Distributed networks, the importance of nodes, positive feedback mechanisms and network consensus. What is a 51 percent attack.
One of the main aspects of blockchains is their strength compared to other types of databases, whose architectures make them more vulnerable. While blockchains are not immune to hacking, their distributed nature makes them more resilient.
The fact that there is no single point of attack, but rather that each blockchain exists as a copy on the computers of all its full nodes, makes the possibility of an attack involving the entire network difficult.
It is very difficult to carry out a denial of service (DDoS), because although important nodes or services connected to the blockchain can be attacked, the rest of the nodes could continue doing their work.
In this sense, the distribution of the blockchain is a great strength that increases as new nodes connect to the network. When a blockchain grows in trust and more users join, it also grows in security. This positive feedback mechanism is one of the most important sources of resilience in blockchains.
On the other hand, it is very important for any blockchain that its nodes cooperate and there is consensus on which is the longest chain of data and, therefore, the one that is valid.
In addition to a distributed system for transferring information and value, blockchains are a protection mechanism.
The 51 Percent Attack
If someone controls 51 percent of the network’s computing power (hash power), they can rewrite subsequent blocks as they please. However, the high cost of concentrating such hashing power acts as a barrier to these types of attacks.
The more full nodes and miners connected to a blockchain, the more the chance of them suffering from a 51 percent attack decreases. And also the other way around: the fewer miners and hash power it has, the more vulnerable it is to this type of attack, as happened recently with the Ethereum Classic blockchain, a fork of the Ethereum network.
In that sense, the consensus or agreement of the majority of the nodes on which blockchain to follow is a very valuable asset of each blockchain, which is lost with each fork.
Transparency
Differences between public and private blockchains. How to navigate a blockchain. Data accessibility versus denial of access.
Most blockchains are public, which means their data is also public and therefore available for any user to review.
As we saw in the respective chapters of other guides, the information on the blockchains of different cryptocurrencies can be navigated very simply on pages such as blockchain.com/explorer (for Bitcoin) or etherscan.io (for Ethereum).
These sites provide information ranging from the hash power of a certain network, to the identifiers of each transaction made, to the number of approved operations.
While in crypto most blockchains are public, this technology also reached the private sector.
In the case of private blockchains, much of that information is not available. Although there are also private blockchains whose information is public, such as XRP.
Private blockchains differ radically from public ones in that some type of authorization is required to participate in them. In that sense, they are on the opposite philosophical path to most crypto users.
However, in addition to being permissionless, a private blockchain has to deny access to your data to anyone who is not authorized. This model is the one most safely applied in companies that, for example, use technology for logistics issues.
In that case, blockchains work like any other software, without any type of disruptive difference other than lowering certain costs.
Stability
The role of users, miners and full nodes in the stability of blockchains. Computing power, outages and denials of service.
The stability of a blockchain is closely related to the number of nodes that comprise it. Thus, the more users, full nodes and miners a blockchain has, the more stable it will be.
Stability is then related to computing power and the possibility of using the services of a certain blockchain. For this reason, Bitcoin «never goes down»: that is, it has no moments when the service cannot be provided.
Behind the benefits of blockchains is a distributed technology that ensures their stability.
These situations do tend to occur in centralized service models, such as when Twitter is saturated, or WhatsApp stops working for a day, or Instagram is «down» and becomes inaccessible.
The greater the computing power involved in a blockchain, and the more full nodes and miners working on it, the risk of a “crash” is dramatically reduced.
