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dkg/gennaro/round2.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"
+)
+
+type Round2Bcast = []*v1.ShareVerifier
+
+// Round2 computes the second round for Gennaro DKG
+// Algorithm 3 - Gennaro DKG Round 2
+// bcast contains all Round1 broadcast from other participants to this participant
+// p2p contains all Round1 P2P send message from other participants to this participant
+func (dp *Participant) Round2(
+	bcast map[uint32]Round1Bcast,
+	p2p map[uint32]*Round1P2PSendPacket,
+) (Round2Bcast, error) {
+	// Check participant is not empty
+	if dp == nil || dp.curve == nil {
+		return nil, internal.ErrNilArguments
+	}
+
+	// Check participant has the correct dkg round number
+	if dp.round != 2 {
+		return nil, internal.ErrInvalidRound
+	}
+
+	// Check the input is valid
+	if bcast == nil || p2p == nil || len(bcast) == 0 || len(p2p) == 0 {
+		return nil, internal.ErrNilArguments
+	}
+
+	// 1. set sk = x_{ii}
+	sk := dp.pedersenResult.SecretShares[dp.id-1].Value
+
+	// 2. for j in 1,...,n
+	for id := range bcast {
+
+		// 3. if i = j continue
+		if id == dp.id {
+			continue
+		}
+
+		// Ensure a valid p2p entry exists
+		if p2p[id] == nil {
+			return nil, fmt.Errorf("missing p2p packet for id=%v", id)
+		}
+
+		// 4. If PedersenVerify(E, Q, x_ji, r_ji, {X_ji,...,X_jt}) = false, abort
+		xji := p2p[id].SecretShare
+		rji := p2p[id].BlindingShare
+		bvs := bcast[id]
+		if ok, err := dp.pedersen.Verify(xji, rji, bvs); !ok {
+			if err != nil {
+				return nil, err
+			} else {
+				return nil, fmt.Errorf("invalid share for participant id=%v", id)
+			}
+		}
+
+		// Store other participants' shares xji for usage in round 3
+		dp.otherParticipantShares[id].Share = p2p[id].SecretShare
+
+		// 5. sk = (sk+xji) mod q
+		// NOTE: we use the EcScalar class to add instead of
+		// just using big.Int Add and Mod
+		// because Ed25519 will fail with the big.Int Add and Mod
+		// and Ed25519 uses different little endian vs big endian
+		// in big.Int
+		t1 := sk.BigInt()
+		t2 := xji.Value.BigInt()
+		r := dp.scalar.Add(t1, t2)
+
+		sk = sk.Field().NewElement(r)
+	}
+
+	// Update internal state
+	dp.round = 3
+
+	// 7. Store ski as participant i's secret key share
+	dp.skShare = sk
+
+	// 6. EchoBroadcast {R_1,...,R_t} to all other participants.
+	return dp.pedersenResult.Verifiers, nil
+}