Checksum

A checksum is a small value computed from data to detect accidental corruption — a flipped bit during transmission or storage. Common examples are CRC32 and Adler-32, used in Ethernet, ZIP, PNG, and zlib.

Checksums are fast and excellent at catching random errors and burst errors, but they are not cryptographic:

• They are not collision resistant — it is trivial to craft two inputs with the same checksum.
• Many (like CRC) are linear, so an attacker can modify data and patch the checksum to match.

That makes checksums fine for detecting accidental damage, but useless against a deliberate attacker. For integrity that must resist tampering — signatures, deduplication, content addressing — use a cryptographic hash like SHA-256 or BLAKE3 instead.

Compute CRC32 and other checksums in your browser, or see how cryptographic hashing works.