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dkg/gennaro/round3.go

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+//
+// Copyright Coinbase, Inc. All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+package gennaro
+
+import (
+	"fmt"
+
+	"github.com/sonr-io/sonr/crypto/internal"
+	v1 "github.com/sonr-io/sonr/crypto/sharing/v1"
+)
+
+// Round3Bcast contains values that will be broadcast to other participants.
+type Round3Bcast = v1.ShareVerifier
+
+// Round3 computes the third round for Gennaro DKG
+// Algorithm 4 - Gennaro DKG Round 3
+// bcast contains all Round2 broadcast from other participants to this participant.
+func (dp *Participant) Round3(bcast map[uint32]Round2Bcast) (*Round3Bcast, *v1.ShamirShare, error) {
+	// Check participant is not empty
+	if dp == nil || dp.curve == nil {
+		return nil, nil, internal.ErrNilArguments
+	}
+
+	// Check participant has the correct dkg round number
+	if dp.round != 3 {
+		return nil, nil, internal.ErrInvalidRound
+	}
+
+	// Check the input is valid
+	if len(bcast) == 0 {
+		return nil, nil, internal.ErrNilArguments
+	}
+
+	// 1. SetBigInt Pk = R_i1
+	Pk := dp.pedersenResult.Verifiers[0]
+
+	// 2. for j in 1,...,n
+	for id := range bcast {
+		// 3. if i = j continue
+		if id == dp.id {
+			continue
+		}
+
+		// 4. If FeldmanVerify(E, xji, {R_j1,...,R_jt}) = false; abort
+		xji := dp.otherParticipantShares[id].Share
+		vs := bcast[id]
+		if ok, err := dp.feldman.Verify(xji, vs); !ok {
+			if err != nil {
+				return nil, nil, err
+			} else {
+				return nil, nil, fmt.Errorf("invalid share for participant #{id}")
+			}
+		}
+
+		// Store the feldman verifiers for round 4
+		dp.otherParticipantShares[id].Verifiers = vs
+
+		// 5. Pk = Pk+R_j1
+		temp, err := Pk.Add(bcast[id][0])
+		if err != nil {
+			return nil, nil, fmt.Errorf("error in computing Pk+R_j1")
+		}
+		Pk = temp
+	}
+
+	// This is a sanity check to make sure nothing went wrong
+	// when computing the public key
+	if !Pk.IsOnCurve() || Pk.IsIdentity() {
+		return nil, nil, fmt.Errorf("invalid public key")
+	}
+
+	// 6. Store Pk as the public verification key
+	dp.verificationKey = Pk
+
+	// Update internal state
+	dp.round = 4
+
+	skShare := v1.ShamirShare{
+		Identifier: dp.id,
+		Value:      dp.skShare,
+	}
+
+	// Output Pk as the public verification key
+	return Pk, &skShare, nil
+}