Using SHARP (Shared Prover)

SHARP (formerly known as GPS) is a service that generates proofs attesting to the validity of the executions of Cairo programs. Then, it sends those proofs to an Ethereum testnet (Ropsten) where they are verified by a smart contract. You can read more in Cairo for Blockchain Developers and in Playground & GPS Alpha.

To send a proof you can use the cairo-sharp command line utility. It allows you to send programs to SHARP and to query their status, until they are successfully verified on-chain.

Sending a program to SHARP

Let’s create a small program (proving that you know the square root of a given number) to send to SHARP. Create a file named sharp_test.cairo with the following code:

%builtins output

func main(output_ptr : felt*) -> (output_ptr : felt*):
    alloc_locals
    local x
    %{ ids.x = program_input['x'] %}
    assert [output_ptr] = x * x
    return (output_ptr=output_ptr + 1)
end

Create a file named input.json with the program input:

{
    "x": 17
}

The following command will compile the program, run it on the given input and send it to SHARP. Make sure you have the latest version of the cairo-lang package installed (currently, 0.1.0), see Setting up the environment.

cairo-sharp submit --source sharp_test.cairo \
    --program_input input.json

The output should look like:

Compiling...
Running...
Submitting to SHARP...
Job sent.
Job key: 1f38cbf0-7153-4114-9442-44501bfed8eb
Fact: 0xf457e4311f8229ab7b08191a6658112a29a962a9f2fe95d7a3d4f1200eef0195

The job key is a unique identifier assigned to your job by SHARP. The fact is the result of a hash function on the program hash and the program output (which in our case includes the square of \(x\)). See Playground & GPS Alpha.

You can now use the job key to query the state of the job in the SHARP service:

cairo-sharp status 1f38cbf0-7153-4114-9442-44501bfed8eb

Once the status of your job is PROCESSED, it means that it was sent to the blockchain for verification. To see if when your fact is successfully registered you can use cairo-sharp is_verified (make sure to use the job’s fact and not the job key and to supply the URL of an Ethereum node):

cairo-sharp is_verified \
    0xf457e4311f8229ab7b08191a6658112a29a962a9f2fe95d7a3d4f1200eef0195 \
    --node_url=<URL_of_an_Ethereum_node>