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Comment by moviuro | Hacker News Reader

1. Without giving it much thought, it's probably impossible to prevent "replay" attacks. If I have listed tens of valid signatures, I can use them on my new fake bars on the other side of the world, hoping my fake bar with good signature never meets its genuine alter-ego.

2. This sounds sane and feasible, but I'm not sure how anyone would deal with a bar leaving and then re-entering the system. If I'm a jeweller, I might buy a kilobar and melt it for rings, etc. It's inscribed as having left my seller's stock, just as the bar I bought as a random individual. One bar is meant to reenter the market, the other one not so much... how would you deal with that?

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> One bar is meant to reenter the market, the other one not so much... how would you deal with that?

I'm not super knowledgeable about blockchain, but couldn't we arrange for jewelers and such to gift it to a special individual called dev_null, whose wallet keys have been intentionally lost?

The jeweler could be able to mark his bar as destroyed in the chain, perhaps registering the rings in a separate chain?

That way, if every entity that handles or processes gold did the same, you could have a good idea of where each piece of gold comes from.

The originator of the bar/signature could track each one and disavow the ones they lost track of.

Not a great solution, but it would reduce replay attacks.

The jeweler could notify the originator that they destroyed a bar.

> disavow the ones they lost track of

So as an individual, I have to trust the originator to keep the whereabouts of my kilobar private?... This is most probably a very bad idea.

Sure, it wouldn't serve all purposes. But for a jeweler that wanted an auditable supply chain, it would be fine.

For buyers wanting privacy, the could have a mechanism for the seller to tell them to discard the signature. It makes it useless for future transactions of course, but it would prevent replay up until point.

Why would you melt marked gold to make jewlery and diminish its value? You can use regular gold for that.

At that point why use gold at all? If the value is in the marking, not the gold itself, then there are much better ways to create hard to duplicate markings than stamping them into gold bars...

You can view it as certified gold, where the certificate is stamped directly on the item by the CA (refinery). There is a certain added value in the marking because the marked piece is standardised in purity and weight, so one used to be sure they were getting the real deal. Well, not anymore. That's exactly what the forgers are speculating: the market price difference between regular and marked gold.

That’s not speculation. That’s arbitrage.

But it’s also not traditional arbitrage. The producers of these counterfeit bars would likely be delighted to have the real gold minting houses certify and stamp their gold for a reasonable price. But they can’t because of sanctions or possibly capital controls. This counterfeiting is about bypassing market controls to trade illicit gold.

They are not looking to actually obtain any exposure on the stamped gold or illicit gold. The goal here is to arbitrage between these two prices and while doing so convert dirty money into clean money. Speculation is the last thing these people are doing or want.

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