Fix missing dpk (#786)

packages/drng/dispatcher.go

@@ -38,6 +38,11 @@ func (d *DRNG) Dispatch(issuer ed25519.PublicKey, timestamp time.Time, payload *
 			return err
 		}
 
+		// update the dpk (if not set) from the valid beacon
+		if len(d.State[cbEvent.InstanceID].committee.DistributedPK) == 0 {
+			d.State[cbEvent.InstanceID].UpdateDPK(cbEvent.Dpk)
+		}
+
 		// trigger RandomnessEvent
 		d.Events.Randomness.Trigger(d.State[cbEvent.InstanceID])
 

packages/drng/drng.go

@@ -125,6 +125,14 @@ func (s *State) UpdateCommittee(c *Committee) {
 	s.committee = c
 }
 
+// UpdateDPK updates the distributed public key of the DRNG state
+func (s *State) UpdateDPK(dpk []byte) {
+	s.mutex.Lock()
+	defer s.mutex.Unlock()
+	s.committee.DistributedPK = make([]byte, PublicKeySize)
+	copy(s.committee.DistributedPK[:], dpk[:PublicKeySize])
+}
+
 // Committee returns the committee of the DRNG state
 func (s *State) Committee() Committee {
 	s.mutex.RLock()