Blockchain networks are secured by a variety of mechanisms that include advanced cryptographic techniques and mathematical models of behavior and decision-making. Blockchain technology is the fundamental structure of most cryptocurrency systems and is what prevents this type of digital money from being duplicated or destroyed.
The use of Blockchain technology is also being explored in other contexts where immutability and data security are highly valuable. Some examples include recording and tracking donations to charities, medical databases, and supply chain management.
However, Blockchain security is far from a simple matter. Therefore, it is important to understand the basic concepts and mechanisms that ensure robust protection for these innovative systems.
Concepts of immutability and consensus
Although there are many resources that act on the security associated with Blockchain, two of the most important are the concepts of immutability and consensus. Consensus refers to the ability of nodes within a distributed Blockchain network to agree on the true state of the network and the validity of transactions. Typically, the process of achieving consensus is dependent on so-called consensus algorithms.
Immutability, on the other hand, refers to Blockchain's ability to prevent the alteration of transactions that have already been confirmed. While these transactions are generally related to the transfer of cryptocurrencies, they can also refer to the recording of other non-monetary forms of digital data.
Combined, consensus and immutability provide the framework for data security in Blockchain networks. While consensus algorithms ensure that system rules are being followed and that all parties involved agree on the current state of the network, immutability guarantees the integrity of data records and transactions after each new block of data is confirmed as valid.
The Role of Cryptography in Blockchain Security
Blockchain networks rely heavily on cryptography to achieve the security of your data. One cryptographic function that is extremely important in such a context is hashing. Hashing is a process by which an algorithm known as a hash function takes an input of any size and returns a determined output that contains a value of fixed length.
Regardless of the size of the input, the output will always be the same size. If the input changes, the output will be completely different. However, if the input doesn't change, the resulting hash will always be the same - no matter how many times you run the hash function.
Within Blockchain networks, these output values, known as hashes, are used as unique identifiers for blocks of data. The hash of each block is generated in relation to the hash of the previous block, and this is what connects the blocks, forming a chain of blocks. Additionally, the block's hash depends on the data contained in that block, meaning that any change made to the data would require a change to the block's hash.
Therefore, the hash of each block is generated based on the data contained in that block and the hash of the previous block. These hash identifiers play an important role in ensuring the security and immutability of the blockchain.
Hashing is also used in the consensus algorithms used to validate transactions. On the Bitcoin blockchain, for example, the Proof of Work (PoW) algorithm used to achieve consensus and to mine new coins uses a hash function called SHA-256. As the name suggests, the SHA-256 function takes input data and returns a 256-bit or 64-character hash.
In addition to providing protection for transaction records on ledgers, cryptography also plays an important role in ensuring the security of wallets used to store cryptocurrencies. The public and private keys that respectively allow users to receive and send payments are created through the use of public key cryptography (also known as asymmetric cryptography). Private keys are used to generate digital signatures for transactions, making it possible to authenticate ownership of the coins being sent.
While the details are beyond the scope of this article, the nature of asymmetric encryption prevents anyone other than the holder of the private key from accessing funds stored in a cryptocurrency wallet, thus keeping those funds safe until the owner decides to spend them. (as long as the private key is not shared or compromised).
Criptoeconomia
In addition to cryptography, a relatively new concept known as cryptoeconomics also plays a role in maintaining the security of blockchain networks. It is related to a field of study known as game theory, which mathematically models decision-making by rational agents in situations with predefined rules and rewards. While traditional game theory can be broadly applied to a variety of cases, cryptoeconomics specifically models and describes the behavior of nodes in distributed blockchain systems.
In short, cryptoeconomics is the study of the economy within blockchain protocols and the possible results that their design can present based on the behavior of its participants. Security through the cryptoeconomy is based on the notion that blockchain systems provide greater incentives for nodes to act honestly rather than adopting malicious or faulty behaviors. The Proof of Work consensus algorithm used in Bitcoin mining provides a good example of this incentive structure.
When Satoshi Nakamoto created the framework for Bitcoin mining, it was intentionally designed to be an expensive and resource-intensive process. Due to its complexity and computational demands, PoW mining involves a considerable investment of time and money - regardless of where the mining node is and who it is. Therefore, such a structure provides a strong disincentive to malicious activity and significant incentives for honest mining activities. Rogue or inefficient nodes will be quickly kicked out of the blockchain network, while honest and efficient miners will have the potential to reap substantial rewards.
Likewise, this balance of risks and rewards also provides protection against potential attacks that could undermine consensus by placing the majority of a blockchain network's hash rate in the hands of a single group or entity. Such an attack, known as a 51% attack, can be extremely damaging if carried out successfully. Due to the competitiveness of Proof of Work mining and the magnitude of the Bitcoin network, the likelihood of a malicious actor taking control of most nodes is extremely small.
Furthermore, the cost in terms of computing power required to gain 51% control of a massive blockchain network would be astronomical, providing an immediate disincentive to make such a large investment for a relatively small potential reward. This fact contributes to a feature of blockchains known as Byzantine Fault Tolerance (BFT), which is essentially the ability of a distributed system to continue functioning normally even if some nodes are compromised or act maliciously.
As long as the cost of establishing the majority of nodes remains prohibitive and there are better incentives for honest activity, the system will be able to thrive without significant disruption. It is worth noting, however, that small blockchain networks are certainly susceptible to this type of attack because the total hash rate dedicated to these systems is considerably lower than that of the Bitcoin system.
Final considerations
Through the combined use of game theory and cryptography, blockchains are able to achieve high levels of security as distributed systems. As in almost all systems, however, it is essential that these two fields of knowledge are applied appropriately. A careful balance between decentralization and security is vital to building a reliable and effective cryptocurrency network.
As blockchain's uses continue to evolve, its security systems will also change to meet the needs of different applications. The private blockchains now being developed for commercial enterprises, for example, rely much more on security through access control than on the game theory (or cryptoeconomics) mechanisms that are indispensable to the security of most public blockchains.