Can anybody explain the term "anonymous admissible timestamp" to me? Could you show a case where it is useful to apply it?
I came across this term in the comments of a question on the StackExchange Computer Science site.
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What he meant is quite unclear. It could be that he's referring to a Timestamping Authority (TA) (See related RFC like 3161). What they do is basically sign a document/hash with the current time and date and sequential transaction id (IIRC).
Ideally, the TA is public and anonymous, allowing anyone to submit any hash and get a signed timestamp for it, the list of signed transaction freely available for anyone to check and verify.
If I refer to the scenario, the bar could issue anonymous 'tickets' containing a unique and untraceable identifier, meaning the bar doesn't keep tabs (pun intended) to whom a given identifier belongs to. In practical terms, they might just have a check to avoid giving multiple tickets to the same person. When the user wants to get his beer, he gets a stamp from the TA by submitting the ticket content (or hash thereof), and forward the stamp to the bartender. Receiving the stamp, the bartender execute a lookup request to match the ticket to all the related transactions and check the date of the two last transactions (validating the stamp signature as well obviously). If they are separated by at least an hour, the stamp is deemed valid.
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$\begingroup$ I did not understand how you want to avoid documenting to whom a given identifier belongs to, and at the same time avoid giving multiple tickets to the same person (did you mean before he cashes his current ticket?).... Also, if you do have a clever way to avoid giving multiple tickets to the same person, then instead of working with tickets, you can just give them a beer on the first time they show up, and then if they showed up again too soon, you wouldn't give them a beer and tell them to wait (you could do this because you had some way to avoid giving multiple things to the same person). $\endgroup$– raptCommented Dec 6, 2018 at 18:14
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$\begingroup$ That's the problem with analogy, it's difficult to match to the real problem. It could just be a list of clients, with a 'check-mark: has received free beer ticket'. After that, you can't track how much one client drinks, while still restricting the free beer to one per hour. Obviously, if you don't have some kind of control as to whom you give the tickets in the first place, it becomes complicated. $\endgroup$– M'vyCommented Dec 6, 2018 at 20:53
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$\begingroup$ This list of beer receivers will require people to prove their identity, e.g. by showing a passport, which is kinda strict, NSA heaven. Do you see any chance to work around it? And another thing - how do you actually implement the "untraceable" part in "anonymous 'tickets' containing a unique and untraceable identifier" in an online system? Let's say I send my passport docs and the system creates my account and puts there my 1st ticket with some ID, which the system associates with my account. Then all the next times I submit a ticket, the system knows it's from my account, thus from me. $\endgroup$– raptCommented Dec 7, 2018 at 20:40
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$\begingroup$ If you want anonymity, but still uniqueness, you need a party to take care of the uniqueness, and giving out the tickets which the second party can't use to track (or if first = second party, hand tickets out and 'forget' the id on the ticket). The question is about the timestamping part, if you need more details on the scenario, you should probably make a new question with more details about this scenario. $\endgroup$– M'vyCommented Dec 7, 2018 at 22:21
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$\begingroup$ Thank you! Your answer definitely clarified the term I asked about in my question. $\endgroup$– raptCommented Dec 8, 2018 at 21:58