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Hypercore Protocol

The Hypercore Protocol is the technical foundation of the Dat project and the primary implementation of its protocols. It is a collection of modules written in JavaScript that run on the Node.js runtime.

Its primary data structure is Hypercore, a cryptographically secure append-only plus an efficient replication protocol. Each hypercore is identified by a unique public key, and internally uses merkle trees to efficiently verify that all entries to the hypercore are signed by the single matching secret key. The hypercore protocol is a binary protocol to sync two hypercores both sparsely and live over any binary stream (usually, a network socket).

The primary networking scheme of the hyperstack is hyperswarm, a distributed networking stack for connecting peers. It allows processes and machines to find each other on mutual interest in a topic. Peers are found both in the local network and through a distributed hash table of peers. To establish connections through a variety of network configurations hyperswarm uses NAT holepunching.

Furthermore, the hyperstack includes several data structures built on top of Hypercore, namely:

  • Hypertrie, a distributed key-value store. It allows to find any key in the keyspace with a small number of lookups, when all you have is the latest entry of an append-only log to start with.
  • Hyperdrive, a distributed file system built upon Hypercore and Hypertrie. It maps the primitives of a POSIX file system onto a hypertrie (for directory and file lookup plus metadata) and an additional hypercore for the actual file contents. On many systems hyperdrives can be mounted as a user-space filesystem that appears like a regular folder on your local device (through hyperdrive-fuse and the hyperdrive-daemon).

All of these data structure are by default single-writer, which means that only one secret key is allowed to publish updates to the data, and that single key is expected to reside only on a single device (otherwise forks would arise, which is not something the stack is designed to make use of and are currently considered data corruption).

Hypertrie and Hyperdrive have a concept of mounts, where specific paths in a tree may point to another tree. Because these data structures are efficient also when only sparsely synced, this opens the door to the idea of a huge grid of interlinked data structures.

The hyperstack is in the process of going though a major version upgrade oftenly dubbed Dat2. It includes Hypercore 8, hypercore protocol 7, hyperdrive 10 and the migration from discovery-swarm to hyperswarm. Sonar only uses this new major version of the stack (which is incompatible to earlier versions), and other Dat projects like Beakerbrowser are in the process of upgrading.