Partshas

Partshas are per-part cryptographic hash values associated with subdivisions of a data object, used to verify integrity, support incremental updates, and enable partial recovery in distributed systems. A partshas set typically comprises a manifest that lists each part’s offset, length, and its hash, along with the overall object hash for quick coarse verification. The term blends "part" with "hash," and the approach is widely used in chunked verification practices in modern storage and transmission protocols.

Partshas can be computed by partitioning the data into fixed-size segments, hashing each segment with a cryptographic hash function such as SHA-256 or BLAKE2, and recording the results. For efficient verification of multiple parts, a Merkle tree over the per-part hashes may be used, allowing a client to prove inclusion of a part with a short path of hashes.

Applications include distributed file systems, backup and synchronization tools, streaming services, and content-addressable storage, where partial data verification can reduce bandwidth and speed up recovery. Benefits include localized error detection, parallelizable processing, and efficient resynchronization after partial data loss. Limitations involve metadata overhead, fixed partition size sensitivity, and the need to agree on the hash function and partition scheme across systems.

Implementation notes: choose partition size according to data object size and network characteristics; store the manifest alongside the object; ensure secure hash selection and regular rotation in long-term archives.

See also: checksums, hash functions, Merkle trees, content-addressable storage.