What Is Hashing?

 Different hash functions produce outputs of varying sizes, but the output size for each hashing algorithm is always constant. For example, the SHA-256 algorithm generates outputs of 256 bits, while SHA-1 consistently produces a 160-bit digest. To demonstrate this, let's apply the SHA-256 hashing algorithm (the one used in Bitcoin) to the words "CrossPay " and "CrossPay"It's important to note that even a small change (such as altering the casing of the first letter) leads to a completely different hash value. However, because we are using SHA-256, the outputs will consistently be 256 bits (or 64 characters) in size, regardless of the input size. Furthermore, no matter how many times we process the two words through the algorithm, the outputs will remain unchanged.  In contrast, if we apply the same inputs to the SHA-1 hashing algorithm, Notably, the acronym SHA stands for Secure Hash Algorithms. It refers to a set of cryptographic hash functions that include the SHA-0 and SHA-1 algorithms along with the SHA-2 and SHA-3 groups. The SHA-256 is part of the SHA-2 group, along with SHA-512 and other variants. Currently, only the SHA-2 and SHA-3 groups are considered secure.

  Conventional hash functions have a variety of applications, including database lookups, large file analyses, and data management. In contrast, cryptographic hash functions are widely used in information security applications such as message authentication and digital fingerprinting. In the case of Bitcoin, cryptographic hash functions are integral to the mining process and are also involved in generating new addresses and keys.  The true strength of hashing becomes evident when handling large amounts of information. For example, you can run a large file or dataset through a hash function and use the output to quickly verify the data's accuracy and integrity. This capability stems from the deterministic nature of hash functions, where the input consistently produces a simplified, condensed output (hash). This method eliminates the need to store and "remember" large volumes of data.Hashing is especially important in the context of blockchain technology. The Bitcoin blockchain performs numerous operations involving hashing, particularly during the mining process. In fact, nearly all cryptocurrency protocols utilize hashing to link and condense groups of transactions into blocks, as well as to create cryptographic links between each block, effectively forming a blockchain.

 A hash function that employs cryptographic techniques is referred to as a cryptographic hash function. Generally, breaking a cryptographic hash function requires numerous brute-force attempts. For someone to “reverse” a cryptographic hash function, they would need to guess the input through trial and error until the matching output is generated. However, there is also the potential for different inputs to yield the same output, resulting in a “collision.”For a cryptographic hash function to be considered effectively secure, it must meet three key properties: collision resistance, preimage resistance, and second preimage resistance.Before diving into each property, here’s a brief summary of their logic in three concise statements:

• Collision Resistance: It is infeasible to find two distinct inputs that generate the same hash output.
• Preimage Resistance: It is infeasible to reverse the hash function (i.e., determine the input from a given output).
• Second-Preimage Resistance: It is infeasible to find a second input that produces a collision with a specified input.

As previously mentioned, a collision occurs when different inputs produce the same hash output. A hash function is deemed collision-resistant until a collision is discovered. It's important to note that collisions are inevitable for any hash function, as the range of possible inputs is infinite while the outputs are finite In other words, a hash function is considered collision-resistant if the likelihood of finding a collision is so minuscule that it would require millions of years of computational effort. Therefore, although no hash function can be completely free of collisions, some are robust enough to be classified as collision-resistant, such as SHA-256. Among the various SHA algorithms, the SHA-0 and SHA-1 families are no longer secure, as collisions have been identified within them. Currently, the SHA-2 and SHA-3 families are regarded as resistant to collisions.

The concept of preimage resistance is tied to one-way functions. A hash function is classified as preimage-resistant when the likelihood of someone discovering the input that produced a specific output is very low.This property differs from collision resistance, as an attacker in this case would be attempting to determine the input based on a given output. In contrast, a collision occurs when two different inputs yield the same output, regardless of which inputs were used.Preimage resistance is important for data protection because it allows for a simple hash of a message to verify its authenticity without revealing the actual information. In practice, many service providers and web applications store and utilize hashes generated from passwords instead of keeping the passwords in plaintext.

In simpler terms, second-preimage resistance can be viewed as a property that falls between the other two. A second-preimage attack occurs when an attacker successfully finds a specific input that produces the same output as another known input as other words, a second-preimage attack aims to identify a collision, but instead of looking for two random inputs that yield the same hash, the attacker seeks an input that generates the same hash as that produced by a specific known input as a result, any hash function that is resistant to collisions will also be resistant to second-preimage attacks, since a successful second-preimage attack inherently results in a collision. However, it is still possible to execute a preimage attack on a collision-resistant function, as this involves identifying a single input based on a given output.

 Bitcoin mining involves several steps that utilize hash functions, including checking balances, linking transaction inputs and outputs, and hashing transactions within a block to create a Merkle Tree. One of the primary reasons for the security of the Bitcoin blockchain is that miners must perform numerous hashing operations to discover a valid solution for the next block.Specifically, a miner tries various inputs to generate a hash value for their candidate block. They can only validate their block if they produce an output hash that begins with a specific number of zeros. The required number of zeros determines the mining difficulty, which varies based on the hash rate dedicated to the network.  In this context, the hash rate indicates the amount of computational power being utilized for Bitcoin mining. If the network's hash rate increases, the Bitcoin protocol automatically adjusts the mining difficulty to keep the average time needed to mine a block around 10 minutes. Conversely, if several miners stop mining, leading to a significant drop in the hash rate, the mining difficulty will be adjusted to make it easier to mine, until the average block time returns to 10 minutes.  It's important to note that miners don't need to find collisions, as there are multiple hashes they can generate that qualify as valid outputs (those starting with a specific number of zeros). Thus, there are several potential solutions for a given block, and miners only need to discover one that meets the threshold set by the mining difficulty.  Since Bitcoin mining is a resource-intensive process, miners have no incentive to cheat the system, as doing so would result in substantial financial losses. The more miners that join a blockchain, the larger and more robust it becomes.

There is no doubt that hash functions are crucial tools in computer science, particularly when managing large volumes of data. When integrated with cryptography, hashing algorithms become highly versatile, providing security and authentication in various contexts. Consequently, cryptographic hash functions are essential to almost all cryptocurrency networks, making it important for anyone interested in blockchain technology to understand their properties and operational mechanisms.