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// This file is part of Substrate.
// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0
// 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.
//! Primitives for BABE.
#![deny(warnings)]
#![forbid(unsafe_code, missing_docs, unused_variables, unused_imports)]
#![cfg_attr(not(feature = "std"), no_std)]
extern crate alloc;
pub mod digests;
pub mod inherents;
#[cfg(not(feature = "std"))]
use alloc::vec::Vec;
use codec::{Decode, Encode, MaxEncodedLen};
use scale_info::TypeInfo;
#[cfg(feature = "serde")]
use serde::{Deserialize, Serialize};
use sp_runtime::{traits::Header, ConsensusEngineId, RuntimeDebug};
use crate::digests::{NextConfigDescriptor, NextEpochDescriptor};
pub use sp_core::sr25519::vrf::{
VrfInput, VrfPreOutput, VrfProof, VrfSignData, VrfSignature, VrfTranscript,
};
/// Key type for BABE module.
pub const KEY_TYPE: sp_core::crypto::KeyTypeId = sp_application_crypto::key_types::BABE;
mod app {
use sp_application_crypto::{app_crypto, key_types::BABE, sr25519};
app_crypto!(sr25519, BABE);
}
/// VRF context used for per-slot randomness generation.
pub const RANDOMNESS_VRF_CONTEXT: &[u8] = b"BabeVRFInOutContext";
/// VRF output length for per-slot randomness.
pub const RANDOMNESS_LENGTH: usize = 32;
/// Randomness type required by BABE operations.
pub type Randomness = [u8; RANDOMNESS_LENGTH];
/// A Babe authority keypair. Necessarily equivalent to the schnorrkel public key used in
/// the main Babe module. If that ever changes, then this must, too.
#[cfg(feature = "std")]
pub type AuthorityPair = app::Pair;
/// A Babe authority signature.
pub type AuthoritySignature = app::Signature;
/// A Babe authority identifier. Necessarily equivalent to the schnorrkel public key used in
/// the main Babe module. If that ever changes, then this must, too.
pub type AuthorityId = app::Public;
/// The `ConsensusEngineId` of BABE.
pub const BABE_ENGINE_ID: ConsensusEngineId = *b"BABE";
/// The length of the public key
pub const PUBLIC_KEY_LENGTH: usize = 32;
/// How many blocks to wait before running the median algorithm for relative time
/// This will not vary from chain to chain as it is not dependent on slot duration
/// or epoch length.
pub const MEDIAN_ALGORITHM_CARDINALITY: usize = 1200; // arbitrary suggestion by w3f-research.
/// The index of an authority.
pub type AuthorityIndex = u32;
pub use sp_consensus_slots::{Slot, SlotDuration};
/// An equivocation proof for multiple block authorships on the same slot (i.e. double vote).
pub type EquivocationProof<H> = sp_consensus_slots::EquivocationProof<H, AuthorityId>;
/// The weight of an authority.
// NOTE: we use a unique name for the weight to avoid conflicts with other
// `Weight` types, since the metadata isn't able to disambiguate.
pub type BabeAuthorityWeight = u64;
/// The cumulative weight of a BABE block, i.e. sum of block weights starting
/// at this block until the genesis block.
///
/// Primary blocks have a weight of 1 whereas secondary blocks have a weight
/// of 0 (regardless of whether they are plain or vrf secondary blocks).
pub type BabeBlockWeight = u32;
/// Make VRF input suitable for BABE's randomness generation.
pub fn make_vrf_transcript(randomness: &Randomness, slot: Slot, epoch: u64) -> VrfInput {
VrfInput::new(
&BABE_ENGINE_ID,
&[
(b"slot number", &slot.to_le_bytes()),
(b"current epoch", &epoch.to_le_bytes()),
(b"chain randomness", randomness),
],
)
}
/// Make VRF signing data suitable for BABE's protocol.
pub fn make_vrf_sign_data(randomness: &Randomness, slot: Slot, epoch: u64) -> VrfSignData {
make_vrf_transcript(randomness, slot, epoch).into()
}
/// An consensus log item for BABE.
#[derive(Decode, Encode, Clone, PartialEq, Eq)]
pub enum ConsensusLog {
/// The epoch has changed. This provides information about the _next_
/// epoch - information about the _current_ epoch (i.e. the one we've just
/// entered) should already be available earlier in the chain.
#[codec(index = 1)]
NextEpochData(NextEpochDescriptor),
/// Disable the authority with given index.
#[codec(index = 2)]
OnDisabled(AuthorityIndex),
/// The epoch has changed, and the epoch after the current one will
/// enact different epoch configurations.
#[codec(index = 3)]
NextConfigData(NextConfigDescriptor),
}
/// Configuration data used by the BABE consensus engine.
#[derive(Clone, PartialEq, Eq, Encode, Decode, RuntimeDebug)]
pub struct BabeConfigurationV1 {
/// The slot duration in milliseconds for BABE. Currently, only
/// the value provided by this type at genesis will be used.
///
/// Dynamic slot duration may be supported in the future.
pub slot_duration: u64,
/// The duration of epochs in slots.
pub epoch_length: u64,
/// A constant value that is used in the threshold calculation formula.
