Hashsjekk

Hashsjekk is a method for verifying data integrity by computing a cryptographic hash of a file or message and comparing it with a reference value. A hash function converts input data of any size into a fixed-length string; small changes in the input produce a different hash, enabling detection of corruption or tampering.

Typically, a software distributor or data custodian provides the expected hash value for a file (a checksum). After download, the user computes the hash of their copy and compares it to the reference. A match indicates the data are likely intact; a mismatch suggests corruption or tampering and a re-download or further verification is advised.

Common hash algorithms include MD5, SHA-1, SHA-256, SHA-3, and BLAKE2. MD5 and SHA-1 are now considered weak for collision resistance, so modern use favors SHA-256, SHA-3, or BLAKE2. It is important to note that a hash check verifies integrity, not authenticity; it does not prove the file came from a trusted source unless combined with a digital signature or a trusted channel.

In practice, hash checks are widely used for software distribution, data backups, and file transfers. Tools to compute hashes include sha256sum on Linux, CertUtil or Get-FileHash on Windows, and shasum on macOS and other platforms. Users should ensure they obtain both the file and its associated hash from the official source.