grin/wallet/src/libtx/slate.rs

// Copyright 2018 The Grin Developers
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Functions for building partial transactions to be passed
//! around during an interactive wallet exchange
use rand::thread_rng;
use uuid::Uuid;

use core::core::committed::Committed;
use core::core::{amount_to_hr_string, Transaction};
use keychain::{BlindSum, BlindingFactor, Keychain};
use libtx::error::{Error, ErrorKind};
use libtx::{aggsig, build, tx_fee};

use util::secp::key::{PublicKey, SecretKey};
use util::secp::Signature;
use util::{secp, LOGGER};

/// Public data for each participant in the slate

#[derive(Serialize, Deserialize, Debug, Clone)]
pub struct ParticipantData {
	/// Id of participant in the transaction. (For now, 0=sender, 1=rec)
	pub id: u64,
	/// Public key corresponding to private blinding factor
	pub public_blind_excess: PublicKey,
	/// Public key corresponding to private nonce
	pub public_nonce: PublicKey,
	/// Public partial signature
	pub part_sig: Option<Signature>,
}

impl ParticipantData {
	/// A helper to return whether this participant
	/// has completed round 1 and round 2;
	/// Round 1 has to be completed before instantiation of this struct
	/// anyhow, and for each participant consists of:
	/// -Inputs added to transaction
	/// -Outputs added to transaction
	/// -Public signature nonce chosen and added
	/// -Public contribution to blinding factor chosen and added
	/// Round 2 can only be completed after all participants have
	/// performed round 1, and adds:
	/// -Part sig is filled out
	pub fn is_complete(&self) -> bool {
		self.part_sig.is_some()
	}
}

/// A 'Slate' is passed around to all parties to build up all of the public
/// transaction data needed to create a finalized transaction. Callers can pass
/// the slate around by whatever means they choose, (but we can provide some
/// binary or JSON serialization helpers here).

#[derive(Serialize, Deserialize, Debug, Clone)]
pub struct Slate {
	/// The number of participants intended to take part in this transaction
	pub num_participants: usize,
	/// Unique transaction ID, selected by sender
	pub id: Uuid,
	/// The core transaction data:
	/// inputs, outputs, kernels, kernel offset
	pub tx: Transaction,
	/// base amount (excluding fee)
	pub amount: u64,
	/// fee amount
	pub fee: u64,
	/// Block height for the transaction
	pub height: u64,
	/// Lock height
	pub lock_height: u64,
	/// Participant data, each participant in the transaction will
	/// insert their public data here. For now, 0 is sender and 1
	/// is receiver, though this will change for multi-party
	pub participant_data: Vec<ParticipantData>,
}

impl Slate {
	/// Create a new slate
	pub fn blank(num_participants: usize) -> Slate {
		Slate {
			num_participants: num_participants,
			id: Uuid::new_v4(),
			tx: Transaction::empty(),
			amount: 0,
			fee: 0,
			height: 0,
			lock_height: 0,
			participant_data: vec![],
		}
	}

	/// Adds selected inputs and outputs to the slate's transaction
	/// Returns blinding factor
	pub fn add_transaction_elements<K>(
		&mut self,
		keychain: &K,
		mut elems: Vec<Box<build::Append<K>>>,
	) -> Result<BlindingFactor, Error>
	where
		K: Keychain,
	{
		// Append to the exiting transaction
		if self.tx.kernels.len() != 0 {
			elems.insert(0, build::initial_tx(self.tx.clone()));
		}
		let (tx, blind) = build::partial_transaction(elems, keychain)?;
		self.tx = tx;
		Ok(blind)
	}

	/// Completes callers part of round 1, adding public key info
	/// to the slate
	pub fn fill_round_1<K>(
		&mut self,
		keychain: &K,
		sec_key: &mut SecretKey,
		sec_nonce: &SecretKey,
		participant_id: usize,
	) -> Result<(), Error>
	where
		K: Keychain,
	{
		// Whoever does this first generates the offset
		if self.tx.offset == BlindingFactor::zero() {
			self.generate_offset(keychain, sec_key)?;
		}
		self.add_participant_info(keychain, &sec_key, &sec_nonce, participant_id, None)?;
		Ok(())
	}

