logos-execution-zone/node_core/src/executions/se.rs

use k256::Scalar;
use secp256k1_zkp::{compute_adaptive_blinding_factor, verify_commitments_sum_to_equal, CommitmentSecrets, Generator, PedersenCommitment, Tag, Tweak, SECP256K1};
use rand::thread_rng;
use sha2::{Digest, Sha256};
use serde::{Serialize, Deserialize};
use storage::{commitment::Commitment, commitments_sparse_merkle_tree::CommitmentsSparseMerkleTree, nullifier::UTXONullifier, nullifier_sparse_merkle_tree::NullifierSparseMerkleTree};
use utxo::{
    utxo_core::{UTXOPayload, UTXO},
    utxo_tree::UTXOSparseMerkleTree,
};
use monotree::hasher::Blake3;
use monotree::{Hasher, Monotree, Proof};
use bincode;

fn commitment_secrets_random(value: u64) -> CommitmentSecrets {
    CommitmentSecrets {
        value,
        value_blinding_factor: Tweak::new(&mut thread_rng()),
        generator_blinding_factor: Tweak::new(&mut thread_rng()),
    }
}

pub fn tag_random() -> Tag {
    use rand::thread_rng;
    use rand::RngCore;

    let mut bytes = [0u8; 32];
    thread_rng().fill_bytes(&mut bytes);

    Tag::from(bytes)
}

pub fn commit(comm: &CommitmentSecrets, tag: Tag) -> PedersenCommitment {
    let generator = Generator::new_blinded(SECP256K1, tag, comm.generator_blinding_factor);

    PedersenCommitment::new(SECP256K1, comm.value, comm.value_blinding_factor, generator)
}

// Hash function placeholder (replace with your cryptographic library's hash).
fn hash(input: &[u8]) -> Vec<u8> {
    Sha256::digest(input).to_vec()
}

// Generate nullifiers

// takes the pedersen_commitment and nsk then 
// returns a list of nullifiers, where the nullifier = hash(pedersen_commitment || nsk) where the hash function will be determined 

pub fn generate_nullifiers(pedersen_commitment: &PedersenCommitment, nsk: &[u8]) -> Vec<u8> {
    let mut input = pedersen_commitment.serialize().to_vec();
    input.extend_from_slice(nsk);
    hash(&input)
}

// Generate commitments for output UTXOs

// uses the list of output_utxos[] and 
// returns out_commitments[] where each out_commitments[i] = Commitment(output_utxos[i]) 
// where the commitment will be determined
pub fn generate_commitments(output_utxos: &[UTXO]) -> Vec<Vec<u8>> {
    output_utxos
        .iter()
        .map(|utxo| {
            let serialized = bincode::serialize(utxo).unwrap(); // Serialize UTXO.
            hash(&serialized)
        })
        .collect()
}

// Validate inclusion proof for in_commitments

// takes the pedersen_commitment as a leaf, the root hash root_commitment and the path in_commitments_proof[], 
// returns True if the pedersen_commitment is in the tree with root hash root_commitment 
// otherwise 
// returns False, as membership proof.
pub fn validate_in_commitments_proof(
    pedersen_commitment: &PedersenCommitment,
    root_commitment: Vec<u8>,
    in_commitments_proof: &[Vec<u8>],
) -> bool {
    let mut nsmt = CommitmentsSparseMerkleTree {
        curr_root: Option::Some(root_commitment),
        tree: Monotree::default(),
        hasher: Blake3::new(),
    };

    let commitments: Vec<_> = in_commitments_proof.into_iter().map(|n_p| Commitment { commitment_hash: n_p.clone() }).collect();
    nsmt.insert_items(commitments).unwrap();

    nsmt.get_non_membership_proof(pedersen_commitment.serialize().to_vec()).unwrap().1.is_some()
}

// Validate non-membership proof for nullifiers

// takes the nullifier, path nullifiers_proof[] and the root hash root_nullifier, 
// returns True if the nullifier is not in the tree with root hash root_nullifier 
// otherwise 
// returns False, as non-membership proof.
pub fn validate_nullifiers_proof(
    nullifier: [u8; 32],
    root_nullifier: [u8; 32],
    nullifiers_proof: &[[u8; 32]],
) -> bool {
    let mut nsmt = NullifierSparseMerkleTree {
        curr_root: Option::Some(root_nullifier),
        tree: Monotree::default(),
        hasher: Blake3::new(),
    };

    let nullifiers: Vec<_> = nullifiers_proof.into_iter().map(|n_p| UTXONullifier { utxo_hash: *n_p }).collect();
    nsmt.insert_items(nullifiers).unwrap();


    nsmt.get_non_membership_proof(nullifier).unwrap().1.is_none()
}

// Check balances

//  takes the public_info and output_utxos[], 
// returns the True if the token amount in public_info matches the sum of all output_utxos[], otherwise return False.
pub fn check_balances(public_info: u128, output_utxos: &[UTXO]) -> bool {
    let total_output: u128 = output_utxos.iter().map(|utxo| utxo.amount).sum();
    public_info == total_output
}

// Verify Pedersen commitment

// takes the public_info, secret_r and pedersen_commitment and 
// checks that commitment(public_info,secret_r) is equal pedersen_commitment where the commitment is pedersen commitment.
pub fn verify_commitment(public_info: u64, secret_r: &[u8], pedersen_commitment: &PedersenCommitment) -> bool {
    let commitment_secrets = CommitmentSecrets {
        value: public_info,
        value_blinding_factor: Tweak::from_slice(secret_r).unwrap(),
        generator_blinding_factor: Tweak::new(&mut thread_rng()),
    };

    let tag = tag_random();
    let commitment = commit(&commitment_secrets, tag);

    commitment == *pedersen_commitment
}

fn se_kernel(
    root_commitment: &[u8],
    root_nullifier: [u8; 32],
    public_info: u64,
    pedersen_commitment: PedersenCommitment,
    secret_r: &[u8],
    output_utxos: &[UTXO],
    in_commitments_proof: &[Vec<u8>],
    nullifiers_proof: &[[u8; 32]],
    nullifier_secret_key: Scalar,
) -> (Vec<u8>, Vec<Vec<u8>>, Vec<u8>) {
    check_balances(public_info as u128, output_utxos);

    let out_commitments = generate_commitments(output_utxos);

    let nullifier = generate_nullifiers(&pedersen_commitment, &nullifier_secret_key.to_bytes());

    validate_in_commitments_proof(&pedersen_commitment, root_commitment.to_vec(), in_commitments_proof);

    verify_commitment(public_info, secret_r, &pedersen_commitment);

    (vec![], out_commitments, nullifier)
}