openethereum/secret_store/src/key_server_cluster/admin_sessions/share_add_session.rs

// Copyright 2015-2017 Parity Technologies (UK) Ltd.
// This file is part of Parity.

// Parity 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 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.  If not, see <http://www.gnu.org/licenses/>.

use std::sync::Arc;
use std::collections::{BTreeSet, BTreeMap};
use ethkey::{Public, Secret, Signature};
use parking_lot::{Mutex, Condvar};
use key_server_cluster::{Error, SessionId, NodeId, DocumentKeyShare, KeyStorage};
use key_server_cluster::cluster::Cluster;
use key_server_cluster::cluster_sessions::ClusterSession;
use key_server_cluster::math;
use key_server_cluster::message::{Message, ShareAddMessage, ShareAddConsensusMessage, ConsensusMessageWithServersSecretMap,
	InitializeConsensusSessionWithServersSecretMap, KeyShareCommon, NewAbsoluteTermShare, NewKeysDissemination, ShareAddError,
	ConfirmConsensusInitialization};
use key_server_cluster::jobs::job_session::JobTransport;
use key_server_cluster::jobs::dummy_job::{DummyJob, DummyJobTransport};
use key_server_cluster::jobs::servers_set_change_access_job::{ServersSetChangeAccessJob, ServersSetChangeAccessRequest};
use key_server_cluster::jobs::consensus_session::{ConsensusSessionParams, ConsensusSessionState, ConsensusSession};
use key_server_cluster::admin_sessions::ShareChangeSessionMeta;

/// Share addition session API.
pub trait Session: Send + Sync + 'static {
	/// Wait until session is completed.
	fn wait(&self) -> Result<(), Error>;
}

/// Share addition session transport.
pub trait SessionTransport: Clone + JobTransport<PartialJobRequest=ServersSetChangeAccessRequest, PartialJobResponse=bool> {
	/// Send message to given node.
	fn send(&self, node: &NodeId, message: ShareAddMessage) -> Result<(), Error>;
	/// Set all nodes id numbers (required for consensus messages).
	fn set_id_numbers(&mut self, id_numbers: BTreeMap<NodeId, Secret>);
}

/// Share addition session.
/// Based on "Efficient Multi-Party Digital Signature using Adaptive Secret Sharing for Low-Power Devices in Wireless Networks" paper:
/// http://www.wu.ece.ufl.edu/mypapers/msig.pdf
/// Brief overview:
/// 1) initialization: master node (which has received request for shares addition the message) asks all other nodes to support addition
/// 2) key refreshing distribution (KRD): node generates new random polynom && sends required data to all other nodes
/// 3) key refreshing verification (KRV): node verifies received data
/// 4) node updates its own key share using generated (&& received) data
pub struct SessionImpl<T: SessionTransport> {
	/// Session core.
	core: SessionCore<T>,
	/// Session data.
	data: Mutex<SessionData<T>>,
}

/// Immutable session data.
struct SessionCore<T: SessionTransport> {
	/// Session metadata.
	pub meta: ShareChangeSessionMeta,
	/// Session-level nonce.
	pub nonce: u64,
	/// Original key share (for old nodes only).
	pub key_share: Option<DocumentKeyShare>,
	/// Session transport to communicate to other cluster nodes.
	pub transport: T,
	/// Key storage.
	pub key_storage: Arc<KeyStorage>,
	/// Administrator public key.
	pub admin_public: Option<Public>,
	/// SessionImpl completion condvar.
	pub completed: Condvar,
}

/// Share add consensus session type.
type ShareAddChangeConsensusSession<T> = ConsensusSession<ServersSetChangeAccessJob, T, DummyJob, DummyJobTransport>;

/// Mutable session data.
struct SessionData<T: SessionTransport> {
	/// Session state.
	pub state: SessionState,
	/// Consensus session.
	pub consensus_session: Option<ShareAddChangeConsensusSession<T>>,
	/// Consensus result: nodes-specific data.
	pub nodes: Option<BTreeMap<NodeId, NodeData>>,
	/// Sum of old polynom1 and new polynom1.
	pub refreshed_polynom1_sum: Option<Vec<Secret>>,
	/// NewKeyShare: threshold.
	pub key_share_threshold: Option<usize>,
	/// NewKeyShare: author.
	pub key_share_author: Option<Public>,
	/// NewKeyShare: Common (shared) encryption point.
	pub key_share_common_point: Option<Public>,
	/// NewKeyShare: Encrypted point.
	pub key_share_encrypted_point: Option<Public>,
	/// Share add change result.
	pub result: Option<Result<(), Error>>,
}

/// Single node data.
#[derive(Debug)]
struct NodeData {
	// === Values, filled during initialization phase ===
	/// Random unique scalar. Persistent.
	pub id_number: Option<Secret>,
	/// Has node confirmed session initialization?
	pub is_initialization_confirmed: bool,
	/// Is this a new node?
	pub is_new_node: bool,

	// === Values, filled during KRD phase ===
	/// Absolute term share, received from this node (for new nodes only).
	pub absolute_term_share: Option<Secret>,
	/// Refreshed secret value, which has been received from this node.
	pub refreshed_secret1: Option<Secret>,
	/// Refreshed Public values, which have been received from this node.
	pub refreshed_publics: Option<Vec<Public>>,
}

/// Session state.
#[derive(Debug, PartialEq)]
enum SessionState {
	/// State when consensus is establishing.
	ConsensusEstablishing,
	/// Waiting for absolute term share.
	WaitingForAbsoluteTermShare,
	/// Waiting for keys dissemination.
	WaitingForKeysDissemination,
	/// Session is completed.
	Finished,
}

/// SessionImpl creation parameters
pub struct SessionParams<T: SessionTransport> {
	/// Session metadata.
	pub meta: ShareChangeSessionMeta,
	/// Session transport.
	pub transport: T,
	/// Key storage.
	pub key_storage: Arc<KeyStorage>,
	/// Administrator public key.
	pub admin_public: Option<Public>,
	/// Session nonce.
	pub nonce: u64,
}

