Explanation
The same input always yields the same hash; one changed character yields a completely different one. The linkage between blocks in a blockchain rests on this.
01
A digital fingerprint
A hash function turns any input — one letter or a whole book — into a fixed-length string. The same input always gives the same output, but changing one character yields a completely different string. Working back from output to input is practically impossible, and that is exactly what makes it useful.
02
Where it shows up
Hashes link blocks together, underpin addresses, serve as proof in proof of work and let you verify a file is unchanged. When you download wallet software and compare the checksum, you are using exactly this property to see whether anyone swapped the file in transit.
Key takeaways
- Same input, same output — always.
- Not reversible in practice.
- Basis of addresses, blocks and proofs.