5.6 KiB
BFT-CRDT PoC
This is a proof of concept implementation of a BFT-CRDT blockchain-like system. It is willfully, wildly insecure as a blockchain right now. Think of it as an experiment which is strictly for fun and poking at ideas.
This code is based on the ideas of Martin Kleppmann and the ideas and code of Jacky Zhao. Have a read, they are both excellent writers and have some of the most interesting computing ideas I've run across in quite a while.
It is not clear what this thing is for, yet. It's not a blockchain. It makes a kind of secure DAG. It uses BFT-CRDTs to make a Sybil-proof and secure information transmission system for messages, with eventual consistency guarantees.
The idea that it could be possible to set up a secure Sybil-proof system, negating the energy burn required for proof of work, the financially exclusionary proof of stake, or the meat space hassle of a proof of personhood ceremony, is too attractive to ignore. At least, if you're interested in cool P2P systems.
Prerequisites
Install a recent version of Rust.
Running in development
Run the watcher first:
cd crdt-relayer
cargo watch -x run
To init a Side node:
cd crdt-node
cargo run -- init node1
cargo run -- init node2
cargo run -- init node3
cargo run -- init node4
To start a node with a cargo watch for development purposes (from the crdt-node dir), open up a few terminals and run:
cargo watch -x "run -- run -- node1"
cargo watch -x "run -- run -- node2"
cargo watch -x "run -- run -- node3"
cargo watch -x "run -- run -- node4"
You can then type directly into each of the Crdt Node consoles. Messages will be relayed to each Crdt Node, and the transaction history will end up being the same on all nodes.
Discussion
What we have here is a very simple system comprised of two parts: the Crdt Node, and the Crdt Relayer.
Crdt Node(s)
The Crdt Nodes make up a system of BFT-CRDT-producing nodes that can make a sort of wildly insecure blockchain. Currently, they can reliably send transactions to each other in a secure way, such that all nodes they communicate with can tell whether received transactions are obeying the rules of the system.
The Crdt Node does not download any chain state, and if one goes off-line it will miss transactions. This is expected at the moment and fairly easy to fix, with a bit of work.
Crdt Relayer
The Crdt Relayer replicates transactions between nodes using a websocket. We aim to eliminate this component from the architecture, but for the moment it simplifies networking and consensus agreement while we experiment with higher-value concepts.
Later, we will aim to remove the Crdt Relayer from the architecture, by (a) moving to pure P2P transactions between Crdt Nodes, and (b) doing leader election of a Crdt Node to reach agreement on the submitted block.
Bitcoin integration
There is a Bitcoin client integrated into the node, which can do simple coin transfers using esplora and the Mutinynet server's Signet (30 second blocktime).
The client's demo driver can be run by doing:
cargo run -- init dave
cargo run -- init sammy
cargo run -- btc
You'll need to have funded the "dave" address prior to running the btc command - otherwise the transfer will fail gracefully.
I was using this primarily as a way to experiment with constructing and broadcasting Bitcoin transactions, with the hope that it would be possible to move on to more advanced constructions (e.g. state channels). However, now that I look at all the options, it seems that multi-party state channels in Bitcoin are (probably) impossible to construct.
There is a second, unused Bitcoin client in place which uses Blockstream's Electrum server, but this didn't seem to be working properly with respect to Signet Bitcoin network during my testing, so I went with the esplora / Mutiny version instead.
Possible uses
DKG
It strikes me that there are many, many systems which rely on a trusted setup, and which might be able to use Distributed Key Generation (DKG) instead. SNARK systems for instance all have this problem. Could BFT-CRDTs help here?
It is not necessarily the case that e.g. signer participants and Cosmos validators are the same entities. Being able to quickly spin up a blockchain and use it to sign (potentially temporary or ephemeral) keyshare data might be pretty useful.
Cross chain transfers
Might the ability to be part of multiple consensus groups at once provide new opportunities for cross-chain transfers?
Next dev tasks:
- we don't need a relayer, the first crdt node can act as a leader until people decide they don't want to trust it any more
- the leader node can have a timer in it for block creation
- code up the ability to switch leaders (can be a human decision at first, later an (optional) automated choice)
- pick a commit and reveal scheme to remove MEV. One thing to investigate is single-use seals
- enable Crdt Nodes should download current P2P chain/dag state so that they start - out with a consistent copy of transaction data, and also do catch-up after going off-line
- remove the proc macro code from bft-json-crdt, it's not really needed in this implementation
- add smart contract execution engine (CosmWasm would be a good first choice)
- enable Crdt Nodes to download contract code for a given contract
- enable Crdt Nodes to download current contract state for a given contract
- switch to full P2P messaging instead of websockets