What is a checksumA small value calculated from a file, used to check that it has not changed or been corrupted

TimeBinder adds a layer of protection against AI and human fraud and disputes.

The file stays on your device. Your browser makes a digital fingerprint of the file. TimeBinder records the fingerprint and the time, not the file.

Short answer

A checksum is a short value calculated from a file or block of data and used to check it has not changed or been corrupted. If you recalculate it and get a different value, the data differs. Simple checksums catch accidents, while cryptographic hashes such as SHA-256 also resist deliberate tampering.

Checksum, hash and fingerprint

“Checksum” is a general term. Basic ones, such as parity bits or CRC values, are designed to catch accidental errors during storage or transfer. They are quick, but someone can deliberately craft changes that keep the same value.

A cryptographic hash such as SHA-256 is often used as a stronger checksum, because finding two different files with the same value is not known to be practical. See the glossary entry and what is a file hash.

Checking one yourself

You can compare two copies of a file by calculating the same checksum for each and checking the values match. The SHA-256 file hash checker does this in your browser. A TimeBind records a SHA-256 fingerprint of the exact file and a time, anchored to Bitcoin. The fingerprint is made in your browser and the file is not uploaded.

A matching checksum shows the files are identical. It does not show who made the file or that its contents are true.

Make a TimeBind: first one free →

First Pooled TimeBind free, no card, then from US$5. An ASAP TimeBind is US$15.

Frequently asked questions

Is a checksum the same as a hash?

Related but not identical. A checksum is any value used to check data. A cryptographic hash is a stronger kind designed to resist deliberate tampering.

What does a checksum mismatch mean?

The two files are not identical. The cause may be a failed download, corruption or an edit.

Can a checksum be faked?

Simple checksums can be matched deliberately. For cryptographic hashes, no practical way is known to produce a different file with the same value.

Does a checksum prove a file is safe?

No. It only shows the file matches the one the checksum was made from.

Sources

NIST, Glossary: checksum.
TimeBinder, SHA-256 file hash checker.

Related guides and tools

Your file’s fingerprint, anchored to a global network secured by real electricity and cryptography.

Editing a file—including with AI—changes its fingerprint, not its existing network record.

How this works

Your file’s SHA-256 fingerprint, a short code worked out from its exact contents, is made in your browser, and the file itself stays on your device. A cryptographic commitment to that fingerprint, which may be combined with others, is then anchored in a block on the Bitcoin blockchain. Bitcoin is secured by proof of work: computers around the world spend real electricity to add each block, and changing an earlier block would mean redoing that work faster than the rest of the network. Until that block is confirmed, your proof is pending. Once the Bitcoin anchoring is confirmed, you can verify the proof against that recorded commitment. The confirmed record can then be checked; Pooled TimeBinds are checked through TimeBinder, while ASAP TimeBinds can also be checked independently. If you check the file later and its fingerprint still matches, that shows the file existed no later than the recorded time. The record doesn’t show who made the file, whether AI was used, or that its contents are true.

Your filestays on your device
FingerprintSHA-256
Network timestampon Bitcoin

Record a fingerprint of the file you rely on

Add a layer of protection against AI and human fraud and disputes: a dated, checkable record of the exact file you hold.

Open the app and sign in with email or Google.
Add your files. They stay on your computer.
Seal them and download your Proof of Time certificates.

Open TimeBinder →

First Pooled TimeBind free, no card, then from US$5. See pricing.

Related glossary entries: message digest and preimage resistance.