/// Isolated ShareAdd session transport.
#[derive(Clone)]
pub struct IsolatedSessionTransport {
	/// Key id.
	session: SessionId,
	/// Session-level nonce.
	nonce: u64,
	/// ID numbers of all participating nodes.
	id_numbers: Option<BTreeMap<NodeId, Secret>>,
	/// Cluster.
	cluster: Arc<Cluster>,
}

impl<T> SessionImpl<T> where T: SessionTransport {
	/// Create new share addition session.
	pub fn new(params: SessionParams<T>) -> Result<Self, Error> {
		let key_id = params.meta.id.clone();
		// it is ok for new nodes not to have key shares => ignore here
		let key_share = params.key_storage.get(&key_id).ok();
		if key_share.as_ref().map(|ks| ks.polynom1.len() != ks.threshold + 1).unwrap_or_default() {
			return Err(Error::KeyStorage("unsupported key share in storage".into()));
		}

		Ok(SessionImpl {
			core: SessionCore {
				meta: params.meta,
				nonce: params.nonce,
				key_share: key_share,
				transport: params.transport,
				key_storage: params.key_storage,
				admin_public: params.admin_public,
				completed: Condvar::new(),
			},
			data: Mutex::new(SessionData {
				consensus_session: None,
				state: SessionState::ConsensusEstablishing,
				nodes: None,
				refreshed_polynom1_sum: None,
				key_share_threshold: None,
				key_share_author: None,
				key_share_common_point: None,
				key_share_encrypted_point: None,
				result: None,
			}),
		})
	}

	/// Set pre-established consensus data.
	pub fn set_consensus_output(&self, old_nodes_set: BTreeSet<NodeId>, mut new_nodes_set: BTreeMap<NodeId, Option<Secret>>) -> Result<(), Error> {
		let mut data = self.data.lock();

		// check state
		if data.state != SessionState::ConsensusEstablishing || data.consensus_session.is_some() || data.nodes.is_some() {
			return Err(Error::InvalidStateForRequest);
		}

		// check && update passed data
		match self.core.key_share.as_ref() {
			Some(key_share) => {
				// old_nodes_set should be exactly the same as when key was generated
				if old_nodes_set.symmetric_difference(&key_share.id_numbers.keys().cloned().collect()).nth(0).is_some() {
					return Err(Error::InvalidNodesConfiguration);
				}
				// update id_numbers for old nodes
				for (new_node, new_node_id) in new_nodes_set.iter_mut().filter(|&(_, ref v)| v.is_none()) {
					match key_share.id_numbers.get(new_node) {
						Some(old_node_id) => *new_node_id = Some(old_node_id.clone()),
						None => return Err(Error::InvalidNodesConfiguration),
					}
				}
			},
			None => {
				if old_nodes_set.contains(&self.core.meta.self_node_id)
					|| !new_nodes_set.contains_key(&self.core.meta.self_node_id) {
					return Err(Error::InvalidNodesConfiguration);
				}
			},
		}

		check_nodes_set(&old_nodes_set, &new_nodes_set)?;
		data.nodes = Some(new_nodes_set.into_iter()
			.map(|(n, nn)| (n, NodeData::new(nn, !old_nodes_set.contains(&n))))
			.collect());

		Ok(())
	}

	/// Initialize share add session on master node.
	pub fn initialize(&self, new_nodes_set: Option<BTreeSet<NodeId>>, old_set_signature: Option<Signature>, new_set_signature: Option<Signature>) -> Result<(), Error> {
		debug_assert_eq!(self.core.meta.self_node_id, self.core.meta.master_node_id);

		let mut data = self.data.lock();

		// check state
		if data.state != SessionState::ConsensusEstablishing || data.consensus_session.is_some() {
			return Err(Error::InvalidStateForRequest);
		}

		// if consensus is not yet established => start consensus session
		let is_consensus_pre_established = data.nodes.is_some();
		if !is_consensus_pre_established {
			// TODO: when session is started on the node, which doesn't have share, it must be delegated to another node
			// this is also true for other sessions (signing, decryption, ...)
			let key_share = self.core.key_share.as_ref().ok_or(Error::KeyStorage("key share is not found on master node".into()))?;
			let new_nodes_set = new_nodes_set.ok_or(Error::InvalidMessage)?;
			let old_nodes_set: BTreeSet<_> = key_share.id_numbers.keys().cloned().collect();
			let new_nodes_map = new_nodes_set.iter()
				.map(|n| key_share.id_numbers.get(n)
					.cloned()
					.map(Ok)
					.unwrap_or_else(|| math::generate_random_scalar())
					.map(|nn| (n.clone(), Some(nn))))
				.collect::<Result<BTreeMap<_, _>, _>>()?;
			check_nodes_set(&old_nodes_set, &new_nodes_map)?;

			let old_set_signature = old_set_signature.ok_or(Error::InvalidMessage)?;
			let new_set_signature = new_set_signature.ok_or(Error::InvalidMessage)?;
			let admin_public = self.core.admin_public.clone().ok_or(Error::InvalidMessage)?;
			let mut consensus_transport = self.core.transport.clone();
			consensus_transport.set_id_numbers(new_nodes_map.iter()
				.map(|(k, v)| (k.clone(), v.clone().expect("new_nodes_map is updated above so that every value is_some; qed")))
				.collect());
			let mut consensus_session = ConsensusSession::new(ConsensusSessionParams {
				meta: self.core.meta.clone().into_consensus_meta(new_nodes_set.len()),
				consensus_executor: ServersSetChangeAccessJob::new_on_master(admin_public,
					old_nodes_set.clone(),
					old_nodes_set.clone(),
					new_nodes_set.clone(),
					old_set_signature,
					new_set_signature),
				consensus_transport: consensus_transport,
			})?;
			consensus_session.initialize(new_nodes_set)?;
			data.consensus_session = Some(consensus_session);
			data.nodes = Some(new_nodes_map.into_iter()
				.map(|(n, nn)| (n, NodeData::new(nn, !old_nodes_set.contains(&n))))
				.collect());
			return Ok(());
		}

		// otherwise => start sending ShareAdd-specific messages
		Self::on_consensus_established(&self.core, &mut *data)
	}

	/// Process single message.
	pub fn process_message(&self, sender: &NodeId, message: &ShareAddMessage) -> Result<(), Error> {
		if self.core.nonce != message.session_nonce() {
			return Err(Error::ReplayProtection);
		}

		match message {
			&ShareAddMessage::ShareAddConsensusMessage(ref message) =>
				self.on_consensus_message(sender, message),
			&ShareAddMessage::KeyShareCommon(ref message) =>
				self.on_common_key_share_data(sender, message),
			&ShareAddMessage::NewAbsoluteTermShare(ref message) =>
				self.on_new_absolute_term(sender, message),
			&ShareAddMessage::NewKeysDissemination(ref message) =>
				self.on_new_keys_dissemination(sender, message),
			&ShareAddMessage::ShareAddError(ref message) =>
				self.on_session_error(sender, message),
		}
	}

