Add randomness contract support to AuthorityRound. (#10946)

* Add randomness contract support to Authority Round.

Changes have been cherry-picked from poanetwork's aura-pos branch.
Most of the work has been done by @mbr.

* Address review comments for randomness contract.

Co-Authored-By: David <dvdplm@gmail.com>

* Rename revealSecret to revealNumber

* Update Randomness contract bytecode

* Use H256, rename secret to random number.

* Use get_commit_and_cipher

* Clean up Miner::prepare_block.

* Remove is_reveal_phase call.

* Add more comments, require randomness contract map.

* Simplify run_randomness_phase

* Address review comments.

* Remove Client::transact_contract.

Cargo.lock

@@ -172,8 +172,12 @@ dependencies = [
  "block-reward 0.1.0",
  "client-traits 0.1.0",
  "common-types 0.1.0",
+ "derive_more 0.15.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "engine 0.1.0",
  "env_logger 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ethabi 9.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ethabi-contract 9.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ethabi-derive 9.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "ethcore 1.12.0",
  "ethcore-accounts 0.1.0",
  "ethcore-io 1.12.0",
@@ -186,8 +190,10 @@ dependencies = [
  "lru-cache 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "machine 0.1.0",
  "macros 0.1.0",
+ "parity-bytes 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "parity-crypto 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.7.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "rlp 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 1.0.40 (registry+https://github.com/rust-lang/crates.io-index)",
  "spec 0.1.0",

ethcore/Cargo.toml

@@ -73,7 +73,6 @@ blooms-db = { path = "../util/blooms-db" }
 criterion = "0.3"
 engine = { path = "./engine", features = ["test-helpers"] }
 env_logger = "0.5"
-ethash = { path = "../ethash" }
 ethcore-accounts = { path = "../accounts" }
 ethcore-builtin = { path = "./builtin" }
 ethjson = { path = "../json", features = ["test-helpers"] }

ethcore/client-traits/src/lib.rs

@@ -42,7 +42,7 @@ use common_types::{
 	pruning_info::PruningInfo,
 	receipt::LocalizedReceipt,
 	trace_filter::Filter as TraceFilter,
-	transaction::{self, LocalizedTransaction, CallError, SignedTransaction, UnverifiedTransaction},
+	transaction::{self, Action, LocalizedTransaction, CallError, SignedTransaction, UnverifiedTransaction},
 	tree_route::TreeRoute,
 	verification::{VerificationQueueInfo, Unverified},
 };
@@ -395,8 +395,66 @@ pub trait BlockChainClient:
 	/// Returns information about pruning/data availability.
 	fn pruning_info(&self) -> PruningInfo;
 
-	/// Schedule state-altering transaction to be executed on the next pending block.
+	/// Returns a transaction signed with the key configured in the engine signer.
-	fn transact_contract(&self, address: Address, data: Bytes) -> Result<(), transaction::Error>;
+	fn create_transaction(&self, tx_request: TransactionRequest) -> Result<SignedTransaction, transaction::Error>;
+
+	/// Schedule state-altering transaction to be executed on the next pending
+	/// block with the given gas and nonce parameters.
+	fn transact(&self, tx_request: TransactionRequest) -> Result<(), transaction::Error>;
+}
+
+/// The data required for a `Client` to create a transaction.
+///
+/// Gas limit, gas price, or nonce can be set explicitly, e.g. to create service
+/// transactions with zero gas price, or sequences of transactions with consecutive nonces.
+pub struct TransactionRequest {
+	pub action: Action,
+	pub data: Bytes,
+	pub gas: Option<U256>,
+	pub gas_price: Option<U256>,
+	pub nonce: Option<U256>,
+}
+
+impl TransactionRequest {
+	/// Creates a request to call a contract at `address` with the specified call data.
+	pub fn call(address: Address, data: Bytes) -> TransactionRequest {
+		TransactionRequest {
+			action: Action::Call(address),
+			data,
+			gas: None,
+			gas_price: None,
+			nonce: None,
+		}
+	}
+
+	/// Creates a request to create a new contract, with the specified bytecode.
+	pub fn create(data: Bytes) -> TransactionRequest {
+		TransactionRequest {
+			action: Action::Create,
+			data,
+			gas: None,
+			gas_price: None,
+			nonce: None,
+		}
+	}
+
+	/// Sets a gas limit. If this is not specified, a sensible default is used.
+	pub fn gas(mut self, gas: U256) -> TransactionRequest {
+		self.gas = Some(gas);
+		self
+	}
+
+	/// Sets a gas price. If this is not specified, a sensible default is used.
+	pub fn gas_price(mut self, gas_price: U256) -> TransactionRequest {
+		self.gas_price = Some(gas_price);
+		self
+	}
+
+	/// Sets a nonce. If this is not specified, the appropriate latest nonce for the author is used.
+	pub fn nonce(mut self, nonce: U256) -> TransactionRequest {
+		self.nonce = Some(nonce);
+		self
+	}
 }
 
 /// resets the blockchain

ethcore/engine/src/engine.rs

@@ -32,7 +32,7 @@ use common_types::{
 	},
 	errors::{EthcoreError as Error, EngineError},
 	snapshot::Snapshotting,
-	transaction::{self, UnverifiedTransaction},
+	transaction::{self, SignedTransaction, UnverifiedTransaction},
 };
 use client_traits::EngineClient;
 
@@ -185,6 +185,14 @@ pub trait Engine: Sync + Send {
 	/// Allow mutating the header during seal generation. Currently only used by Clique.
 	fn on_seal_block(&self, _block: &mut ExecutedBlock) -> Result<(), Error> { Ok(()) }
 
+	/// Returns a list of transactions for a new block if we are the author.
+	///
+	/// This is called when the miner prepares a new block that this node will author and seal. It returns a list of
+	/// transactions that will be added to the block before any other transactions from the queue.
+	fn generate_engine_transactions(&self, _block: &ExecutedBlock) -> Result<Vec<SignedTransaction>, Error> {
+		Ok(Vec::new())
+	}
+
 	/// Returns the engine's current sealing state.
 	fn sealing_state(&self) -> SealingState { SealingState::External }
 

ethcore/engine/src/signer.rs

@@ -17,7 +17,7 @@
 //! A signer used by Engines which need to sign messages.
 
 use ethereum_types::{H256, Address};
-use parity_crypto::publickey::{Signature, KeyPair, Error};
+use parity_crypto::publickey::{ecies, Public, Signature, KeyPair, Error};
 
 /// Everything that an Engine needs to sign messages.
 pub trait EngineSigner: Send + Sync {
@@ -26,6 +26,12 @@ pub trait EngineSigner: Send + Sync {
 
 	/// Signing address
 	fn address(&self) -> Address;
+
+	/// Decrypt a message that was encrypted to this signer's key.
+	fn decrypt(&self, auth_data: &[u8], cipher: &[u8]) -> Result<Vec<u8>, Error>;
+
+	/// The signer's public key, if available.
+	fn public(&self) -> Option<Public>;
 }
 
 /// Creates a new `EngineSigner` from given key pair.
@@ -40,7 +46,15 @@ impl EngineSigner for Signer {
 		parity_crypto::publickey::sign(self.0.secret(), &hash)
 	}
 
+	fn decrypt(&self, auth_data: &[u8], cipher: &[u8]) -> Result<Vec<u8>, Error> {
+		ecies::decrypt(self.0.secret(), auth_data, cipher)
+	}
+
 	fn address(&self) -> Address {
 		self.0.address()
 	}
+
+	fn public(&self) -> Option<Public> {
+		Some(*self.0.public())
+	}
 }

ethcore/engine/src/test_helpers.rs

@@ -20,7 +20,7 @@ use std::sync::Arc;
 
 use ethereum_types::{Address, H256};
 use ethkey::Password;
-use parity_crypto::publickey::{Signature, Error};
+use parity_crypto::publickey::{Public, Signature, Error};
 use log::warn;
 use accounts::{self, AccountProvider, SignError};
 
@@ -44,7 +44,18 @@ impl EngineSigner for (Arc<AccountProvider>, Address, Password) {
 		}
 	}
 
+	fn decrypt(&self, auth_data: &[u8], cipher: &[u8]) -> Result<Vec<u8>, Error> {
+		self.0.decrypt(self.1, None, auth_data, cipher).map_err(|e| {
+			warn!("Unable to decrypt message: {:?}", e);
+			Error::InvalidMessage
+		})
+	}
+
 	fn address(&self) -> Address {
 		self.1
 	}
+
+	fn public(&self) -> Option<Public> {
+		self.0.account_public(self.1, &self.2).ok()
+	}
 }

ethcore/engines/authority-round/Cargo.toml

@@ -10,6 +10,10 @@ license = "GPL-3.0"
 block-reward = { path = "../../block-reward" }
 client-traits = { path = "../../client-traits" }
 common-types = { path = "../../types" }
+derive_more = "0.15.0"
+ethabi = "9.0.1"
+ethabi-contract = "9.0.0"
+ethabi-derive = "9.0.1"
 ethereum-types = "0.8.0"
 ethjson = { path = "../../../json" }
 parity-crypto = { version = "0.4.2", features = ["publickey"] }
@@ -22,7 +26,9 @@ log = "0.4"
 lru-cache = "0.1"
 machine = { path = "../../machine" }
 macros = { path = "../../../util/macros" }
+parity-bytes = "0.1"
 parking_lot = "0.9"
+rand = "0.7"
 rlp = "0.4.0"
 time-utils = { path = "../../../util/time-utils" }
 unexpected = { path = "../../../util/unexpected" }

ethcore/engines/authority-round/src/lib.rs

@@ -40,7 +40,7 @@ use std::sync::{Weak, Arc};
 use std::time::{UNIX_EPOCH, Duration};
 use std::u64;
 
