Explainer1 min readUpdated June 29, 2026

What is a hash function?

Short answer

A hash function takes any input and produces a fixed-length string, its hash or digest. The same input always gives the same hash, but you cannot reverse the hash back into the original. It is a fingerprint, not encryption.

A fixed-length fingerprint

No matter how large the input, a hash function returns a short value of fixed length. Change a single character of the input and the output changes completely, which makes hashes ideal for detecting whether data has changed.

"hello"  -> 2cf24dba5fb0a30e26e83b2ac5b9e29e...
"hellp"  -> 9c2 d4c0 ... (completely different)

SHA-256 of two near-identical inputs

What makes a hash function good

Deterministic: the same input always produces the same hash
Fast to compute for any input
One-way: you cannot recover the input from the hash
Collision-resistant: it is impractical to find two inputs with the same hash

Hashing is not encryptionEncryption is reversible with a key; hashing is one-way by design. Do not expect to decode a hash back to its input.

Try it: Hash GeneratorGenerate SHA-256 and other hashes from text locally in your browser.Open tool

Where hashes are used

Verifying that a downloaded file was not corrupted or tampered with
Storing passwords as salted hashes instead of plain text
Deduplicating data by comparing fingerprints
Building digital signatures and content addresses

References

Questions

Can two different inputs have the same hash?

In theory yes, that is called a collision, but for a strong modern hash like SHA-256 finding one is computationally infeasible. Avoid older, broken hashes like MD5 and SHA-1 for security.

Should I hash passwords with SHA-256?

Not directly. Passwords should use a slow, salted password-hashing algorithm such as bcrypt, scrypt, or Argon2, which are designed to resist brute-force guessing.

Does this send my data anywhere?

No. Utilumo's developer tools parse and transform input inside the browser tab. Nothing is uploaded, stored, or logged.