If the off-chain data is "incorrect", what are you going to do? Can anybody mint those NFTs? What's the point then? The government is the only one who can kick you out of that house irl.
The minting process could be managed by the government or some entity using an on-chain contract or it could just be a manual process that the government does in conjunction with banks. The enforcement of the ownership records would still be held with the government. The point of having property records as NFT on-chain data is it enables easy to verify ownership of property records, transparency/auditability of property records, and easy transfers of property records to new owners.
Correct, which means that there has to be an ultimate source of truth that everyone agrees on that is independent of the blockchain. Which means there has to be an authoritative central agency of some sort to handle that. Which means that the blockchain has not, in fact, accomplished the stated goal.
So those don't look like things that NFTs make better in this space.
Let's suppose that the off-chain data is a PDF containing all the information for the property deed. If the hash values don't match then it means the PDF should be disregarded. If the off-chain data was kept in multiple locations, then one could potentially still retrieve a good copy of the PDF whose hash matches and then can be trusted.
Now, just because a blockchain can be used as the system of record for property deeds does not mean one wouldn't need to still have laws and other organizations enforcing that system of record. The blockchain is just a tool that makes some aspects of the record keeping easier and opens up some interesting possibilities as I've outlined in other comments of this thread.
> If you could do that, then you could be breaking into all sorts of systems.
Absolutely. And this is one of the methods that is used to do just that. I'm not talking about a theoretical security issue here, this is a weakness that has been leveraged in the real world for a long time.
> Cryptographic one-way hash functions are actually the preferred way to secure passwords.
Yes, but they're also not considered bulletproof. They're a bit of a compromise effort. That's why the leaking of password files is considered a security problem even when the passwords are salted hashes.
And, like with password hashes, it's not actually necessary to break the hash in order to alter the hashed record while maintaining the same hash. There are mathematical shortcuts to doing this, but you can even just brute force it if you have enough computing power or time.
Oh really? Care to share some examples of SHA-256 and SHA-3 collisions?
That said, there are readily available tools that use things like rainbow tables to "crack" SHA-256 salted password hashes. By "crack", I mean to come up with a password that hashes to the same value.
These tools are in successful use every day.
Cracking SHA-256 with rainbow tables is a fundamentally different exercise as you are relying on someone having selected a weak password that you can then generate a hash for. The weakness is not in SHA-256, but in the weak user selected password.
That's fine, I don't expect you to believe me without evidence. But I have seen this happen more than once in my work.
> you are relying on someone having selected a weak password
Stated another way, you are relying on having some idea of what the original data looked like, so you can reduce the search space. Absolutely correct.
However, if you're hashing public records like real estate, where you literally have the clear text, that's a much simpler problem than cracking passwords. All you need to do is alter the document in the way that you want, then find what other changes are needed to create a collision with the original hash. This is not very computationally intensive compared to password cracking.
Add in that the amount of money on the line with real estate can be high enough that it would make it worth throwing serious resources at it -- more than the average password cracker could even begin to summon -- and my confidence in the security of the hashes is greatly reduced.
Here's an interesting general overview of the problem: https://medium.com/asecuritysite-when-bob-met-alice/can-i-cr...