementations, such as in the case of payment cards, public transport tickets, etc. Furthermore it makes the system much less vulnerable against denial of service attacks. To clarify: There are only two cases which require one of the transaction parties to talk to the mint during the transaction: The recipient is unknown, or the payment amount is unknown. In all other cases the transaction can be structured so that no communication with the mint is required during the transaction.
To me this kind of reads like you have to know the recipient but I thought that DBC doesn’t require accounts. Also when we speak of double spend, I don’t believe there is any issue with double spending in the system itself but maybe what we are referring to is someone handing off a DBC offline saying it holds value and the recipient possibly being duped before redemption as the details or keys of the DBC were recorded and the value already swept. Is that what we’re talking about here @jlpell? You have any ideas? When I have more time soon I plan on seeing if there are any previously used solutions.