sjekksum

Sjekksum, or checksum, is a small value derived from a data set, used to detect errors or changes in the data. In computing, checksums are generated from the content of a file, message, or block of data and serve as a quick verification that the data has not been altered in transit or storage. They are not secret keys and are intended to reveal accidental alterations rather than intentional tampering.

Checksums can be created in several ways. Simple methods include additive or parity-based checksums, which sum bytes or bits to produce a limited result. More robust methods include cyclic redundancy checks (CRC), which are widely used in storage and transmission to detect common error patterns. Cryptographic hash functions (such as MD5, SHA-1, SHA-256) also produce fixed-length digests; while often used as checksums for integrity verification, they are designed to be resistant to collisions and intended to be harder to reverse. For security-sensitive purposes, cryptographic hashes are typically used together with signatures or HMACs rather than as standalone authenticity guarantees.

Applications of sjekksum include software distribution, where developers publish a file’s checksum so users can verify downloads; backups and file transfer systems to detect corruption; and data integrity checks in file systems and archives. Verifying a checksum involves recomputing the digest on the recipient side and comparing it to the published value. If they match, the data is presumed intact; if not, the data should be re-transferred or inspected.

Limitations include that ordinary checksums do not prove authenticity; they can’t prevent tampering unless combined with authentication mechanisms such as digital signatures. For stronger integrity guarantees, use robust cryptographic hashes and signatures rather than simple checksums.