In short, a DoS attack or Denial-of-Service attack is a method used to disrupt legitimate users' access to a targeted network or web resource. This is usually achieved by overloading the target (often a web server) with an overwhelming amount of browsing or by sending malicious requests that cause the target resource to malfunction or crash completely.
The first documented case of a denial-of-service attack was in February 2000 when a 15-year-old Canadian hacker targeted the Amazon and eBay web servers with such an attack. Since then, many people have used DoS attacks to disrupt targets in many industries.
Types of denial of service (DoS) attacks
Some types of denial-of-service attacks aim to disable a specific target individual's access to a network or resource, while others intend to make the resource completely inaccessible. These attacks can last from minutes to hours and in some rare cases last for days. These types of outages often cause significant financial losses to companies that become targets and that do not have strategies to reduce or mitigate them.
DoS attacks come in different shapes and sizes since not all devices and networks are vulnerable in the same way. Those who try to do harm often have to get creative in the ways they can exploit various loopholes in the system's configuration.
Some known vulnerabilities for DoS attacks include:
Buffer overflow attack
It is the most common type of vulnerabilities. The Buffer Overflow attack depends on sending a lot of visits to the site, and the number of visits is greater than the number that the site developers specified, so that the site cannot accommodate the volume of visits, and this is what allows the attacker to control the target or even disable it.
ICMP flood
An ICMP flood attack targets an incorrectly configured device on the target network, forcing the device to distribute bogus packets to every node (computer) on the target network instead of a single node, thus increasing the load on the network.
This type of attack is often referred to as the Ping of Death or Smurf Attack.
SYN flood
A SYN flood attack sends a request to connect to a web server but never fully authenticates the connection and then targets all remaining open ports on the web server until it forces the server to crash.
DoS vs DDoS attacks
Another similar term you're likely to encounter is a DDoS attack, which stands for Distributed Denial-of-Service attack. The difference between a DoS attack and a DDoS attack is that during a DDoS attack, multiple malicious devices are directed to target a single resource.
A distributed denial-of-service attack is likely to be more successful than a denial-of-service attack originating from just one resource. Attackers also tend to prefer this method as it becomes increasingly difficult to trace the attack back to its source as the attack comes from multiple points.
Can a DDoS attack affect cryptocurrencies?
In most cases DoS attacks have been used to target the web servers of major companies such as banks, online retailers, and even governments and public services. However, it is important to consider that any device, server or network connected to the Internet can be a potential target for these types of attacks.
Cryptocurrencies have gained popularity in recent years, making trading platforms more vulnerable to distributed denial-of-service attacks. For example, when Bitcoin Gold was officially launched, it immediately became the target of a large-scale DDoS attack that ended up taking its website down for several hours.
However, the decentralized aspect of blockchain creates strong protection against DDoS and other cyber attacks. Even if many nodes fail to connect to the Internet or simply go offline, the blockchain is able to continue operating and validating transactions. When downed nodes are able to return to work, they are resynchronized with the latest data provided by the unaffected nodes.
The degree of protection of each blockchain against these attacks is related to the number of nodes and hash rate in the network. Such as the largest and oldest digital currency, Bitcoin, whose blockchain is considered the most secure. This means that DDoS and other cyber attacks are less likely to cause disruption.
The Proof of Work algorithm ensures that all network data is secured with cryptographic proofs. This means that it is almost impossible to change previously verified blocks. Changing the Bitcoin blockchain requires the entire structure to be exposed log by log which is practically impossible for even the most powerful computers.
Therefore a successful attack will likely only be able to modify transactions of a few recent blocks and for a short period of time. Even if an attacker gains control of more than 50% of Bitcoin's power to perform a so-called 51% attack (or majority attack), the underlying protocol will be quickly updated in response to the attack.