/// Expressed as a rational where the first member of the tuple is the
/// numerator and the second is the denominator. The rational should
/// represent a value between 0 and 1.
/// In the threshold formula calculation, `1 - c` represents the probability
/// of a slot being empty.
pub c: (u64, u64),
/// The authorities for the genesis epoch.
pub authorities: Vec<(AuthorityId, BabeAuthorityWeight)>,
/// The randomness for the genesis epoch.
pub randomness: Randomness,
/// Whether this chain should run with secondary slots, which are assigned
/// in round-robin manner.
pub secondary_slots: bool,
}
impl From<BabeConfigurationV1> for BabeConfiguration {
fn from(v1: BabeConfigurationV1) -> Self {
Self {
slot_duration: v1.slot_duration,
epoch_length: v1.epoch_length,
c: v1.c,
authorities: v1.authorities,
randomness: v1.randomness,
allowed_slots: if v1.secondary_slots {
AllowedSlots::PrimaryAndSecondaryPlainSlots
} else {
AllowedSlots::PrimarySlots
},
}
}
}
/// Configuration data used by the BABE consensus engine.
#[derive(Clone, PartialEq, Eq, Encode, Decode, RuntimeDebug, TypeInfo)]
pub struct BabeConfiguration {
/// The slot duration in milliseconds for BABE. Currently, only
/// the value provided by this type at genesis will be used.
///
/// Dynamic slot duration may be supported in the future.
pub slot_duration: u64,
/// The duration of epochs in slots.
pub epoch_length: u64,
/// A constant value that is used in the threshold calculation formula.
/// Expressed as a rational where the first member of the tuple is the
/// numerator and the second is the denominator. The rational should
/// represent a value between 0 and 1.
/// In the threshold formula calculation, `1 - c` represents the probability
/// of a slot being empty.
pub c: (u64, u64),
/// The authorities
pub authorities: Vec<(AuthorityId, BabeAuthorityWeight)>,
/// The randomness
pub randomness: Randomness,
/// Type of allowed slots.
pub allowed_slots: AllowedSlots,
}
impl BabeConfiguration {
/// Convenience method to get the slot duration as a `SlotDuration` value.
pub fn slot_duration(&self) -> SlotDuration {
SlotDuration::from_millis(self.slot_duration)
}
}
/// Types of allowed slots.
#[derive(Clone, Copy, PartialEq, Eq, Encode, Decode, RuntimeDebug, MaxEncodedLen, TypeInfo)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub enum AllowedSlots {
/// Only allow primary slots.
PrimarySlots,
/// Allow primary and secondary plain slots.
PrimaryAndSecondaryPlainSlots,
/// Allow primary and secondary VRF slots.
PrimaryAndSecondaryVRFSlots,
}
impl AllowedSlots {
/// Whether plain secondary slots are allowed.
pub fn is_secondary_plain_slots_allowed(&self) -> bool {
*self == Self::PrimaryAndSecondaryPlainSlots
}
/// Whether VRF secondary slots are allowed.
pub fn is_secondary_vrf_slots_allowed(&self) -> bool {
*self == Self::PrimaryAndSecondaryVRFSlots
}
}
/// Configuration data used by the BABE consensus engine that may change with epochs.
#[derive(Clone, PartialEq, Eq, Encode, Decode, RuntimeDebug, MaxEncodedLen, TypeInfo)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub struct BabeEpochConfiguration {
/// A constant value that is used in the threshold calculation formula.
/// Expressed as a rational where the first member of the tuple is the
/// numerator and the second is the denominator. The rational should
/// represent a value between 0 and 1.
/// In the threshold formula calculation, `1 - c` represents the probability
/// of a slot being empty.
pub c: (u64, u64),
/// Whether this chain should run with secondary slots, which are assigned
/// in round-robin manner.
pub allowed_slots: AllowedSlots,
}
impl Default for BabeEpochConfiguration {
fn default() -> Self {
Self { c: (1, 4), allowed_slots: AllowedSlots::PrimaryAndSecondaryVRFSlots }
}
}
/// Verifies the equivocation proof by making sure that: both headers have
/// different hashes, are targeting the same slot, and have valid signatures by
/// the same authority.
pub fn check_equivocation_proof<H>(proof: EquivocationProof<H>) -> bool
where
H: Header,
{
use digests::*;
use sp_application_crypto::RuntimeAppPublic;
let find_pre_digest =
|header: &H| header.digest().logs().iter().find_map(|log| log.as_babe_pre_digest());
let verify_seal_signature = |mut header: H, offender: &AuthorityId| {
let seal = header.digest_mut().pop()?.as_babe_seal()?;
let pre_hash = header.hash();
if !offender.verify(&pre_hash.as_ref(), &seal) {
return None
}
Some(())
};
let verify_proof = || {
// we must have different headers for the equivocation to be valid
if proof.first_header.hash() == proof.second_header.hash() {
return None
}
let first_pre_digest = find_pre_digest(&proof.first_header)?;
let second_pre_digest = find_pre_digest(&proof.second_header)?;
// both headers must be targeting the same slot and it must
// be the same as the one in the proof.