-use client_traits::{EngineClient, ForceUpdateSealing};
+use client_traits::{EngineClient, ForceUpdateSealing, TransactionRequest};
 use engine::{Engine, ConstructedVerifier};
 use block_reward::{self, BlockRewardContract, RewardKind};
 use ethjson;
@@ -55,6 +55,7 @@ use engine::signer::EngineSigner;
 use parity_crypto::publickey::Signature;
 use io::{IoContext, IoHandler, TimerToken, IoService};
 use itertools::{self, Itertools};
+use rand::rngs::OsRng;
 use rlp::{encode, Decodable, DecoderError, Encodable, RlpStream, Rlp};
 use ethereum_types::{H256, H520, Address, U128, U256};
 use parking_lot::{Mutex, RwLock};
@@ -72,13 +73,17 @@ use common_types::{
 		machine::{Call, AuxiliaryData},
 	},
 	errors::{BlockError, EthcoreError as Error, EngineError},
+	ids::BlockId,
 	snapshot::Snapshotting,
+	transaction::SignedTransaction,
 };
 use unexpected::{Mismatch, OutOfBounds};
 
 use validator_set::{ValidatorSet, SimpleList, new_validator_set};
 
 mod finality;
+mod randomness;
+pub(crate) mod util;
 
 use self::finality::RollingFinality;
 
@@ -117,6 +122,8 @@ pub struct AuthorityRoundParams {
 	pub maximum_empty_steps: usize,
 	/// Transition block to strict empty steps validation.
 	pub strict_empty_steps_transition: u64,
+	/// If set, enables random number contract integration. It maps the transition block to the contract address.
+	pub randomness_contract_address: BTreeMap<u64, Address>,
 }
 
 const U16_MAX: usize = ::std::u16::MAX as usize;
@@ -168,6 +175,11 @@ impl From<ethjson::spec::AuthorityRoundParams> for AuthorityRoundParams {
 				BlockRewardContract::new_from_address(address.into())
 			);
 		}
+		let randomness_contract_address = p.randomness_contract_address.map_or_else(BTreeMap::new, |transitions| {
+			transitions.into_iter().map(|(ethjson::uint::Uint(block), addr)| {
+				(block.as_u64(), addr.into())
+			}).collect()
+		});
 		AuthorityRoundParams {
 			step_durations,
 			validators: new_validator_set(p.validators),
@@ -183,6 +195,7 @@ impl From<ethjson::spec::AuthorityRoundParams> for AuthorityRoundParams {
 			maximum_empty_steps: p.maximum_empty_steps.map_or(0, Into::into),
 			two_thirds_majority_transition: p.two_thirds_majority_transition.map_or_else(BlockNumber::max_value, Into::into),
 			strict_empty_steps_transition: p.strict_empty_steps_transition.map_or(0, Into::into),
+			randomness_contract_address,
 		}
 	}
 }
@@ -550,6 +563,8 @@ pub struct AuthorityRound {
 	machine: Machine,
 	/// History of step hashes recently received from peers.
 	received_step_hashes: RwLock<BTreeMap<(u64, Address), H256>>,
+	/// If set, enables random number contract integration. It maps the transition block to the contract address.
+	randomness_contract_address: BTreeMap<u64, Address>,
 }
 
 // header-chain validator.
@@ -851,6 +866,7 @@ impl AuthorityRound {
 				strict_empty_steps_transition: our_params.strict_empty_steps_transition,
 				machine,
 				received_step_hashes: RwLock::new(Default::default()),
+				randomness_contract_address: our_params.randomness_contract_address,
 			});
 
 		// Do not initialize timeouts for tests.
@@ -1045,6 +1061,41 @@ impl AuthorityRound {
 	fn address(&self) -> Option<Address> {
 		self.signer.read().as_ref().map(|s| s.address() )
 	}
+
+	/// Make calls to the randomness contract.
+	fn run_randomness_phase(&self, block: &ExecutedBlock) -> Result<Vec<SignedTransaction>, Error> {
+		let contract_addr = match self.randomness_contract_address.range(..=block.header.number()).last() {
+			Some((_, &contract_addr)) => contract_addr,
+			None => return Ok(Vec::new()), // No randomness contract.
+		};
+
+		let opt_signer = self.signer.read();
+		let signer = match opt_signer.as_ref() {
+			Some(signer) => signer,
+			None => return Ok(Vec::new()), // We are not a validator, so we shouldn't call the contracts.
+		};
+		let our_addr = signer.address();
+		let client = self.client.read().as_ref().and_then(|weak| weak.upgrade()).ok_or_else(|| {
+			debug!(target: "engine", "Unable to prepare block: missing client ref.");
+			EngineError::RequiresClient
+		})?;
+		let full_client = client.as_full_client()
+			.ok_or_else(|| EngineError::FailedSystemCall("Failed to upgrade to BlockchainClient.".to_string()))?;
+
+		// Random number generation
+		let contract = util::BoundContract::new(&*client, BlockId::Latest, contract_addr);
+		let phase = randomness::RandomnessPhase::load(&contract, our_addr)
+			.map_err(|err| EngineError::Custom(format!("Randomness error in load(): {:?}", err)))?;
+		let data = match phase.advance(&contract, &mut OsRng, signer.as_ref())
+				.map_err(|err| EngineError::Custom(format!("Randomness error in advance(): {:?}", err)))? {
+			Some(data) => data,
+			None => return Ok(Vec::new()), // Nothing to commit or reveal at the moment.
+		};
+
+		let nonce = block.state.nonce(&our_addr)?;
+		let tx_request = TransactionRequest::call(contract_addr, data).gas_price(U256::zero()).nonce(nonce);
+		Ok(vec![full_client.create_transaction(tx_request)?])
+	}
 }
 
 fn unix_now() -> Duration {
@@ -1326,7 +1377,6 @@ impl Engine for AuthorityRound {
 					// report any skipped primaries between the parent block and
 					// the block we're sealing, unless we have empty steps enabled
 					if header.number() < self.empty_steps_transition {
-						trace!(target: "engine", "generate_seal: reporting misbehaviour for step={}, block=#{}", step, header.number());
 						self.report_skipped(header, step, parent_step, &*validators, epoch_transition_number);
 					}
 
@@ -1430,6 +1480,10 @@ impl Engine for AuthorityRound {
 		block_reward::apply_block_rewards(&rewards, block, &self.machine)
 	}
 
+	fn generate_engine_transactions(&self, block: &ExecutedBlock) -> Result<Vec<SignedTransaction>, Error> {
+		self.run_randomness_phase(block)
+	}
+
 	/// Check the number of seal fields.
 	fn verify_block_basic(&self, header: &Header) -> Result<(), Error> {
 		if header.number() >= self.validate_score_transition && *header.difficulty() >= U256::from(U128::max_value()) {
@@ -1805,19 +1859,22 @@ mod tests {
 	use std::time::Duration;
 	use keccak_hash::keccak;
 	use accounts::AccountProvider;
+	use ethabi_contract::use_contract;
 	use ethereum_types::{Address, H520, H256, U256};
 	use parity_crypto::publickey::Signature;
 	use common_types::{
 		header::Header,
 		engines::{Seal, params::CommonParams},
+		ids::BlockId,
 		errors::{EthcoreError as Error, EngineError},
 		transaction::{Action, Transaction},
 	};
 	use rlp::encode;
 	use ethcore::{
 		block::*,
+		miner::{Author, MinerService},
 		test_helpers::{
-			generate_dummy_client_with_spec, get_temp_state_db,
+			generate_dummy_client_with_spec, generate_dummy_client_with_spec_and_data, get_temp_state_db,
 			TestNotify
 		},
 	};
@@ -1831,7 +1888,7 @@ mod tests {
 
 	use super::{
 		AuthorityRoundParams, AuthorityRound, EmptyStep, SealedEmptyStep, StepDurationInfo,
-		calculate_score,
+		calculate_score, util::BoundContract,
 	};
 
 	fn build_aura<F>(f: F) -> Arc<AuthorityRound> where
@@ -1852,6 +1909,7 @@ mod tests {
 			block_reward_contract_transitions: Default::default(),
 			strict_empty_steps_transition: 0,
 			two_thirds_majority_transition: 0,
+			randomness_contract_address: BTreeMap::new(),
 		};
 
