openethereum/ethcore/private-tx/src/lib.rs

// Copyright 2015-2019 Parity Technologies (UK) Ltd.
// This file is part of Parity Ethereum.

// Parity Ethereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Parity Ethereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Parity Ethereum.  If not, see <http://www.gnu.org/licenses/>.

//! Private transactions module.

// Recursion limit required because of
// error_chain foreign_links.
#![recursion_limit = "256"]

mod encryptor;
mod error;
mod key_server_keys;
mod messages;
mod private_transactions;

extern crate common_types as types;
extern crate ethabi;
extern crate ethcore;
extern crate ethcore_call_contract as call_contract;
extern crate ethcore_io as io;
extern crate ethcore_miner;
extern crate ethereum_types;
extern crate ethjson;
extern crate ethkey;
extern crate fetch;
extern crate futures;
extern crate heapsize;
extern crate keccak_hash as hash;
extern crate parity_bytes as bytes;
extern crate parity_crypto as crypto;
extern crate parking_lot;
extern crate patricia_trie_ethereum as ethtrie;
extern crate rlp;
extern crate rustc_hex;
extern crate transaction_pool as txpool;
extern crate trie_db as trie;
extern crate url;
#[macro_use]
extern crate log;
#[macro_use]
extern crate ethabi_derive;
#[macro_use]
extern crate ethabi_contract;
extern crate derive_more;
#[macro_use]
extern crate rlp_derive;

#[cfg(test)]
extern crate env_logger;
#[cfg(test)]
extern crate rand;

pub use encryptor::{Encryptor, EncryptorConfig, NoopEncryptor, SecretStoreEncryptor};
pub use error::Error;
pub use key_server_keys::{KeyProvider, SecretStoreKeys, StoringKeyProvider};
pub use messages::{PrivateTransaction, SignedPrivateTransaction};
pub use private_transactions::{
    PrivateTransactionSigningDesc, SigningStore, VerificationStore, VerifiedPrivateTransaction,
};

use bytes::Bytes;
use call_contract::CallContract;
use ethabi::FunctionOutputDecoder;
use ethcore::{
    client::{
        BlockId, BlockInfo, Call, ChainMessageType, ChainNotify, Client, ClientIoMessage, NewBlocks,
    },
    contract_address as ethcore_contract_address,
    executed::Executed,
    executive::{Executive, TransactOptions},
    miner::{self, pool_client::NonceCache, Miner, MinerService},
    state, state_db,
    trace::{Tracer, VMTracer},
};
use ethereum_types::{Address, H128, H256, U256};
use ethkey::{public_to_address, recover, Signature};
use hash::keccak;
use io::IoChannel;
use parking_lot::RwLock;
use rlp::*;
use rustc_hex::FromHex;
use std::{
    collections::{BTreeMap, HashMap, HashSet},
    sync::{Arc, Weak},
};
use types::transaction::{Action, SignedTransaction, Transaction, UnverifiedTransaction};

// Source avaiable at https://github.com/parity-contracts/private-tx/blob/master/contracts/PrivateContract.sol
const DEFAULT_STUB_CONTRACT: &'static str = include_str!("../res/private.evm");

use_contract!(private_contract, "res/private.json");

/// Initialization vector length.
const INIT_VEC_LEN: usize = 16;

/// Size of nonce cache
const NONCE_CACHE_SIZE: usize = 128;

/// Version for the initial private contract wrapper
const INITIAL_PRIVATE_CONTRACT_VER: usize = 1;

/// Version for the private contract notification about private state changes added
const PRIVATE_CONTRACT_WITH_NOTIFICATION_VER: usize = 2;

/// Configurtion for private transaction provider
#[derive(Default, PartialEq, Debug, Clone)]
pub struct ProviderConfig {
    /// Accounts that can be used for validation
    pub validator_accounts: Vec<Address>,
    /// Account used for signing public transactions created from private transactions
    pub signer_account: Option<Address>,
}

#[derive(Debug)]
/// Private transaction execution receipt.
pub struct Receipt {
    /// Private transaction hash.
    pub hash: H256,
    /// Contract address.
    pub contract_address: Address,
    /// Execution status.
    pub status_code: u8,
}

/// Payload signing and decrypting capabilities.
pub trait Signer: Send + Sync {
    /// Decrypt payload using private key of given address.
    fn decrypt(
        &self,
        account: Address,
        shared_mac: &[u8],
        payload: &[u8],
    ) -> Result<Vec<u8>, Error>;
    /// Sign given hash using provided account.
    fn sign(&self, account: Address, hash: ethkey::Message) -> Result<Signature, Error>;
}