	/// Completes caller's part of round 2, completing signatures
	pub fn fill_round_2<K>(
		&mut self,
		keychain: &K,
		sec_key: &SecretKey,
		sec_nonce: &SecretKey,
		participant_id: usize,
	) -> Result<(), Error>
	where
		K: Keychain,
	{
		self.check_fees()?;
		self.verify_part_sigs(keychain.secp())?;
		let sig_part = aggsig::calculate_partial_sig(
			keychain.secp(),
			sec_key,
			sec_nonce,
			&self.pub_nonce_sum(keychain.secp())?,
			self.fee,
			self.lock_height,
		)?;
		self.participant_data[participant_id].part_sig = Some(sig_part);
		Ok(())
	}

	/// Creates the final signature, callable by either the sender or recipient
	/// (after phase 3: sender confirmation)
	/// TODO: Only callable by receiver at the moment
	pub fn finalize<K>(&mut self, keychain: &K) -> Result<(), Error>
	where
		K: Keychain,
	{
		let final_sig = self.finalize_signature(keychain)?;
		self.finalize_transaction(keychain, &final_sig)
	}

	/// Return the sum of public nonces
	fn pub_nonce_sum(&self, secp: &secp::Secp256k1) -> Result<PublicKey, Error> {
		let pub_nonces = self.participant_data
			.iter()
			.map(|p| &p.public_nonce)
			.collect();
		match PublicKey::from_combination(secp, pub_nonces) {
			Ok(k) => Ok(k),
			Err(e) => Err(ErrorKind::Secp(e))?,
		}
	}

	/// Return the sum of public blinding factors
	fn pub_blind_sum(&self, secp: &secp::Secp256k1) -> Result<PublicKey, Error> {
		let pub_blinds = self.participant_data
			.iter()
			.map(|p| &p.public_blind_excess)
			.collect();
		match PublicKey::from_combination(secp, pub_blinds) {
			Ok(k) => Ok(k),
			Err(e) => Err(ErrorKind::Secp(e))?,
		}
	}

	/// Return vector of all partial sigs
	fn part_sigs(&self) -> Vec<&Signature> {
		self.participant_data
			.iter()
			.map(|p| p.part_sig.as_ref().unwrap())
			.collect()
	}

	/// Adds participants public keys to the slate data
	/// and saves participant's transaction context
	/// sec_key can be overridden to replace the blinding
	/// factor (by whoever split the offset)
	fn add_participant_info<K>(
		&mut self,
		keychain: &K,
		sec_key: &SecretKey,
		sec_nonce: &SecretKey,
		id: usize,
		part_sig: Option<Signature>,
	) -> Result<(), Error>
	where
		K: Keychain,
	{
		// Add our public key and nonce to the slate
		let pub_key = PublicKey::from_secret_key(keychain.secp(), &sec_key)?;
		let pub_nonce = PublicKey::from_secret_key(keychain.secp(), &sec_nonce)?;
		self.participant_data.push(ParticipantData {
			id: id as u64,
			public_blind_excess: pub_key,
			public_nonce: pub_nonce,
			part_sig: part_sig,
		});

		Ok(())
	}

	/// Somebody involved needs to generate an offset with their private key
	/// For now, we'll have the transaction initiator be responsible for it
	/// Return offset private key for the participant to use later in the
	/// transaction
	fn generate_offset<K>(&mut self, keychain: &K, sec_key: &mut SecretKey) -> Result<(), Error>
	where
		K: Keychain,
	{
		// Generate a random kernel offset here
		// and subtract it from the blind_sum so we create
		// the aggsig context with the "split" key
		self.tx.offset =
			BlindingFactor::from_secret_key(SecretKey::new(&keychain.secp(), &mut thread_rng()));
		let blind_offset = keychain.blind_sum(&BlindSum::new()
			.add_blinding_factor(BlindingFactor::from_secret_key(sec_key.clone()))
			.sub_blinding_factor(self.tx.offset))?;
		*sec_key = blind_offset.secret_key(&keychain.secp())?;
		Ok(())
	}