 		// mutate aura params
@@ -2578,6 +2636,54 @@ mod tests {
 		)
 	}
 
+	#[test]
+	fn randomness_contract() -> Result<(), super::util::CallError> {
+		use_contract!(rand_contract, "../../res/contracts/test_authority_round_random.json");
+
+		env_logger::init();
+
+		let contract_addr = Address::from_str("0000000000000000000000000000000000000042").unwrap();
+		let client = generate_dummy_client_with_spec_and_data(
+			spec::new_test_round_randomness_contract, 0, 0, &[], true
+		);
+
+		let tap = Arc::new(AccountProvider::transient_provider());
+
+		let addr1 = tap.insert_account(keccak("1").into(), &"1".into()).unwrap();
+		// Unlock account so that the engine can decrypt the secret.
+		tap.unlock_account_permanently(addr1, "1".into()).expect("unlock");
+
+		let signer = Box::new((tap.clone(), addr1, "1".into()));
+		client.miner().set_author(Author::Sealer(signer.clone()));
+		client.miner().set_gas_range_target((U256::from(1000000), U256::from(1000000)));
+
+		let engine = client.engine();
+		engine.set_signer(Some(signer));
+		engine.register_client(Arc::downgrade(&client) as _);
+		let bc = BoundContract::new(&*client, BlockId::Latest, contract_addr);
+
+		// First the contract is in the commit phase, and we haven't committed yet.
+		assert!(bc.call_const(rand_contract::functions::is_commit_phase::call())?);
+		assert!(!bc.call_const(rand_contract::functions::is_committed::call(0, addr1))?);
+
+		// We produce a block and commit.
+		engine.step();
+		assert!(bc.call_const(rand_contract::functions::is_committed::call(0, addr1))?);
+
+		// After two more blocks we are in the reveal phase...
+		engine.step();
+		engine.step();
+		assert!(bc.call_const(rand_contract::functions::is_reveal_phase::call())?);
+		assert!(!bc.call_const(rand_contract::functions::sent_reveal::call(0, addr1))?);
+		assert!(bc.call_const(rand_contract::functions::get_value::call())?.is_zero());
+
+		// ...so in the next step, we reveal our random value, and the contract's random value is not zero anymore.
+		engine.step();
+		assert!(bc.call_const(rand_contract::functions::sent_reveal::call(0, addr1))?);
+		assert!(!bc.call_const(rand_contract::functions::get_value::call())?.is_zero());
+		Ok(())
+	}
+
 	#[test]
 	fn extra_info_from_seal() {
 		let (spec, tap, accounts) = setup_empty_steps();

ethcore/engines/authority-round/src/randomness.rs

@@ -0,0 +1,257 @@
+// 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/>.
+
+//! On-chain randomness generation for authority round
+//!
+//! This module contains the support code for the on-chain randomness generation used by AuRa. Its
+//! core is the finite state machine `RandomnessPhase`, which can be loaded from the blockchain
+//! state, then asked to perform potentially necessary transaction afterwards using the `advance()`
+//! method.
+//!
+//! No additional state is kept inside the `RandomnessPhase`, it must be passed in each time.
+//!
+//! The process of generating random numbers is a simple finite state machine:
+//!
+//! ```text
+//!                                                       +
+//!                                                       |
+//!                                                       |
+//!                                                       |
+//! +--------------+                              +-------v-------+
+//! |              |                              |               |
+//! | BeforeCommit <------------------------------+    Waiting    |
+//! |              |          enter commit phase  |               |
+//! +------+-------+                              +-------^-------+
+//!        |                                              |
+//!        |  call                                        |
+//!        |  `commitHash()`                              |  call
+//!        |                                              |  `revealNumber()`
+//!        |                                              |
+//! +------v-------+                              +-------+-------+
+//! |              |                              |               |
+//! |  Committed   +------------------------------>    Reveal     |
+//! |              |  enter reveal phase          |               |
+//! +--------------+                              +---------------+
+//! ```
+//!
+//! Phase transitions are performed by the smart contract and simply queried by the engine.
+//!
+//! Randomness generation works as follows:
+//! * During the commit phase, all validators locally generate a random number, and commit that number's hash to the
+//!   contract.
+//! * During the reveal phase, all validators reveal their local random number to the contract. The contract should
+//!   verify that it matches the committed hash.
+//! * Finally, the XOR of all revealed numbers is used as an on-chain random number.
+//!
+//! An adversary can only influence that number by either controlling _all_ validators who committed, or, to a lesser
+//! extent, by not revealing committed numbers.
+//! The length of the commit and reveal phases, as well as any penalties for failure to reveal, are defined by the
+//! contract.
+//!
+//! A typical case of using `RandomnessPhase` is:
+//!
+//! 1. `RandomnessPhase::load()` the phase from the blockchain data.
+//! 2. Call `RandomnessPhase::advance()`.
+//!
+//! A production implementation of a randomness contract can be found here:
+//! https://github.com/poanetwork/posdao-contracts/blob/4fddb108993d4962951717b49222327f3d94275b/contracts/RandomAuRa.sol
+
+use derive_more::Display;
+use ethabi::Hash;
+use ethabi_contract::use_contract;
+use ethereum_types::{Address, H256, U256};
+use keccak_hash::keccak;
+use log::{debug, error};
+use parity_crypto::publickey::{ecies, Error as CryptoError};
+use parity_bytes::Bytes;
+use rand::Rng;
+use engine::signer::EngineSigner;
+
+use crate::util::{BoundContract, CallError};
+
+/// Random number type expected by the contract: This is generated locally, kept secret during the commit phase, and
+/// published in the reveal phase.
+pub type RandNumber = H256;
+
+use_contract!(aura_random, "../../res/contracts/authority_round_random.json");
+
+/// Validated randomness phase state.
+#[derive(Debug)]
+pub enum RandomnessPhase {
+	// NOTE: Some states include information already gathered during `load` (e.g. `our_address`,
+	//       `round`) for efficiency reasons.
+	/// Waiting for the next phase.
+	///
+	/// This state indicates either the successful revelation in this round or having missed the
+	/// window to make a commitment, i.e. having failed to commit during the commit phase.
+	Waiting,
+	/// Indicates a commitment is possible, but still missing.
+	BeforeCommit,
+	/// Indicates a successful commitment, waiting for the commit phase to end.
+	Committed,
+	/// Indicates revealing is expected as the next step.
+	Reveal { our_address: Address, round: U256 },
+}
+
+/// Phase loading error for randomness generation state machine.
+///
+/// This error usually indicates a bug in either the smart contract, the phase loading function or
+/// some state being lost.
+///
+/// `BadRandNumber` will usually result in punishment by the contract or the other validators.
+#[derive(Debug, Display)]
+pub enum PhaseError {
+	/// The smart contract reported that we already revealed something while still being in the
+	/// commit phase.
+	#[display(fmt = "Revealed during commit phase")]
+	RevealedInCommit,
+	/// Failed to load contract information.
+	#[display(fmt = "Error loading randomness contract information: {:?}", _0)]
+	LoadFailed(CallError),
+	/// Failed to load the stored encrypted random number.
+	#[display(fmt = "Failed to load random number from the randomness contract")]
+	BadRandNumber,
+	/// Failed to encrypt random number.
+	#[display(fmt = "Failed to encrypt random number: {}", _0)]
+	Crypto(CryptoError),
+	/// Failed to get the engine signer's public key.
+	#[display(fmt = "Failed to get the engine signer's public key")]
+	MissingPublicKey,
+}
+
+impl From<CryptoError> for PhaseError {
+	fn from(err: CryptoError) -> PhaseError {
+		PhaseError::Crypto(err)
+	}
+}
+
+impl RandomnessPhase {
+	/// Determine randomness generation state from the contract.
+	///
+	/// Calls various constant contract functions to determine the precise state that needs to be
+	/// handled (that is, the phase and whether or not the current validator still needs to send
+	/// commitments or reveal random numbers).
+	pub fn load(
+		contract: &BoundContract,
+		our_address: Address,
+	) -> Result<RandomnessPhase, PhaseError> {
+		// Determine the current round and which phase we are in.
+		let round = contract
+			.call_const(aura_random::functions::current_collect_round::call())
+			.map_err(PhaseError::LoadFailed)?;
+		let is_commit_phase = contract
+			.call_const(aura_random::functions::is_commit_phase::call())
+			.map_err(PhaseError::LoadFailed)?;
+
+		// Ensure we are not committing or revealing twice.
+		let committed = contract
+			.call_const(aura_random::functions::is_committed::call(
+				round,
+				our_address,
+			))
+			.map_err(PhaseError::LoadFailed)?;
+		let revealed: bool = contract
+			.call_const(aura_random::functions::sent_reveal::call(
+				round,
+				our_address,
+			))
+			.map_err(PhaseError::LoadFailed)?;
+
+		// With all the information known, we can determine the actual state we are in.
+		if is_commit_phase {
+			if revealed {
+				return Err(PhaseError::RevealedInCommit);
+			}
+
+			if !committed {
+				Ok(RandomnessPhase::BeforeCommit)
+			} else {
+				Ok(RandomnessPhase::Committed)
+			}
+		} else {
+			if !committed {
+				// We apparently entered too late to make a commitment, wait until we get a chance again.
+				return Ok(RandomnessPhase::Waiting);
+			}
+
+			if !revealed {
+				Ok(RandomnessPhase::Reveal { our_address, round })
+			} else {
+				Ok(RandomnessPhase::Waiting)
+			}
+		}
+	}
+
+	/// Advance the random seed construction process as far as possible.
+	///
+	/// Returns the encoded contract call necessary to advance the randomness contract's state.
+	///
+	/// **Warning**: After calling the `advance()` function, wait until the returned transaction has been included in
+	/// a block before calling it again; otherwise spurious transactions resulting in punishments might be executed.
+	pub fn advance<R: Rng>(
+		self,
+		contract: &BoundContract,
+		rng: &mut R,
+		signer: &dyn EngineSigner,
+	) -> Result<Option<Bytes>, PhaseError> {
+		match self {
+			RandomnessPhase::Waiting | RandomnessPhase::Committed => Ok(None),
+			RandomnessPhase::BeforeCommit => {
+				// Generate a new random number, but don't reveal it yet. Instead, we publish its hash to the
+				// randomness contract, together with the number encrypted to ourselves. That way we will later be
+				// able to decrypt and reveal it, and other parties are able to verify it against the hash.
+				let number: RandNumber = rng.gen();
+				let number_hash: Hash = keccak(number.as_bytes());
+				let public = signer.public().ok_or(PhaseError::MissingPublicKey)?;
+				let cipher = ecies::encrypt(&public, &number_hash.0, number.as_bytes())?;
+
+				debug!(target: "engine", "Randomness contract: committing {}.", number_hash);
+				// Return the call data for the transaction that commits the hash and the encrypted number.
+				let (data, _decoder) = aura_random::functions::commit_hash::call(number_hash, cipher);
+				Ok(Some(data))
+			}
+			RandomnessPhase::Reveal { round, our_address } => {
+				// Load the hash and encrypted number that we stored in the commit phase.
+				let call = aura_random::functions::get_commit_and_cipher::call(round, our_address);
+				let (committed_hash, cipher) = contract
+					.call_const(call)
+					.map_err(PhaseError::LoadFailed)?;
+
+				// Decrypt the number and check against the hash.
+				let number_bytes = signer.decrypt(&committed_hash.0, &cipher)?;
+				let number = if number_bytes.len() == 32 {
+					RandNumber::from_slice(&number_bytes)
+				} else {
+					// This can only happen if there is a bug in the smart contract,
+					// or if the entire network goes awry.
+					error!(target: "engine", "Decrypted random number has the wrong length.");
+					return Err(PhaseError::BadRandNumber);
+				};
+				let number_hash: Hash = keccak(number.as_bytes());
+				if number_hash != committed_hash {
+					error!(target: "engine", "Decrypted random number doesn't agree with the hash.");
+					return Err(PhaseError::BadRandNumber);
+				}
+
+				debug!(target: "engine", "Randomness contract: scheduling tx to reveal our random number {} (round={}, our_address={}).", number_hash, round, our_address);
+				// We are now sure that we have the correct secret and can reveal it. So we return the call data for the
+				// transaction that stores the revealed random bytes on the contract.
+				let (data, _decoder) = aura_random::functions::reveal_number::call(number.as_bytes());
+				Ok(Some(data))
+			}
+		}
+	}
+}