/// Signer implementation that errors on any request.
pub struct DummySigner;
impl Signer for DummySigner {
    fn decrypt(
        &self,
        _account: Address,
        _shared_mac: &[u8],
        _payload: &[u8],
    ) -> Result<Vec<u8>, Error> {
        Err("Decrypting is not supported.".to_owned())?
    }

    fn sign(&self, _account: Address, _hash: ethkey::Message) -> Result<Signature, Error> {
        Err("Signing is not supported.".to_owned())?
    }
}

/// Signer implementation using multiple keypairs
pub struct KeyPairSigner(pub Vec<ethkey::KeyPair>);
impl Signer for KeyPairSigner {
    fn decrypt(
        &self,
        account: Address,
        shared_mac: &[u8],
        payload: &[u8],
    ) -> Result<Vec<u8>, Error> {
        let kp = self
            .0
            .iter()
            .find(|k| k.address() == account)
            .ok_or(ethkey::Error::InvalidAddress)?;
        Ok(ethkey::crypto::ecies::decrypt(
            kp.secret(),
            shared_mac,
            payload,
        )?)
    }

    fn sign(&self, account: Address, hash: ethkey::Message) -> Result<Signature, Error> {
        let kp = self
            .0
            .iter()
            .find(|k| k.address() == account)
            .ok_or(ethkey::Error::InvalidAddress)?;
        Ok(ethkey::sign(kp.secret(), &hash)?)
    }
}

/// Manager of private transactions
pub struct Provider {
    encryptor: Box<dyn Encryptor>,
    validator_accounts: HashSet<Address>,
    signer_account: Option<Address>,
    notify: RwLock<Vec<Weak<dyn ChainNotify>>>,
    transactions_for_signing: RwLock<SigningStore>,
    transactions_for_verification: VerificationStore,
    client: Arc<Client>,
    miner: Arc<Miner>,
    accounts: Arc<dyn Signer>,
    channel: IoChannel<ClientIoMessage>,
    keys_provider: Arc<dyn KeyProvider>,
}

#[derive(Debug)]
pub struct PrivateExecutionResult<T, V>
where
    T: Tracer,
    V: VMTracer,
{
    code: Option<Bytes>,
    state: Bytes,
    contract_address: Address,
    result: Executed<T::Output, V::Output>,
}

impl Provider {
    /// Create a new provider.
    pub fn new(
        client: Arc<Client>,
        miner: Arc<Miner>,
        accounts: Arc<dyn Signer>,
        encryptor: Box<dyn Encryptor>,
        config: ProviderConfig,
        channel: IoChannel<ClientIoMessage>,
        keys_provider: Arc<dyn KeyProvider>,
    ) -> Self {
        keys_provider.update_acl_contract();
        Provider {
            encryptor,
            validator_accounts: config.validator_accounts.into_iter().collect(),
            signer_account: config.signer_account,
            notify: RwLock::default(),
            transactions_for_signing: RwLock::default(),
            transactions_for_verification: VerificationStore::default(),
            client,
            miner,
            accounts,
            channel,
            keys_provider,
        }
    }

    // TODO [ToDr] Don't use `ChainNotify` here!
    // Better to create a separate notification type for this.
    /// Adds an actor to be notified on certain events
    pub fn add_notify(&self, target: Arc<dyn ChainNotify>) {
        self.notify.write().push(Arc::downgrade(&target));
    }

    fn notify<F>(&self, f: F)
    where
        F: Fn(&dyn ChainNotify),
    {
        for np in self.notify.read().iter() {
            if let Some(n) = np.upgrade() {
                f(&*n);
            }
        }
    }

