The hash is critical as it is what enables you to verify that the off-chain data is correct. What exactly did you think was technojargon? I'll be happy to elaborate.
That's I wrote. Sure, it enables data integrity (maybe, but let's be charitable). Now what? How does the fact that token knows about external data prevents that data from being manipulated if needed? Or do you propose banning inheritances, lawsuits and other actions which apply to the real world artifacts just because blockchain can't deal with that? :)
That won't happen.
It doesn't prevent the manipulation, but it does assist in detecting it. If someone manipulates the off-chain data, then when that off-chain data is hashed and re-verified against the hash stored in the NFT on-chain then there will be a mismatch in the hash values.
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.
We don't need detecting unwanted manipulation (clarification, we do, but that is a small and rare problem), we need to deal with expected manipulation.
Let's say I was phished and some tokenbro across the globe now owns the NFT with a deed to my house, initially this info also got propagated into the centralised DB with stores actual data with deeds and related stuff. I go to police, then to the court and they reaffirm my ownership of the house. Then they restore correct information in the CDB. Now everything is all right, excep that blockchain is now outdated and show a tokenbro as an owner of NFT pointing to deed for my house, and hash is of course not matching now. Now what?
Code is not law (surprise), and blockchain doesn't override laws. It is technically useless for this task.
Why not just check the off-chain database and sidestep the hash stuff in the first place?
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.
Since the on-chain hash is part of an immutable object that no one can change, then anyone can use it to verify that the off-chain data is valid at anytime. (No one needs to go ask someone else whether it is valid they can check for themselves) If the off-chain data was found to be invalid, then a correct version of that off-chain data would need to be provided or a process would have to be developed that would handle exceptions where the document is no longer available and now a new NFT would need to be minted.
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.
> then a correct version of that off-chain data would need to be provided
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.
The purpose of having property deeds represented as NFTs on a blockchain is not to eliminate the need for a governing body, but to make the ownership transparent, trivially verifiable, and easy to transfer. I've outlined this many times in this thread at this point. In the event, that a valid copy of off-chain data could not be recovered, then the governing body could use a longer and more manual process to identify the rightful owner and mint a new NFT.
Perhaps the difficulty is that how deeds are handled right now already makes ownership transparent and easily verifiable, and not much more difficult to transfer ownership of (because transferring the "token" of ownership isn't where the friction is).
So those don't look like things that NFTs make better in this space.
It's possible to intentionally alter data that a hash has been computed from in such a way that it still computes to the same hash. Hashing alone is a weak way of ensuring that data has not been altered.
It is extremely hard to break cryptographic hash functions to the point it is considered impossible. If you could do that, then you could be breaking into all sorts of systems. Cryptographic one-way hash functions are actually the preferred way to secure passwords.
It isn't trivial, but it's not as hard as you make out. In the case of real estate which is often worth a great deal of money, plenty of people will be willing to put the effort in to do this.
> 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.
> 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.
Oh really? Care to share some examples of SHA-256 and SHA-3 collisions?
Not sure what would count as examples here, honestly. The ones I know of were what I encountered when I was working in cryptographic security, and I don't think any of those incidents were made publicly available.
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.
Yeah, I didn't think so. :) I know of no single incident of SHA-256 or SHA-3 having collisions successfully generated.
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.
> I know of no single incident of SHA-256 or SHA-3 having collisions successfully generated.
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.