ethcore/engines/authority-round/src/util.rs

@@ -0,0 +1,94 @@
+// 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/>.
+
+//! Utility functions.
+//!
+//! Contains small functions used by the AuRa engine that are not strictly limited to that scope.
+
+use std::fmt;
+
+use client_traits::EngineClient;
+use common_types::ids::BlockId;
+use ethabi;
+use ethereum_types::Address;
+
+/// A contract bound to a client and block number.
+///
+/// A bound contract is a combination of a `Client` reference, a `BlockId` and a contract `Address`.
+/// These three parts are enough to call a contract's function; return values are automatically
+/// decoded.
+pub struct BoundContract<'a> {
+	client: &'a dyn EngineClient,
+	block_id: BlockId,
+	contract_addr: Address,
+}
+
+/// Contract call failed error.
+#[derive(Debug)]
+pub enum CallError {
+	/// The call itself failed.
+	CallFailed(String),
+	/// Decoding the return value failed or the decoded value was a failure.
+	DecodeFailed(ethabi::Error),
+	/// The passed in client reference could not be upgraded to a `BlockchainClient`.
+	NotFullClient,
+}
+
+impl<'a> fmt::Debug for BoundContract<'a> {
+	fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+		fmt.debug_struct("BoundContract")
+			.field("client", &(self.client as *const dyn EngineClient))
+			.field("block_id", &self.block_id)
+			.field("contract_addr", &self.contract_addr)
+			.finish()
+	}
+}
+
+impl<'a> BoundContract<'a> {
+	/// Create a new `BoundContract`.
+	pub fn new(client: &dyn EngineClient, block_id: BlockId, contract_addr: Address) -> BoundContract {
+		BoundContract {
+			client,
+			block_id,
+			contract_addr,
+		}
+	}
+
+	/// Perform a function call to an Ethereum machine that doesn't create a transaction or change the state.
+	///
+	/// Runs a constant function call on `client`. The `call` value can be serialized by calling any
+	/// api function generated by the `use_contract!` macro. This does not create any transactions, it only produces a
+	/// result based on the state at the current block: It is constant in the sense that it does not alter the EVM
+	/// state.
+	pub fn call_const<D>(&self, call: (ethabi::Bytes, D)) -> Result<D::Output, CallError>
+	where
+		D: ethabi::FunctionOutputDecoder,
+	{
+		let (data, output_decoder) = call;
+
+		let call_return = self
+			.client
+			.as_full_client()
+			.ok_or(CallError::NotFullClient)?
+			.call_contract(self.block_id, self.contract_addr, data)
+			.map_err(CallError::CallFailed)?;
+
+		// Decode the result and return it.
+		output_decoder
+			.decode(call_return.as_slice())
+			.map_err(CallError::DecodeFailed)
+	}
+}

ethcore/engines/validator-set/src/contract.rs

@@ -33,7 +33,7 @@ use common_types::{
 	engines::machine::{Call, AuxiliaryData},
 };
 
-use client_traits::EngineClient;
+use client_traits::{EngineClient, TransactionRequest};
 use engine::SystemCall;
 
 use crate::{
@@ -68,7 +68,7 @@ impl ValidatorContract {
 
 		match client.as_full_client() {
 			Some(c) => {
-				c.transact_contract(self.contract_address, data)
+				c.transact(TransactionRequest::call(self.contract_address, data))
 					.map_err(|e| format!("Transaction import error: {}", e))?;
 				Ok(())
 			},
@@ -149,7 +149,7 @@ mod tests {
 	use accounts::AccountProvider;
 	use call_contract::CallContract;
 	use common_types::{header::Header, ids::BlockId};
-	use client_traits::{BlockChainClient, ChainInfo, BlockInfo};
+	use client_traits::{BlockChainClient, ChainInfo, BlockInfo, TransactionRequest};
 	use ethcore::{
 		miner::{self, MinerService},
 		test_helpers::generate_dummy_client_with_spec,
@@ -225,7 +225,7 @@ mod tests {
 		assert_eq!(client.chain_info().best_block_number, 2);
 
 		// Check if misbehaving validator was removed.
-		client.transact_contract(Default::default(), Default::default()).unwrap();
+		client.transact(TransactionRequest::call(Default::default(), Default::default())).unwrap();
 		client.engine().step();
 		client.engine().step();
 		assert_eq!(client.chain_info().best_block_number, 2);

ethcore/engines/validator-set/src/multi.rs

@@ -161,11 +161,13 @@ mod tests {
 		ids::BlockId,
 		verification::Unverified,
 	};
-	use client_traits::{BlockChainClient, BlockInfo, ChainInfo, ImportBlock, EngineClient, ForceUpdateSealing};
+	use client_traits::{
+		BlockChainClient, BlockInfo, ChainInfo, ImportBlock, EngineClient, ForceUpdateSealing, TransactionRequest
+	};
 	use engine::EpochChange;
 	use ethcore::{
 		miner::{self, MinerService},
-		test_helpers::{generate_dummy_client_with_spec, generate_dummy_client_with_spec_and_data},
+		test_helpers::generate_dummy_client_with_spec,
 	};
 	use ethereum_types::Address;
 	use parity_crypto::publickey::Secret;
@@ -190,7 +192,7 @@ mod tests {
 		// Wrong signer for the first block.
 		let signer = Box::new((tap.clone(), v1, "".into()));
 		client.miner().set_author(miner::Author::Sealer(signer));
-		client.transact_contract(Default::default(), Default::default()).unwrap();
+		client.transact(TransactionRequest::call(Default::default(), Default::default())).unwrap();
 		EngineClient::update_sealing(&*client, ForceUpdateSealing::No);
 		assert_eq!(client.chain_info().best_block_number, 0);
 		// Right signer for the first block.
@@ -199,7 +201,7 @@ mod tests {
 		EngineClient::update_sealing(&*client, ForceUpdateSealing::No);
 		assert_eq!(client.chain_info().best_block_number, 1);
 		// This time v0 is wrong.
-		client.transact_contract(Default::default(), Default::default()).unwrap();
+		client.transact(TransactionRequest::call(Default::default(), Default::default())).unwrap();
 		EngineClient::update_sealing(&*client, ForceUpdateSealing::No);
 		assert_eq!(client.chain_info().best_block_number, 1);
 		let signer = Box::new((tap.clone(), v1, "".into()));
@@ -207,12 +209,12 @@ mod tests {
 		EngineClient::update_sealing(&*client, ForceUpdateSealing::No);
 		assert_eq!(client.chain_info().best_block_number, 2);
 		// v1 is still good.
-		client.transact_contract(Default::default(), Default::default()).unwrap();
+		client.transact(TransactionRequest::call(Default::default(), Default::default())).unwrap();
 		EngineClient::update_sealing(&*client, ForceUpdateSealing::No);
 		assert_eq!(client.chain_info().best_block_number, 3);
 