    /// 1. Create private transaction from the signed transaction
    /// 2. Executes private transaction
    /// 3. Save it with state returned on prev step to the queue for signing
    /// 4. Broadcast corresponding message to the chain
    pub fn create_private_transaction(
        &self,
        signed_transaction: SignedTransaction,
    ) -> Result<Receipt, Error> {
        trace!(target: "privatetx", "Creating private transaction from regular transaction: {:?}", signed_transaction);
        if self.signer_account.is_none() {
            warn!(target: "privatetx", "Signing account not set");
            return Err(Error::SignerAccountNotSet);
        }
        let tx_hash = signed_transaction.hash();
        let contract = Self::contract_address_from_transaction(&signed_transaction)
            .map_err(|_| Error::BadTransactionType)?;
        let data = signed_transaction.rlp_bytes();
        let encrypted_transaction = self.encrypt(
            &contract,
            &Self::iv_from_transaction(&signed_transaction),
            &data,
        )?;
        let private = PrivateTransaction::new(encrypted_transaction, contract);
        // TODO #9825 [ToDr] Using BlockId::Latest is bad here,
        // the block may change in the middle of execution
        // causing really weird stuff to happen.
        // We should retrieve hash and stick to that. IMHO
        // best would be to change the API and only allow H256 instead of BlockID
        // in private-tx to avoid such mistakes.
        let contract_nonce = self.get_contract_nonce(&contract, BlockId::Latest)?;
        let private_state =
            self.execute_private_transaction(BlockId::Latest, &signed_transaction)?;
        trace!(target: "privatetx", "Private transaction created, encrypted transaction: {:?}, private state: {:?}", private, private_state);
        let contract_validators = self.get_validators(BlockId::Latest, &contract)?;
        trace!(target: "privatetx", "Required validators: {:?}", contract_validators);
        let private_state_hash = self.calculate_state_hash(&private_state, contract_nonce);
        trace!(target: "privatetx", "Hashed effective private state for sender: {:?}", private_state_hash);
        self.transactions_for_signing.write().add_transaction(
            private.hash(),
            signed_transaction,
            contract_validators,
            private_state,
            contract_nonce,
        )?;
        self.broadcast_private_transaction(private.hash(), private.rlp_bytes());
        Ok(Receipt {
            hash: tx_hash,
            contract_address: contract,
            status_code: 0,
        })
    }

    /// Calculate hash from united private state and contract nonce
    pub fn calculate_state_hash(&self, state: &Bytes, nonce: U256) -> H256 {
        let state_hash = keccak(state);
        let mut state_buf = [0u8; 64];
        state_buf[..32].clone_from_slice(&state_hash);
        state_buf[32..].clone_from_slice(&H256::from(nonce));
        keccak(AsRef::<[u8]>::as_ref(&state_buf[..]))
    }

    fn pool_client<'a>(
        &'a self,
        nonce_cache: &'a NonceCache,
        local_accounts: &'a HashSet<Address>,
    ) -> miner::pool_client::PoolClient<'a, Client> {
        let engine = self.client.engine();
        miner::pool_client::PoolClient::new(
            &*self.client,
            nonce_cache,
            engine,
            local_accounts,
            None, // refuse_service_transactions = true
        )
    }

    /// Retrieve and verify the first available private transaction for every sender
    fn process_verification_queue(&self) -> Result<(), Error> {
        let process_transaction = |transaction: &VerifiedPrivateTransaction| -> Result<_, String> {
            let private_hash = transaction.private_transaction.hash();
            match transaction.validator_account {
                None => {
                    trace!(target: "privatetx", "Propagating transaction further");
                    self.broadcast_private_transaction(
                        private_hash,
                        transaction.private_transaction.rlp_bytes(),
                    );
                    return Ok(());
                }
                Some(validator_account) => {
                    if !self.validator_accounts.contains(&validator_account) {
                        trace!(target: "privatetx", "Propagating transaction further");
                        self.broadcast_private_transaction(
                            private_hash,
                            transaction.private_transaction.rlp_bytes(),
                        );
                        return Ok(());
                    }
                    let contract =
                        Self::contract_address_from_transaction(&transaction.transaction)
                            .map_err(|_| "Incorrect type of action for the transaction")?;
                    // TODO #9825 [ToDr] Usage of BlockId::Latest
                    let contract_nonce = self.get_contract_nonce(&contract, BlockId::Latest);
                    if let Err(e) = contract_nonce {
                        return Err(format!("Cannot retrieve contract nonce: {:?}", e).into());
                    }
                    let contract_nonce = contract_nonce.expect("Error was checked before");
                    let private_state =
                        self.execute_private_transaction(BlockId::Latest, &transaction.transaction);
                    if let Err(e) = private_state {
                        return Err(format!("Cannot retrieve private state: {:?}", e).into());
                    }
                    let private_state = private_state.expect("Error was checked before");
                    let private_state_hash =
                        self.calculate_state_hash(&private_state, contract_nonce);
                    trace!(target: "privatetx", "Hashed effective private state for validator: {:?}", private_state_hash);
                    let signed_state = self.accounts.sign(validator_account, private_state_hash);
                    if let Err(e) = signed_state {
                        return Err(format!("Cannot sign the state: {:?}", e).into());
                    }
                    let signed_state = signed_state.expect("Error was checked before");
                    let signed_private_transaction =
                        SignedPrivateTransaction::new(private_hash, signed_state, None);
                    trace!(target: "privatetx", "Sending signature for private transaction: {:?}", signed_private_transaction);
                    self.broadcast_signed_private_transaction(
                        signed_private_transaction.hash(),
                        signed_private_transaction.rlp_bytes(),
                    );
                }
            }
            Ok(())
        };
        let nonce_cache = NonceCache::new(NONCE_CACHE_SIZE);
        let local_accounts = HashSet::new();
        let ready_transactions = self
            .transactions_for_verification
            .drain(self.pool_client(&nonce_cache, &local_accounts));
        for transaction in ready_transactions {
            if let Err(e) = process_transaction(&transaction) {
                warn!(target: "privatetx", "Error: {:?}", e);
            }
        }
        Ok(())
    }

