Blockchain Vulnerabilities: DDoS Attack

Blockchain technology was developed more as a test of scientific theories, at least in the context of bitcoin. Naturally, network security was an important component, but this does not mean that the ideology itself does not contain potential vulnerability to certain attacks

DDoS attack - what kind of beast?

The name of the attack comes from the acronym for Distributed Denial of Service. And Distributed here characterizes not the purpose of the attack, but the way in which it is implemented. 

In the case of an attack on network resources (and websites, in particular), such an attack is not aimed at compromising information (hacking the system), but at creating interruptions in the operation of the service, up to the complete unavailability of the resource. This type of attack is called distributed because in most cases it is carried out not by one computer connected to the network (it would be easy to localize and neutralize it), but by a network of machines, most often infected with malicious software (virus or Trojan).  

It would seem - how can you attack in this way a distributed network that contains tens of thousands of computers located in all parts of the world? But there is no need for this. An attack on the blockchain is not carried out on the network itself, but is aimed at the impossibility or severe slowdown of transactions. After all, today most of the blockchain-based systems are used as cryptocurrencies.

DDoS on the blockchain?

I’ll say right away that implementing such an attack is extremely expensive and technically it’s also not so easy to implement. The method of carrying out such an attack is to fill the network with a large number of small transactions - we remember, in the same bitcoin, the cost of a transaction does not depend on its volume in financial terms, but only on the volume of data and is not fixed. Simply put, the attacker begins to spam the network with a large number of small transfers. Of course, this pleasure is not cheap, but it can greatly poison the lives of everyone who uses the attacked cryptocurrency. 

Since the volume of a block, for example Bitcoin, is limited to 1 megabyte, real, working transactions may simply not be included in it. Or - wait for your turn for a very long time. Something similar was observed in the bitcoin network, for example, in the early summer of 2017. There were even versions that the attack was aimed at promoting Bitcoin Cash - as an alternative with fast transactions and a large volume of blocks.

In the short term, such an attack slows down transactions on the network and artificially increases miners' fees.. However, even after the end of the attack, its consequences will be felt for many years. The first and obvious thing is the growth in the size of the blockchain database, because it is impossible to identify and cross out “garbage” transactions. They remain in the database forever and increase the volume of stored data. 

The second, not so obvious, inconvenience is associated with the blockchain organization itself, at least in the implementation adopted in bitcoin and its forks. The fact is that the network does not store the state of the address - there is no special place where it is written “Bob’s address contains five bitcoins.” Instead, the amount at the address is the sum of all incoming transactions minus the sum of all outgoing transactions. Thus, in order to determine the current balance of each wallet/address on the network, it is necessary to check at least once all transactions recorded in the blokchain to find out how much was received at a particular address and how much was sent from it. 

This process usually occurs when the bitcoin client is initially launched and can itself take several days. And as the volume of the blockchain grows, this process becomes longer and longer.

In fact, the creators of bitcoin thought about protection from such attacks, for example, the network provides a commission for transactions exceeding a certain volume. However, it is almost impossible to completely protect against such an attack. The only limiting factor is that such an attack cannot be free, and the attacker will have to fork out a lot of money. 

The question remains - why would anyone need such an attack? 

The first and obvious answer is competing cryptocurrencies that have entered into a mortal battle for the sympathy of users. 

The second option, which cannot be excluded, is government agencies. Potentially, if the state decides to fight any cryptocurrency, this is a completely possible scenario. We recently had an article about how you can destroy bitcoin, and so, the described attack does not allow you to destroy the blockchain, but with some effort it can make its existence meaningless, at least for some period of time.