 		// Check syncing.
-		let sync_client = generate_dummy_client_with_spec_and_data(spec::new_validator_multi, 0, 0, &[]);
+		let sync_client = generate_dummy_client_with_spec(spec::new_validator_multi);
 		sync_client.engine().register_client(Arc::downgrade(&sync_client) as _);
 		for i in 1..4 {
 			sync_client.import_block(Unverified::from_rlp(client.block(BlockId::Number(i)).unwrap().into_inner()).unwrap()).unwrap();

ethcore/engines/validator-set/src/safe_contract.rs

@@ -468,7 +468,7 @@ mod tests {
 	use engine::{EpochChange, Proof};
 	use ethcore::{
 		miner::{self, MinerService},
-		test_helpers::{generate_dummy_client_with_spec, generate_dummy_client_with_spec_and_data}
+		test_helpers::generate_dummy_client_with_spec
 	};
 	use parity_crypto::publickey::Secret;
 	use ethereum_types::Address;
@@ -551,7 +551,7 @@ mod tests {
 		assert_eq!(client.chain_info().best_block_number, 3);
 
 		// Check syncing.
-		let sync_client = generate_dummy_client_with_spec_and_data(spec::new_validator_safe_contract, 0, 0, &[]);
+		let sync_client = generate_dummy_client_with_spec(spec::new_validator_safe_contract);
 		sync_client.engine().register_client(Arc::downgrade(&sync_client) as _);
 		for i in 1..4 {
 			sync_client.import_block(Unverified::from_rlp(client.block(BlockId::Number(i)).unwrap().into_inner()).unwrap()).unwrap();

ethcore/res/authority_round_randomness_contract.json

@@ -0,0 +1,100 @@
+{
+	"name": "TestAuthorityRoundRandomnessContract",
+	"engine": {
+		"authorityRound": {
+			"params": {
+				"stepDuration": 1,
+				"startStep": 2,
+				"validators": {
+					"list": [
+						"0x7d577a597b2742b498cb5cf0c26cdcd726d39e6e"
+					]
+				},
+				"immediateTransitions": true,
+				"maximumEmptySteps": "2",
+				"randomnessContractAddress": {
+					"0": "0x0000000000000000000000000000000000000042"
+				}
+			}
+		}
+	},
+	"params": {
+		"gasLimitBoundDivisor": "0x0400",
+		"accountStartNonce": "0x0",
+		"maximumExtraDataSize": "0x20",
+		"minGasLimit": "0x1388",
+		"networkID" : "0x69",
+		"eip140Transition": "0x0",
+		"eip211Transition": "0x0",
+		"eip214Transition": "0x0",
+		"eip658Transition": "0x0"
+	},
+	"genesis": {
+		"seal": {
+			"authorityRound": {
+				"step": "0x0",
+				"signature": "0x0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+			}
+		},
+		"difficulty": "0x20000",
+		"author": "0x0000000000000000000000000000000000000000",
+		"timestamp": "0x00",
+		"parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
+		"extraData": "0x",
+		"gasLimit": "0x222222"
+	},
+	"accounts": {
+		"0x7d577a597b2742b498cb5cf0c26cdcd726d39e6e": { "balance": "100000000000" },
+		"0000000000000000000000000000000000000001": { "balance": "1", "nonce": "1048576", "builtin": { "name": "ecrecover", "pricing": { "linear": { "base": 3000, "word": 0 } } } },
+		"0000000000000000000000000000000000000002": { "balance": "1", "nonce": "1048576", "builtin": { "name": "sha256", "pricing": { "linear": { "base": 60, "word": 12 } } } },
+		"0000000000000000000000000000000000000003": { "balance": "1", "nonce": "1048576", "builtin": { "name": "ripemd160", "pricing": { "linear": { "base": 600, "word": 120 } } } },
+		"0000000000000000000000000000000000000004": { "balance": "1", "nonce": "1048576", "builtin": { "name": "identity", "pricing": { "linear": { "base": 15, "word": 3 } } } },
+		"0000000000000000000000000000000000000005": { "balance": "1", "builtin": { "name": "modexp", "activate_at": 0, "pricing": { "modexp": { "divisor": 20 } } } },
+		"0000000000000000000000000000000000000006": {
+			"balance": "1",
+			"builtin": {
+				"name": "alt_bn128_add",
+				"pricing": {
+					"0x0": {
+						"price": { "linear": { "base": 500, "word": 0 }}
+					},
+					"0x7fffffffffffff": {
+						"price": { "linear": { "base": 150, "word": 0 }}
+					}
+				}
+			}
+		},
+		"0000000000000000000000000000000000000007": {
+			"balance": "1",
+			"builtin": {
+				"name": "alt_bn128_mul",
+				"pricing": {
+					"0x0": {
+						"price": { "linear": { "base": 40000, "word": 0 }}
+					},
+					"0x7fffffffffffff": {
+						"price": { "linear": { "base": 6000, "word": 0 }}
+					}
+				}
+			}
+		},
+		"0000000000000000000000000000000000000008": {
+			"balance": "1",
+			"builtin": {
+				"name": "alt_bn128_pairing",
+				"pricing": {
+					"0x0": {
+						"price": { "alt_bn128_pairing": { "base": 100000, "pair": 80000 }}
+					},
+					"0x7fffffffffffff": {
+						"price": { "alt_bn128_pairing": { "base": 45000, "pair": 34000 }}
+					}
+				}
+			}
+		},
+		"0000000000000000000000000000000000000042": {
+			"balance": "1",
+			"constructor": "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"
+		}
+	}
+}

ethcore/res/contracts/authority_round_random.json

@@ -0,0 +1,133 @@
+[{
+		"constant": false,
+		"inputs": [{
+				"name": "_secretHash",
+				"type": "bytes32"
+			},
+			{
+				"name": "_cipher",
+				"type": "bytes"
+			}
+		],
+		"name": "commitHash",
+		"outputs": [],
+		"payable": false,
+		"stateMutability": "nonpayable",
+		"type": "function"
+	},
+	{
+		"constant": false,
+		"inputs": [{
+			"name": "_number",
+			"type": "uint256"
+		}],
+		"name": "revealNumber",
+		"outputs": [],
+		"payable": false,
+		"stateMutability": "nonpayable",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [],
+		"name": "currentCollectRound",
+		"outputs": [{
+			"name": "",
+			"type": "uint256"
+		}],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [
+			{
+				"name": "_collectRound",
+				"type": "uint256"
+			},
+			{
+				"name": "_miningAddress",
+				"type": "address"
+			}
+		],
+		"name": "getCommitAndCipher",
+		"outputs": [
+			{
+				"name": "",
+				"type": "bytes32"
+			},
+			{
+				"name": "",
+				"type": "bytes"
+			}
+		],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [{
+				"name": "_collectRound",
+				"type": "uint256"
+			},
+			{
+				"name": "_validator",
+				"type": "address"
+			}
+		],
+		"name": "isCommitted",
+		"outputs": [{
+			"name": "",
+			"type": "bool"
+		}],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [],
+		"name": "isCommitPhase",
+		"outputs": [{
+			"name": "",
+			"type": "bool"
+		}],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [],
+		"name": "isRevealPhase",
+		"outputs": [{
+			"name": "",
+			"type": "bool"
+		}],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [{
+				"name": "_collectRound",
+				"type": "uint256"
+			},
+			{
+				"name": "_validator",
+				"type": "address"
+			}
+		],
+		"name": "sentReveal",
+		"outputs": [{
+			"name": "",
+			"type": "bool"
+		}],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	}
+]

