Kontrollsummen

Kontrollsummen is a value derived from data used to verify its integrity. In computing, it is produced by applying a checksum algorithm to a sequence of bytes or symbols. The resulting fixed-size value is stored or transmitted with the data, and recalculated on receipt to detect discrepancies.

Common forms include simple parity, ones' complement or sum-based checksums, and cyclic redundancy checks (CRC). CRCs, in particular CRC-32, are widely used in network protocols and storage devices. Another class consists of cryptographic hashes (MD5, SHA-1, SHA-256) used for verifying file integrity; these are more resistant to accidental errors but are designed for security and not primarily error detection, so they are often referred to as hashes rather than simple checksums. In many software distributions, a separate checksum file contains the MD5 or SHA-256 value.

Calculation and use: The algorithm processes the data to produce the fixed-length kontrollsumm. For a CRC, the data is processed through polynomial division in GF(2).

Applications: Kontrollsummen are used for error detection in data transmission, storage media, and file downloads; they appear in formats and protocols such as ZIP archives, Ethernet frames, and TCP/IP.

Limitations: They are not foolproof and can fail to detect certain errors or collisions. They are not cryptographically secure by design, so relying solely on them does not guarantee data integrity or authenticity. They are best used for error detection together with additional security measures when needed.