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// Copyright (C) 2019-2023 Algorand, Inc.
// This file is part of go-algorand
//
// go-algorand is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// go-algorand is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with go-algorand. If not, see <https://www.gnu.org/licenses/>.
package stateproof
import (
"errors"
"fmt"
"github.com/algorand/go-algorand/crypto"
"github.com/algorand/go-algorand/crypto/merklearray"
)
// Errors for the StateProof verifier
var (
ErrCoinNotInRange = errors.New("coin is not within slot weight range")
ErrNoRevealInPos = errors.New("no reveal for position")
ErrTreeDepthTooLarge = errors.New("tree depth is too large")
)
// Verifier is used to verify a state proof. those fields represent all the verifier's trusted data
type Verifier struct {
strengthTarget uint64
lnProvenWeight uint64 // ln(provenWeight) as integer with 16 bits of precision
participantsCommitment crypto.GenericDigest
}
// MkVerifier constructs a verifier to check the state proof. the arguments for this function
// represent all the verifier's trusted data
func MkVerifier(partcom crypto.GenericDigest, provenWeight uint64, strengthTarget uint64) (*Verifier, error) {
lnProvenWt, err := LnIntApproximation(provenWeight)
if err != nil {
return nil, err
}
return &Verifier{
strengthTarget: strengthTarget,
lnProvenWeight: lnProvenWt,
participantsCommitment: partcom,
}, nil
}
// MkVerifierWithLnProvenWeight constructs a verifier to check the state proof. the arguments for this function
// represent all the verifier's trusted data. This function uses the Ln(provenWeight) approximation value
func MkVerifierWithLnProvenWeight(partcom crypto.GenericDigest, lnProvenWt uint64, strengthTarget uint64) *Verifier {
return &Verifier{
strengthTarget: strengthTarget,
lnProvenWeight: lnProvenWt,
participantsCommitment: partcom,
}
}
// Verify checks if s is a valid state proof for the data on a round.
// it uses the trusted data from the Verifier struct
func (v *Verifier) Verify(round uint64, data MessageHash, s *StateProof) error {
if err := verifyStateProofTreesDepth(s); err != nil {
return err
}
nr := uint64(len(s.PositionsToReveal))
if err := verifyWeights(s.SignedWeight, v.lnProvenWeight, nr, v.strengthTarget); err != nil {
return err
}
version := s.MerkleSignatureSaltVersion
for _, reveal := range s.Reveals {
if err := reveal.SigSlot.Sig.ValidateSaltVersion(version); err != nil {
return err
}
}
sigs := make(map[uint64]crypto.Hashable)
parts := make(map[uint64]crypto.Hashable)
for pos, r := range s.Reveals {
sig, err := buildCommittableSignature(r.SigSlot)
if err != nil {
return err
}
sigs[pos] = sig
parts[pos] = r.Part
// verify that the msg and the signature is valid under the given participant's Pk
err = r.Part.PK.VerifyBytes(
round,
data[:],
&r.SigSlot.Sig,
)
if err != nil {
return fmt.Errorf("signature in reveal pos %d does not verify. error is %w", pos, err)
}
}
// verify all the reveals proofs on the signature commitment.
if err := merklearray.VerifyVectorCommitment(s.SigCommit[:], sigs, &s.SigProofs); err != nil {
return err
}
// verify all the reveals proofs on the participant commitment.
if err := merklearray.VerifyVectorCommitment(v.participantsCommitment[:], parts, &s.PartProofs); err != nil {
return err
}
choice := coinChoiceSeed{
partCommitment: v.participantsCommitment,
lnProvenWeight: v.lnProvenWeight,
sigCommitment: s.SigCommit,
signedWeight: s.SignedWeight,
data: data,
}
coinHash := makeCoinGenerator(&choice)
for j := uint64(0); j < nr; j++ {
pos := s.PositionsToReveal[j]
reveal, exists := s.Reveals[pos]
if !exists {
return fmt.Errorf("%w: %d", ErrNoRevealInPos, pos)
}
coin := coinHash.getNextCoin()
if !(reveal.SigSlot.L <= coin && coin < reveal.SigSlot.L+reveal.Part.Weight) {
return fmt.Errorf("%w: for reveal pos %d and coin %d, ", ErrCoinNotInRange, pos, coin)
}
}
return nil
}
func verifyStateProofTreesDepth(s *StateProof) error {
if s.SigProofs.TreeDepth > MaxTreeDepth {
return fmt.Errorf("%w. sigTree depth is %d", ErrTreeDepthTooLarge, s.SigProofs.TreeDepth)
}
if s.PartProofs.TreeDepth > MaxTreeDepth {
return fmt.Errorf("%w. partTree depth is %d", ErrTreeDepthTooLarge, s.PartProofs.TreeDepth)
}
return nil
}
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