    /// Add signed private transaction into the store
    /// Creates corresponding public transaction if last required signature collected and sends it to the chain
    pub fn process_signature(&self, signed_tx: &SignedPrivateTransaction) -> Result<(), Error> {
        trace!(target: "privatetx", "Processing signed private transaction");
        let private_hash = signed_tx.private_transaction_hash();
        let desc = match self.transactions_for_signing.read().get(&private_hash) {
            None => {
                // Not our transaction, broadcast further to peers
                self.broadcast_signed_private_transaction(signed_tx.hash(), signed_tx.rlp_bytes());
                return Ok(());
            }
            Some(desc) => desc,
        };
        let last = self.last_required_signature(&desc, signed_tx.signature())?;

        if last {
            let mut signatures = desc.received_signatures.clone();
            signatures.push(signed_tx.signature());
            let rsv: Vec<Signature> = signatures
                .into_iter()
                .map(|sign| sign.into_electrum().into())
                .collect();
            // Create public transaction
            let signer_account = self
                .signer_account
                .ok_or_else(|| Error::SignerAccountNotSet)?;
            let state = self
                .client
                .state_at(BlockId::Latest)
                .ok_or(Error::StatePruned)?;
            let nonce = state.nonce(&signer_account)?;
            let public_tx = self.public_transaction(
                desc.state.clone(),
                &desc.original_transaction,
                &rsv,
                nonce,
                desc.original_transaction.gas_price,
            )?;
            trace!(target: "privatetx", "Last required signature received, public transaction created: {:?}", public_tx);
            // Sign and add it to the queue
            let chain_id = desc.original_transaction.chain_id();
            let hash = public_tx.hash(chain_id);
            let signature = self.accounts.sign(signer_account, hash)?;
            let signed = SignedTransaction::new(public_tx.with_signature(signature, chain_id))?;
            match self
                .miner
                .import_own_transaction(&*self.client, signed.into())
            {
                Ok(_) => trace!(target: "privatetx", "Public transaction added to queue"),
                Err(err) => {
                    warn!(target: "privatetx", "Failed to add transaction to queue, error: {:?}", err);
                    return Err(err.into());
                }
            }
            // Notify about state changes
            let contract = Self::contract_address_from_transaction(&desc.original_transaction)?;
            // TODO #9825 Usage of BlockId::Latest
            if self.get_contract_version(BlockId::Latest, &contract)
                >= PRIVATE_CONTRACT_WITH_NOTIFICATION_VER
            {
                match self.state_changes_notify(
                    BlockId::Latest,
                    &contract,
                    &desc.original_transaction.sender(),
                    desc.original_transaction.hash(),
                ) {
                    Ok(_) => {
                        trace!(target: "privatetx", "Notification about private state changes sent")
                    }
                    Err(err) => {
                        warn!(target: "privatetx", "Failed to send private state changed notification, error: {:?}", err)
                    }
                }
            }
            // Remove from store for signing
            if let Err(err) = self.transactions_for_signing.write().remove(&private_hash) {
                warn!(target: "privatetx", "Failed to remove transaction from signing store, error: {:?}", err);
                return Err(err);
            }
        } else {
            // Add signature to the store
            match self
                .transactions_for_signing
                .write()
                .add_signature(&private_hash, signed_tx.signature())
            {
                Ok(_) => trace!(target: "privatetx", "Signature stored for private transaction"),
                Err(err) => {
                    warn!(target: "privatetx", "Failed to add signature to signing store, error: {:?}", err);
                    return Err(err);
                }
            }
        }
        Ok(())
    }