ethcore/res/contracts/test_authority_round_random.json

@@ -0,0 +1,265 @@
+[
+	{
+		"constant": true,
+		"inputs": [
+			{
+				"name": "",
+				"type": "uint256"
+			},
+			{
+				"name": "",
+				"type": "address"
+			}
+		],
+		"name": "ciphers",
+		"outputs": [
+			{
+				"name": "",
+				"type": "bytes"
+			}
+		],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [
+			{
+				"name": "_collectRound",
+				"type": "uint256"
+			},
+			{
+				"name": "_miningAddress",
+				"type": "address"
+			}
+		],
+		"name": "getCipher",
+		"outputs": [
+			{
+				"name": "",
+				"type": "bytes"
+			}
+		],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": false,
+		"inputs": [
+			{
+				"name": "_secretHash",
+				"type": "bytes32"
+			},
+			{
+				"name": "_cipher",
+				"type": "bytes"
+			}
+		],
+		"name": "commitHash",
+		"outputs": [],
+		"payable": false,
+		"stateMutability": "nonpayable",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [],
+		"name": "getValue",
+		"outputs": [
+			{
+				"name": "",
+				"type": "uint256"
+			}
+		],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [
+			{
+				"name": "",
+				"type": "uint256"
+			},
+			{
+				"name": "",
+				"type": "address"
+			}
+		],
+		"name": "hashes",
+		"outputs": [
+			{
+				"name": "",
+				"type": "bytes32"
+			}
+		],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [],
+		"name": "value",
+		"outputs": [
+			{
+				"name": "",
+				"type": "uint256"
+			}
+		],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [
+			{
+				"name": "",
+				"type": "uint256"
+			},
+			{
+				"name": "",
+				"type": "address"
+			}
+		],
+		"name": "secrets",
+		"outputs": [
+			{
+				"name": "",
+				"type": "uint256"
+			}
+		],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [
+			{
+				"name": "_collectRound",
+				"type": "uint256"
+			},
+			{
+				"name": "_miningAddress",
+				"type": "address"
+			}
+		],
+		"name": "sentReveal",
+		"outputs": [
+			{
+				"name": "",
+				"type": "bool"
+			}
+		],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [],
+		"name": "isCommitPhase",
+		"outputs": [
+			{
+				"name": "",
+				"type": "bool"
+			}
+		],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": false,
+		"inputs": [
+			{
+				"name": "_number",
+				"type": "uint256"
+			}
+		],
+		"name": "revealNumber",
+		"outputs": [],
+		"payable": false,
+		"stateMutability": "nonpayable",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [],
+		"name": "getRound",
+		"outputs": [
+			{
+				"name": "",
+				"type": "uint256"
+			}
+		],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [
+			{
+				"name": "_collectRound",
+				"type": "uint256"
+			},
+			{
+				"name": "_miningAddress",
+				"type": "address"
+			}
+		],
+		"name": "isCommitted",
+		"outputs": [
+			{
+				"name": "",
+				"type": "bool"
+			}
+		],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [],
+		"name": "isRevealPhase",
+		"outputs": [
+			{
+				"name": "",
+				"type": "bool"
+			}
+		],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	},
+	{
+		"constant": true,
+		"inputs": [
+			{
+				"name": "_collectRound",
+				"type": "uint256"
+			},
+			{
+				"name": "_miningAddress",
+				"type": "address"
+			}
+		],
+		"name": "getCommit",
+		"outputs": [
+			{
+				"name": "",
+				"type": "bytes32"
+			}
+		],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	}
+]

ethcore/res/contracts/test_authority_round_random.sol

@@ -0,0 +1,102 @@
+pragma solidity 0.5.10;
+
+/// @dev Randomness test contract based on https://github.com/poanetwork/posdao-contracts.
+/// Generates and stores random numbers in a RANDAO manner and accumulates a random seed.
+contract Random {
+    mapping(uint256 => mapping(address => bytes32)) public hashes;
+    mapping(uint256 => mapping(address => bytes)) public ciphers;
+    mapping(uint256 => mapping(address => uint256)) public secrets;
+    uint256 public value;
+
+    /// @dev Called by the validator's node to store a hash and a cipher of the validator's secret on each collection
+    /// round. The validator's node must use its mining address to call this function.
+    /// This function can only be called once per collection round (during the `commits phase`).
+    /// @param _secretHash The Keccak-256 hash of the validator's secret.
+    /// @param _cipher The cipher of the validator's secret. Can be used by the node to decrypt and reveal.
+    function commitHash(bytes32 _secretHash, bytes calldata _cipher) external {
+        require(block.coinbase == msg.sender);
+        require(_isCommitPhase(block.number - 1));
+        uint256 round = _collectRound(block.number - 1);
+        require(!isCommitted(round, msg.sender));
+        hashes[round][msg.sender] = _secretHash;
+        ciphers[round][msg.sender] = _cipher;
+    }
+
+    /// @dev Called by the validator's node to XOR its secret with the current random seed.
+    /// The validator's node must use its mining address to call this function.
+    /// This function can only be called once per collection round (during the `reveals phase`).
+    /// @param _number The validator's secret.
+    function revealNumber(uint256 _number) external {
+        require(block.coinbase == msg.sender);
+        require(_isRevealPhase(block.number - 1));
+        uint256 round = _collectRound(block.number - 1);
+        require(!sentReveal(round, msg.sender));
+        require(hashes[round][msg.sender] == keccak256(abi.encodePacked(_number)));
+        secrets[round][msg.sender] = _number;
+        value ^= _number;
+    }
+
+	/// @dev Returns the Keccak-256 hash and cipher of the validator's secret for the specified collection round
+    /// and the specified validator stored by the validator through the `commitHash` function.
+    /// @param _collectRound The serial number of the collection round for which hash and cipher should be retrieved.
+    /// @param _miningAddress The mining address of validator.
+    function getCommitAndCipher(
+        uint256 _collectRound,
+        address _miningAddress
+    ) public view returns(bytes32, bytes memory) {
+        return (hashes[_collectRound][_miningAddress], ciphers[_collectRound][_miningAddress]);
+    }
+
+    /// @dev Returns a boolean flag indicating whether the specified validator has committed their secret's hash for the
+    /// specified collection round.
+    /// @param _collectRound The serial number of the collection round for which the checkup should be done.
+    /// @param _miningAddress The mining address of the validator.
+    function isCommitted(uint256 _collectRound, address _miningAddress) public view returns(bool) {
+        return hashes[_collectRound][_miningAddress] != bytes32(0);
+    }
+
+    /// @dev Returns a boolean flag indicating whether the current phase of the current collection round
+    /// is a `commits phase`. Used by the validator's node to determine if it should commit the hash of
+    /// the secret during the current collection round.
+    function isCommitPhase() public view returns(bool) {
+        return _isCommitPhase(block.number);
+    }
+
+    /// @dev Returns a boolean flag indicating whether the current phase of the current collection round
+    /// is a `reveals phase`. Used by the validator's node to determine if it should reveal the secret during
+    /// the current collection round.
+    function isRevealPhase() public view returns(bool) {
+        return _isRevealPhase(block.number);
+    }
+
+    /// @dev Returns a boolean flag of whether the specified validator has revealed their secret for the
+    /// specified collection round.
+    /// @param _collectRound The serial number of the collection round for which the checkup should be done.
+    /// @param _miningAddress The mining address of the validator.
+    function sentReveal(uint256 _collectRound, address _miningAddress) public view returns(bool) {
+        return secrets[_collectRound][_miningAddress] != uint256(0);
+    }
+
+    /// @dev Returns the current collect round number.
+    function currentCollectRound() public view returns(uint256) {
+        return _collectRound(block.number);
+    }
+
+    /// @dev Returns the current random value.
+    function getValue() public view returns(uint256) {
+        return value;
+    }
+
+    function _collectRound(uint256 blockNumber) private pure returns(uint256) {
+        return blockNumber / 6;
+    }
+
+    function _isCommitPhase(uint256 blockNumber) private pure returns(bool) {
+        return blockNumber % 6 < 3;
+    }
+
+    function _isRevealPhase(uint256 blockNumber) private pure returns(bool) {
+        return blockNumber % 6 >= 3;
+    }
+}
+

ethcore/snapshot/snapshot-tests/src/service.rs

@@ -50,7 +50,7 @@ use journaldb::Algorithm;
 #[test]
 fn sends_async_messages() {
 	let gas_prices = vec![1.into(), 2.into(), 3.into(), 999.into()];
-	let client = generate_dummy_client_with_spec_and_data(spec::new_null, 400, 5, &gas_prices);
+	let client = generate_dummy_client_with_spec_and_data(spec::new_null, 400, 5, &gas_prices, false);
 	let service = IoService::<ClientIoMessage<Client>>::start().unwrap();
 	let spec = spec::new_test();
 
@@ -143,7 +143,7 @@ fn restored_is_equivalent() {
 	const TX_PER: usize = 5;
 
 	let gas_prices = vec![1.into(), 2.into(), 3.into(), 999.into()];
-	let client = generate_dummy_client_with_spec_and_data(spec::new_null, NUM_BLOCKS, TX_PER, &gas_prices);
+	let client = generate_dummy_client_with_spec_and_data(spec::new_null, NUM_BLOCKS, TX_PER, &gas_prices, false);
 
 	let tempdir = TempDir::new("").unwrap();
 	let client_db = tempdir.path().join("client_db");
@@ -207,7 +207,7 @@ fn restored_is_equivalent() {
 #[test]
 fn guards_delete_folders() {
 	let gas_prices = vec![1.into(), 2.into(), 3.into(), 999.into()];
-	let client = generate_dummy_client_with_spec_and_data(spec::new_null, 400, 5, &gas_prices);
+	let client = generate_dummy_client_with_spec_and_data(spec::new_null, 400, 5, &gas_prices, false);
 
 	let spec = spec::new_null();
 	let tempdir = TempDir::new("").unwrap();
@@ -266,7 +266,7 @@ fn keep_ancient_blocks() {
 	let gas_prices = vec![1.into(), 2.into(), 3.into(), 999.into()];
 	let spec_f = spec::new_null;
 	let spec = spec_f();
-	let client = generate_dummy_client_with_spec_and_data(spec_f, NUM_BLOCKS as u32, 5, &gas_prices);
+	let client = generate_dummy_client_with_spec_and_data(spec_f, NUM_BLOCKS as u32, 5, &gas_prices, false);
 
 	let bc = client.chain();
 