	/// When consensus-related message is received.
	pub fn on_consensus_message(&self, sender: &NodeId, message: &ShareAddConsensusMessage) -> Result<(), Error> {
		debug_assert!(self.core.meta.id == *message.session);
		debug_assert!(sender != &self.core.meta.self_node_id);

		// start slave consensus session if needed
		let mut data = self.data.lock();
		if data.consensus_session.is_none() && sender == &self.core.meta.master_node_id {
			match &message.message {
				&ConsensusMessageWithServersSecretMap::InitializeConsensusSession(ref message) => {
					let admin_public = self.core.admin_public.clone().ok_or(Error::InvalidMessage)?;
					let current_nodes_set = self.core.key_share.as_ref()
						.map(|ks| ks.id_numbers.keys().cloned().collect())
						.unwrap_or_else(|| message.old_nodes_set.clone().into_iter().map(Into::into).collect());
					data.consensus_session = Some(ConsensusSession::new(ConsensusSessionParams {
						meta: self.core.meta.clone().into_consensus_meta(message.new_nodes_set.len()),
						consensus_executor: ServersSetChangeAccessJob::new_on_slave(admin_public, current_nodes_set),
						consensus_transport: self.core.transport.clone(),
					})?);
				},
				_ => return Err(Error::InvalidStateForRequest),
			}
		}

		let (is_establishing_consensus, is_consensus_established, new_nodes_set) = {
			let consensus_session = data.consensus_session.as_mut().ok_or(Error::InvalidMessage)?;
			let is_establishing_consensus = consensus_session.state() == ConsensusSessionState::EstablishingConsensus;
			let new_nodes_set = match &message.message {
				&ConsensusMessageWithServersSecretMap::InitializeConsensusSession(ref message) => {
					consensus_session.on_consensus_partial_request(sender, ServersSetChangeAccessRequest::from(message))?;
					let new_nodes_set = message.new_nodes_set.iter()
						.map(|(n, nn)| (n.clone().into(), Some(nn.clone().into())))
						.collect();
					// check nodes set on old nodes
					if let Some(key_share) = self.core.key_share.as_ref() {
						check_nodes_set(&key_share.id_numbers.keys().cloned().collect(), &new_nodes_set)?;
					}
					Some(new_nodes_set.into_iter()
						.map(|(n, nn)| (n, NodeData::new(nn, !message.old_nodes_set.contains(&n.clone().into()))))
						.collect())
				},
				&ConsensusMessageWithServersSecretMap::ConfirmConsensusInitialization(ref message) => {
					consensus_session.on_consensus_partial_response(sender, message.is_confirmed)?;
					None
				},
			};

			(
				is_establishing_consensus,
				consensus_session.state() == ConsensusSessionState::ConsensusEstablished,
				new_nodes_set
			)
		};
		if let Some(new_nodes_set) = new_nodes_set {
			data.nodes = Some(new_nodes_set);
		}
		if self.core.meta.self_node_id != self.core.meta.master_node_id || !is_establishing_consensus || !is_consensus_established {
			return Ok(());
		}

		Self::on_consensus_established(&self.core, &mut *data)
	}

	/// When common key share data is received by new node.
	pub fn on_common_key_share_data(&self, sender: &NodeId, message: &KeyShareCommon) -> Result<(), Error> {
		debug_assert!(self.core.meta.id == *message.session);
		debug_assert!(sender != &self.core.meta.self_node_id);

		// only master can send this message
		if sender != &self.core.meta.master_node_id {
			return Err(Error::InvalidMessage);
		}

		let mut data = self.data.lock();

		// check state
		if data.state == SessionState::ConsensusEstablishing && data.nodes.is_some() {
			data.state = SessionState::WaitingForAbsoluteTermShare;
		} else if data.state != SessionState::WaitingForAbsoluteTermShare {
			return Err(Error::InvalidStateForRequest);
		}

		{
			// only new nodes are waiting for absolute term share
			let nodes = data.nodes.as_ref()
				.expect("nodes are filled during consensus establishing; WaitingForAbsoluteTermShare starts after consensus is established; qed");
			if !nodes[&self.core.meta.self_node_id].is_new_node {
				return Err(Error::InvalidMessage);
			}

			// we only expect this message once
			if data.key_share_threshold.is_some() || data.key_share_author.is_some() || data.key_share_common_point.is_some() || data.key_share_encrypted_point.is_some() {
				return Err(Error::InvalidStateForRequest);
			}
		}

		data.key_share_threshold = Some(message.threshold);
		data.key_share_author = Some(message.author.clone().into());
		data.key_share_common_point = message.common_point.clone().map(Into::into);
		data.key_share_encrypted_point = message.encrypted_point.clone().map(Into::into);

		Ok(())
	}

	/// When absolute term share is received.
	pub fn on_new_absolute_term(&self, sender: &NodeId, message: &NewAbsoluteTermShare) -> Result<(), Error> {
		debug_assert!(self.core.meta.id == *message.session);
		debug_assert!(sender != &self.core.meta.self_node_id);

		let mut data = self.data.lock();

		// check state
		if data.state == SessionState::ConsensusEstablishing && data.nodes.is_some() {
			data.state = SessionState::WaitingForAbsoluteTermShare;
		} else if data.state != SessionState::WaitingForAbsoluteTermShare {
			return Err(Error::InvalidStateForRequest);
		}

		let refreshed_polynom1_sum = {
			// only new nodes are waiting for absolute term share
			let threshold = data.key_share_threshold.clone().ok_or(Error::InvalidMessage)?;
			let nodes = data.nodes.as_mut()
				.expect("nodes are filled during consensus establishing; WaitingForAbsoluteTermShare starts after consensus is established; qed");
			if !nodes[&self.core.meta.self_node_id].is_new_node {
				return Err(Error::InvalidMessage);
			}

			// update node data
			{
				let node_data = nodes.get_mut(sender).ok_or(Error::InvalidMessage)?;
				if node_data.absolute_term_share.is_some() {
					return Err(Error::InvalidStateForRequest);
				}
				if node_data.id_number.is_some() {
					if node_data.id_number != Some(message.sender_id.clone().into()) {
						return Err(Error::InvalidMessage);
					}
				}

				node_data.id_number = Some(message.sender_id.clone().into());
				node_data.absolute_term_share = Some(message.absolute_term_share.clone().into());
			}

