lssa/program_methods/guest/src/bin/privacy_preserving_circuit.rs

use std::collections::HashMap;

use nssa_core::{
    Commitment, CommitmentSetDigest, DUMMY_COMMITMENT_HASH, EncryptionScheme, Nullifier,
    NullifierPublicKey, PrivacyPreservingCircuitInput, PrivacyPreservingCircuitOutput,
    account::{Account, AccountId, AccountWithMetadata},
    compute_digest_for_path,
    encryption::Ciphertext,
    program::{DEFAULT_PROGRAM_ID, MAX_NUMBER_CHAINED_CALLS, validate_execution},
};
use risc0_zkvm::{guest::env, serde::to_vec};

fn main() {
    let PrivacyPreservingCircuitInput {
        program_outputs,
        visibility_mask,
        private_account_nonces,
        private_account_keys,
        private_account_nsks,
        private_account_membership_proofs,
        mut program_id,
    } = env::read();

    let mut pre_states: Vec<AccountWithMetadata> = Vec::new();
    let mut state_diff: HashMap<AccountId, Account> = HashMap::new();

    let num_calls = program_outputs.len();
    if num_calls > MAX_NUMBER_CHAINED_CALLS {
        panic!("Max chained calls depth is exceeded");
    }

    let Some(last_program_call) = program_outputs.last() else {
        panic!("Program outputs is empty")
    };

    if !last_program_call.chained_calls.is_empty() {
        panic!("Call stack is incomplete");
    }

    for window in program_outputs.windows(2) {
        let caller = &window[0];
        let callee = &window[1];

        if caller.chained_calls.len() > 1 {
            panic!("Privacy Multi-chained calls are not supported yet");
        }

        // TODO: Modify when multi-chain calls are supported in the circuit
        let Some(caller_chained_call) = &caller.chained_calls.first() else {
            panic!("Expected chained call");
        };

        // Check that instruction data in caller is the instruction data in callee
        if caller_chained_call.instruction_data != callee.instruction_data {
            panic!("Invalid instruction data");
        }

        // Check that account pre_states in caller are the ones in calle
        if caller_chained_call.pre_states != callee.pre_states {
            panic!("Invalid pre states");
        }
    }

    for (i, program_output) in program_outputs.iter().enumerate() {
        let mut program_output = program_output.clone();

        // Check that `program_output` is consistent with the execution of the corresponding
        // program.
        let program_output_words =
            &to_vec(&program_output).expect("program_output must be serializable");
        env::verify(program_id, program_output_words)
            .expect("program output must match the program's execution");

        // Check that the program is well behaved.
        // See the # Programs section for the definition of the `validate_execution` method.
        if !validate_execution(
            &program_output.pre_states,
            &program_output.post_states,
            program_id,
        ) {
            panic!("Bad behaved program");
        }

        // The invoked program claims the accounts with default program id.
        for post in program_output
            .post_states
            .iter_mut()
            .filter(|post| post.requires_claim())
        {
            // The invoked program can only claim accounts with default program id.
            if post.account().program_owner == DEFAULT_PROGRAM_ID {
                post.account_mut().program_owner = program_id;
            } else {
                panic!("Cannot claim an initialized account")
            }
        }

        for (pre, post) in program_output
            .pre_states
            .iter()
            .zip(&program_output.post_states)
        {
            if let Some(account_pre) = state_diff.get(&pre.account_id) {
                if account_pre != &pre.account {
                    panic!("Invalid input");
                }
            } else {
                pre_states.push(pre.clone());
            }
            state_diff.insert(pre.account_id, post.account().clone());
        }

        // TODO: Modify when multi-chain calls are supported in the circuit
        if let Some(next_chained_call) = &program_output.chained_calls.first() {
            program_id = next_chained_call.program_id;
        } else if i != program_outputs.len() - 1 {
            panic!("Inner call without a chained call found")
        };
    }

    let n_accounts = pre_states.len();
    if visibility_mask.len() != n_accounts {
        panic!("Invalid visibility mask length");
    }

