> It can not be spoofed due to having been signed by a verified key

Let's say I have a Rolex watch. This "item" has an entry in a publicly available blockchain available to everyone. Who's to stop anyone from producing a "Rolex" watch pointing to the exact same entry on the blockchain?

> The link/hash can of course also be encoded in a QR code.

Indeed. So how exactly does blockchain protect against counterfeit goods?

Whenever the key is checked, the software that checks the key creates an entry in the blockchain.

Using your example of a Rolex, the code can be scanned by the authorised dealer and buyer. Those events are then stored in the blockchain next to the cryptographic hashes of both entities.

Any authorised dealer who buys one for resale would scan the QR code so ownership can be transferred in the same way on a public ledger.

If there's a public record that this Rolex has been purchased already and you scan it, this record would show up. It could even show exactly where and when it was purchased.

Clearly, for someone to put a real cryptographic key on a fake Rolex, they need to have taken it from a real one.

So if someone tries to sell you a "Rolex" and you scan it, you'll have the history of the watch right there. If they try to claim it's new, you'll know that's a lie. If they try to sell it to an authorised dealer, they'll get caught.

This could still leave space for fake Rolexes to be sold as used on eBay or something of course, but then if you buy a "Rolex" on eBay from a random seller (not an AD) you kind of know what you're getting already don't you?

(Although even in those situations, knowing exactly when and where the real watch was last purchased makes it easy to just make a phone call and get a better idea of legitimacy. Currently, even ADs send the watches to Rolex for verification because the fakes are so good.)

Your example seems to be mostly coordinated through Rolex and authorized dealers, so what is the advantage of a blockchain? Why not just have Rolex keep track of who owns a watch through e.g. a web interface tied to a serial number + username/password combination, that also allows transferring of the ownership of a watch to a different user? This would be much more user friendly, since you could have features such as "forgot my password" which are (by design) impossible to implement on top of a blockchain.

> Whenever the key is checked, the software that checks the key creates an entry in the blockchain.

Right. So on top of a blockchain there's some software that inputs something on the blockchain.

What's to stop me from creating software that won't create those events, but will still check the key?

> Any authorised dealer

> so ownership can be transferred in the same way

Curioser and curioser. So now there are centralised dealers that can transfer ownership. So only selected few can create events on the great decentralised blockchain. Tangential question: if I want to give the watch as a gift, do I have to have Rolex's blessed authorised software to do that?

Also, if "authorised dealers" have the power to do this, it means they have the cryptographic keys. This also means that the rest of the world has them.

> So if someone tries to sell you a "Rolex" and you scan it, you'll have the history of the watch right there.

Indeed. So, the counterfeit watch comes up with a real history. Rolex produces almost a million watches a year. It will be ridiculously easy to pick up numbers for the counterfeit watches that are new.

Those that are not "new" can be sold at second hand markets.

> but then if you buy a "Rolex" on eBay from a random seller (not an AD) you kind of know what you're getting already don't you?

Ah. And here it is: "blockchain can help verify authenticity with near 100% certainty" devolves into "you know what you're getting into" in the span of three comments.

> Who's to stop anyone from producing a "Rolex" watch pointing to the exact same entry on the blockchain?

No one. But only one is signed by Rolex's keys, and therefore considered legitimate.

> Indeed. So how exactly does blockchain protect against counterfeit goods?

It depends on who you are if it does or not. It can 1) prevent inconsistencies in different databases in different orgs, 2) prevent companies trying to hide their tracks or muddy the waters, 3) provide near-instantaneous settlement and coordination

Let me ask you this; if you buy a Rolex watch on eBay that includes a QR code as proof of authenticity, how can you be confident that the same QR code has not been included with 100 other duplicate watches otherwise?

(I had this happen with fake Bose headphones, BTW. A correct blockchain implementation would have allowed me to spot that within minutes of receiving the package as well as irrefutable proof to present to eBay/law enforcement, as opposed to months later when they failed and vague evidence)

> But only one is signed by Rolex's keys

How do you sign a physical watch with keys?

> Let me ask you this; if you buy a Rolex watch on eBay that includes a QR code as proof of authenticity, how can you be confident that the same QR code has not been included with 100 other duplicate watches otherwise?

I can't be confident. So, once again, how does blockchain help?

> A correct blockchain implementation would have allowed me to spot that within minutes of receiving the package as well as irrefutable proof to present to eBay/law enforcement

- What's a "correct blockchain" and who implements it?

- How would it help if both watches/headphones/whatnot point to the same record in the ledger?

- more in two comments to this: https://news.ycombinator.com/item?id=27435785

> How would it help if both watches/headphones/whatnot point to the same record in the ledger?

The watch has an ID/serial number. The record on the ledger is transferred to the new owner. If both new owners check the ledger, only one of them will have been assigned the watch with the corresponding SN.

the payment could even be done atomically with the assignment of the (authentic) watch. As long as the buyer validates it, the only one who could forge watches would be Rolex.

> The record on the ledger is transferred to the new owner.

This. How does this magical transfer happen? The moment you say "authorised resellers", please read comments to this: https://news.ycombinator.com/item?id=27435785

> the payment could even be done atomically with the assignment

What's to stop an automatic payment with the assignment of the counterfeit watch?

> As long as the buyer validates it, the only one who could forge watches would be Rolex.

Why?

It sounds like you need to review some blockchain fundamentals. None of the above should be unclear in any way if you have a basic understanding. I could go on and try to address your questions, but really, at this point you may as well just be trolling. The way you have been strongly arguing above is not founded on reality if your last questions are honest.