			// if we haven't received shares from all old nodes => wait for more
			if nodes.values().any(|nd| !nd.is_new_node && nd.absolute_term_share.is_none()) {
				return Ok(());
			}

			// all old nodes have sent us its shares => generate/calculate secret polynom
			{
				let absolute_term_shares = nodes.values().filter_map(|nd| nd.absolute_term_share.as_ref());
				generate_refreshed_polynoms_for_new_nodes(absolute_term_shares, threshold)?
			}
		};
		data.refreshed_polynom1_sum = Some(refreshed_polynom1_sum);

		// now it is time to disseminate keys to all other nodes
		data.state = SessionState::WaitingForKeysDissemination;
		Self::disseminate_keys(&self.core, &mut *data)
	}

	/// When keys dissemination message is received.
	pub fn on_new_keys_dissemination(&self, sender: &NodeId, message: &NewKeysDissemination) -> Result<(), Error> {
		debug_assert!(self.core.meta.id == *message.session);
		debug_assert!(sender != &self.core.meta.self_node_id);

		let mut data = self.data.lock();

		// check state
		if data.state == SessionState::ConsensusEstablishing && data.nodes.is_some() {
			data.state = SessionState::WaitingForKeysDissemination;
		} else if data.state == SessionState::WaitingForAbsoluteTermShare {
			return Err(Error::TooEarlyForRequest);
		} else if data.state != SessionState::WaitingForKeysDissemination {
			return Err(Error::InvalidStateForRequest);
		}

		// check message
		let threshold = self.core.key_share.as_ref().map(|ks| ks.threshold)
			.unwrap_or_else(|| data.key_share_threshold.clone()
				.expect("on old nodes key_share is_some; on new nodes key_share_threshold is_some after common share data is received; qed"));
		if message.refreshed_publics.len() != threshold + 1 {
			return Err(Error::InvalidMessage);
		}

		// update node data
		let is_new_node = {
			let nodes = data.nodes.as_mut()
				.expect("nodes are filled during consensus establishing; WaitingForKeysDissemination starts after consensus is established; qed");
			{
				let node_data = nodes.get_mut(&sender).ok_or(Error::InvalidMessage)?;
				if node_data.refreshed_secret1.is_some() || node_data.refreshed_publics.is_some() {
					return Err(Error::InvalidStateForRequest);
				}

				node_data.refreshed_secret1 = Some(message.refreshed_secret1.clone().into());
				node_data.refreshed_publics = Some(message.refreshed_publics.iter().cloned().map(Into::into).collect());
			}

			nodes[&self.core.meta.self_node_id].is_new_node
		};

		// receiving this message from master node on old node means that initialization has completed => disseminate our own keys
		if !is_new_node && sender == &self.core.meta.master_node_id {
			Self::disseminate_absolute_term_shares(&self.core, &mut *data)?;
			Self::disseminate_keys(&self.core, &mut *data)?;
		}

		// check if we have received keys from every other node
		if data.nodes.as_ref()
			.expect("nodes are filled during consensus establishing; WaitingForKeysDissemination starts after consensus is established; qed")
			.iter().any(|(node_id, node_data)| node_id != &self.core.meta.self_node_id &&
			(node_data.refreshed_publics.is_none() || node_data.refreshed_secret1.is_none())) {
			return Ok(())
		}

		// verify keys && complete session if keys are ok
		Self::verify_keys(&self.core, &mut *data)?;
		Self::complete_session(&self.core, &mut *data)
	}

	/// When error has occured on another node.
	pub fn on_session_error(&self, sender: &NodeId, message: &ShareAddError) -> Result<(), Error> {
		let mut data = self.data.lock();

		warn!("{}: share add session failed with error: {} from {}", self.core.meta.self_node_id, message.error, sender);

		data.state = SessionState::Finished;
		data.result = Some(Err(Error::Io(message.error.clone())));
		self.core.completed.notify_all();

		Ok(())
	}

	/// Start sending ShareAdd-specific messages, when consensus is established.
	fn on_consensus_established(core: &SessionCore<T>, data: &mut SessionData<T>) -> Result<(), Error> {
		// update state
		let is_old_node = !data.nodes.as_ref()
			.expect("consensus is about nodes set; consensus is established; qed")
			[&core.meta.self_node_id].is_new_node;
		data.state = if is_old_node { SessionState::WaitingForKeysDissemination } else { SessionState::WaitingForAbsoluteTermShare };

		// if on master node, send common shared data to every new node
		let is_master_node = core.meta.self_node_id == core.meta.master_node_id;
		if is_master_node {
			Self::disseminate_common_share_data(core, data)?;
		}

		// if on old node, send absolute term shares to every new node
		if is_old_node {
			Self::disseminate_absolute_term_shares(core, data)?;
		}

		// if on old node, send keys to every node
		if is_old_node {
			Self::disseminate_keys(core, data)?;
		}

		Ok(())
	}

	/// Disseminate absolute term of polynom1 data.
	fn disseminate_absolute_term_shares(core: &SessionCore<T>, data: &mut SessionData<T>) -> Result<(), Error> {
		// compute/generate refreshed polynom1
		let old_key_share = core.key_share.as_ref()
			.expect("disseminate_absolute_term_shares is only called on old nodes; key_share is filled in initialization phase on old nodes; qed");
		let nodes = data.nodes.as_ref()
			.expect("nodes are filled during consensus establishing; absolute term shares are sent after consensus is established; qed");
		let num_new_nodes = nodes.values().filter(|nd| nd.is_new_node).count();
		let (absolute_term_shares, refreshed_polynom1_sum) = generate_refreshed_polynoms_for_existing_nodes(
			num_new_nodes, old_key_share.threshold, &old_key_share.polynom1)?;
		data.refreshed_polynom1_sum = Some(refreshed_polynom1_sum);

		// send absolute term share to every new node
		let sender_id: &Secret = nodes[&core.meta.self_node_id].id_number.as_ref()
			.expect("id_numbers are filled during consensus establishing; this method is called after consensus establishing; qed");
		for (i, new_node) in nodes.iter().filter(|&(_, nd)| nd.is_new_node).map(|(n, _)| n).enumerate() {
			core.transport.send(new_node, ShareAddMessage::NewAbsoluteTermShare(NewAbsoluteTermShare {
				session: core.meta.id.clone().into(),
				session_nonce: core.nonce,
				sender_id: sender_id.clone().into(),
				absolute_term_share: absolute_term_shares[i].clone().into(),
			}))?;
		}