    // These lists will be the public outputs of this circuit
    // and will be populated next.
    let mut public_pre_states: Vec<AccountWithMetadata> = Vec::new();
    let mut public_post_states: Vec<Account> = Vec::new();
    let mut ciphertexts: Vec<Ciphertext> = Vec::new();
    let mut new_commitments: Vec<Commitment> = Vec::new();
    let mut new_nullifiers: Vec<(Nullifier, CommitmentSetDigest)> = Vec::new();

    let mut private_nonces_iter = private_account_nonces.iter();
    let mut private_keys_iter = private_account_keys.iter();
    let mut private_nsks_iter = private_account_nsks.iter();
    let mut private_membership_proofs_iter = private_account_membership_proofs.iter();

    let mut output_index = 0;
    for i in 0..n_accounts {
        match visibility_mask[i] {
            0 => {
                // Public account
                public_pre_states.push(pre_states[i].clone());

                let mut post = state_diff.get(&pre_states[i].account_id).unwrap().clone();

                if post.program_owner == DEFAULT_PROGRAM_ID {
                    // Claim account
                    post.program_owner = program_id;
                }
                public_post_states.push(post);
            }
            1 | 2 => {
                let new_nonce = private_nonces_iter.next().expect("Missing private nonce");
                let (npk, shared_secret) = private_keys_iter.next().expect("Missing keys");

                if AccountId::from(npk) != pre_states[i].account_id {
                    panic!("AccountId mismatch");
                }

                if visibility_mask[i] == 1 {
                    // Private account with authentication
                    let nsk = private_nsks_iter.next().expect("Missing nsk");

                    // Verify the nullifier public key
                    let expected_npk = NullifierPublicKey::from(nsk);
                    if &expected_npk != npk {
                        panic!("Nullifier public key mismatch");
                    }

                    // Check pre_state authorization
                    if !pre_states[i].is_authorized {
                        panic!("Pre-state not authorized");
                    }

                    let membership_proof_opt = private_membership_proofs_iter
                        .next()
                        .expect("Missing membership proof");
                    let (nullifier, set_digest) = membership_proof_opt
                        .as_ref()
                        .map(|membership_proof| {
                            // Compute commitment set digest associated with provided auth path
                            let commitment_pre = Commitment::new(npk, &pre_states[i].account);
                            let set_digest =
                                compute_digest_for_path(&commitment_pre, membership_proof);

                            // Compute update nullifier
                            let nullifier = Nullifier::for_account_update(&commitment_pre, nsk);
                            (nullifier, set_digest)
                        })
                        .unwrap_or_else(|| {
                            if pre_states[i].account != Account::default() {
                                panic!("Found new private account with non default values.");
                            }

                            // Compute initialization nullifier
                            let nullifier = Nullifier::for_account_initialization(npk);
                            (nullifier, DUMMY_COMMITMENT_HASH)
                        });
                    new_nullifiers.push((nullifier, set_digest));
                } else {
                    // Private account without authentication
                    if pre_states[i].account != Account::default() {
                        panic!("Found new private account with non default values.");
                    }

                    if pre_states[i].is_authorized {
                        panic!("Found new private account marked as authorized.");
                    }

                    let membership_proof_opt = private_membership_proofs_iter
                        .next()
                        .expect("Missing membership proof");
                    assert!(
                        membership_proof_opt.is_none(),
                        "Membership proof must be None for unauthorized accounts"
                    );
                    let nullifier = Nullifier::for_account_initialization(npk);
                    new_nullifiers.push((nullifier, DUMMY_COMMITMENT_HASH));
                }

                // Update post-state with new nonce
                let mut post_with_updated_values =
                    state_diff.get(&pre_states[i].account_id).unwrap().clone();
                post_with_updated_values.nonce = *new_nonce;

                if post_with_updated_values.program_owner == DEFAULT_PROGRAM_ID {
                    // Claim account
                    post_with_updated_values.program_owner = program_id;
                }

                // Compute commitment
                let commitment_post = Commitment::new(npk, &post_with_updated_values);

                // Encrypt and push post state
                let encrypted_account = EncryptionScheme::encrypt(
                    &post_with_updated_values,
                    shared_secret,
                    &commitment_post,
                    output_index,
                );

                new_commitments.push(commitment_post);
                ciphertexts.push(encrypted_account);
                output_index += 1;
            }
            _ => panic!("Invalid visibility mask value"),
        }
    }

    if private_nonces_iter.next().is_some() {
        panic!("Too many nonces");
    }

    if private_keys_iter.next().is_some() {
        panic!("Too many private account keys");
    }

    if private_nsks_iter.next().is_some() {
        panic!("Too many private account authentication keys");
    }

    if private_membership_proofs_iter.next().is_some() {
        panic!("Too many private account membership proofs");
    }

    let output = PrivacyPreservingCircuitOutput {
        public_pre_states,
        public_post_states,
        ciphertexts,
        new_commitments,
        new_nullifiers,
    };

    env::commit(&output);
}