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operator.go
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operator.go
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/*
Copyright © 2020 ConsenSys
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package rollup
import (
"bytes"
"hash"
"math/big"
"github.com/consensys/gnark-crypto/accumulator/merkletree"
"github.com/consensys/gnark-crypto/ecc/bn254/fr/mimc"
)
var hFunc = mimc.NewMiMC()
// BatchSize size of a batch of transactions to put in a snark
var BatchSize = 10
// Queue queue for storing the transfers (fixed size queue)
type Queue struct {
listTransfers chan Transfer
}
// NewQueue creates a new queue, BatchSizeCircuit is the capacity
func NewQueue(BatchSizeCircuit int) Queue {
resChan := make(chan Transfer, BatchSizeCircuit)
var res Queue
res.listTransfers = resChan
return res
}
// Operator represents a rollup operator
type Operator struct {
State []byte // list of accounts: index ∥ nonce ∥ balance ∥ pubkeyX ∥ pubkeyY, each chunk is 256 bits
HashState []byte // Hashed version of the state, each chunk is 256bits: ... ∥ H(index ∥ nonce ∥ balance ∥ pubkeyX ∥ pubkeyY)) ∥ ...
AccountMap map[string]uint64 // hashmap of all available accounts (the key is the account.pubkey.X), the value is the index of the account in the state
nbAccounts int // number of accounts managed by this operator
h hash.Hash // hash function used to build the Merkle Tree
q Queue // queue of transfers
batch int // current number of transactions in a batch
witnesses Circuit // witnesses for the snark circuit
}
// NewOperator creates a new operator.
// nbAccounts is the number of accounts managed by this operator, h is the hash function for the merkle proofs
func NewOperator(nbAccounts int) Operator {
res := Operator{}
// create a list of empty accounts
res.State = make([]byte, SizeAccount*nbAccounts)
// initialize hash of the state
res.HashState = make([]byte, hFunc.Size()*nbAccounts)
for i := 0; i < nbAccounts; i++ {
hFunc.Reset()
_, _ = hFunc.Write(res.State[i*SizeAccount : i*SizeAccount+SizeAccount])
s := hFunc.Sum([]byte{})
copy(res.HashState[i*hFunc.Size():(i+1)*hFunc.Size()], s)
}
res.AccountMap = make(map[string]uint64)
res.nbAccounts = nbAccounts
res.h = hFunc
res.q = NewQueue(BatchSize)
res.batch = 0
return res
}
// readAccount reads the account located at index i
func (o *Operator) readAccount(i uint64) (Account, error) {
var res Account
err := Deserialize(&res, o.State[int(i)*SizeAccount:int(i)*SizeAccount+SizeAccount])
if err != nil {
return res, err
}
return res, nil
}
// updateAccount updates the state according to transfer
// numTransfer is the number of the transfer currently handled (between 0 and BatchSizeCircuit)
func (o *Operator) updateState(t Transfer, numTransfer int) error {
var posSender, posReceiver uint64
var ok bool
// ext := strconv.Itoa(numTransfer)
segmentSize := o.h.Size()
// read sender's account
b := t.senderPubKey.A.X.Bytes()
if posSender, ok = o.AccountMap[string(b[:])]; !ok {
return ErrNonExistingAccount
}
senderAccount, err := o.readAccount(posSender)
if err != nil {
return err
}
if senderAccount.index != posSender {
return ErrIndexConsistency
}
// read receiver's account
b = t.receiverPubKey.A.X.Bytes()
if posReceiver, ok = o.AccountMap[string(b[:])]; !ok {
return ErrNonExistingAccount
}
receiverAccount, err := o.readAccount(posReceiver)
if err != nil {
return err
}
if receiverAccount.index != posReceiver {
return ErrIndexConsistency
}
// set witnesses for the leaves
o.witnesses.LeafReceiver[numTransfer] = posReceiver
o.witnesses.LeafSender[numTransfer] = posSender
// set witnesses for the public keys
o.witnesses.PublicKeysSender[numTransfer].A.X = senderAccount.pubKey.A.X
o.witnesses.PublicKeysSender[numTransfer].A.Y = senderAccount.pubKey.A.Y
o.witnesses.PublicKeysReceiver[numTransfer].A.X = receiverAccount.pubKey.A.X
o.witnesses.PublicKeysReceiver[numTransfer].A.Y = receiverAccount.pubKey.A.Y
// set witnesses for the accounts before update
o.witnesses.SenderAccountsBefore[numTransfer].Index = senderAccount.index
o.witnesses.SenderAccountsBefore[numTransfer].Nonce = senderAccount.nonce
o.witnesses.SenderAccountsBefore[numTransfer].Balance = senderAccount.balance
o.witnesses.ReceiverAccountsBefore[numTransfer].Index = receiverAccount.index
o.witnesses.ReceiverAccountsBefore[numTransfer].Nonce = receiverAccount.nonce
o.witnesses.ReceiverAccountsBefore[numTransfer].Balance = receiverAccount.balance
// Set witnesses for the proof of inclusion of sender and receivers account before update
var buf bytes.Buffer
_, err = buf.Write(o.HashState)
if err != nil {
return err
}
merkleRootBefore, proofInclusionSenderBefore, numLeaves, err := merkletree.BuildReaderProof(&buf, o.h, segmentSize, posSender)
if err != nil {
return err
}
// verify the proof in plain go...
