# EPF - Update 6

## Progress Overview

* Project Proposal is merged and it's [live](https://github.com/eth-protocol-fellows/cohort-six/blob/master/projects/grandine_beacon_zkVMs_snarkification.md) on EPF repo.
* Read the grandine zkVM codebase and understood the integration of risc0.
* Successfully ran existing risc0 test cases.

## Breakdown

#### How risc0 implemenation works

The system has two parts: a **host program** that manages data and coordinates execution, and a **guest program** that runs inside the zkVM to perform the actual state transition computation.

#### Key Implementation Details

**Reference Execution (Host Program):**

let block_ssz = get_or_download(/*...*/)?;
let state_ssz = get_or_download(/*...*/)?;

let (expected_root, cache) = {
    let block = SignedBeaconBlock::<Mainnet>::from_ssz(&config, block_ssz.clone())?;
    let mut state = BeaconState::<Mainnet>::from_ssz(&config, state_ssz.clone())?;
    let cache = PubkeyCache::load(Database::in_memory());

    // performing on the host to get the cache object that speed up the zkVM processing
    state_transition(&config, &cache, &mut state, &block)?;

    (state.hash_tree_root(), cache.to_ssz().unwrap())
};

//...
let vm = Vm::new()?;
let (output_bytes, proof) = vm.prove(state_ssz, block_ssz, cache)?;
let state_root = H256(output_bytes.try_into().unwrap());

We get `expected_root` when we run STF outside zkVM. We use this to compare with `state_root` which we get by running the STF inside risc0.

**Guest Program Execution:**

let env = ExecutorEnv::builder()
    .write_slice(&state_ssz)  // Send beacon state to guest
    .write_slice(&block_ssz)  // Send beacon block to guest  
    .write_slice(&cache_ssz)  // Send validator cache to guest
    .build()?;

//..
let elf = RISC0_GRANDINE_STATE_TRANSITION_ELF;  // Compiled guest program binary
let prove_info = prover.prove(env, elf)?;       // Execute guest inside zkVM
let receipt = prove_info.receipt;               // Get results and proof

The guest program runs the same state transition inside the provable environment.

#### Test Cases Results

You can see the test cases result [here](https://hackmd.io/@0xprivateChaos/SJDpxLQwex).

## Next Steps
I have to do a similar integration with zisk zkVM. So will learn about zisk, which would be a challenging part because it doesn't have any technical in-depth documentation at present.