    fn contract_address_from_transaction(
        transaction: &SignedTransaction,
    ) -> Result<Address, Error> {
        match transaction.action {
            Action::Call(contract) => Ok(contract),
            _ => {
                warn!(target: "privatetx", "Incorrect type of action for the transaction");
                return Err(Error::BadTransactionType);
            }
        }
    }

    fn last_required_signature(
        &self,
        desc: &PrivateTransactionSigningDesc,
        sign: Signature,
    ) -> Result<bool, Error> {
        if desc.received_signatures.contains(&sign) {
            return Ok(false);
        }
        let state_hash = self.calculate_state_hash(&desc.state, desc.contract_nonce);
        match recover(&sign, &state_hash) {
            Ok(public) => {
                let sender = public_to_address(&public);
                match desc.validators.contains(&sender) {
                    true => Ok(desc.received_signatures.len() + 1 == desc.validators.len()),
                    false => {
                        warn!(target: "privatetx", "Sender's state doesn't correspond to validator's");
                        return Err(Error::StateIncorrect);
                    }
                }
            }
            Err(err) => {
                warn!(target: "privatetx", "Sender's state doesn't correspond to validator's, error {:?}", err);
                return Err(err.into());
            }
        }
    }

    /// Broadcast the private transaction message to the chain
    fn broadcast_private_transaction(&self, transaction_hash: H256, message: Bytes) {
        self.notify(|notify| {
            notify.broadcast(ChainMessageType::PrivateTransaction(
                transaction_hash,
                message.clone(),
            ))
        });
    }

    /// Broadcast signed private transaction message to the chain
    fn broadcast_signed_private_transaction(&self, transaction_hash: H256, message: Bytes) {
        self.notify(|notify| {
            notify.broadcast(ChainMessageType::SignedPrivateTransaction(
                transaction_hash,
                message.clone(),
            ))
        });
    }

    fn iv_from_transaction(transaction: &SignedTransaction) -> H128 {
        let nonce = keccak(&transaction.nonce.rlp_bytes());
        let (iv, _) = nonce.split_at(INIT_VEC_LEN);
        H128::from_slice(iv)
    }

    fn iv_from_address(contract_address: &Address) -> H128 {
        let address = keccak(&contract_address.rlp_bytes());
        let (iv, _) = address.split_at(INIT_VEC_LEN);
        H128::from_slice(iv)
    }

    fn encrypt(
        &self,
        contract_address: &Address,
        initialisation_vector: &H128,
        data: &[u8],
    ) -> Result<Bytes, Error> {
        trace!(target: "privatetx", "Encrypt data using key(address): {:?}", contract_address);
        Ok(self
            .encryptor
            .encrypt(contract_address, initialisation_vector, data)?)
    }

    fn decrypt(&self, contract_address: &Address, data: &[u8]) -> Result<Bytes, Error> {
        trace!(target: "privatetx", "Decrypt data using key(address): {:?}", contract_address);
        Ok(self.encryptor.decrypt(contract_address, data)?)
    }

    fn get_decrypted_state(&self, address: &Address, block: BlockId) -> Result<Bytes, Error> {
        let (data, decoder) = private_contract::functions::state::call();
        let value = self.client.call_contract(block, *address, data)?;
        let state = decoder
            .decode(&value)
            .map_err(|e| Error::Call(format!("Contract call failed {:?}", e)))?;
        self.decrypt(address, &state)
    }

    fn get_decrypted_code(&self, address: &Address, block: BlockId) -> Result<Bytes, Error> {
        let (data, decoder) = private_contract::functions::code::call();
        let value = self.client.call_contract(block, *address, data)?;
        let state = decoder
            .decode(&value)
            .map_err(|e| Error::Call(format!("Contract call failed {:?}", e)))?;
        self.decrypt(address, &state)
    }

    pub fn get_contract_nonce(&self, address: &Address, block: BlockId) -> Result<U256, Error> {
        let (data, decoder) = private_contract::functions::nonce::call();
        let value = self.client.call_contract(block, *address, data)?;
        decoder
            .decode(&value)
            .map_err(|e| Error::Call(format!("Contract call failed {:?}", e)).into())
    }