if proof.slot != first_pre_digest.slot() ||
first_pre_digest.slot() != second_pre_digest.slot()
{
return None
}
// both headers must have been authored by the same authority
if first_pre_digest.authority_index() != second_pre_digest.authority_index() {
return None
}
// we finally verify that the expected authority has signed both headers and
// that the signature is valid.
verify_seal_signature(proof.first_header, &proof.offender)?;
verify_seal_signature(proof.second_header, &proof.offender)?;
Some(())
};
// NOTE: we isolate the verification code into an helper function that
// returns `Option<()>` so that we can use `?` to deal with any intermediate
// errors and discard the proof as invalid.
verify_proof().is_some()
}
/// An opaque type used to represent the key ownership proof at the runtime API
/// boundary. The inner value is an encoded representation of the actual key
/// ownership proof which will be parameterized when defining the runtime. At
/// the runtime API boundary this type is unknown and as such we keep this
/// opaque representation, implementors of the runtime API will have to make
/// sure that all usages of `OpaqueKeyOwnershipProof` refer to the same type.
#[derive(Decode, Encode, PartialEq, TypeInfo)]
pub struct OpaqueKeyOwnershipProof(Vec<u8>);
impl OpaqueKeyOwnershipProof {
/// Create a new `OpaqueKeyOwnershipProof` using the given encoded
/// representation.
pub fn new(inner: Vec<u8>) -> OpaqueKeyOwnershipProof {
OpaqueKeyOwnershipProof(inner)
}
/// Try to decode this `OpaqueKeyOwnershipProof` into the given concrete key
/// ownership proof type.
pub fn decode<T: Decode>(self) -> Option<T> {
Decode::decode(&mut &self.0[..]).ok()
}
}
/// BABE epoch information
#[derive(Decode, Encode, PartialEq, Eq, Clone, Debug, TypeInfo)]
pub struct Epoch {
/// The epoch index.
pub epoch_index: u64,
/// The starting slot of the epoch.
pub start_slot: Slot,
/// The duration of this epoch.
pub duration: u64,
/// The authorities and their weights.
pub authorities: Vec<(AuthorityId, BabeAuthorityWeight)>,
/// Randomness for this epoch.
pub randomness: Randomness,
/// Configuration of the epoch.
pub config: BabeEpochConfiguration,
}
/// Returns the epoch index the given slot belongs to.
pub fn epoch_index(slot: Slot, genesis_slot: Slot, epoch_duration: u64) -> u64 {
*slot.saturating_sub(genesis_slot) / epoch_duration
}
/// Returns the first slot at the given epoch index.
pub fn epoch_start_slot(epoch_index: u64, genesis_slot: Slot, epoch_duration: u64) -> Slot {
// (epoch_index * epoch_duration) + genesis_slot
const PROOF: &str = "slot number is u64; it should relate in some way to wall clock time; \
if u64 is not enough we should crash for safety; qed.";
epoch_index
.checked_mul(epoch_duration)
.and_then(|slot| slot.checked_add(*genesis_slot))
.expect(PROOF)
.into()
}
sp_api::decl_runtime_apis! {
/// API necessary for block authorship with BABE.
#[api_version(2)]
pub trait BabeApi {
/// Return the configuration for BABE.
fn configuration() -> BabeConfiguration;
/// Return the configuration for BABE. Version 1.
#[changed_in(2)]
fn configuration() -> BabeConfigurationV1;
/// Returns the slot that started the current epoch.
fn current_epoch_start() -> Slot;
/// Returns information regarding the current epoch.
fn current_epoch() -> Epoch;
/// Returns information regarding the next epoch (which was already
/// previously announced).
fn next_epoch() -> Epoch;
/// Generates a proof of key ownership for the given authority in the
/// current epoch. An example usage of this module is coupled with the
/// session historical module to prove that a given authority key is
/// tied to a given staking identity during a specific session. Proofs
/// of key ownership are necessary for submitting equivocation reports.
/// NOTE: even though the API takes a `slot` as parameter the current
/// implementations ignores this parameter and instead relies on this
/// method being called at the correct block height, i.e. any point at
/// which the epoch for the given slot is live on-chain. Future
/// implementations will instead use indexed data through an offchain
/// worker, not requiring older states to be available.
fn generate_key_ownership_proof(
slot: Slot,
authority_id: AuthorityId,
) -> Option<OpaqueKeyOwnershipProof>;
/// Submits an unsigned extrinsic to report an equivocation. The caller
/// must provide the equivocation proof and a key ownership proof
/// (should be obtained using `generate_key_ownership_proof`). The
/// extrinsic will be unsigned and should only be accepted for local
/// authorship (not to be broadcast to the network). This method returns
/// `None` when creation of the extrinsic fails, e.g. if equivocation
/// reporting is disabled for the given runtime (i.e. this method is
/// hardcoded to return `None`). Only useful in an offchain context.
fn submit_report_equivocation_unsigned_extrinsic(
equivocation_proof: EquivocationProof<Block::Header>,
key_owner_proof: OpaqueKeyOwnershipProof,
) -> Option<()>;
}
}