	/// Checks the fees in the transaction in the given slate are valid
	fn check_fees(&self) -> Result<(), Error> {
		// double check the fee amount included in the partial tx
		// we don't necessarily want to just trust the sender
		// we could just overwrite the fee here (but we won't) due to the sig
		let fee = tx_fee(
			self.tx.inputs.len(),
			self.tx.outputs.len(),
			self.tx.input_proofs_count(),
			None,
		);
		if fee > self.tx.fee() {
			return Err(ErrorKind::Fee(
				format!("Fee Dispute Error: {}, {}", self.tx.fee(), fee,).to_string(),
			))?;
		}

		if fee > self.amount + self.fee {
			let reason = format!(
				"Rejected the transfer because transaction fee ({}) exceeds received amount ({}).",
				amount_to_hr_string(fee),
				amount_to_hr_string(self.amount + self.fee)
			);
			info!(LOGGER, "{}", reason);
			return Err(ErrorKind::Fee(reason.to_string()))?;
		}

		Ok(())
	}

	/// Verifies all of the partial signatures in the Slate are valid
	fn verify_part_sigs(&self, secp: &secp::Secp256k1) -> Result<(), Error> {
		// collect public nonces
		for p in self.participant_data.iter() {
			if p.is_complete() {
				aggsig::verify_partial_sig(
					secp,
					p.part_sig.as_ref().unwrap(),
					&self.pub_nonce_sum(secp)?,
					&p.public_blind_excess,
					self.fee,
					self.lock_height,
				)?;
			}
		}
		Ok(())
	}

	/// This should be callable by either the sender or receiver
	/// once phase 3 is done
	///
	/// Receive Part 3 of interactive transactions from sender, Sender
	/// Confirmation Return Ok/Error
	/// -Receiver receives sS
	/// -Receiver verifies sender's sig, by verifying that
	/// kS * G + e *xS * G = sS* G
	/// -Receiver calculates final sig as s=(sS+sR, kS * G+kR * G)
	/// -Receiver puts into TX kernel:
	///
	/// Signature S
	/// pubkey xR * G+xS * G
	/// fee (= M)
	///
	/// Returns completed transaction ready for posting to the chain

	fn finalize_signature<K>(&mut self, keychain: &K) -> Result<Signature, Error>
	where
		K: Keychain,
	{
		self.verify_part_sigs(keychain.secp())?;

		let part_sigs = self.part_sigs();
		let pub_nonce_sum = self.pub_nonce_sum(keychain.secp())?;
		let final_pubkey = self.pub_blind_sum(keychain.secp())?;
		// get the final signature
		let final_sig = aggsig::add_signatures(&keychain.secp(), part_sigs, &pub_nonce_sum)?;

		// Calculate the final public key (for our own sanity check)

		// Check our final sig verifies
		aggsig::verify_sig_build_msg(
			&keychain.secp(),
			&final_sig,
			&final_pubkey,
			self.fee,
			self.lock_height,
		)?;

		Ok(final_sig)
	}

	/// builds a final transaction after the aggregated sig exchange
	fn finalize_transaction<K>(
		&mut self,
		keychain: &K,
		final_sig: &secp::Signature,
	) -> Result<(), Error>
	where
		K: Keychain,
	{
		let kernel_offset = self.tx.offset;

		self.check_fees()?;

		let mut final_tx = self.tx.clone();

		// build the final excess based on final tx and offset
		let final_excess = {
			// TODO - do we need to verify rangeproofs here?
			for x in &final_tx.outputs {
				x.verify_proof()?;
			}

			// sum the input/output commitments on the final tx
			let overage = final_tx.fee() as i64;
			let tx_excess = final_tx.sum_commitments(overage, None)?;

			// subtract the kernel_excess (built from kernel_offset)
			let offset_excess = keychain
				.secp()
				.commit(0, kernel_offset.secret_key(&keychain.secp())?)?;
			keychain
				.secp()
				.commit_sum(vec![tx_excess], vec![offset_excess])?
		};

		// update the tx kernel to reflect the offset excess and sig
		assert_eq!(final_tx.kernels.len(), 1);
		final_tx.kernels[0].excess = final_excess.clone();
		final_tx.kernels[0].excess_sig = final_sig.clone();

		// confirm the kernel verifies successfully before proceeding
		debug!(LOGGER, "Validating final transaction");
		final_tx.kernels[0].verify()?;

		// confirm the overall transaction is valid (including the updated kernel)
		let _ = final_tx.validate()?;

		self.tx = final_tx;
		Ok(())
	}
}