Basics

The easiest way to understand how to write programs for the SP1 zkVM is to look at some examples.

Example: Fibonacci

This program is from the examples directory in the SP1 repo which contains several example programs of varying complexity.

//! A simple program that takes a number `n` as input, and writes the `n-1`th and `n`th fibonacci
//! number as an output.

// These two lines are necessary for the program to properly compile.
//
// Under the hood, we wrap your main function with some extra code so that it behaves properly
// inside the zkVM.
#![no_main]
sp1_zkvm::entrypoint!(main);

pub fn main() {
    // Read an input to the program.
    //
    // Behind the scenes, this compiles down to a system call which handles reading inputs
    // from the prover.
    let n = sp1_zkvm::io::read::<u32>();

    // Write n to public input
    sp1_zkvm::io::commit(&n);

    // Compute the n'th fibonacci number, using normal Rust code.
    let mut a = 0;
    let mut b = 1;
    for _ in 0..n {
        let mut c = a + b;
        c %= 7919; // Modulus to prevent overflow.
        a = b;
        b = c;
    }

    // Write the output of the program.
    //
    // Behind the scenes, this also compiles down to a system call which handles writing
    // outputs to the prover.
    sp1_zkvm::io::commit(&a);
    sp1_zkvm::io::commit(&b);
}

As you can see, writing programs is as simple as writing normal Rust.

After you've written your program, you must compile it to an ELF that the SP1 zkVM can prove. To read more about compiling programs, refer to the section on Compiling Programs. To read more about how inputs and outputs work, refer to the section on Inputs & Outputs.