merkletree.VerifyProof(o.h, merkleRootBefore, proofInclusionSenderBefore, posSender, numLeaves)
buf.Reset() // the buffer needs to be reset
_, err = buf.Write(o.HashState)
if err != nil {
return err
}
_, proofInclusionReceiverBefore, _, err := merkletree.BuildReaderProof(&buf, o.h, segmentSize, posReceiver)
if err != nil {
return err
}
o.witnesses.RootHashesBefore[numTransfer] = merkleRootBefore
o.witnesses.MerkleProofReceiverBefore[numTransfer].RootHash = merkleRootBefore
o.witnesses.MerkleProofSenderBefore[numTransfer].RootHash = merkleRootBefore
for i := 0; i < len(proofInclusionSenderBefore); i++ {
o.witnesses.MerkleProofReceiverBefore[numTransfer].Path[i] = proofInclusionReceiverBefore[i]
o.witnesses.MerkleProofSenderBefore[numTransfer].Path[i] = proofInclusionSenderBefore[i]
}
// set witnesses for the transfer
o.witnesses.Transfers[numTransfer].Amount = t.amount
o.witnesses.Transfers[numTransfer].Signature.R.X = t.signature.R.X
o.witnesses.Transfers[numTransfer].Signature.R.Y = t.signature.R.Y
o.witnesses.Transfers[numTransfer].Signature.S = t.signature.S[:]
// verifying the signature. The msg is the hash (o.h) of the transfer
// nonce ∥ amount ∥ senderpubKey(x&y) ∥ receiverPubkey(x&y)
resSig, err := t.Verify(o.h)
if err != nil {
return err
}
if !resSig {
return ErrWrongSignature
}
// checks if the amount is correct
var bAmount, bBalance big.Int
receiverAccount.balance.BigInt(&bBalance)
t.amount.BigInt(&bAmount)
if bAmount.Cmp(&bBalance) == 1 {
return ErrAmountTooHigh
}
// check if the nonce is correct
if t.nonce != senderAccount.nonce {
return ErrNonce
}
// update balances
senderAccount.balance.Sub(&senderAccount.balance, &t.amount)
receiverAccount.balance.Add(&receiverAccount.balance, &t.amount)
// update the nonce of the sender
senderAccount.nonce++
// set the witnesses for the account after update
o.witnesses.ReceiverAccountsAfter[numTransfer].Index = receiverAccount.index
o.witnesses.ReceiverAccountsAfter[numTransfer].Nonce = receiverAccount.nonce
o.witnesses.ReceiverAccountsAfter[numTransfer].Balance = receiverAccount.balance
o.witnesses.SenderAccountsAfter[numTransfer].Index = senderAccount.index
o.witnesses.SenderAccountsAfter[numTransfer].Nonce = senderAccount.nonce
o.witnesses.SenderAccountsAfter[numTransfer].Balance = senderAccount.balance
// update the state of the operator
copy(o.State[int(posSender)*SizeAccount:], senderAccount.Serialize())
o.h.Reset()
_, _ = o.h.Write(senderAccount.Serialize())
bufSender := o.h.Sum([]byte{})
copy(o.HashState[int(posSender)*o.h.Size():(int(posSender)+1)*o.h.Size()], bufSender)
copy(o.State[int(posReceiver)*SizeAccount:], receiverAccount.Serialize())
o.h.Reset()
_, _ = o.h.Write(receiverAccount.Serialize())
bufReceiver := o.h.Sum([]byte{})
copy(o.HashState[int(posReceiver)*o.h.Size():(int(posReceiver)+1)*o.h.Size()], bufReceiver)
// Set witnesses for the proof of inclusion of sender and receivers account after update
buf.Reset()
_, err = buf.Write(o.HashState)
if err != nil {
return err
}
merkleRootAfer, proofInclusionSenderAfter, _, err := merkletree.BuildReaderProof(&buf, o.h, segmentSize, posSender)
if err != nil {
return err
}
// merkleProofHelperSenderAfter := merkle.GenerateProofHelper(proofInclusionSenderAfter, posSender, numLeaves)
buf.Reset() // the buffer needs to be reset
_, err = buf.Write(o.HashState)
if err != nil {
return err
}
_, proofInclusionReceiverAfter, _, err := merkletree.BuildReaderProof(&buf, o.h, segmentSize, posReceiver)
if err != nil {
return err
}
// merkleProofHelperReceiverAfter := merkle.GenerateProofHelper(proofInclusionReceiverAfter, posReceiver, numLeaves)
o.witnesses.RootHashesAfter[numTransfer] = merkleRootAfer
o.witnesses.MerkleProofReceiverAfter[numTransfer].RootHash = merkleRootAfer
o.witnesses.MerkleProofSenderAfter[numTransfer].RootHash = merkleRootAfer
for i := 0; i < len(proofInclusionSenderAfter); i++ {
o.witnesses.MerkleProofReceiverAfter[numTransfer].Path[i] = proofInclusionReceiverAfter[i]
o.witnesses.MerkleProofSenderAfter[numTransfer].Path[i] = proofInclusionSenderAfter[i]
}
return nil
}