Babe VRF Signing in keystore (#6225)

* Introduce trait

* Implement VRFSigner in keystore

* Use vrf_sign from keystore

* Convert output to VRFInOut

* Simplify conversion

* vrf_sign secondary slot using keystore

* Fix RPC call to claim_slot

* Use Public instead of Pair

* Check primary threshold in signer

* Fix interface to return error

* Move vrf_sign to BareCryptoStore

* Fix authorship_works test

* Fix BABE logic leaks

* Acquire a read lock once

* Also fix RPC acquiring the read lock once

* Implement a generic way to construct VRF Transcript

* Use make_transcript_data to call sr25519_vrf_sign

* Make sure VRFTranscriptData is serializable

* Cleanup

* Move VRF to it's own module

* Implement & test VRF signing in testing module

* Remove leftover

* Fix feature requirements

* Revert removing vec macro

* Drop keystore pointer to prevent deadlock

* Nitpicks

* Add test to make sure make_transcript works

* Fix mismatch in VRF transcript

* Add a test to verify transcripts match in babe

* Return VRFOutput and VRFProof from keystore

substrate/primitives/consensus/babe/src/lib.rs

@@ -31,6 +31,8 @@ pub use merlin::Transcript;
 use codec::{Encode, Decode};
 use sp_std::vec::Vec;
 use sp_runtime::{ConsensusEngineId, RuntimeDebug};
+#[cfg(feature = "std")]
+use sp_core::vrf::{VRFTranscriptData, VRFTranscriptValue};
 use crate::digests::{NextEpochDescriptor, NextConfigDescriptor};
 
 mod app {
@@ -94,6 +96,23 @@ pub fn make_transcript(
 	transcript
 }
 
+/// Make a VRF transcript data container
+#[cfg(feature = "std")]
+pub fn make_transcript_data(
+	randomness: &Randomness,
+	slot_number: u64,
+	epoch: u64,
+) -> VRFTranscriptData {
+	VRFTranscriptData {
+		label: &BABE_ENGINE_ID,
+		items: vec![
+			("slot number", VRFTranscriptValue::U64(slot_number)),
+			("current epoch", VRFTranscriptValue::U64(epoch)),
+			("chain randomness", VRFTranscriptValue::Bytes(&randomness[..])),
+		]
+	}
+}
+
 /// An consensus log item for BABE.
 #[derive(Decode, Encode, Clone, PartialEq, Eq)]
 pub enum ConsensusLog {