Hashed meaning refers to the process of generating a fixed-size output from an input of variable size. Hashing is done through the use of mathematical formulas known as hash functions.
Although not all hash functions involve the use of cryptography, the so-called cryptographic hash functions are at the core of cryptocurrencies. Blockchains and other distributed systems use cryptographic hash functions to achieve significant levels of data integrity and security.
Usually, hashing algorithms of cryptocurrencies are designed as one-way functions, meaning they cannot be easily reverted without large amounts of computing time and resources. In other words, it is quite easy to create the output from the input, but relatively difficult to generate the input from the output. By doing so, this makes the hash function very secure, as other people are not able to generate the true value of one’s private keys from one’s hash value.
How does a hash function work?
Now that we know what is hashed meaning in crypto, let us explore how a hash function works.
Different hash functions will produce outputs of differing sizes, but the possible output sizes for each hashing algorithm is always constant. For instance, the SHA-256 algorithm can only produce outputs of 256 bits, while the SHA-1 will always generate a 160-bits digest.
A very minor change (such as changing an uppercase letter to a lowercase letter) resulted in a totally different hash value. But since we are using SHA-256, the outputs will always have a fixed size of 256-bits (or 64 characters), regardless of the input size. Moreover, it doesn’t matter how many times we run the two words through the algorithm, the two outputs will remain constant.
Why are hash functions important?
Hashing is extremely powerful when dealing with enormous amounts of information. For instance, one can run a big file or dataset through a hash function and then use its output to quickly verify the accuracy and integrity of the data. This is possible because of the deterministic nature of hash functions: the input will always result in a simplified, condensed output (hash). Such a technique removes the need to store large amounts of data.
Blockchains use hashing to condense and store large amounts of information. The Bitcoin blockchain has several operations that involve hashing, most of them within the process of mining. In fact, nearly all cryptocurrency protocols rely on hashing to link and condense groups of transactions into blocks, and also to produce cryptographic links between each block, effectively creating a blockchain.
Cryptographic hash functions
A hash function that deploys cryptographic techniques may be defined as a cryptographic hash function. In general, breaking a cryptographic hash function requires a myriad of brute-force attempts. For a person to “revert” a cryptographic hash function, they would need to guess what the input was by trial and error until the corresponding output is produced. However, there is also the possibility of different inputs producing the exact same output, in which case a “collision” occurs.
Technically, a cryptographic hash function needs to follow three properties to be considered effectively secure. These properties are collision resistance, preimage resistance, and second preimage resistance.
Collision resistance
As mentioned, a collision happens when different inputs produce the exact same hash. Thus, a hash function is considered collision-resistant until the moment someone finds a collision. Collisions are inevitable for any hash function because the possible inputs are infinite, while the possible outputs are finite.
Therefore, a hash function is collision-resistant when the possibility of finding a collision is so low that it would require a very long time of computation. So despite the fact that there are no collision-free hash functions, some of them are strong enough to be considered resistant (e.g., SHA-256).
Among the various SHA algorithms, the SHA-0 and SHA-1 groups are no longer secure because collisions have been found. Currently, the SHA-2 and SHA-3 groups are considered resistant to collisions.
Preimage resistance
The property of preimage resistance is related to the concept of one-way functions. A hash function is considered preimage-resistant when there is a very low probability of someone finding the input that generated a particular output.
The property of preimage resistance is valuable for protecting data because a simple hash of a message can prove its authenticity, without the need to disclose the information. In practice, many service providers and web applications store and use hashes generated from passwords rather than the passwords in plaintext.
Second-preimage resistance
To simplify, we may say that the second-preimage resistance is somewhere in between the other two properties. A second-preimage attack occurs when someone is able to find a specific input that generates the same output of another input that they already know.
In other words, a second-preimage attack involves finding a collision, but instead of searching for two random inputs that generate the same hash, they search for an input that generates the same hash that was generated by another specific input.
Therefore, any hash function that is resistant to collisions is also resistant to second-preimage attacks, as the latter will always imply a collision. However, one can still perform a preimage attack on a collision-resistant function as it implies finding a single input from a single output.
In Conclusion
Hashed meaning refers to generating a fixed output from an input of variable size. Hashing has many uses in privacy and security, especially in cryptocurrency and blockchains.