		Ok(())
	}

	/// Send common share data to evey new node.
	fn disseminate_common_share_data(core: &SessionCore<T>, data: &SessionData<T>) -> Result<(), Error> {
		let old_key_share = core.key_share.as_ref()
			.expect("disseminate_common_share_data is only called on master node; key_share is filled in initialization phase on master node; qed");
		let nodes = data.nodes.as_ref()
			.expect("nodes are filled during consensus establishing; common share data sent after consensus is established; qed");
		for new_node in nodes.iter().filter(|&(_, nd)| nd.is_new_node).map(|(n, _)| n) {
			core.transport.send(new_node, ShareAddMessage::KeyShareCommon(KeyShareCommon {
				session: core.meta.id.clone().into(),
				session_nonce: core.nonce,
				threshold: old_key_share.threshold,
				author: old_key_share.author.clone().into(),
				common_point: old_key_share.common_point.clone().map(Into::into),
				encrypted_point: old_key_share.encrypted_point.clone().map(Into::into),
			}))?;
		}

		Ok(())
	}

	/// Disseminate key refreshing data.
	fn disseminate_keys(core: &SessionCore<T>, data: &mut SessionData<T>) -> Result<(), Error> {
		// send required messages
		let threshold = core.key_share.as_ref().map(|ks| ks.threshold)
			.unwrap_or_else(|| data.key_share_threshold.clone()
				.expect("this is new node; on new nodes this field is filled before KRD; session is completed after KRD; qed"));
		let refreshed_polynom1_sum = data.refreshed_polynom1_sum.as_ref()
			.expect("disseminate_keys is only called after generating refreshed_polynom1_sum; qed");
		let refreshed_publics = math::refreshed_public_values_generation(threshold, &refreshed_polynom1_sum)?;

		// send calculated values
		let nodes = data.nodes.as_mut()
			.expect("nodes are filled during consensus establishing; keys are disseminated after consensus is established; qed");
		for (node, node_number) in nodes.iter().filter(|&(n, _)| n != &core.meta.self_node_id).map(|(n, nd)| (n, &nd.id_number)) {
			// also send keys to every other node
			let refreshed_secret1 = math::compute_polynom(refreshed_polynom1_sum, node_number.as_ref()
				.expect("id_numbers are filled during consensus establishing; keys are disseminated after consensus is established; qed"))?;
			core.transport.send(node, ShareAddMessage::NewKeysDissemination(NewKeysDissemination {
				session: core.meta.id.clone().into(),
				session_nonce: core.nonce,
				refreshed_secret1: refreshed_secret1.into(),
				refreshed_publics: refreshed_publics.iter().cloned().map(Into::into).collect(),
			}))?;
		}

		// 'receive' data from self
		let self_node_data = nodes.get_mut(&core.meta.self_node_id)
			.expect("data.nodes contains entry for every session node; this node is a part of the session; qed");
		self_node_data.refreshed_secret1 = Some(math::compute_polynom(refreshed_polynom1_sum, &self_node_data.id_number.as_ref()
			.expect("id_numbers are filled during consensus establishing; keys are disseminated after consensus is established; qed"))?);
		self_node_data.refreshed_publics = Some(refreshed_publics);

		Ok(())
	}

	/// Verify received keys values.
	fn verify_keys(core: &SessionCore<T>, data: &mut SessionData<T>) -> Result<(), Error> {
		let threshold = core.key_share.as_ref().map(|ks| ks.threshold)
			.unwrap_or_else(|| data.key_share_threshold.clone()
				.expect("on old nodes key_share is_some; on new nodes key_share_threshold is_some after common share data is received; qed"));
		let nodes = data.nodes.as_ref()
			.expect("nodes are filled during consensus establishing; keys are verified after consensus is established; qed");
		let number_id = nodes[&core.meta.self_node_id].id_number.as_ref()
			.expect("id_numbers are filled during consensus establishing; keys are verified after consensus is established; qed");
		for node_data in nodes.iter().filter(|&(n, _)| n != &core.meta.self_node_id).map(|(_, nd)| nd) {
			let refreshed_secret1 = node_data.refreshed_secret1.as_ref().expect("keys received on KRD phase; KRV phase follows KRD phase; qed");
			let refreshed_publics = node_data.refreshed_publics.as_ref().expect("keys received on KRD phase; KRV phase follows KRD phase; qed");
			let is_key_verification_ok = math::refreshed_keys_verification(threshold, &number_id, refreshed_secret1, refreshed_publics)?;

			if !is_key_verification_ok {
				// node has sent us incorrect values. In original ECDKG protocol we should have sent complaint here.
				return Err(Error::InvalidMessage);
			}
		}

		Ok(())
	}

	/// Complete session.
	fn complete_session(core: &SessionCore<T>, data: &mut SessionData<T>) -> Result<(), Error> {
		// compose updated key share
		let nodes = data.nodes.as_ref()
			.expect("nodes are filled during consensus establishing; session is completed after consensus is established; qed");
		let refreshed_key_share = DocumentKeyShare {
			// values with the same value as before beginning of the session
			threshold: core.key_share.as_ref().map(|ks| ks.threshold)
				.unwrap_or_else(|| data.key_share_threshold.clone()
					.expect("this is new node; on new nodes this field is filled before KRD; session is completed after KRD; qed")),
			author: core.key_share.as_ref().map(|ks| ks.author.clone())
				.unwrap_or_else(|| data.key_share_author.clone()
					.expect("this is new node; on new nodes this field is filled before KRD; session is completed after KRD; qed")),
			common_point: core.key_share.as_ref().map(|ks| ks.common_point.clone())
				.unwrap_or_else(|| data.key_share_common_point.clone()),
			encrypted_point: core.key_share.as_ref().map(|ks| ks.encrypted_point.clone())
				.unwrap_or_else(|| data.key_share_encrypted_point.clone()),
			// below are updated values
			id_numbers: nodes.iter().map(|(node_id, node_data)| (node_id.clone(), node_data.id_number.as_ref()
				.expect("id_numbers are filled during consensus establishing; session is completed after consensus is established; qed").clone())).collect(),
			polynom1: data.refreshed_polynom1_sum.clone().expect("this field is filled during KRD; session is completed after KRD; qed"),
			secret_share: math::compute_secret_share(nodes.values()
				.filter_map(|nd| nd.refreshed_secret1.as_ref()))?,
		};