@@ -374,7 +374,7 @@ fn recover_aborted_recovery() {
 
 	const NUM_BLOCKS: u32 = 400;
 	let gas_prices = vec![1.into(), 2.into(), 3.into(), 999.into()];
-	let client = generate_dummy_client_with_spec_and_data(spec::new_null, NUM_BLOCKS, 5, &gas_prices);
+	let client = generate_dummy_client_with_spec_and_data(spec::new_null, NUM_BLOCKS, 5, &gas_prices, false);
 
 	let spec = spec::new_null();
 	let tempdir = TempDir::new("").unwrap();

ethcore/spec/src/chain.rs

@@ -86,6 +86,7 @@ bundle_test_spec! {
 	"authority_round" => new_test_round,
 	"authority_round_block_reward_contract" => new_test_round_block_reward_contract,
 	"authority_round_empty_steps" => new_test_round_empty_steps,
+	"authority_round_randomness_contract" => new_test_round_randomness_contract,
 	"constructor" => new_test_constructor,
 	"ethereum/byzantium_test" => new_byzantium_test,
 	"ethereum/constantinople_test" => new_constantinople_test,

ethcore/src/client/client.rs

@@ -79,6 +79,7 @@ use client_traits::{
 	StateOrBlock,
 	Tick,
 	TransactionInfo,
+	TransactionRequest,
 	ForceUpdateSealing
 };
 use db::{keys::BlockDetails, Readable, Writable};
@@ -2154,29 +2155,35 @@ impl BlockChainClient for Client {
 		}
 	}
 
-	fn transact_contract(&self, address: Address, data: Bytes) -> Result<(), transaction::Error> {
+	fn create_transaction(&self, TransactionRequest { action, data, gas, gas_price, nonce }: TransactionRequest)
+		-> Result<SignedTransaction, transaction::Error>
+	{
 		let authoring_params = self.importer.miner.authoring_params();
 		let service_transaction_checker = self.importer.miner.service_transaction_checker();
 		let gas_price = if let Some(checker) = service_transaction_checker {
 			match checker.check_address(self, authoring_params.author) {
 				Ok(true) => U256::zero(),
-				_ => self.importer.miner.sensible_gas_price(),
+				_ => gas_price.unwrap_or_else(|| self.importer.miner.sensible_gas_price()),
 			}
 		} else {
 			self.importer.miner.sensible_gas_price()
 		};
 		let transaction = transaction::Transaction {
-			nonce: self.latest_nonce(&authoring_params.author),
+			nonce: nonce.unwrap_or_else(|| self.latest_nonce(&authoring_params.author)),
-			action: Action::Call(address),
+			action,
-			gas: self.importer.miner.sensible_gas_limit(),
+			gas: gas.unwrap_or_else(|| self.importer.miner.sensible_gas_limit()),
 			gas_price,
 			value: U256::zero(),
-			data: data,
+			data,
 		};
 		let chain_id = self.engine.signing_chain_id(&self.latest_env_info());
 		let signature = self.engine.sign(transaction.hash(chain_id))
 			.map_err(|e| transaction::Error::InvalidSignature(e.to_string()))?;
-		let signed = SignedTransaction::new(transaction.with_signature(signature, chain_id))?;
+		Ok(SignedTransaction::new(transaction.with_signature(signature, chain_id))?)
+	}
+
+	fn transact(&self, tx_request: TransactionRequest) -> Result<(), transaction::Error> {
+		let signed = self.create_transaction(tx_request)?;
 		self.importer.miner.import_own_transaction(self, signed.into())
 	}
 }
@@ -2978,7 +2985,7 @@ mod tests {
 
 	#[test]
 	fn should_mark_finalization_correctly_for_parent() {
-		let client = generate_dummy_client_with_spec_and_data(spec::new_test_with_finality, 2, 0, &[]);
+		let client = generate_dummy_client_with_spec_and_data(spec::new_test_with_finality, 2, 0, &[], false);
 		let chain = client.chain();
 
 		let block1_details = chain.block_hash(1).and_then(|h| chain.block_details(&h));

ethcore/src/miner/miner.rs

@@ -327,6 +327,13 @@ impl Miner {
 	///
 	/// NOTE This should be only used for tests.
 	pub fn new_for_tests(spec: &Spec, accounts: Option<HashSet<Address>>) -> Miner {
+		Miner::new_for_tests_force_sealing(spec, accounts, false)
+	}
+
+	/// Creates new instance of miner with given spec and accounts.
+	///
+	/// NOTE This should be only used for tests.
+	pub fn new_for_tests_force_sealing(spec: &Spec, accounts: Option<HashSet<Address>>, force_sealing: bool) -> Miner {
 		let minimal_gas_price = 0.into();
 		Miner::new(MinerOptions {
 			pool_verification_options: pool::verifier::Options {
@@ -336,6 +343,7 @@ impl Miner {
 				no_early_reject: false,
 			},
 			reseal_min_period: Duration::from_secs(0),
+			force_sealing,
 			..Default::default()
 		}, GasPricer::new_fixed(minimal_gas_price), spec, accounts.unwrap_or_default())
 	}
@@ -422,7 +430,8 @@ impl Miner {
 		let chain_info = chain.chain_info();
 
 		// Open block
-		let (mut open_block, original_work_hash) = {
+		// Some engines add transactions to the block for their own purposes, e.g. AuthorityRound RANDAO.
+		let (mut open_block, original_work_hash, engine_txs) = {
 			let mut sealing = self.sealing.lock();
 			let last_work_hash = sealing.queue.peek_last_ref().map(|pb| pb.header.hash());
 			let best_hash = chain_info.best_block_hash;
@@ -433,27 +442,40 @@ impl Miner {
 			//   if at least one was pushed successfully, close and enqueue new ClosedBlock;
 			//   otherwise, leave everything alone.
 			// otherwise, author a fresh block.
-			let mut open_block = match sealing.queue.get_pending_if(|b| b.header.parent_hash() == &best_hash) {
+			match sealing.queue.get_pending_if(|b| b.header.parent_hash() == &best_hash) {
 				Some(old_block) => {
 					trace!(target: "miner", "prepare_block: Already have previous work; updating and returning");
 					// add transactions to old_block
-					chain.reopen_block(old_block)
+					(chain.reopen_block(old_block), last_work_hash, Vec::new())
 				}
 				None => {
 					// block not found - create it.
 					trace!(target: "miner", "prepare_block: No existing work - making new block");
 					let params = self.params.read().clone();
 
-					match chain.prepare_open_block(
+					let block = match chain.prepare_open_block(
 						params.author,
 						params.gas_range_target,
 						params.extra_data,
 					) {
 						Ok(block) => block,
 						Err(err) => {
-							warn!(target: "miner", "Open new block failed with error {:?}. This is likely an error in chain specificiations or on-chain consensus smart contracts.", err);
+							warn!(target: "miner", "Open new block failed with error {:?}. This is likely an error in \
+								  chain specification or on-chain consensus smart contracts.", err);
 							return None;
 						}
+					};
+
+					// Before adding from the queue to the new block, give the engine a chance to add transactions.
+					match self.engine.generate_engine_transactions(&block) {
+						Ok(transactions) => (block, last_work_hash, transactions),
+						Err(err) => {
+							error!(target: "miner", "Failed to prepare engine transactions for new block: {:?}. \
+								   This is likely an error in chain specification or on-chain consensus smart \
+								   contracts.", err);
+							return None;
+						}
+					}
 				}
 			}
 		};
@@ -462,9 +484,6 @@ impl Miner {
 			open_block.remove_gas_limit();
 		}
 
-			(open_block, last_work_hash)
-		};
-
 		let mut invalid_transactions = HashSet::new();
 		let mut not_allowed_transactions = HashSet::new();
 		let mut senders_to_penalize = HashSet::new();
@@ -488,13 +507,13 @@ impl Miner {
 			MAX_SKIPPED_TRANSACTIONS.saturating_add(cmp::min(*open_block.header.gas_limit() / min_tx_gas, u64::max_value().into()).as_u64() as usize)
 		};
 
