What is SHA-256?
Crypto Glossary Definition
A method of encryption. Stands for Secure Hash Algorithm. Is involved in the mining process for Bitcoin and other cryptocurrencies.
Why SHA-256 Matters
SHA-256 is the specific cryptographic hash function Bitcoin uses for mining and for generating addresses — it takes any input and produces a fixed-length, effectively irreversible output, which is the core trick that makes Proof-of-Work mining computationally hard but easy to verify.
SHA-256 in Practice
A Bitcoin miner's specialized hardware repeatedly takes a candidate block's data, combined with a changing number called a nonce, and runs it through the SHA-256 hash function to see whether the resulting output happens to fall below the network's current target difficulty. Because SHA-256 produces a completely different, unpredictable output for even a tiny change in input, and because there's no shortcut to work backward from a desired output to find the input that produces it, the only real strategy is brute force: try billions of different nonce values per second until one happens to produce a qualifying hash. Once a miner finds a valid one, every other node on the network can verify the result in a fraction of a second by simply running that same input through SHA-256 once and checking the output, which is the asymmetry — hard to find, trivial to verify — that makes Proof-of-Work security work at all. The same function also underlies how Bitcoin addresses are derived from public keys and how each block cryptographically links to the one before it, since altering any past transaction would change that block's hash and break every subsequent block's link to it, which is precisely what makes the blockchain's history so difficult to rewrite.
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