		// save encrypted data to the key storage
		data.state = SessionState::Finished;
		if core.key_share.is_some() {
			// TODO: if db was updated on some nodes && wasn't updated on others, this could lead to secret loss
			// => need mechanism to confirm insert/update OR store all versions of shares and negotiate version on session start (part of consensus)
			core.key_storage.update(core.meta.id.clone(), refreshed_key_share.clone())
		} else {
			core.key_storage.insert(core.meta.id.clone(), refreshed_key_share.clone())
		}.map_err(|e| Error::KeyStorage(e.into()))?;

		// signal session completion
		data.state = SessionState::Finished;
		data.result = Some(Ok(()));
		core.completed.notify_all();

		Ok(())
	}
}

impl<T> Session for SessionImpl<T> where T: SessionTransport + Send + Sync + 'static {
	fn wait(&self) -> Result<(), Error> {
		let mut data = self.data.lock();
		if !data.result.is_some() {
			self.core.completed.wait(&mut data);
		}

		data.result.clone()
			.expect("checked above or waited for completed; completed is only signaled when result.is_some(); qed")
	}
}

impl<T> ClusterSession for SessionImpl<T> where T: SessionTransport {
	fn is_finished(&self) -> bool {
		self.data.lock().state == SessionState::Finished
	}

	fn on_session_timeout(&self) {
		let mut data = self.data.lock();

		warn!("{}: share add session failed with timeout", self.core.meta.self_node_id);

		data.state = SessionState::Finished;
		data.result = Some(Err(Error::NodeDisconnected));
		self.core.completed.notify_all();
	}

	fn on_node_timeout(&self, node: &NodeId) {
		let mut data = self.data.lock();

		warn!("{}: share add session failed because {} connection has timeouted", self.core.meta.self_node_id, node);

		data.state = SessionState::Finished;
		data.result = Some(Err(Error::NodeDisconnected));
		self.core.completed.notify_all();
	}
}

impl NodeData {
	/// Create new node data.
	pub fn new(id_number: Option<Secret>, is_new_node: bool) -> Self {
		NodeData {
			id_number: id_number,
			is_initialization_confirmed: false,
			is_new_node: is_new_node,
			absolute_term_share: None,
			refreshed_secret1: None,
			refreshed_publics: None,
		}
	}
}

impl IsolatedSessionTransport {
	pub fn new(session_id: SessionId, nonce: u64, cluster: Arc<Cluster>) -> Self {
		IsolatedSessionTransport {
			session: session_id,
			nonce: nonce,
			cluster: cluster,
			id_numbers: None,
		}
	}
}

impl JobTransport for IsolatedSessionTransport {
	type PartialJobRequest = ServersSetChangeAccessRequest;
	type PartialJobResponse = bool;

	fn send_partial_request(&self, node: &NodeId, request: ServersSetChangeAccessRequest) -> Result<(), Error> {
		let id_numbers = self.id_numbers.as_ref()
			.expect("partial requests are sent from master node only; on master node id_numers are filled during creation; qed");
		self.cluster.send(node, Message::ShareAdd(ShareAddMessage::ShareAddConsensusMessage(ShareAddConsensusMessage {
			session: self.session.clone().into(),
			session_nonce: self.nonce,
			message: ConsensusMessageWithServersSecretMap::InitializeConsensusSession(InitializeConsensusSessionWithServersSecretMap {
				old_nodes_set: request.old_servers_set.into_iter().map(Into::into).collect(),
				new_nodes_set: request.new_servers_set.into_iter().map(|n| (n.into(), id_numbers[&n].clone().into())).collect(),
				old_set_signature: request.old_set_signature.into(),
				new_set_signature: request.new_set_signature.into(),
			}),
		})))
	}

	fn send_partial_response(&self, node: &NodeId, response: bool) -> Result<(), Error> {
		self.cluster.send(node, Message::ShareAdd(ShareAddMessage::ShareAddConsensusMessage(ShareAddConsensusMessage {
			session: self.session.clone().into(),
			session_nonce: self.nonce,
			message: ConsensusMessageWithServersSecretMap::ConfirmConsensusInitialization(ConfirmConsensusInitialization {
				is_confirmed: response,
			}),
		})))
	}
}

impl SessionTransport for IsolatedSessionTransport {
	fn set_id_numbers(&mut self, id_numbers: BTreeMap<NodeId, Secret>) {
		self.id_numbers = Some(id_numbers);
	}

	fn send(&self, node: &NodeId, message: ShareAddMessage) -> Result<(), Error> {
		self.cluster.send(node, Message::ShareAdd(message))
	}
}

fn check_nodes_set(old_nodes_set: &BTreeSet<NodeId>, new_nodes_set: &BTreeMap<NodeId, Option<Secret>>) -> Result<(), Error> {
	// it is impossible to remove nodes using share add session
	if old_nodes_set.iter().any(|n| !new_nodes_set.contains_key(n)) {
		return Err(Error::InvalidNodesConfiguration);
	}
	// it is impossible to not to add any nodes using share add session
	if new_nodes_set.len() == old_nodes_set.len() {
		return Err(Error::InvalidNodesConfiguration);
	}

	Ok(())
}

fn generate_refreshed_polynoms_for_existing_nodes(new_nodes: usize, threshold: usize, existing_polynom1: &Vec<Secret>) -> Result<(Vec<Secret>, Vec<Secret>), Error> {
	// TODO: optimization: could add secrets instead of polynoms
	let refreshed_polynoms1 = (0..new_nodes).map(|_| math::generate_random_polynom(threshold)).collect::<Result<Vec<_>, _>>()?;
	let mut refreshed_polynom1_sum = existing_polynom1.clone();
	for refreshed_polynom1 in &refreshed_polynoms1 {
		refreshed_polynom1_sum = math::add_polynoms(&refreshed_polynom1_sum, refreshed_polynom1, false)?;
	}

