Glossary
Hash functions
Blockchain technology relies heavily on cryptographic hash functions to ensure data integrity and security. Cryptographic hash functions are mathematical algorithms that generate a unique fixed-length string of characters, known as a hash or digest, from any input data. Hash functions have three main properties that must be satisfied to be considered a cryptographic hash function:
- Determinism: Applying the same hash function to the same input will always produce the same output hash value. This property is essential for verifying the integrity of data stored in the blockchain.
- Collision Resistance: It is computationally infeasible to find two different input values that result in the same output hash value. Hash functions are designed to minimize the possibility of collisions, which can compromise data integrity.
- Pre-image Resistance: Given a hash value, it is computationally infeasible to determine the original input data that produced that hash value. This property is essential for ensuring the confidentiality of data stored in the blockchain.
To better understand the concept of hash functions, consider the analogy of fingerprints for people. Just as each person has a unique fingerprint, no two data files can have the same hash value. Hash functions turn any data file, including text, photos, songs, and movies, into a fixed-size fingerprint. This fingerprint cannot be used to recreate the original data file, just as a fingerprint cannot be used to recreate a person.
Blockchain technology’s most widely used hash functions are SHA-256, RIPEMD160, and Keccak256. Bitcoin and Neo use SHA-256 and RIPEMD160, with SHA-256 producing an output of 256 bits and RIPEMD160 producing an output of 160 bits.
Ethereum uses Keccak256, which also produces an output of 256 bits or 32 bytes.
An example of using hash functions in the blockchain is to create a fingerprint for each block. The hash of the header of one block is placed in the header of the next block, creating a chain of blocks. Any attempt to modify a previous block, such as changing the value of a transaction, will alter the block’s hash and break the chain. This makes hash functions an essential ingredient in maintaining the integrity and security of any blockchain.
