checksummed

Checksummed is an adjective used to describe data, files, or transmissions for which a checksum value has been computed and stored alongside the data. A checksum is a short, fixed-size value derived from the content using a checksum algorithm. The intention is to detect accidental corruption that may occur during storage, transmission, or processing.

In practice, a checksum is computed on the original data, and the resulting value is stored or transmitted with the data. Upon receipt, the same algorithm is applied to the received data and the computed value is compared to the original checksum. A match indicates the data is likely intact; a mismatch signals possible corruption and may trigger re-transfer or repair.

Common algorithms include CRC (cyclic redundancy check), Adler-32, MD5, SHA-1, and SHA-256. CRCs are fast and good for detecting random errors in storage and transmission. Cryptographic hashes such as MD5 and SHA-1 are designed for uniqueness but have known weaknesses; MD5/SHA-1 are generally discouraged for security purposes, though still used for checksums where security is not critical.

Uses of checksums include software distributions, archives (zip, tar), package managers, backups, and distributed file systems that store per-block checksums to verify integrity. Many download sites publish a manifest or separate checksum file listing the checksums of individual files so users can verify their downloads.

Limitations: checksums detect accidental corruption but do not prove authenticity unless the source is trusted. They do not prevent tampering. For security today, checksums are often complemented by digital signatures or secure channels to verify provenance.