	Ok((
		refreshed_polynoms1.into_iter().map(|p| p[0].clone()).collect(),
		refreshed_polynom1_sum,
	))
}

fn generate_refreshed_polynoms_for_new_nodes<'a, I>(absolute_term_shares: I, threshold: usize) -> Result<Vec<Secret>, Error> where I: Iterator<Item=&'a Secret> {
	let mut new_polynom1 = math::generate_random_polynom(threshold)?;
	let new_polynom_absolute_term = math::compute_additional_polynom1_absolute_term(absolute_term_shares)?;
	new_polynom1[0] = new_polynom_absolute_term;
	Ok(new_polynom1)
}

#[cfg(test)]
pub mod tests {
	use std::sync::Arc;
	use std::collections::{VecDeque, BTreeMap, BTreeSet};
	use ethkey::{Random, Generator, Public, KeyPair, Signature, sign};
	use key_server_cluster::{NodeId, SessionId, Error, KeyStorage, DummyKeyStorage};
	use key_server_cluster::cluster::Cluster;
	use key_server_cluster::cluster::tests::DummyCluster;
	use key_server_cluster::cluster_sessions::ClusterSession;
	use key_server_cluster::generation_session::tests::{Node as GenerationNode, generate_nodes_ids};
	use key_server_cluster::math;
	use key_server_cluster::message::Message;
	use key_server_cluster::servers_set_change_session::tests::generate_key;
	use key_server_cluster::jobs::servers_set_change_access_job::ordered_nodes_hash;
	use key_server_cluster::admin_sessions::ShareChangeSessionMeta;
	use super::{SessionImpl, SessionParams, IsolatedSessionTransport};

	struct Node {
		pub cluster: Arc<DummyCluster>,
		pub key_storage: Arc<DummyKeyStorage>,
		pub session: SessionImpl<IsolatedSessionTransport>,
	}

	struct MessageLoop {
		pub admin_key_pair: KeyPair,
		pub original_key_pair: KeyPair,
		pub old_nodes_set: BTreeSet<NodeId>,
		pub new_nodes_set: BTreeSet<NodeId>,
		pub old_set_signature: Signature,
		pub new_set_signature: Signature,
		pub nodes: BTreeMap<NodeId, Node>,
		pub queue: VecDeque<(NodeId, NodeId, Message)>,
	}

	fn create_session(mut meta: ShareChangeSessionMeta, admin_public: Public, self_node_id: NodeId, cluster: Arc<Cluster>, key_storage: Arc<KeyStorage>) -> SessionImpl<IsolatedSessionTransport> {
		let session_id = meta.id.clone();
		meta.self_node_id = self_node_id;
		SessionImpl::new(SessionParams {
			meta: meta.clone(),
			transport: IsolatedSessionTransport::new(session_id, 1, cluster),
			key_storage: key_storage,
			admin_public: Some(admin_public),
			nonce: 1,
		}).unwrap()
	}

	fn create_node(meta: ShareChangeSessionMeta, admin_public: Public, node: GenerationNode) -> Node {
		Node {
			cluster: node.cluster.clone(),
			key_storage: node.key_storage.clone(),
			session: create_session(meta, admin_public, node.session.node().clone(), node.cluster, node.key_storage),
		}
	}

	/// This only works for schemes where threshold = 1
	pub fn check_secret_is_preserved(joint_key_pair: KeyPair, nodes: BTreeMap<NodeId, Arc<DummyKeyStorage>>) {
		let n = nodes.len();
		let document_secret_plain = math::generate_random_point().unwrap();
		for n1 in 0..n {
			for n2 in n1+1..n {
				let share1 = nodes.values().nth(n1).unwrap().get(&SessionId::default()).unwrap();
				let share2 = nodes.values().nth(n2).unwrap().get(&SessionId::default()).unwrap();
				let id_number1 = share1.id_numbers[nodes.keys().nth(n1).unwrap()].clone();
				let id_number2 = share1.id_numbers[nodes.keys().nth(n2).unwrap()].clone();

				// now encrypt and decrypt data
				let (document_secret_decrypted, document_secret_decrypted_test) =
					math::tests::do_encryption_and_decryption(1,
						joint_key_pair.public(),
						&[id_number1, id_number2],
						&[share1.secret_share, share2.secret_share],
						Some(joint_key_pair.secret()),
						document_secret_plain.clone());

				assert_eq!(document_secret_plain, document_secret_decrypted_test);
				assert_eq!(document_secret_plain, document_secret_decrypted);
			}
		}
	}

	impl MessageLoop {
		pub fn new(t: usize, master_node_id: NodeId, old_nodes_set: BTreeSet<NodeId>, new_nodes_set: BTreeSet<NodeId>) -> Self {
			// generate admin key pair
			let admin_key_pair = Random.generate().unwrap();
			let admin_public = admin_key_pair.public().clone();

			// run initial generation session
			let gml = generate_key(t, old_nodes_set.clone());
			let original_secret = math::compute_joint_secret(gml.nodes.values()
				.map(|nd| nd.key_storage.get(&SessionId::default()).unwrap().polynom1[0].clone())
				.collect::<Vec<_>>()
				.iter()).unwrap();
			let original_key_pair = KeyPair::from_secret(original_secret).unwrap();

			// prepare sessions on all nodes
			let meta = ShareChangeSessionMeta {
				id: SessionId::default(),
				self_node_id: NodeId::default(),
				master_node_id: master_node_id,
			};
			let new_nodes = new_nodes_set.iter()
				.filter(|n| !old_nodes_set.contains(&n))
				.map(|new_node_id| {
					let new_node_cluster = Arc::new(DummyCluster::new(new_node_id.clone()));
					let new_node_key_storage = Arc::new(DummyKeyStorage::default());
					let new_node_session = create_session(meta.clone(), admin_public.clone(), new_node_id.clone(), new_node_cluster.clone(), new_node_key_storage.clone());
					Node {
						cluster: new_node_cluster,
						key_storage: new_node_key_storage,
						session: new_node_session,
					}
				});
			let old_nodes = gml.nodes.into_iter().map(|gn| create_node(meta.clone(), admin_public.clone(), gn.1));
			let nodes = old_nodes.chain(new_nodes).map(|n| (n.session.core.meta.self_node_id.clone(), n)).collect();

			let old_set_signature = sign(admin_key_pair.secret(), &ordered_nodes_hash(&old_nodes_set)).unwrap();
			let new_set_signature = sign(admin_key_pair.secret(), &ordered_nodes_hash(&new_nodes_set)).unwrap();
			MessageLoop {
				admin_key_pair: admin_key_pair,
				original_key_pair: original_key_pair,
				old_nodes_set: old_nodes_set.clone(),
				new_nodes_set: new_nodes_set.clone(),
				old_set_signature: old_set_signature,
				new_set_signature: new_set_signature,
				nodes: nodes,
				queue: Default::default(),
			}
		}

