Guests

Guests contain functions for Jolt to prove. Currently, these functions must be written using no_std Rust. If you have a function that does not require the standard library, making it provable is as easy as ensuring it is inside the guest package and adding the jolt::provable macro above it.

Let's take a look at a simple guest program to better understand it.

#![allow(unused)]
#![cfg_attr(feature = "guest", no_std)]
#![no_main]

fn main() {
#[jolt::provable]
fn add(x: u32, y: u32) -> u32 {
    x + y
}
}

As we can see, the guest looks like a normal no_std Rust library. The only major change is the addition of the jolt::provable macro, which lets Jolt know of the function's existence. Other than no_std, the only requirement of these functions is that its inputs are serializable and outputs are deserializable with serde. Fortunately serde is prevalent throughout the Rust ecosystem, so most types will support it by default.

There is no requirement that just a single function lives within the guest, and we are free to add as many as we need. Additionally, we can import any no_std compatible library just as we normally would in Rust.

#![allow(unused)]
#![cfg_attr(feature = "guest", no_std)]
#![no_main]

fn main() {
use sha2::{Sha256, Digest};
use sha3::{Keccak256, Digest};

#[jolt::provable]
fn sha2(input: &[u8]) -> [u8; 32] {
    let mut hasher = Sha256::new();
    hasher.update(input);
    let result = hasher.finalize();
    Into::<[u8; 32]>::into(result)
}

#[jolt::provable]
fn sha3(input: &[u8]) -> [u8; 32] {
    let mut hasher = Keccak256::new();
    hasher.update(input);
    let result = hasher.finalize();
    Into::<[u8; 32]>::into(result)
}
}