Module risc0_zkvm::guest

The RISC Zero zkVM’s guest-side RISC-V API.

Code that is validated by the RISC Zero zkVM is run inside the guest. In almost all practical cases, the guest will want to read private input data from the host and write public data to the journal. This can be done with env::read and env::commit, respectively; additional I/O functionality is also available in env.

Installation

To build and run RISC Zero zkVM code, you will need to install the RISC Zero toolchain, which can be done using the cargo-risczero tool:

cargo install cargo-binstall
cargo binstall cargo-risczero
cargo risczero install

Example

The following guest code¹ proves a number is composite by multiplying two unsigned integers, and panicking if either is 1 or if the multiplication overflows:

#![no_main]
#![no_std]

use risc0_zkvm::guest::env;

risc0_zkvm::guest::entry!(main);

fn main() {
    // Load the first number from the host
    let a: u64 = env::read();
    // Load the second number from the host
    let b: u64 = env::read();
    // Verify that neither of them are 1 (i.e. nontrivial factors)
    if a == 1 || b == 1 {
        panic!("Trivial factors")
    }
    // Compute the product while being careful with integer overflow
    let product = a.checked_mul(b).expect("Integer overflow");
    env::commit(&product);
}

Notice how env::read is used to load the two factors, and env::commit is used to make their composite product publically available. All input an output of your guest is private except for what is written to the journal with env::commit.

By default, the guest only has the Rust core libraries and not std. A partial implementation of the Rust standard libraries can be enabled with the std feature on this crate. When this feature is not enabled, the lines including #![no_std] and #![no_main] are required, as well as the use of the crate::guest::entry macro. When std is enabled, these three lines can be omitted and many features of std can be used.

If you encounter problems building zkVM guest code, you can see if we have a known workaround for your issue by looking in our rust guest workarounds tag on GitHub.

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1. The example is based on the Factors example. ↩

Modules

• env
  Functions for interacting with the host environment.
• sha
  Functions for computing SHA-256 hashes.

Macros

• entry
  Used for defining the guest’s entrypoint and main function.

Functions

• abort
  Aborts the guest with the given message.
• memory_barrier
  Require that accesses to behind the given pointer before the memory barrier don’t get optimized away or reordered to after the memory barrier.