		pub fn run(&mut self) {
			while let Some((from, to, message)) = self.take_message() {
				self.process_message((from, to, message)).unwrap();
			}
		}

		pub fn take_message(&mut self) -> Option<(NodeId, NodeId, Message)> {
			self.nodes.values()
				.filter_map(|n| n.cluster.take_message().map(|m| (n.session.core.meta.self_node_id.clone(), m.0, m.1)))
				.nth(0)
				.or_else(|| self.queue.pop_front())
		}

		pub fn process_message(&mut self, msg: (NodeId, NodeId, Message)) -> Result<(), Error> {
			match { match msg.2 {
				Message::ShareAdd(ref message) =>
					self.nodes[&msg.1].session.process_message(&msg.0, message),
				_ => unreachable!("only servers set change messages are expected"),
			} } {
				Ok(_) => Ok(()),
				Err(Error::TooEarlyForRequest) => {
					self.queue.push_back(msg);
					Ok(())
				},
				Err(err) => Err(err),
			}
		}
	}

	#[test]
	fn node_add_fails_if_nodes_removed() {
		let old_nodes_set = generate_nodes_ids(3);
		let master_node_id = old_nodes_set.iter().cloned().nth(0).unwrap();
		let node_to_remove_id = old_nodes_set.iter().cloned().nth(1).unwrap();
		let mut new_nodes_set: BTreeSet<_> = old_nodes_set.clone().into_iter().chain(generate_nodes_ids(1)).collect();
		new_nodes_set.remove(&node_to_remove_id);
		let ml = MessageLoop::new(1, master_node_id.clone(), old_nodes_set, new_nodes_set.clone());
		assert_eq!(ml.nodes[&master_node_id].session.initialize(Some(new_nodes_set),
			Some(ml.old_set_signature.clone()),
			Some(ml.new_set_signature.clone())
		).unwrap_err(), Error::InvalidNodesConfiguration);
	}

	#[test]
	fn node_add_fails_if_no_nodes_added() {
		let old_nodes_set = generate_nodes_ids(3);
		let master_node_id = old_nodes_set.iter().cloned().nth(0).unwrap();
		let new_nodes_set = old_nodes_set.clone();
		let ml = MessageLoop::new(1, master_node_id.clone(), old_nodes_set, new_nodes_set.clone());
		assert_eq!(ml.nodes[&master_node_id].session.initialize(Some(new_nodes_set),
			Some(ml.old_set_signature.clone()),
			Some(ml.new_set_signature.clone())
		).unwrap_err(), Error::InvalidNodesConfiguration);
	}

	#[test]
	fn node_add_fails_if_started_on_adding_node() {
		let old_nodes_set = generate_nodes_ids(3);
		let nodes_to_add_set = generate_nodes_ids(1);
		let master_node_id = nodes_to_add_set.iter().cloned().nth(0).unwrap();
		let new_nodes_set: BTreeSet<_> = old_nodes_set.clone().into_iter().chain(nodes_to_add_set.into_iter()).collect();
		let ml = MessageLoop::new(1, master_node_id.clone(), old_nodes_set, new_nodes_set.clone());
		assert_eq!(ml.nodes[&master_node_id].session.initialize(Some(new_nodes_set),
			Some(ml.old_set_signature.clone()),
			Some(ml.new_set_signature.clone())
		).unwrap_err(), Error::KeyStorage("key share is not found on master node".into()));
	}

	#[test]
	fn node_add_fails_if_initialized_twice() {
		let old_nodes_set = generate_nodes_ids(3);
		let master_node_id = old_nodes_set.iter().cloned().nth(0).unwrap();
		let new_nodes_set: BTreeSet<_> = old_nodes_set.clone().into_iter().chain(generate_nodes_ids(1)).collect();
		let ml = MessageLoop::new(1, master_node_id.clone(), old_nodes_set, new_nodes_set.clone());
		assert_eq!(ml.nodes[&master_node_id].session.initialize(Some(new_nodes_set.clone()),
			Some(ml.old_set_signature.clone()),
			Some(ml.new_set_signature.clone())
		), Ok(()));
		assert_eq!(ml.nodes[&master_node_id].session.initialize(Some(new_nodes_set),
			Some(ml.old_set_signature.clone()),
			Some(ml.new_set_signature.clone())
		), Err(Error::InvalidStateForRequest));
	}

	#[test]
	fn node_add_fails_if_started_without_signatures() {
		let old_nodes_set = generate_nodes_ids(3);
		let master_node_id = old_nodes_set.iter().cloned().nth(0).unwrap();
		let new_nodes_set: BTreeSet<_> = old_nodes_set.clone().into_iter().chain(generate_nodes_ids(1)).collect();
		let ml = MessageLoop::new(1, master_node_id.clone(), old_nodes_set, new_nodes_set.clone());
		assert_eq!(ml.nodes[&master_node_id].session.initialize(None, None, None), Err(Error::InvalidMessage));
	}

	#[test]
	fn nodes_added_using_share_add() {
		let test_cases = vec![(3, 1), (3, 3)];
		for (n, nodes_to_add) in test_cases {
			// generate key && prepare ShareAdd sessions
			let old_nodes_set = generate_nodes_ids(n);
			let new_nodes_set: BTreeSet<_> = old_nodes_set.clone().into_iter().chain(generate_nodes_ids(nodes_to_add)).collect();
			let master_node_id = old_nodes_set.iter().cloned().nth(0).unwrap();
			let mut ml = MessageLoop::new(1, master_node_id.clone(), old_nodes_set, new_nodes_set.clone());

			// initialize session on master node && run to completion
			ml.nodes[&master_node_id].session.initialize(Some(new_nodes_set),
				Some(ml.old_set_signature.clone()),
				Some(ml.new_set_signature.clone())).unwrap();
			ml.run();

			// check that session has completed on all nodes
			assert!(ml.nodes.values().all(|n| n.session.is_finished()));
			
			// check that secret is still the same as before adding the share
			check_secret_is_preserved(ml.original_key_pair.clone(), ml.nodes.iter().map(|(k, v)| (k.clone(), v.key_storage.clone())).collect());
		}
	}
}