BABE signing and verification (#2270)

* Add basic BABE consensus type

* Update core/consensus/babe/slots/Cargo.toml

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* Fix parameterization and run `rustfmt`

* Respond to review comments

* Update various Cargo.lock files

* Revert "Update various Cargo.lock files"

This reverts commit af53d7624752a744320e9cbb25749fdd8e6f46d2.

* `BabeSealSignature` → `BabeSeal`

* Move slot code to its own crate

This was highly non-trivial, due to cyclic dependencies.

* Remove redundancy between AuRa and BABE

Some of the code duplication was removed using a macro.

* Fix build error

* Avoid non-`#[doc(hidden)]` re-exports

Also, bump some library versions in `Cargo.toml`.

* Remove dead code in AuRa

* Remove impl_slot macro

It was more trouble than it was worth.

Also, delete useless dependencies on Serde.

* AuRa and BABE need different DB keys

* Bring back `aura::Network`, but deprecate it.

* Improve docs and add `slot_duration` inherent method

* Add docs to `substrate_consensus_aura::SlotDuration`

* Add missing documentation and #![forbid(missing_docs, unsafe_code)]

* Add a #![forbid(missing_docs)]

* Remove dependency of `test-runtime` on `slots`

* Update core/consensus/babe/src/lib.rs

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* Remove wrongly added file

* Fix copyright notice

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* Bump `impl_version` and `spec_version`

* Add more code to BABE

Most of it is copied from AuRa code, but at least the initial core is
there.

* Stuck on horrible compiler error message

* add missing files

* Spaces → tabs

* Simplify code

* Fix compilation

This involved fixing dependencies and adding a `Mutex`.

* More work on BABE

* Fix deprecation version

* Fix deprecation version; remove spurious carets

* Fix Cargo.toml

* Implement VRF signing logic

* The import queue code compiles, though it probably doesn’t work.

* Add VRF verification

* Update Cargo.lock

* Update dependencies

* Move test network to sr25519 authority keys

* Fix accidental build bustage

* Trying to get the tests to work

* Add logging messages and remove dead code

There seems to be a problem with the test network.  Since AuRa and BABE
are both affected, this is most likely due to the switch from ed25519 to
sr25519.

* Trying to get the tests to work

* Add logging messages and remove dead code

There seems to be a problem with the test network.  Since AuRa and BABE
are both affected, this is most likely due to the switch from ed25519 to
sr25519.

* Working testsuite at last!

The problem was with serialization and deserialization.  Normally,
those functions are generated automatically, but those for `BabeSeal`
had to be written manually.  The hand-written versions were not
correct, however, as shown by the decoder not being able to decode the
output of the encoder.

* Enable BabeSeal::Encode asserts in --release tests

* Bump runtime and dependency versions

* Fix wasm compilation

The wasm build was broken because of a typo in
`core/test-runtime/src/lib.rs`, and missing gates on the `std` feature
in `core/consensus/{aura,babe}/primitives/Cargo.toml`.  Additionally,
improve the quotation in the build scripts.

* Merge Cargo.lock

* Change expected JSON string

The test was also broken on `master`, so I suspect that the test was
incorrect.

* Responded to review

* Remove hard-coded threshold from production code

A hard-coded threshold is now only used in tests.

* Fix swapped doc comments

* Fix unused import warnings

* fix ci error

* fix typo

* Fix spacing in docs

* Minor changes suggested by @joepetrowski

on https://github.com/paritytech/substrate/pull/2372

* Remove unnecessary getters

* fix compile error

* Fix silly unused-variable error

* Improve documentation formatting

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* Add issue links

* Revert excess verbosity and #![forbid(warnings)]

