All terms
A fixed length fingerprint of any piece of data.
A hash function takes any input and produces a fixed length output. Change one character of the input and the output changes completely and unpredictably. You cannot work backward from a hash to the original data.
Blockchains use hashes everywhere: to link blocks together, to identify transactions, to commit to data without revealing it, and in proof of work to make mining costly.
Bitcoin uses SHA-256. Mining is the search for an input whose hash starts with a certain number of zeros.
That a hash is a form of encryption. Encryption is reversible with a key; a hash is not reversible at all. It is a fingerprint, which is why it can prove a file has not changed but can never be turned back into the file.
Common questions
Can two different files have the same hash?
Can I get the original data back from a hash?
Where to go next
More foundations terms
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