Would it be possible to create a blockchain that uses only X+ active blocks?

Question

Every blockchain has a beginning, the Block 0 or also known as "Genesis Block". But wouldn't it be possible to have a blockchain or a coin, where only the last 1000 blocks are saved and 1001+ get deleted automaticly?

My question is, because it would save very much problems.

1. Full anonymity: Yes, you could save 1001+ blocks but if you need only 1000 blocks, you can delete the others. So at a specific point in time, you could create a real 100% anonymous cryptocurrency because the other blocks would no longer exists.
2. Saves disk space: It does not longer need much space to download the blockchain. Also that means, that blocksizes could be bigger.
3. Finally, this is one of my favorite points. When people know that they can use a blockchain where they don't need to download a blockchain for 10 hours before being able to using it, more people would and that would mean that the blockchain would be more decentralized and so it would be more secure.

Now the negative or dangerous points, that I'm not sure about. So currently, the "computer" goes through all blocks and checks if the transactions are correct and if the user x had enough coins to send to user y. That's possible through algorithms that are not reversable. I still wonder if you could hack through 1000 blocks. Next point is, that a 51% attack would be much more likely to happen. But maybe you can combine the coin with POS. And maybe you can not save only 1.000 but 50.000. But combined with ethereum and bitcoin, it would still be 10x less blocks AND the blocks will still be deleted so the disk space keeps at stable at a point. I mean, the basic problem is not the block amount, but more the danger if one person/institution/group holds the most power. And then it would no longer matter how much blocks there are, they'd be successful in any coin.

I'm interested in knowing about why that wouldn't be possible. And I really hope that that's not a basic blockchain thing and I'm embarassing myself, lol.

Answer 1

Full anonymity: Yes, you could save 1001+ blocks but if you need only 1000 blocks, you can delete the others. So at a specific point in time, you could create a real 100% anonymous cryptocurrency because the other blocks would no longer exists.

No, that is not true at all. Someone, somewhere will store the entire blockchain and make it publicly available. This does not guarantee anonymity, and some people, even if they don't have all of the historic data, will still store the blocks from when they came online. Nothing about deleting blocks can help anonymity unless it is somehow enforced by consensus that you can only keep X number of blocks, but even then people have backups and such which means the data is not actually gone forever. You cannot achieve anonymity by trying to delete all data.

But wouldn't it be possible to have a blockchain or a coin, where only the last 1000 blocks are saved and 1001+ get deleted automaticly?

It is certainly possible to make it so that nodes do not have to download the entire blockchain. All a node really needs is the UTXO set, so each block can contain the hash of the UTXO set so a node can download the UTXO set from somewhere else and just start with the block that contained the hash of that UTXO set. However, this method has flaws and is vulnerable to various attacks and introduces a lot of trust into the system.

For example, an attacker could create a false UTXO set and commit it into his own short blockchain. Because you do not have the entire blockchain history, you cannot verify that the UTXO set that the attacker provided is actually correct. Furthermore, you cannot determine whether that short blockchain is even the right blockchain. The attacker could have mined it with a low difficulty and you wouldn't know that the difficulty is incorrect because you don't have the full history. This method thus introduces trust because your node has to trust that the nodes around it are giving it the correct data.