Zcash-flyclient

An implementation in Python of the flyclient protocol for the Zcash blockchain. It is currently able to verify a flyclient proof provided by a full node. The purpose of this project is to create a proof-of-concept implementation of the flyclient protocol to be later referenced when developing a client intended to run on resource-constrained hardware.

Usage

To validate a blockchain using a flyclient proof, the script needs to download Merkle Mountain Range (MMR) tree nodes from a Zcash full node (zebrad). The current main branch of zebrad does not support downloading arbitrary MMR nodes, so you will need to use my own fork of zebrad which implements this function via RPC.

Warning

This fork of zebrad will update the database version to 27.1.0 to store history nodes (the MMR nodes). This is required for the flyclient protocol to work correctly. Do not point it to your main configuration file if you don't want this to happen to your main database.

Clone and build zebrad:

git clone https://github.com/Metalcape/zebra.git
git checkout flyclient
cargo build --bin zebrad --release

Run zebrad (make sure to enable RPC and disable cookie authentication in zebrad.toml):

./target/release/zebrad start

The first time you run zebrad, you will have to wait for the database upgrade to complete (will take a few minutes on testnet, a few hours on mainnet)

Now clone this repository and install the requirements:

git clone https://github.com/Metalcape/zcash-flyclient.git
virtualenv venv
source venv/bin/activate
pip install -r requirements.txt

To connect to your zebrad instance, place a zcash.conf file with the following information in the same directory as zcash_client.py (username and password are not used for now and can be whatever):

rpcuser = yourusername
rpcpassword = yourpassword
rpcport = 8232
rpcbind = 127.0.0.1

Finally, run python ./flyclient.py. The script will print information about the verification process. You can also use zcash_client.py to send any RPC commands to zebrad:

python ./zcash_client.py getblockchaininfo

Roadmap

• Verify sampled blocks' rightmost MMR tree leaf using the header's own chainhistoryroot
• Verify block headers' proof-of-work
• Use the authdataroot field to verify the blockcommitments field in the header
• Implement difficulty-based sampling of blocks using the $(c, L)$ parametrized adversary model
• Non-interactive proof using Fiat-Shamir heuristic