It's been proposed that [cryptocurrency] is a good tag for discussions about Wiesner's protocol and other quantum monies. I'm OK with it, but I'm wondering if there would be something better?

The security of cryptocurrencies is, in general, derived from a distributed consensus of the trusted "longest chain" of a ledger. Bitcoin and others famously require a proof-of-work to generate the longest ledger, which is based on the presumed difficulty of inverting a cryptographic hash.

The security of quantum money schemes, going all the way back to Wiesner, are derived from some version of the no-cloning theorem, which is based on the presumed linearity of quantum mechanics.

At first blush, they seem different. Hybrid systems are being envisioned, wherein the serial number of a quantum coin is put onto a classical distributed ledger, etc., but, as far as I can tell, the development of quantum moneys has mostly been on a separate intellectual path from that of cryptocurrencies, maybe only recently merging. (There's a footnote to Bitcoin in Aaronson and Christiano, which came out at about the same time).

Furthermore, the ECDSA system underlying the accounting of Bitcoin is insecure under a quantum computer over Shor, while the SHA256 "proof-of-work" system has not been shown to be insecure under a quantum computer. Thus, the perennial question about quantum computers and Bitcoin security is not a question about quantum money, ala Wiesner.

The mouse-over for [cryptocurrency] reminds askers to focus on "quantum" aspects. Also, a tag for [cryptocurrency] might encourage spammers?

If there are questions unique to Wiesner's scheme, or Aaonson and Christiano or FGHLS, is [cryptocurrency] still the best tag for now?

  • $\begingroup$ quantum-money & quantum-cryptocurrency both seem like valid tags $\endgroup$
    – user820789
    Commented Jul 13, 2018 at 5:53

1 Answer 1


It seems that you made the tag on 14 August 2018, about 1 month after this Meta post. I suppose that would be the tag to use on such questions! However with only 8 questions having that tag, after more than 3 years on the site, and with 7 out of 8 of the tag also having the tag (which itself only has 11 questions right now), the need for such a tag is questionable.

The only question which doesn't have the tag is this one (by you!): Do we have to trust the bank in "Quantum Money from Hidden Subspaces?". It does have the tag though. Are you sure there is not possible justification whatsoever, to give this the tag?

Also I'll point out that has only 2 watchers (maybe one is you, MarkS?) and has 0 watchers (so perhaps could be merged with ).

Finally I'll point out that 5/8 of the questions with the are asked by yourself (MarkS). Maybe we can wait longer before having further discussions about what to do with these tags, but at present it does seem like they are very niche tags that might be better off merged or synonymized with other more healthy tags.

  • $\begingroup$ I was kind of new to the game a while ago when I asked this question and didn't have the know-how or the rep to add the tag when I asked the q. But you're right! I am one of the watchers on quantum-money, which I think is wholeheartedly a better tag than cryptocurrency, as cryptocurrency might invite spam, and also e.g. Wiesner's scheme etc. has nothing to do with [cryptocurrency]. Although it's niche within q-computing, it certainly is or has been an active area of research by many in the field (Farhi, Shor, Aaronson, Watrous, Sattath, etc.) more so that c-currency... $\endgroup$ Commented Apr 16, 2021 at 23:02

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