WARNING: This software is still experimental, we do not recommend it for production use (see Security section).
RISC Zero is a zero-knowledge verifiable general computing platform based on zk-STARKs and the RISC-V microarchitecture.
A zero knowledge proof allows one party (the prover) to convince another party (the verifier) that something is true without revealing all the details. In the case of RISC Zero, the prover can show they correctly executed some code (known to both parties), while only revealing to the verifier the output of the code, not any of its inputs or any state during execution.
The code runs in a special virtual machine, called the ZKVM. The RISC Zero ZKVM emulates a small RISC-V computer, allowing it to run arbitrary code in any language, so long as a compiler toolchain exists that targets RISC-V. Currently, SDK support exists for Rust, C, and C++.
First, the code to be proven must be compiled from its implementation language into a method. A method is represented by a RISC-V ELF file with a special entry point that runs the code of the method. Additionally, one can compute for a given method its method ID which is a special type of cryptographic hash of the ELF file, and is required for verification.
Next, the prover runs the method inside the ZKVM. The logical RISC-V machine running inside the ZKVM is called the guest and the prover running the ZKVM is called the host. The guest and the host can communicate with each other during the execution of the method, but the host cannot modify the execution of the guest in any way, or the proof being generated will be invalid. During execution, the guest code can write to a special append only log called the journal that represents the official output of the computation.
Presuming the method terminated correctly, a receipt is produced, which provides the proof of correct execution. This receipt consists of 3 parts: the method ID of the method run, the journal written during execution, and a blob of opaque cryptographic data called the seal.
The verifier can then verify the receipt and examine the log. If any tampering was done to the method ID, the journal, or the seal, the receipt will fail to verify. Additionally, it is cryptographically infeasible to generate a valid receipt unless the output of the journal is the exactly correct output for some valid execution of the method whose method ID is in the receipt. In summary, the receipt acts as a zero knowledge proof of correct execution.
Additionally, since the protocol is zero knowledge, the verifier cannot infer anything about the details of the execution or any data passed between the host and the guest (aside from what is implied by the data written to the journal and the correct execution of the code).
This code is based on the well studied zk-STARK protocol, which has been proven secure under the random oracle model, with the only assumption being the security of the cryptographic hash used. Our implementation uses SHA-256 for that hash and targets a security factor of 100 bits of security.
That said, this code is still under heavy development and has not been audited. There may be bugs in the zk-STARK implementation, the arithmetic circuit used to instantiate the RISC-V ZKVM, or any other element of the code's implementation. Such bugs may impact the security of receipts, leak information, or cause any other manner of problems. Caveat emptor.
In addition to the RISC Zero proof system, we include a number of small examples, each with their own README, in the 'examples' directory.
We use Bazel for its strong multi-language multi-platform features and performance.
We recommend using Bazelisk to make bazel version management seamless.
In order to build RISC Zero executables you'll need a RISC-V toolchain. Bazel will automatically fetch and manage the toolchain for the following platforms:
- Linux - Ubuntu 18+ (x86_64)
- macOS (x86_64)
- macOS (arm64)
- Windows (x86_64)
Other platforms will be supported in the future.
You should be able to build and run all tests with:
bazelisk test //...
A C++ compiler must be installed; both gcc and clang should work. Let us know if you run into any issues.
RISC Zero development on macOS requires a full installation of Xcode (not just command line tools).
Our usage of Bazel requires symlink support to be enabled. This is possible on Windows by enabling Developer Mode, or by running Bazel as an administrator.
A C++ compiler must be installed. Visual Studio 2019 Build Tools is known to work (as does the Community edition). Let us know if you run into any issues.