We previously discussed that the four core technologies of blockchain are cryptography, distributed ledger, consensus mechanism, and smart contracts. Among these, cryptography is the most crucial part because it safeguards the security of the blockchain system. It can be said to be the cornerstone of blockchain, as the other technologies are built upon it to construct the towering edifice of blockchain.
The cryptography primarily used in blockchain consists of two parts: hash algorithms and asymmetric encryption. This article will focus on explaining what a "hash algorithm" is in blockchain cryptography.
Simply put, a hash algorithm is a special function. No matter how long the input string is, as long as it passes through this function, a fixed-length output value can be obtained. It’s like our ID numbers—whether you’re from Beijing or Shanghai, everyone’s ID number is 18 digits long and unique nationwide.
Similarly, a hash is essentially a compression mapping. It can transform an input of any length into a fixed-length output, always 256 bits long. The resulting output value is called a hash value.
Hash algorithms have three key characteristics: one-wayness, tamper resistance, and collision resistance. These properties endow blockchain with features like immutability and anonymity, ensuring the security of the entire blockchain system.
First, let’s discuss the one-wayness property. One-wayness means that in a hash function, the output can be derived from the input, but it is nearly impossible to reverse-engineer the input from the output. For example, if we input a known string A and obtain the hash value F(A), we cannot reverse F(A) to retrieve the original input data.
During the process of packaging data into blocks in blockchain, all data is processed using hash algorithms. It is precisely because of the one-wayness of hash algorithms that blockchain effectively protects the security of our information.
The second characteristic of hash algorithms is tamper resistance. Tamper resistance means that for any input, even a minor change—such as altering a single punctuation mark—will result in a vastly different hash value.
This property plays a critical role in linking blocks together.
Each block in the blockchain uses the hash value of the previous block as an identifier, which is then processed further by the hash algorithm. This ensures that subsequent blocks can not only trace back to all preceding blocks but also verify whether the data in previous blocks has been altered. Unless someone can crack all the hash values on the entire chain, once data is recorded on the blockchain, it cannot be tampered with.
The third characteristic of hash algorithms is collision resistance. A collision occurs when two different inputs produce the same output, much like wearing the same outfit as someone else by chance.
Collision resistance means that for most inputs, a unique output is generated. Note, however, that this only means the probability of a collision is extremely low—it does not mean collisions are impossible, as no existing hash algorithm can mathematically prove that collisions will never occur.
The third characteristic of hash algorithms is primarily applied in blockchain account addresses. In the world of blockchain, every transaction or account address is entirely generated based on hash algorithms. This ensures the uniqueness of transactions or account addresses within the blockchain network. No matter how much money is transferred or how many recipients are involved, each transaction is uniquely recorded in the blockchain’s ledger.
In summary, hash algorithms are the most fundamental component of blockchain technology. They are like the white blood cells in our bodies—not only is every part of blockchain dependent on them, but they also imbue blockchain with its distinctive features, safeguarding the security of the entire blockchain system.
