Universal Zero Knowledge

[!IMPORTANT] main is the development branch. When building applications or running examples, use the latest release instead.

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 a 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+⁠+.

Protocol overview and terminology

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 image ID which is a special type of cryptographic hash of the ELF file, and is required for verification.

Next, the host program runs and proves 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 which 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 2 parts: 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 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 image ID matches the receipt. In summary, the receipt acts as a zero-knowledge proof of correct execution.

Because 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).

Security

This code implements a three-layer recursive proof system, based on the well-studied zk-STARK protocol and Groth16 protocol. An overview of the underlying cryptographic assumptions can be found on our Security Model page. With default parameters, this system achieves perfect zero-knowledgeness and 98 bits of conjectured security. Our STARK protocol is described in Scalable, Transparent Arguments of RISC-V Integrity, and a soundness/security calculator is included in the soundness.rs file.

To run the calculator, use RUST_LOG=risc0_zkp=debug when running a proof.

Getting Started

To start your own project, you can use our cargo risczero tool to write the initial boilerplate and set up a standard directory structure.

First, install Rust if you don't already have it, then install the RISC Zero toolchain installer, rzup. We'll use rzup to install cargo-risczero.

To install rzup run the following command and follow the instructions:

curl -L https://risczero.com/install | bash

Next we can install the RISC Zero toolchain by running rzup install:

rzup install

You can verify the installation was successful by running:

cargo risczero --version

After installation, you can create a new project (named my_project in this example):

cargo risczero new my_project

More details and options for cargo risczero are given in its README.

For more guidance on how to use RISC Zero, how RISC Zero projects are typically structured, and other resources useful to developers new to RISC Zero, see our Getting Started page.

Documentation

Documentation for the zkVM SDK and other Rust crates can be found at docs.rs/risc0-zkvm. All other documentation can be found at dev.risczero.com.

You can build and view the Rust documentation locally by using cargo doc. See CONTRIBUTING.md for dependencies. Source code for the documentation website can be found in the website directory.

Building from source

Building from source requires some additional tools and steps. Please refer to CONTRIBUTING.md for the full instructions.

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