Overview

STARK is a proof system. It uses cutting-edge cryptography to provide poly-logarithmic verification resources and proof size, with minimal and post-quantum-secure assumptions.

This repository contains a prover and a verifier for STARKs, and in particular for the CPU AIR underlying the CairoZero programming language.

Installation instructions

Building using the dockerfile

The root directory contains a dedicated Dockerfile which automatically builds the package and runs the unit tests on a simulated machine. You should have docker installed (see https://docs.docker.com/get-docker/).

Clone the repository:

git clone https://github.com/starkware-libs/stone-prover.git

Build the docker image:

cd stone-prover
docker build --tag prover .

This will run an end-to-end test with an example cairo program. Once the docker image is built, you can fetch the prover and verifier executables using:

container_id=$(docker create prover)
docker cp -L ${container_id}:/bin/cpu_air_prover .
docker cp -L ${container_id}:/bin/cpu_air_verifier .

Creating and verifying a proof of a CairoZero program

To run and prove the example program fibonacci.cairo, install cairo-lang version 0.12.0 (see further instructions in the cairo-lang repository):

pip install cairo-lang==0.12.0

Navigate to the example test directory (e2e_test):

cd e2e_test

Compile fibonacci.cairo:

cairo-compile fibonacci.cairo --output fibonacci_compiled.json --proof_mode

Run the compiled program to generate the prover input files:

cairo-run \
    --program=fibonacci_compiled.json \
    --layout=small \
    --program_input=fibonacci_input.json \
    --air_public_input=fibonacci_public_input.json \
    --air_private_input=fibonacci_private_input.json \
    --trace_file=fibonacci_trace.json \
    --memory_file=fibonacci_memory.json \
    --print_output \
    --proof_mode

Run the prover:

cpu_air_prover \
    --out_file=fibonacci_proof.json \
    --private_input_file=fibonacci_private_input.json \
    --public_input_file=fibonacci_public_input.json \
    --prover_config_file=cpu_air_prover_config.json \
    --parameter_file=cpu_air_params.json

The proof is now available in the file fibonacci_proof.json.

Finally, run the verifier to verify the proof:

cpu_air_verifier --in_file=fibonacci_proof.json && echo "Successfully verified example proof."

Note: The verifier only checks that the proof is consistent with the public input section that appears in the proof file. The public input section itself is not checked. For example, the verifier does not check what CairoZero program is being proved, or that the builtins memory segments are of valid size. These things need to be checked externally.

Configuration for other input sizes

The number of steps affects the size of the trace. Such changes may require modification of cpu_air_params.json. Specifically, the following equation must be satisfied.

log₂(last_layer_degree_bound) + ∑fri_step_list = log₂(#steps) + 4

For instance, assuming a fixed last_layer_degree_bound, a larger number of steps requires changes to the fri_step_list to maintain the equality.

FRI steps should typically be in the range 2-4; the degree bound should be in the range 4-7.

The constant 4 that appears in the equation is hardcoded log₂(trace_rows_per_step) = log₂(16) = 4.

For Mac users

To build the docker, run:

docker build --tag prover . --build-arg CMAKE_ARGS=-DNO_AVX=1

To freely use the cairo-run, cpu_air_prover, and cpu_air_verifier commands, work inside the docker using:

docker run -it prover bash