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ted25519/frost/participant.go

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+//
+// Copyright Coinbase, Inc. All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+// Package frost is an implementation of t-of-n threshold signature of https://eprint.iacr.org/2020/852.pdf
+package frost
+
+import (
+	"fmt"
+
+	"github.com/sonr-io/sonr/crypto/core/curves"
+	"github.com/sonr-io/sonr/crypto/dkg/frost"
+	"github.com/sonr-io/sonr/crypto/internal"
+)
+
+// Signer is a tSchnorr player performing the signing operation.
+type Signer struct {
+	skShare          curves.Scalar // secret signing share for this signer
+	vkShare          curves.Point  // store verification key share
+	verificationKey  curves.Point  // verification key
+	id               uint32        // The ID assigned to this signer's shamir share
+	threshold        uint32
+	curve            *curves.Curve
+	round            uint
+	lCoeffs          map[uint32]curves.Scalar // lCoeffs are Lagrange coefficients of each cosigner.
+	cosigners        []uint32
+	state            *state // Accumulated intermediate values associated with signing
+	challengeDeriver ChallengeDerive
+}
+
+type state struct {
+	// Round 1
+	capD, capE     curves.Point  // capD, capE are commitments this signer generates in signing round 1
+	smallD, smallE curves.Scalar // smallD, smallE are scalars this signer generates in signing round 1
+
+	// Round 2
+	commitments map[uint32]*Round1Bcast // Store commitments broadcast after signing round 1
+	msg         []byte
+	c           curves.Scalar
+	capRs       map[uint32]curves.Point
+	sumR        curves.Point
+}
+
+// NewSigner create a signer from a dkg participant
+// Note that we can pre-assign Lagrange coefficients lcoeffs of each cosigner. This optimizes performance.
+// See paragraph 3 of section 3 in the draft - https://tools.ietf.org/pdf/draft-komlo-frost-00.pdf
+func NewSigner(
+	info *frost.DkgParticipant,
+	id, thresh uint32,
+	lcoeffs map[uint32]curves.Scalar,
+	cosigners []uint32,
+	challengeDeriver ChallengeDerive,
+) (*Signer, error) {
+	if info == nil || len(cosigners) == 0 || len(lcoeffs) == 0 {
+		return nil, internal.ErrNilArguments
+	}
+
+	if thresh > uint32(len(cosigners)) {
+		return nil, fmt.Errorf("threshold is higher than number of signers")
+	}
+
+	if len(lcoeffs) != len(cosigners) {
+		return nil, fmt.Errorf("expected coefficients to be equal to number of cosigners")
+	}
+
+	// Check if cosigners and lcoeffs contain the same IDs
+	for i := 0; i < len(cosigners); i++ {
+		id := cosigners[i]
+		if _, ok := lcoeffs[id]; !ok {
+			return nil, fmt.Errorf("lcoeffs and cosigners have inconsistent ID")
+		}
+	}
+
+	return &Signer{
+		skShare:          info.SkShare,
+		vkShare:          info.VkShare,
+		verificationKey:  info.VerificationKey,
+		id:               id,
+		threshold:        thresh,
+		curve:            info.Curve,
+		round:            1,
+		lCoeffs:          lcoeffs,
+		cosigners:        cosigners,
+		state:            &state{},
+		challengeDeriver: challengeDeriver,
+	}, nil
+}