libhotstuff is a general-purpose BFT state machine replication library with modularity and simplicity, suitable for building hybrid consensus cryptocurrencies.

This repo includes the prototype implementation evaluated in our HotStuff: BFT Consensus in the Lens of Blockchain paper. The consensus protocol is also used by Facebook in Libra project.

Feel free to contact us if you'd like to reproduce the results in the paper, or tweak the code for your own project/product.

• Full paper: https://arxiv.org/abs/1803.05069
• PODC 2019 paper: https://dl.acm.org/citation.cfm?id=3331591

• Simplicity. The protocol core logic implementation is as simple as the one specified in our paper. See consensus.h and consensus.cpp.
• Modular design. You can use abstraction from the lowest level (the core protocol logic) to the highest level (the state machine replication service with network implementation) in your application, or override/redefine the detailed behavior to customize your own consensus.
• Liveness decoupled from safety. The liveness logic is entirely decoupled from safety. By defining your own liveness gadget ("PaceMaker"), you can implement your own liveness heuristics/algorithm. The actual performance varies depending on your liveness implementation, but the safety is always intact.
• Friendly to blockchain systems. A PaceMaker could potentially be PoW-based and it makes it easier to build a hybrid consensus system, or use it at the core of some cryptocurrencies.
• Minimal. The project strives to keep code base small and implement just the basic functionality of state machine replication: to deliver a consistent command sequence to the library user. Application-specific parts are not included, but demonstrated in the demo program.

NOTICE: the project is still in-progress. Try at your own risk, and this section may be incomplete and subject to changes.

# install from the repo
git clone https://github.com/hot-stuff/libhotstuff.git
cd libhotstuff/
git submodule update --init --recursive

# ensure openssl and libevent are installed on your machine
cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_SHARED=ON -DHOTSTUFF_PROTO_LOG=ON
make

# start 4 demo replicas with scripts/run_demo.sh
# start the demo client with scripts/run_demo_client.sh

• Add a PoW-based Pacemaker
• Branch pruning & swapping (the current implementation stores the entire chain in memory)
• Limit the async events (improve robustness)
• Persistent protocol state (recovery?)