However, blockchain security is far from being a simple subject. Therefore, it is important to understand the basic concepts and mechanisms that grant robust protection to these innovative systems.
The concepts of immutability and consensus
Immutability, on the other hand, refers to the ability of blockchains to prevent alteration of transactions that have already been confirmed. Although these transactions are often relating to the transfer of cryptocurrencies, they may also refer to the record of other non-monetary forms of digital data.
The role of cryptography in blockchain security
Regardless of the input size, the output will always present the same length. But 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.
Hashing is also leveraged in the consensus algorithms used to validate transactions. On the Bitcoin blockchain, for example, the Proof of Work (PoW) algorithm utilizes a hash function called SHA-256. As the name implies, SHA-256 takes data input and returns a hash that is 256 bits or 64 characters long.
Though the specifics are beyond the scope of this article, the nature of asymmetric cryptography prevents anyone but the private key holder 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).
As long as the cost of establishing a majority of malicious nodes remains prohibitive and better incentives exist 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 majority attack because the total hash rate devoted to those systems is considerably lower than the one of Bitcoin.
Through the combined use of game theory and cryptography, blockchains are able to attain high levels of security as distributed systems. As with nearly all systems, however, it is critical that these two fields of knowledge are properly applied. A careful balance between decentralization and security is vital to building a reliable and effective cryptocurrency network.