-		let pending: Vec<Arc<_>> = self.transaction_queue.pending(
+		let queue_txs: Vec<Arc<_>> = self.transaction_queue.pending(
 			client.clone(),
 			pool::PendingSettings {
 				block_number: chain_info.best_block_number,
 				current_timestamp: chain_info.best_block_timestamp,
 				nonce_cap,
-				max_len: max_transactions,
+				max_len: max_transactions.saturating_sub(engine_txs.len()),
 				ordering: miner::PendingOrdering::Priority,
 			}
 		);
@@ -504,12 +523,11 @@ impl Miner {
 		};
 
 		let block_start = Instant::now();
-		debug!(target: "miner", "Attempting to push {} transactions.", pending.len());
+		debug!(target: "miner", "Attempting to push {} transactions.", engine_txs.len() + queue_txs.len());
 
-		for tx in pending {
+		for transaction in engine_txs.into_iter().chain(queue_txs.into_iter().map(|tx| tx.signed().clone())) {
 			let start = Instant::now();
 
-			let transaction = tx.signed().clone();
 			let hash = transaction.hash();
 			let sender = transaction.sender();
 

ethcore/src/test_helpers/mod.rs

@@ -118,31 +118,35 @@ pub fn create_test_block_with_data(header: &Header, transactions: &[SignedTransa
 
 /// Generates dummy client (not test client) with corresponding amount of blocks
 pub fn generate_dummy_client(block_number: u32) -> Arc<Client> {
-	generate_dummy_client_with_spec_and_data(spec::new_test, block_number, 0, &[])
+	generate_dummy_client_with_spec_and_data(spec::new_test, block_number, 0, &[], false)
 }
 
 /// Generates dummy client (not test client) with corresponding amount of blocks and txs per every block
 pub fn generate_dummy_client_with_data(block_number: u32, txs_per_block: usize, tx_gas_prices: &[U256]) -> Arc<Client> {
-	generate_dummy_client_with_spec_and_data(spec::new_null, block_number, txs_per_block, tx_gas_prices)
+	generate_dummy_client_with_spec_and_data(spec::new_null, block_number, txs_per_block, tx_gas_prices, false)
 }
 
 /// Generates dummy client (not test client) with corresponding spec and accounts
 pub fn generate_dummy_client_with_spec<F>(test_spec: F) -> Arc<Client> where F: Fn() -> Spec {
-	generate_dummy_client_with_spec_and_data(test_spec, 0, 0, &[])
+	generate_dummy_client_with_spec_and_data(test_spec, 0, 0, &[], false)
 }
 
 /// Generates dummy client (not test client) with corresponding amount of blocks, txs per block and spec
-pub fn generate_dummy_client_with_spec_and_data<F>(test_spec: F, block_number: u32, txs_per_block: usize, tx_gas_prices: &[U256]) -> Arc<Client> where
+pub fn generate_dummy_client_with_spec_and_data<F>(
+	test_spec: F, block_number: u32, txs_per_block: usize, tx_gas_prices: &[U256], force_sealing: bool,
+) -> Arc<Client> where
 	F: Fn() -> Spec
 {
 	let test_spec = test_spec();
 	let client_db = new_db();
 
+	let miner = Miner::new_for_tests_force_sealing(&test_spec, None, force_sealing);
+
 	let client = Client::new(
 		ClientConfig::default(),
 		&test_spec,
 		client_db,
-		Arc::new(Miner::new_for_tests(&test_spec, None)),
+		Arc::new(miner),
 		IoChannel::disconnected(),
 	).unwrap();
 	let test_engine = &*test_spec.engine;

ethcore/src/test_helpers/test_client.rs

@@ -72,7 +72,7 @@ use client::{
 use client_traits::{
 	BlockInfo, Nonce, Balance, ChainInfo, TransactionInfo, BlockChainClient, ImportBlock,
 	AccountData, BlockChain, IoClient, BadBlocks, ScheduleInfo, StateClient, ProvingBlockChainClient,
-	StateOrBlock, ForceUpdateSealing
+	StateOrBlock, ForceUpdateSealing, TransactionRequest
 };
 use engine::Engine;
 use machine::executed::Executed;
@@ -912,18 +912,24 @@ impl BlockChainClient for TestBlockChainClient {
 		}
 	}
 
-	fn transact_contract(&self, address: Address, data: Bytes) -> Result<(), transaction::Error> {
+	fn create_transaction(&self, TransactionRequest { action, data, gas, gas_price, nonce }: TransactionRequest)
+		-> Result<SignedTransaction, transaction::Error>
+	{
 		let transaction = Transaction {
-			nonce: self.latest_nonce(&self.miner.authoring_params().author),
+			nonce: nonce.unwrap_or_else(|| self.latest_nonce(&self.miner.authoring_params().author)),
-			action: Action::Call(address),
+			action,
-			gas: self.spec.gas_limit,
+			gas: gas.unwrap_or(self.spec.gas_limit),
-			gas_price: U256::zero(),
+			gas_price: gas_price.unwrap_or_else(U256::zero),
 			value: U256::default(),
 			data: data,
 		};
 		let chain_id = Some(self.spec.chain_id());
 		let sig = self.spec.engine.sign(transaction.hash(chain_id)).unwrap();
-		let signed = SignedTransaction::new(transaction.with_signature(sig, chain_id)).unwrap();
+		Ok(SignedTransaction::new(transaction.with_signature(sig, chain_id)).unwrap())
+	}
+
+	fn transact(&self, tx_request: TransactionRequest) -> Result<(), transaction::Error> {
+		let signed = self.create_transaction(tx_request)?;
 		self.miner.import_own_transaction(self, signed.into())
 	}
 }

ethcore/types/src/errors/engine_error.rs

@@ -37,6 +37,10 @@ pub enum EngineError {
 	InsufficientProof(String),
 	/// Failed system call.
 	FailedSystemCall(String),
+	/// Failed to decode the result of a system call.
+	SystemCallResultDecoding(String),
+	/// The result of a system call is invalid.
+	SystemCallResultInvalid(String),
 	/// Malformed consensus message.
 	MalformedMessage(String),
 	/// Requires client ref, but none registered.
@@ -91,6 +95,8 @@ impl fmt::Display for EngineError {
 			BadSealFieldSize(ref oob) => format!("Seal field has an unexpected length: {}", oob),
 			InsufficientProof(ref msg) => format!("Insufficient validation proof: {}", msg),
 			FailedSystemCall(ref msg) => format!("Failed to make system call: {}", msg),
+			SystemCallResultDecoding(ref msg) => format!("Failed to decode the result of a system call: {}", msg),
+			SystemCallResultInvalid(ref msg) => format!("The result of a system call is invalid: {}", msg),
 			MalformedMessage(ref msg) => format!("Received malformed consensus message: {}", msg),
 			RequiresClient => format!("Call requires client but none registered"),
 			RequiresSigner => format!("Call requires signer but none registered"),

json/src/spec/authority_round.rs

@@ -95,6 +95,8 @@ pub struct AuthorityRoundParams {
 	pub strict_empty_steps_transition: Option<Uint>,
 	/// First block for which a 2/3 quorum (instead of 1/2) is required.
 	pub two_thirds_majority_transition: Option<Uint>,
+	/// The random number contract's address, or a map of contract transitions.
+	pub randomness_contract_address: Option<BTreeMap<Uint, Address>>,
 }
 
 /// Authority engine deserialization.
@@ -124,7 +126,11 @@ mod tests {
 				"validateStepTransition": 150,
 				"blockReward": 5000000,
 				"maximumUncleCountTransition": 10000000,
-				"maximumUncleCount": 5
+				"maximumUncleCount": 5,
+				"randomnessContractAddress": {
+					"10": "0xaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+					"20": "0xbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"
+				}
 			}
 		}"#;
 
@@ -138,6 +144,10 @@ mod tests {
 		assert_eq!(deserialized.params.immediate_transitions, None);
 		assert_eq!(deserialized.params.maximum_uncle_count_transition, Some(Uint(10_000_000.into())));
 		assert_eq!(deserialized.params.maximum_uncle_count, Some(Uint(5.into())));
-
+		assert_eq!(deserialized.params.randomness_contract_address.unwrap(),
+			vec![
+				(Uint(10.into()), Address(H160::from_str("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa").unwrap())),
+				(Uint(20.into()), Address(H160::from_str("bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb").unwrap())),
+			].into_iter().collect());
 	}
 }

rpc/src/v1/helpers/engine_signer.rs

@@ -18,7 +18,7 @@ use std::sync::Arc;
 
 use accounts::AccountProvider;
 use ethkey::Password;
-use crypto::publickey::{Address, Message, Signature, Error};
+use crypto::publickey::{Address, Message, Public, Signature, Error};
 
 /// An implementation of EngineSigner using internal account management.
 pub struct EngineSigner {
@@ -42,8 +42,19 @@ impl engine::signer::EngineSigner for EngineSigner {
 		}
 	}
 
+	fn decrypt(&self, auth_data: &[u8], cipher: &[u8]) -> Result<Vec<u8>, Error> {
+		self.accounts.decrypt(self.address, None, auth_data, cipher).map_err(|e| {
+			warn!("Unable to decrypt message: {:?}", e);
+			Error::InvalidMessage
+		})
+	}
+
 	fn address(&self) -> Address {
 		self.address
 	}
+
+	fn public(&self) -> Option<Public> {
+		self.accounts.account_public(self.address, &self.password).ok()
+	}
 }