Zebra is the Zcash Foundation's independent, consensus-compatible implementation of the Zcash protocol, currently under development. Please join us on Discord if you'd like to find out more or get involved!
Our first alpha release is planned for December 8th, 2020.
The goals of this release are to:
- participate in the Zcash network,
- replicate the Zcash chain state,
- implement the Zcash proof of work consensus rules, and
- sync on Mainnet under excellent network conditions.
Currently, Zebra does not validate all the Zcash consensus rules. It may be unreliable on Testnet, and under less-than-perfect network conditions. See our current features and roadmap for details.
Building zebrad
requires Rust,
libclang, and a C++ compiler.
- Install
cargo
andrustc
.- Using
rustup
installs the stable Rust toolchain, whichzebrad
targets.
- Using
- Install Zebra's build dependencies:
- libclang: the
libclang
,libclang-dev
,llvm
, orllvm-dev
packages, depending on your package manager - clang or another C++ compiler:
g++
,Xcode
, orMSVC
- libclang: the
- Run
cargo install --locked --git https://github.com/ZcashFoundation/zebra --tag v1.0.0-alpha.0 zebrad
- 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.
If you're having trouble with:
- dependencies:
- install both
libclang
andclang
- they are usually different packages - use
cargo install
without--locked
to build with the latest versions of each dependency
- install both
- 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
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 continuously test that our builds and tests pass on:
- Windows Server 2019
- macOS Big Sur 11.0
- Ubuntu 18.04 / the latest LTS
- Debian Buster
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.
zebrad
's typical network usage is:
- initial sync: 30 GB download
- ongoing updates: 10-50 MB upload and download per day, depending on peer requests
The major constraint we've found on zebrad
performance is the network weather,
especially the ability to make good connections to other Zcash network peers.
Network:
- synchronize the chain from peers
- download gossipped blocks from peers
- answer inbound peer requests for hashes, headers, and blocks
State:
- persist block, transaction, UTXO, and nullifier indexes
- handle chain reorganizations
Proof of Work:
- validate equihash, 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 zcashd
.
This release also implements some other Zcash consensus rules, to check that Zebra's validation architecture supports future work on a full validating node:
- block and transaction structure
- checkpoint-based verification up to Sapling
- transaction validation (incomplete)
- transaction cryptography (incomplete)
- transaction scripts (incomplete)
- batch verification (incomplete)
Zebra primarily depends on pure Rust crates, and some Rust/C++ crates:
There are a few bugs in the Zebra alpha release that we're still working on fixing:
- Occasional panics in the
tokio
time wheel implementation #1452- workaround: restart
zebrad
- workaround: restart
- Occasional panics during client requests #1471
- workaround: restart
zebrad
- workaround: restart
- 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 exitzebrad
, and then restartzebrad
- Duplicate block errors #1372
- these errors can be ignored, unless they happen frequently
In 2021, we intend to add RPC support and 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
The Zebra website contains user documentation, such as how to run or configure Zebra, set up metrics integrations, etc., as well as developer documentation, such as design documents. We also render API documentation for the external API of our crates, as well as internal documentation for private APIs.
Unlike zcashd
, which originated as a Bitcoin Core fork and inherited its
monolithic architecture, 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 inzebra-chain
are defined to enforce structural validity by making invalid states unrepresentable. For instance, theTransaction
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 tozcashd
, 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
provides script validation. Currently, this is implemented by linking to the C++ script verification code fromzcashd
, but in the future we may implement a pure-Rust script implementation. -
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 usestower-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 as updating the nullifier set or 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
andzebra-client
will eventually contain the RPC and wallet functionality, but as mentioned above, our goal is to implement replication of chain state first before asking users to entrust Zebra with their funds.
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").
Zebra is distributed under the terms of both the MIT license and the Apache License (Version 2.0).
See LICENSE-APACHE and LICENSE-MIT.