Checksum

It works by adding up the bytes, or some other basic components in a string of data, and storing the resulting value.

Later, anyone (who has the authentic checksum) can verify that the message was not corrupted by doing the same operation on the data, and "checking" the "sum".

Note: The term 'checksum' is also often used incorrectly to mean a CRC. CRCs are in general more effective than checksums at detecting random errors.

While a checksum is somewhat useful in protecting against accidental modification, it provides no security against a malicious agent as it is trivial to circumvent. Even a reordering of the bytes does not change the checksum. Therefore, the use of a cryptographically strong[?] hash functions is often necessary instead of a checksum.

See also Parity, CRC, CRC32, MD5, Cryptography, Threat model[?], Luhn formula, check digit[?]