[Cryptography] [ANNOUNCE] HashCash Digital Cash

[Patrick Chkoreff]

Rune K. Svendsen wrote on 06/23/2017 12:25 PM:

> With regards to HashCash, I see no way it prevents double-spending,
> except upon redemption. Is this the case? Can a receiver not know
> whether a HashCash coin he gets from a payer is a double-spend, unless
> he tries to redeem it (or otherwise ask the server/issuer)?

Certainly if you receive a coin from someone and you wish to be
absolutely certain it hasn't already been spent, you exchange it at the
vault for a new coin immediately.

However, if you trust the payer, you might hold onto the original coin,
and even pay it to someone else, without exchanging it.


> I've thought about Chaumian cash on top of Bitcoin, but I couldn't find
> a solution to the double-spend problem, so I'm curious to know if you
> have one. If it involves contacting the issuer to ask for validity,
> what's the point of having a digital instrument serve as cash, when you
> need to query a server for its validity anyway? That's not very cash-like.

I am pretty sure you're asking the impossible there.  When you give
someone a digital object, you both have a copy.  Not so with a physical
object.  Therefore to be certain of transfer of ownership of a digital
object, you'll need to contact a server.

To my ears, asking for a digital cash system without any server involved
sounds as unrealistic as asking that two plus two be five.  I really
think it's on the same level of logical absurdity.


-- Patrick