Sharding

JAM allows rollups to change their execution shard boundaries dynamically on every block. This gives unprecedented freedom to developers who can now atomically compose across shards. It is achieved by splitting execution into two phases: Accumulation and Refinement.

Execution

JAM employs a Virtual Machine for a modified RISC-V instruction set: PolkaVM. This enables smart contract developers to use the language of their choice, as long as it can be compiled to RISC-V. Some obvious examples are Rust, YUL (Solidity) or C/C++. And yes, it can even run Doom.

Cryptography

Researchers from the Web3 Foundation and Parity have invented a novel ZK building block: Ring VRF. It combines two primitives: Ring Signatures and Verifiable Random Functions. The Ring property allows members to issue signatures through a pseudonym without revealing their identity. The VRF ensures that some outputs can be treated as sufficiently random for use in consensus algorithms.

Block Production

The Web3 Foundation and Parity developed the block production algorithm SASSAFRAS, of which a simplified version SAFROLE is used. It minimizes the risk of forks and provides high quality entropy. The algorithm operates at a 6 second block time with about 18 second finality.