Using a Non-Fungible token to gain access to a file

Ownership of an NFT can be used to access content.

For example see the Three Year Anniversary Edition of Week In Ethereum News which used the Unlock Protocol

https://weekinethereumnews.com/three-year-anniversary-edition/

I assume you are interested in a token which can be transferred from one person to another. Yes, this is possible if two conditions are met:

1. The key to access the file changes over time. This is obvious because if person A knows the key and they give it to person B, then person A will still know it. So of course person B will need to use a new key.
2. There is communication, possibly using zero knowledge, between person A, person B and your server hosting the file. Because this is a "cross-chain transaction".

If those conditions fit within your problem space then I can deliver a product that works with NFTs to access the file.

I think it must be more extended protocol then just erc721.

The fact is that there should be a connection of a virtual token from the blockchain, with a virtual or real object. Each of last them must be unique. You can get the hash amount as an identifier from the virtual object. Therefore, it will be possible to assign it only after calculating this hash and the erc721 standard does not imply these actions.

We don’t talk about access here, but only about granting property rights for example + you still have to add additional information, such as file size, file name, url link is constant (there may be problems with this, most likely you need to use something like ipfs).

With a real object it’s still harder. An object outside the blockchain can be destroyed, transferred to another address, etc. those. even having the rights to the token and the object assigned to it, we can practically not be the owners of the second, and the actual price of this token becomes zero.

Also, if you develop such a protocol, you need to take into account the points on preventing duplication of unique IDs in person, on validating real property rights, and so on.

I was given a similar task from Moscow customers, thay said that Kaspersky lab., if I dont mistake, doing alike thing since 2017.