    fn snapshot_to_storage(raw: Bytes) -> HashMap<H256, H256> {
        let items = raw.len() / 64;
        (0..items)
            .map(|i| {
                let offset = i * 64;
                let key = H256::from_slice(&raw[offset..(offset + 32)]);
                let value = H256::from_slice(&raw[(offset + 32)..(offset + 64)]);
                (key, value)
            })
            .collect()
    }

    fn snapshot_from_storage(storage: &HashMap<H256, H256>) -> Bytes {
        let mut raw = Vec::with_capacity(storage.len() * 64);
        // Sort the storage to guarantee the order for all parties
        let sorted_storage: BTreeMap<&H256, &H256> = storage.iter().collect();
        for (key, value) in sorted_storage {
            raw.extend_from_slice(key);
            raw.extend_from_slice(value);
        }
        raw
    }

    fn patch_account_state(
        &self,
        contract_address: &Address,
        block: BlockId,
        state: &mut state::State<state_db::StateDB>,
    ) -> Result<(), Error> {
        let contract_code = Arc::new(self.get_decrypted_code(contract_address, block)?);
        let contract_state = self.get_decrypted_state(contract_address, block)?;
        trace!(target: "privatetx", "Patching contract at {:?}, code: {:?}, state: {:?}", contract_address, contract_code, contract_state);
        state.patch_account(
            contract_address,
            contract_code,
            Self::snapshot_to_storage(contract_state),
        )?;
        Ok(())
    }

    pub fn execute_private<T, V>(
        &self,
        transaction: &SignedTransaction,
        options: TransactOptions<T, V>,
        block: BlockId,
    ) -> Result<PrivateExecutionResult<T, V>, Error>
    where
        T: Tracer,
        V: VMTracer,
    {
        let mut env_info = self.client.env_info(block).ok_or(Error::StatePruned)?;
        env_info.gas_limit = transaction.gas;

        let mut state = self.client.state_at(block).ok_or(Error::StatePruned)?;
        // TODO #9825 in case of BlockId::Latest these need to operate on the same state
        let contract_address = match transaction.action {
            Action::Call(ref contract_address) => {
                // Patch current contract state
                self.patch_account_state(contract_address, block, &mut state)?;
                Some(*contract_address)
            }
            Action::Create => None,
        };

        let engine = self.client.engine();
        let sender = transaction.sender();
        let nonce = state.nonce(&sender)?;
        let contract_address = contract_address.unwrap_or_else(|| {
            let (new_address, _) = ethcore_contract_address(
                engine.create_address_scheme(env_info.number),
                &sender,
                &nonce,
                &transaction.data,
            );
            new_address
        });
        // Patch other available private contracts' states as well
        // TODO: #10133 patch only required for the contract states
        if let Some(key_server_account) = self.keys_provider.key_server_account() {
            if let Some(available_contracts) = self
                .keys_provider
                .available_keys(block, &key_server_account)
            {
                for private_contract in available_contracts {
                    if private_contract == contract_address {
                        continue;
                    }
                    self.patch_account_state(&private_contract, block, &mut state)?;
                }
            }
        }
        let machine = engine.machine();
        let schedule = machine.schedule(env_info.number);
        let result = Executive::new(&mut state, &env_info, &machine, &schedule)
            .transact_virtual(transaction, options)?;
        let (encrypted_code, encrypted_storage) = {
            let (code, storage) = state.into_account(&contract_address)?;
            trace!(target: "privatetx", "Private contract executed. code: {:?}, state: {:?}, result: {:?}", code, storage, result.output);
            let enc_code = match code {
                Some(c) => Some(self.encrypt(
                    &contract_address,
                    &Self::iv_from_address(&contract_address),
                    &c,
                )?),
                None => None,
            };
            (
                enc_code,
                self.encrypt(
                    &contract_address,
                    &Self::iv_from_transaction(transaction),
                    &Self::snapshot_from_storage(&storage),
                )?,
            )
        };
        Ok(PrivateExecutionResult {
            code: encrypted_code,
            state: encrypted_storage,
            contract_address: contract_address,
            result,
        })
    }

    fn generate_constructor(validators: &[Address], code: Bytes, storage: Bytes) -> Bytes {
        let constructor_code = DEFAULT_STUB_CONTRACT
            .from_hex()
            .expect("Default contract code is valid");
        private_contract::constructor(
            constructor_code,
            validators.iter().map(|a| *a).collect::<Vec<Address>>(),
            code,
            storage,
        )
    }

    fn generate_set_state_call(signatures: &[Signature], storage: Bytes) -> Bytes {
        private_contract::functions::set_state::encode_input(
            storage,
            signatures
                .iter()
                .map(|s| {
                    let mut v: [u8; 32] = [0; 32];
                    v[31] = s.v();
                    v
                })
                .collect::<Vec<[u8; 32]>>(),
            signatures.iter().map(|s| s.r()).collect::<Vec<&[u8]>>(),
            signatures.iter().map(|s| s.s()).collect::<Vec<&[u8]>>(),
        )
    }

