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!
Every few weeks, we release a new Zebra alpha release.
The goals of the alpha release series 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.
rustupinstalls the stable Rust toolchain, which
- Install Zebra's build dependencies:
- libclang: the
llvm-devpackages, depending on your package manager
- clang or another C++ compiler:
- libclang: the
cargo install --locked --git https://github.com/ZcashFoundation/zebra --tag v1.0.0-alpha.8 zebrad
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:
- install both
clang- they are usually different packages
--lockedto 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.
- synchronize the chain from peers
- download gossiped blocks from peers
- answer inbound peer requests for hashes, headers, and blocks
- 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
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 Canopy
- 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 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
zebrad, and then restart
- Duplicate block errors #1372
- these errors can be ignored, unless they happen frequently
In 2021, 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.
- 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.
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
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-chainare defined to enforce structural validity by making invalid states unrepresentable. For instance, the
Transactionenum 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-chainis 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
connect_isolatedmethod 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-scriptprovides script validation. Currently, this is implemented by linking to the C++ script verification code from
zcashd, but in the future we may implement a pure-Rust script implementation.
zebra-consensusperforms 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-batchto perform automatic, transparent batch processing of contemporaneous verification requests.
zebra-stateis 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.
zebradcontains the full node, which connects these components together and implements logic to handle inbound requests from peers and the chain sync process.
zebra-clientwill 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 has a responsible disclosure policy, which we encourage security researchers to follow.
Zebra is distributed under the terms of both the MIT license and the Apache License (Version 2.0).