Ask HN: Are these possible ways to slow down a blockchain?

[marmalade92]

I am very skeptical for the blockchain technology and although I use it as a gambling addiction (or it uses me) I still use zero crypto based technologies.

Within my skepticism, I started wondering what can make the chain vulnerable?

My first idea was flooding with almost non worthy transactions therefore wasting the miners. This was quickly debunked as I found out the miners would ignore 'empty' transactions.

Another idea is, what if I as user A say want to transfer to user B, but I mention an amount of coins that actually I do not own and spam it. Would the miners have to traverse all the way to the back or are there 'checkpoints' that can assure short travels?

The last one is a bit more difficult. However can a big enough network of nodes, insert itself and start crunching the chain errors-fully on purpose to 'break' the chain?

Excuse my ignorance.

[jakecraige]

It's not so much that miners would ignore empty transactions, it's that the spammer would need to pay the miner fee to get each transaction in the block which would end up being very expensive and unsustainable long term.

For the second idea, this wouldn't really work either. When each node receives a transaction it will validate it first before broadcasting it to other nodes, so it would be stopped from propagating through the network pretty quickly and no one would attempt to include it in a block and run do PoW work it which is the most time consuming part.

I suppose in theory if you had a large enough network and could target a ton of nodes individually you might be able to do some form of damage but that's likely a pretty impossible amount of power and similarly to the previous example you could maybe bloat it a bit but it would be very expensive to sustain an attack like this.

[marmalade92]

the 2nd idea. But in order to validate if I actually own the money it has to traverse through the history. Now, I do not know how fast that is, or how far back it goes. But if it has to check and lets say it takes X amount of time, the spamming it will flood the validation without requiring a fee?

In general the 'attacks' are possible but expensive. However are they government expensive bulletproof? especially if we target less expensive coins aka alt coins.

[wmf]

My first idea was flooding with almost non worthy transactions therefore wasting the miners. This was quickly debunked as I found out the miners would ignore 'empty' transactions.

Also, you have to pay a fee for each transaction and thus you'd have to pay (at least) thousands of dollars of fees to clog a blockchain. https://bravenewcoin.com/news/bitcoin-spam-attack-stressed-n...

Another idea is, what if I as user A say want to transfer to user B, but I mention an amount of coins that actually I do not own and spam it. Would the miners have to traverse all the way to the back or are there 'checkpoints' that can assure short travels?

The miners keep an index of how much money everyone has (unspent transaction output index) so they can immediately ignore such invalid transactions.

The last one is a bit more difficult. However can a big enough network of nodes, insert itself and start crunching the chain errors-fully on purpose to 'break' the chain?

This is similar to what people call the eclipse attack. However, if a victim node can connect to even one other node that gives it a copy of the correct blockchain then the victim will ignore the errors and use the correct chain. https://www.usenix.org/node/190891