    /// Returns the key from the key server associated with the contract
    pub fn contract_key_id(&self, contract_address: &Address) -> Result<H256, Error> {
        Ok(key_server_keys::address_to_key(contract_address))
    }

    /// Create encrypted public contract deployment transaction.
    pub fn public_creation_transaction(
        &self,
        block: BlockId,
        source: &SignedTransaction,
        validators: &[Address],
        gas_price: U256,
    ) -> Result<(Transaction, Address), Error> {
        if let Action::Call(_) = source.action {
            return Err(Error::BadTransactionType);
        }
        let sender = source.sender();
        let state = self.client.state_at(block).ok_or(Error::StatePruned)?;
        let nonce = state.nonce(&sender)?;
        let executed = self.execute_private(source, TransactOptions::with_no_tracing(), block)?;
        let header = self
            .client
            .block_header(block)
            .ok_or(Error::StatePruned)
            .and_then(|h| h.decode().map_err(|_| Error::StateIncorrect).into())?;
        let (executed_code, executed_state) = (executed.code.unwrap_or_default(), executed.state);
        let tx_data =
            Self::generate_constructor(validators, executed_code.clone(), executed_state.clone());
        let mut tx = Transaction {
            nonce: nonce,
            action: Action::Create,
            gas: u64::max_value().into(),
            gas_price: gas_price,
            value: source.value,
            data: tx_data,
        };
        tx.gas = match self
            .client
            .estimate_gas(&tx.clone().fake_sign(sender), &state, &header)
        {
            Ok(estimated_gas) => estimated_gas,
            Err(_) => self.estimate_tx_gas(validators, &executed_code, &executed_state, &[]),
        };

        Ok((tx, executed.contract_address))
    }

    fn estimate_tx_gas(
        &self,
        validators: &[Address],
        code: &Bytes,
        state: &Bytes,
        signatures: &[Signature],
    ) -> U256 {
        let default_gas = 650000
            + validators.len() as u64 * 30000
            + code.len() as u64 * 8000
            + signatures.len() as u64 * 50000
            + state.len() as u64 * 8000;
        default_gas.into()
    }

    /// Create encrypted public contract deployment transaction. Returns updated encrypted state.
    pub fn execute_private_transaction(
        &self,
        block: BlockId,
        source: &SignedTransaction,
    ) -> Result<Bytes, Error> {
        if let Action::Create = source.action {
            return Err(Error::BadTransactionType);
        }
        let result = self.execute_private(source, TransactOptions::with_no_tracing(), block)?;
        Ok(result.state)
    }

    /// Create encrypted public transaction from private transaction.
    pub fn public_transaction(
        &self,
        state: Bytes,
        source: &SignedTransaction,
        signatures: &[Signature],
        nonce: U256,
        gas_price: U256,
    ) -> Result<Transaction, Error> {
        let gas = self.estimate_tx_gas(&[], &Vec::new(), &state, signatures);
        Ok(Transaction {
            nonce: nonce,
            action: source.action.clone(),
            gas: gas.into(),
            gas_price: gas_price,
            value: 0.into(),
            data: Self::generate_set_state_call(signatures, state),
        })
    }

    /// Call into private contract.
    pub fn private_call(
        &self,
        block: BlockId,
        transaction: &SignedTransaction,
    ) -> Result<Executed, Error> {
        let result =
            self.execute_private(transaction, TransactOptions::with_no_tracing(), block)?;
        Ok(result.result)
    }

