![]() ![]() The most notable hash function, SHA-256, produces 256-bit outputs. The output length is oftentimes part of the name of a hash function. The output length, usually denoted in bits, varies depending on the specific hash function. The first notable property of all hash functions is that they consume inputs of variable length and produce an output of fixed length called the hash value, hash digest or simply, hash. If somebody cheats the system and changes the transaction record after the fact, everybody would notice because the fingerprints of the transaction history before and after the manipulation don't match anymore Properties of Hash Functions In a blockchain, we use hash functions to create a fingerprint of the transaction history. If the fingerprints don't match, I know that you changed the text in some way. If both fingerprints match, you have not changed anything about the file. When you send the text file back to me, I could use the hash function again to create a second fingerprint. I could use a hash function to create a fingerprint of the text before I send it to you. Let's say I want to send you a text file and don't want you to change it: You can use a hash function to create a fingerprint for every type of file you can imagine. Deterministic - A given input always needs to produce the same outputĪ hash function is something that we use to create a fingerprint of a file.Collision-resistant - It should be nearly impossible to find two inputs to a hash function producing the same output.If the hash value of the input 2 was 4, the hash of 3 better not be 6.Pseudorandom - A change in the input must result in an unforeseeable change of the output.One-wayness - It has to be easy to calculate an output from a given input but impossible to calculate the input from a given output.As the name suggests, those would not work without hash functions.Ī cryptographic hash function must fulfill the following set of criteria to be viable for use in a blockchain: Previously, we talked about other common data structures, such as hash tables. The use cases of hash functions extend beyond blockchain technology. Verifying the integrity of the blockchain itself.They are applied in several important ways such as: Hash functions are one-way mathematical functions used to verify data in blockchains. ![]() Verifying what data gets added makes a lot of sense, especially as storage on the blockchain is limited. For this to be a valuable feature, the data written to the blockchain must be accurate. Participants need a way to reliably distinguish between valid data and malicious information.īlockchains are a way to record data in an immutable way. The verification of data is an important aspect when building a data structure on a decentralized network.
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