Hashverfahren
Cryptographic Hash Function
Kryptografisches Hashverfahren
A hash function maps arbitrary data to a value of fixed length — the hash or fingerprint. Good cryptographic hash functions are practically irreversible, and even a tiny change in the input completely changes the hash. These properties make them a tool for integrity checking, recognition and forensic evidence preservation.
History & facts. Essential properties of a cryptographic hash function are the one-way property (the input cannot be computed back from the hash) and collision resistance (it is practically impossible to find two different inputs with the same hash). Older functions such as MD5 and SHA-1 are considered broken because collisions became producible; the current standards are the SHA-2 family (such as Secure Hash Algorithm 256-bit (SHA-256)) and SHA-3. Hashes serve, among other things, to identify malicious files, to match indicators and to store passwords securely (with salt).
Outlook & recommendation. In forensics the hash is the backbone of evidence integrity: a hash formed at the time of acquisition proves that a disk image was not altered later. It is practically important to use only unbroken functions and never to store passwords with simple, fast hashes but with slow functions designed for the purpose.