* Apply suggestions from code review

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* Reformat some comments

* Threshold should depend on number of validators

Also, respond to code review

* Fix silly compilation errors

* Reduce logging verbosity

* Fix missing import

substrate/srml/babe/src/lib.rs

@@ -0,0 +1,155 @@
+// Copyright 2019 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate 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.
+
+// Substrate 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 Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Consensus extension module for BABE consensus.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+#![forbid(unsafe_code, warnings)]
+pub use timestamp;
+
+use rstd::{result, prelude::*};
+use srml_support::{decl_storage, decl_module};
+use primitives::traits::As;
+use timestamp::{OnTimestampSet, Trait};
+#[cfg(feature = "std")]
+use timestamp::TimestampInherentData;
+use parity_codec::Decode;
+use inherents::{RuntimeString, InherentIdentifier, InherentData, ProvideInherent, MakeFatalError};
+#[cfg(feature = "std")]
+use inherents::{InherentDataProviders, ProvideInherentData};
+
+/// The BABE inherent identifier.
+pub const INHERENT_IDENTIFIER: InherentIdentifier = *b"babeslot";
+
+/// The type of the BABE inherent.
+pub type InherentType = u64;
+
+/// Auxiliary trait to extract BABE inherent data.
+pub trait BabeInherentData {
+	/// Get BABE inherent data.
+	fn babe_inherent_data(&self) -> result::Result<InherentType, RuntimeString>;
+	/// Replace BABE inherent data.
+	fn babe_replace_inherent_data(&mut self, new: InherentType);
+}
+
+impl BabeInherentData for InherentData {
+	fn babe_inherent_data(&self) -> result::Result<InherentType, RuntimeString> {
+		self.get_data(&INHERENT_IDENTIFIER)
+			.and_then(|r| r.ok_or_else(|| "BABE inherent data not found".into()))
+	}
+
+	fn babe_replace_inherent_data(&mut self, new: InherentType) {
+		self.replace_data(INHERENT_IDENTIFIER, &new);
+	}
+}
+
+/// Provides the slot duration inherent data for BABE.
+#[cfg(feature = "std")]
+pub struct InherentDataProvider {
+	slot_duration: u64,
+}
+
+#[cfg(feature = "std")]
+impl InherentDataProvider {
+	pub fn new(slot_duration: u64) -> Self {
+		Self {
+			slot_duration
+		}
+	}
+}
+
+#[cfg(feature = "std")]
+impl ProvideInherentData for InherentDataProvider {
+	fn on_register(
+		&self,
+		providers: &InherentDataProviders,
+	) -> result::Result<(), RuntimeString> {
+		if !providers.has_provider(&timestamp::INHERENT_IDENTIFIER) {
+			// Add the timestamp inherent data provider, as we require it.
+			providers.register_provider(timestamp::InherentDataProvider)
+		} else {
+			Ok(())
+		}
+	}
+
+	fn inherent_identifier(&self) -> &'static inherents::InherentIdentifier {
+		&INHERENT_IDENTIFIER
+	}
+
+	fn provide_inherent_data(
+		&self,
+		inherent_data: &mut InherentData,
+	) -> result::Result<(), RuntimeString> {
+		let timestamp = inherent_data.timestamp_inherent_data()?;
+		let slot_num = timestamp / self.slot_duration;
+		inherent_data.put_data(INHERENT_IDENTIFIER, &slot_num)
+	}
+
+	fn error_to_string(&self, error: &[u8]) -> Option<String> {
+		RuntimeString::decode(&mut &error[..]).map(Into::into)
+	}
+}
+
+decl_storage! {
+	trait Store for Module<T: Trait> as Babe {
+		// The last timestamp.
+		LastTimestamp get(last): T::Moment;
+	}
+}
+
+decl_module! {
+	pub struct Module<T: Trait> for enum Call where origin: T::Origin { }
+}
+
+impl<T: Trait> Module<T> {
+	/// Determine the BABE slot duration based on the Timestamp module configuration.
+	pub fn slot_duration() -> u64 {
+		// we double the minimum block-period so each author can always propose within
+		// the majority of their slot.
+		<timestamp::Module<T>>::minimum_period().as_().saturating_mul(2)
+	}
+}
+
+impl<T: Trait> OnTimestampSet<T::Moment> for Module<T> {
+	fn on_timestamp_set(_moment: T::Moment) { }
+}
+
+impl<T: Trait> ProvideInherent for Module<T> {
+	type Call = timestamp::Call<T>;
+	type Error = MakeFatalError<RuntimeString>;
+	const INHERENT_IDENTIFIER: InherentIdentifier = INHERENT_IDENTIFIER;
+
+	fn create_inherent(_: &InherentData) -> Option<Self::Call> {
+		None
+	}
+
+	fn check_inherent(call: &Self::Call, data: &InherentData) -> result::Result<(), Self::Error> {
+		let timestamp = match call {
+			timestamp::Call::set(ref timestamp) => timestamp.clone(),
+			_ => return Ok(()),
+		};
+
+		let timestamp_based_slot = timestamp.as_() / Self::slot_duration();
+
+		let seal_slot = data.babe_inherent_data()?;
+
+		if timestamp_based_slot == seal_slot {
+			Ok(())
+		} else {
+			Err(RuntimeString::from("timestamp set in block doesn’t match slot in seal").into())
+		}
+	}
+}