Abrahm Chain

Abrahm is a permissioned Rust blockchain created for educational purposes. It is inspired by the go-ethereum and diem clients. A similarity with Ethereum is that it uses the account-based transaction model, mainly for simplicity. Transaction finality is handled through PBFT consensus (Castro and Liskov, 1999). Diem has been used as a reference to better understand designs of Rust blockchains and as an example of how to produce excellent documentation. A significant part of the drive for this project is to implement the PBFT three-phase consensus protocol from its specification and connect it to the other modules of a blockchain system.

Due to the wide scope, building a functional blockchain from scratch, several trade-offs have been done. The goals have been boiled down to the essentials and the non-goals are many.

Goal (Implementation features)

• Value ("cryptocurrency") transfer from one entity to another
• Prevent a limited set of attack vectors such double spend and masquerading through cryptography
• Mining mechanism based on a BFT algorithm for relatively high throughput
• Messaging protocol to encapsulate all the stages and states in the blockchain lifecycle
• Concurrent, multithreaded, and asynchronous

Non-Goals (Omit) and Limitations

• No smart contract functionality or any other functionality apart from send / receive of value
• No additional networking protocols to upgrade and optimize message passing further
• No internetworking support; only supports LAN
• No unbounded amount of peers and scalability; fixed set of validator peers
• No post-startup synchronization; all peers must boot around the same time
• No cross-platform compatibility; only supports macOS

Architecture

The ambition is to demonstrate the most fundamental components of a working blockchain, albeit with rudimentary functionality. The focus is to deliver a complete and working baseline rather than the most clever, novel, and performant one. The different architectural components are:

• ledger: state database, key management, and chain initialization
• consensus: the state negotiation protocol (PBFT)
• network: peer-to-peer discovery and messaging
• swiss_knife: various helpers
• types: block and transaction types

Dependencies

The main ones are:

• themis for encryption and secure message exchange
• tokio for async and networking
• libp2p for local network discovery (mDNS)
• rocksdb