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About

Zebra-BTC is a fork of Zebra the Zcash Foundation's implementation of the Zcash protocol. Zebra-BTC aims to be a performant, consensus compatible implementation of the Bitcoin Protocol. It is developed as part of the ongoing Bitcoin Warp project.

Roadmap

1. Convert existing Zebra-network from Zcash to Bitcoin (done - compliant up to Protocol Version 70013)
2. Convert existing Zebra-chain (block, tx, etc.) from Zcash to Bitcoin (in-progress)
3. Convert existing Zebra-consensus from Zcash to Bitcoin (not started)
4. Replace zebra-script with an external library (libbitcoin-kernel)
5. Implement missing features including mempool and zebra-script

Alpha Releases

As we work towards our first Alpha release, here are the goals we aim to achieve:

• participate in the Bitcoin network,
• replicate the Bitcoin chain state ("the UTXO set"),
• implement the Bitcoin proof of work consensus rules, and
• sync on Mainnet under excellent network conditions.

The first Alpha release of Zebra-BTC will not validate all the Bitcoin consensus rules. It may be unreliable on Testnet, and under less-than-perfect network conditions. See our current features and roadmap for details.

Getting Started

Building zebrad requires Rust, libclang, and a C++ compiler.

Detailed Build and Run Instructions

1. Install cargo and rustc.
   • Using rustup installs the stable Rust toolchain, which zebrad targets.
2. Install Zebra's build dependencies:
   • libclang: the libclang, libclang-dev, llvm, or llvm-dev packages, depending on your package manager
   • clang or another C++ compiler: g++, Xcode, or MSVC
3. Run cargo install --locked --git https://github.com/ZcashFoundation/zebra --tag v1.0.0-alpha.1 zebrad
4. Run zebrad start

If you're interested in testing out zebrad please feel free, but keep in mind that there is a lot of key functionality still missing.

Build Troubleshooting

If you're having trouble with:

• dependencies:
  • install both libclang and clang - they are usually different packages
  • use cargo install without --locked to build with the latest versions of each dependency
• libclang: check out the clang-sys documentation
• g++ or MSVC++: try using clang or Xcode instead
• rustc: use rustc 1.48 or later
  • Zebra does not have a minimum supported Rust version (MSRV) policy yet

System Requirements

We usually build zebrad on systems with:

• 2+ CPU cores
• 7+ GB RAM
• 14+ GB of disk space

On many-core machines (like, 32-core) the build is very fast; on 2-core machines it's less fast.

We usually run zebrad on systems with:

• 4+ CPU cores
• 16+ GB RAM
• 50GB+ available disk space for finalized state
• 100+ Mbps network connections

zebrad might build and run fine on smaller and slower systems - we haven't tested its exact limits yet.

Network Usage

zebrad's typical network usage is:

• initial sync: 300+ GB download
• ongoing updates: 50+ MB upload and download per day, depending on peer requests

The major constraint we've found on zebrad performance is the network weather.

Alpha Release Features

Network:

• synchronize the chain from peers
• download gossipped blocks from peers
• answer inbound peer requests for hashes, headers, and blocks

State:

• persist block, transaction, and UTXOs
• handle chain reorganizations

Proof of Work:

• validate hash, block difficulty threshold, and difficulty adjustment
• validate transaction merkle roots

Validating proof of work increases the cost of creating a consensus split between zebrad and bitcoind.

This release also implements some other Bitcoin consensus rules, to check that Zebra's validation architecture supports future work on a full validating node:

• block and transaction structure
• transaction validation (incomplete)
• transaction cryptography (incomplete)
• transaction scripts (incomplete)
• batch verification (incomplete)

Dependencies

Zebra primarily depends on pure Rust crates, and some Rust/C++ crates:

• rocksdb

Known Issues

There are a few bugs in Zebra that we're still working on fixing:

• Peer connections sometimes fail permanently #1435
  • these permanent failures can happen after a network disconnection, sleep, or individual peer disconnections
  • workaround: use Control-C to exit zebrad, and then restart zebrad
• Duplicate block errors #1372
  • these errors can be ignored, unless they happen frequently

Future Work

We hope to complete our Alpha relase in 2021.

In 2022, we intend to finish validation, add RPC support, and add wallet integration. This phased approach allows us to test Zebra's independent implementation of the consensus rules, before asking users to entrust it with their funds.

Features:

• full consensus rule validation
• transaction mempool
• wallet functionality
• RPC functionality

Performance and Reliability:

• reliable syncing on Testnet
• reliable syncing under poor network conditions
• batch verification
• performance tuning

Documentation

The Zebra website contains user documentation for Zcash Zebra, most of which is applicable to Zebra-BTC as well. These docs explain how to run or configure Zebra, set up metrics integrations, etc. THey also include developer documentation and as design documents. The Zcash Foundations also renders API documentation for the external API of Zebra's crates, as well as internal documentation for private APIs.

Architecture

Unlike bitcoind, Zebra has a modular, library-first design, with the intent that each component can be independently reused outside of the zebrad full node. For instance, the zebra-network crate containing the network stack can also be used to implement anonymous transaction relay, network crawlers, or other functionality, without requiring a full node.

At a high level, the fullnode functionality required by zebrad is factored into several components:

• zebra-chain, providing definitions of core data structures for Zcash, such as blocks, transactions, addresses, etc., and related functionality. It also contains the implementation of the consensus-critical serialization formats used in Zcash. The data structures in zebra-chain are defined to enforce structural validity by making invalid states unrepresentable. For instance, the Transaction enum has variants for each transaction version, and it's impossible to construct a transaction with, e.g., spend or output descriptions but no binding signature, or, e.g., a version 2 (Sprout) transaction with Sapling proofs. Currently, zebra-chain is oriented towards verifying transactions, but will be extended to support creating them in the future.

• zebra-network, providing an asynchronous, multithreaded implementation of the Zcash network protocol inherited from Bitcoin. In contrast to zcashd, each peer connection has a separate state machine, and the crate translates the external network protocol into a stateless, request/response-oriented protocol for internal use. The crate provides two interfaces:

  • an auto-managed connection pool that load-balances local node requests over available peers, and sends peer requests to a local inbound service, and
  • a connect_isolated method that produces a peer connection completely isolated from all other node state. This can be used, for instance, to safely relay data over Tor, without revealing distinguishing information.

• zebra-script will provide script validation. This will probably use libbitcoin-kernel.

• zebra-consensus performs semantic validation of blocks and transactions: all consensus rules that can be checked independently of the chain state, such as verification of signatures, proofs, and scripts. Internally, the library uses tower-batch to perform automatic, transparent batch processing of contemporaneous verification requests.

• zebra-state is responsible for storing, updating, and querying the chain state. The state service is responsible for contextual verification: all consensus rules that check whether a new block is a valid extension of an existing chain, such checking that transaction inputs remain unspent.

• zebrad contains the full node, which connects these components together and implements logic to handle inbound requests from peers and the chain sync process.

• zebra-rpc will eventually contain the RPC functionality, but as mentioned above, our goal is to implement replication of chain state first.

All of these components can be reused as independent libraries, and all communication between stateful components is handled internally by internal asynchronous RPC abstraction ("microservices in one process").

Security

Zebra has a responsible disclosure policy, which we encourage security researchers to follow.

License

Zebra is distributed under the terms of both the MIT license and the Apache License (Version 2.0).

See LICENSE-APACHE and LICENSE-MIT.