What is a hash?
A hash function turns any amount of data into a short fingerprint of fixed length. The same input always gives the same hash, and changing even one letter gives a completely different one. That makes hashes useful for checking that a file arrived intact, for spotting duplicates and for storing fingerprints instead of the data itself.
Which algorithm to use
- SHA-256 is the everyday choice today: used for software downloads, blockchains and digital signatures.
- SHA-384 and SHA-512 are longer versions of the same family.
- MD5 and SHA-1 are still common as checksums for downloads, but they are broken for security: two different files can be made with the same hash. Do not use them to protect anything.
How to check a download
- Switch to File and choose the file you downloaded.
- Paste the checksum published by the provider into “Check against”.
- Look for the tick. If the row lights up green, the file is exactly what the provider published. If nothing matches, download it again.
Good to know
- Text is hashed as UTF-8, so the result matches command-line tools such as sha256sum when the text is the same, including any final line break.
- Files are read in your browser and never uploaded. Very large files (several gigabytes) can exceed the browser’s memory.
- Hashing is one-way: you cannot turn a hash back into the text.
Frequently asked questions
Can an MD5 hash be decrypted?
No. A hash is not encryption, so there is nothing to decrypt. Short, common passwords can be found by guessing and comparing hashes, which is why passwords should be stored with slow, salted algorithms, not MD5.
Why is my hash different from another tool’s?
Usually the input is not identical: an extra space, a line break at the end, or a different text encoding. Upper and lower case in the hash itself do not matter.
Is my file uploaded to calculate the hash?
No. The file is read and hashed entirely in your browser.