How many nodes?

[aurigae]

How many nodes would an attacker need to control to take full control of a blockchain network?

Im not in any way a blochchain dev - But the question seems quite interesting.

Lets hypothetically consider an attacker could gaincontrol of x% of active nodes - is there a treshhold where the attacker could be considered in full control of the blockchain network?

[achow101]

It depends on what you mean by "control the network". All that an attacker can do with a lot of nodes is conduct a sybil attack on other nodes. They cannot change the blockchain without any mining power, they cannot make coins move that they don't have the private keys for. All an attacker can do is feed bad information to a node and keep that node from the rest of the network.

[Decoded]

If you're referring to a strict percentage, you might be hinting at a 51% attack. AFAIK, you cannot have one with nodes. You can have one with miners, though. The only thing a node can possibly do is alter the blockchain/make your wallet have more or less btc than it actually does. It can basically tamper with your connection to the blockchain, but can't actually do anything.

[aurigae]

The intention of my post came from the possibility to log nodes into a database and perform a exploit attack on that database (for example armitage psql db) . In some "worst case" this would effect a majority of the logged nodes.

So my question wasnt specific enough : "How much in % of the online connected nodes to the network need to be remotely controlled to expose the network to any kind of attack"

Thx for replies anyways, just trying to think like an attacker - i could log nodes and exploit them, right - how much would be too much for the network to become fragile.
@ Decoded, why arent nodes enough (im not a UBER programmer, just curious)

[odolvlobo]

The damage you cause would be limited to nodes that connect only to your nodes. As someone wrote earlier, the damage consists of preventing other nodes from seeing transactions and blocks.

If you could prevent half the miners from seeing the other half, you could create a serious fork in the block chain. Miners are well-connected through multiple channels, so that might not be feasible.

[aurigae]

The damage you cause would be limited to nodes that connect only to your nodes. As someone wrote earlier, the damage consists of preventing other nodes from seeing transactions and blocks.

If you could prevent half the miners from seeing the other half, you could create a serious fork in the block chain. Miners are well-connected through multiple channels, so that might not be feasible.

Thx for your input, shed some light on it for me.