    /// Returns private validators for a contract.
    pub fn get_validators(&self, block: BlockId, address: &Address) -> Result<Vec<Address>, Error> {
        let (data, decoder) = private_contract::functions::get_validators::call();
        let value = self.client.call_contract(block, *address, data)?;
        decoder
            .decode(&value)
            .map_err(|e| Error::Call(format!("Contract call failed {:?}", e)).into())
    }

    fn get_contract_version(&self, block: BlockId, address: &Address) -> usize {
        let (data, decoder) = private_contract::functions::get_version::call();
        match self
            .client
            .call_contract(block, *address, data)
            .and_then(|value| decoder.decode(&value).map_err(|e| e.to_string()))
        {
            Ok(version) => version.low_u64() as usize,
            Err(_) => INITIAL_PRIVATE_CONTRACT_VER,
        }
    }

    fn state_changes_notify(
        &self,
        block: BlockId,
        address: &Address,
        originator: &Address,
        transaction_hash: H256,
    ) -> Result<(), Error> {
        let (data, _) = private_contract::functions::notify_changes::call(
            *originator,
            transaction_hash.0.to_vec(),
        );
        let _value = self.client.call_contract(block, *address, data)?;
        Ok(())
    }
}

pub trait Importer {
    /// Process received private transaction
    fn import_private_transaction(&self, _rlp: &[u8]) -> Result<H256, Error>;

    /// Add signed private transaction into the store
    ///
    /// Creates corresponding public transaction if last required signature collected and sends it to the chain
    fn import_signed_private_transaction(&self, _rlp: &[u8]) -> Result<H256, Error>;
}

// TODO [ToDr] Offload more heavy stuff to the IoService thread.
// It seems that a lot of heavy work (verification) is done in this thread anyway
// it might actually make sense to decouple it from clientService and just use dedicated thread
// for both verification and execution.

impl Importer for Arc<Provider> {
    fn import_private_transaction(&self, rlp: &[u8]) -> Result<H256, Error> {
        trace!(target: "privatetx", "Private transaction received");
        let private_tx: PrivateTransaction = Rlp::new(rlp).as_val()?;
        let private_tx_hash = private_tx.hash();
        let contract = private_tx.contract();
        let contract_validators = self.get_validators(BlockId::Latest, &contract)?;

        let validation_account = contract_validators
            .iter()
            .find(|address| self.validator_accounts.contains(address));

        // Extract the original transaction
        let encrypted_data = private_tx.encrypted();
        let transaction_bytes = self.decrypt(&contract, &encrypted_data)?;
        let original_tx: UnverifiedTransaction = Rlp::new(&transaction_bytes).as_val()?;
        let nonce_cache = NonceCache::new(NONCE_CACHE_SIZE);
        let local_accounts = HashSet::new();
        // Add to the queue for further verification
        self.transactions_for_verification.add_transaction(
            original_tx,
            validation_account.map(|&account| account),
            private_tx,
            self.pool_client(&nonce_cache, &local_accounts),
        )?;
        let provider = Arc::downgrade(self);
        let result = self.channel.send(ClientIoMessage::execute(move |_| {
            if let Some(provider) = provider.upgrade() {
                if let Err(e) = provider.process_verification_queue() {
                    warn!(target: "privatetx", "Unable to process the queue: {}", e);
                }
            }
        }));
        if let Err(e) = result {
            warn!(target: "privatetx", "Error sending NewPrivateTransaction message: {:?}", e);
        }
        Ok(private_tx_hash)
    }

    fn import_signed_private_transaction(&self, rlp: &[u8]) -> Result<H256, Error> {
        let tx: SignedPrivateTransaction = Rlp::new(rlp).as_val()?;
        trace!(target: "privatetx", "Signature for private transaction received: {:?}", tx);
        let private_hash = tx.private_transaction_hash();
        let provider = Arc::downgrade(self);
        let result = self.channel.send(ClientIoMessage::execute(move |_| {
            if let Some(provider) = provider.upgrade() {
                if let Err(e) = provider.process_signature(&tx) {
                    warn!(target: "privatetx", "Unable to process the signature: {}", e);
                }
            }
        }));
        if let Err(e) = result {
            warn!(target: "privatetx", "Error sending NewSignedPrivateTransaction message: {:?}", e);
        }
        Ok(private_hash)
    }
}

impl ChainNotify for Provider {
    fn new_blocks(&self, new_blocks: NewBlocks) {
        if new_blocks.imported.is_empty() || new_blocks.has_more_blocks_to_import {
            return;
        }
        trace!(target: "privatetx", "New blocks imported, try to prune the queue");
        if let Err(err) = self.process_verification_queue() {
            warn!(target: "privatetx", "Cannot prune private transactions queue. error: {:?}", err);
        }
        self.keys_provider.update_acl_contract();
    }
}