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Concept
Cryptography
Cryptographic Hashing (SHA-256)
Why it matters
Hashing is the single primitive doing the most work in Bitcoin — it chains blocks, commits to transactions, and makes proof-of-work measurable. Nearly every part of the system touches it.
What it is
A one-way function that turns any input into a fixed-size fingerprint that is infeasible to reverse or forge. Bitcoin uses SHA-256 for mining, block linking, Merkle trees and addresses.