lssa-zkvm-testing/risc0-selective-privacy-poc/program_methods/guest/src/bin/outer.rs

use risc0_zkvm::{guest::env, serde::to_vec};
use core::{
    account::Account, compute_nullifier, hash, input::InputVisibiility, is_in_tree, types::Nonce,
};

/// Private execution logic.
/// Circuit for proving correct execution of some program with program id
/// equal to `program_id` (last input).
///
/// Currently only supports private execution of a program with two input accounts, one
/// of which must be a fresh new account (`account_2`) (for example a private transfer function).
///
/// This circuit checks:
/// - That accounts pre states and post states are consistent with the execution of the given `program_id`.
/// - That `account_2` is fresh (meaning, for this toy example, that it has 0 balance).
/// - That `program_id` execution didn't change addresses of the accounts.
///
/// Outputs:
/// - The nullifier for the only existing input account (account_1)
/// - The commitments for the private accounts post states.
fn main() {
    let num_inputs: u32 = env::read();
    // Read inputs and outputs
    let mut inputs_outputs: Vec<Account> = env::read();
    assert_eq!(inputs_outputs.len() as u32, num_inputs * 2);

    // Read visibilities
    let input_visibilities: Vec<InputVisibiility> = env::read();
    assert_eq!(input_visibilities.len() as u32, num_inputs);

    // Read nonces for outputs
    let output_nonces: Vec<Nonce> = env::read();
    assert_eq!(output_nonces.len() as u32, num_inputs);

    let commitment_tree_root: [u32; 8] = env::read();
    let program_id: [u32; 8] = env::read();

    // Verify pre states and post states of accounts are consistent
    // with the execution of the `program_id`` program
    env::verify(program_id, &to_vec(&inputs_outputs).unwrap()).unwrap();

    // Split inputs_outputs into two separate vectors
    let (inputs, mut outputs) = {
        let outputs = inputs_outputs.split_off(num_inputs as usize);
        (inputs_outputs, outputs)
    };

    let mut nullifiers = Vec::new();
    for (visibility, input_account) in input_visibilities.iter().zip(inputs.iter()) {
        match visibility {
            InputVisibiility::Private(Some((private_key, auth_path))) => {
                // Prove ownership of input accounts by proving knowledge of the pre-image of their addresses.
                assert_eq!(hash(private_key), input_account.address);
                // Check the input account was created by a previous transaction by checking it belongs to the commitments tree.
                let commitment = input_account.commitment();
                assert!(is_in_tree(commitment, auth_path, commitment_tree_root));
                // Compute nullifier to nullify this private input account.
                let nullifier = compute_nullifier(&commitment, private_key);
                nullifiers.push(nullifier);
            }
            InputVisibiility::Private(None) => {
                // Private accounts without a companion private key are enforced to have default values
                assert_eq!(input_account.balance, 0);
                assert_eq!(input_account.nonce, [0; 8]);
            }
            // No checks on public accounts
            InputVisibiility::Public => continue,
        }
    }

    // Assert `program_id` program didn't modify address fields or nonces
    for (account_pre, account_post) in inputs.iter().zip(outputs.iter()) {
        assert_eq!(account_pre.address, account_post.address);
        assert_eq!(account_pre.nonce, account_post.nonce);
    }

    // Insert new nonces in outputs (including public ones (?!))
    outputs
        .iter_mut()
        .zip(output_nonces)
        .for_each(|(account, new_nonce)| account.nonce = new_nonce);

    // Compute private outputs commitments
    let mut private_outputs = Vec::new();
    for (output, visibility) in outputs.iter().zip(input_visibilities.iter()) {
        match visibility {
            InputVisibiility::Public => continue,
            InputVisibiility::Private(_) => private_outputs.push(output),
        }
    }

    // Get the list of public inputs pre states and their post states
    let mut public_inputs_outputs = Vec::new();
    for (account, visibility) in inputs
        .iter()
        .chain(outputs.iter())
        .zip(input_visibilities.iter().chain(input_visibilities.iter()))
    {
        match visibility {
            InputVisibiility::Public => {
                public_inputs_outputs.push(account);
            }
            InputVisibiility::Private(_) => continue,
        }
    }

    // Compute commitments for every private output
    let private_output_commitments: Vec<_> = private_outputs
        .iter()
        .map(|account| account.commitment())
        .collect();

    // Output nullifier of consumed input accounts and commitments of new output private accounts
    env::commit(&(
        public_inputs_outputs,
        nullifiers,
        private_output_commitments,
        commitment_tree_root,
    ));
}