all: on-chain oracle checkpoint syncing (#19543)

* all: implement simple checkpoint syncing

cmd, les, node: remove callback mechanism

cmd, node: remove callback definition

les: simplify the registrar

les: expose checkpoint rpc services in the light client

les, light: don't store untrusted receipt

cmd, contracts, les: discard stale checkpoint

cmd, contracts/registrar: loose restriction of registeration

cmd, contracts: add replay-protection

all: off-chain multi-signature contract

params: deploy checkpoint contract for rinkeby

cmd/registrar: add raw signing mode for registrar

cmd/registrar, contracts/registrar, les: fixed messages

* cmd/registrar, contracts/registrar: fix lints

* accounts/abi/bind, les: address comments

* cmd, contracts, les, light, params: minor checkpoint sync cleanups

* cmd, eth, les, light: move checkpoint config to config file

* cmd, eth, les, params: address comments

* eth, les, params: address comments

* cmd: polish up the checkpoint admin CLI

* cmd, contracts, params: deploy new version contract

* cmd/checkpoint-admin: add another flag for clef mode signing

* cmd, contracts, les: rename and regen checkpoint oracle with abigen

1 files changed, 158 insertions, 0 deletions

diff --git a/les/checkpointoracle.go b/les/checkpointoracle.go
new file mode 100644
index 000000000..4695fbc16
--- /dev/null
+++ b/les/checkpointoracle.go
@@ -0,0 +1,158 @@
+// Copyright 2019 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library 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 Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package les
+
+import (
+	"encoding/binary"
+	"sync/atomic"
+
+	"github.com/ethereum/go-ethereum/accounts/abi/bind"
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/contracts/checkpointoracle"
+	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/log"
+	"github.com/ethereum/go-ethereum/params"
+)
+
+// checkpointOracle is responsible for offering the latest stable checkpoint
+// generated and announced by the contract admins on-chain. The checkpoint is
+// verified by clients locally during the checkpoint syncing.
+type checkpointOracle struct {
+	config   *params.CheckpointOracleConfig
+	contract *checkpointoracle.CheckpointOracle
+
+	// Whether the contract backend is set.
+	running int32
+
+	getLocal     func(uint64) params.TrustedCheckpoint // Function used to retrieve local checkpoint
+	syncDoneHook func()                                // Function used to notify that light syncing has completed.
+}
+
+// newCheckpointOracle returns a checkpoint registrar handler.
+func newCheckpointOracle(config *params.CheckpointOracleConfig, getLocal func(uint64) params.TrustedCheckpoint) *checkpointOracle {
+	if config == nil {
+		log.Info("Checkpoint registrar is not enabled")
+		return nil
+	}
+	if config.Address == (common.Address{}) || uint64(len(config.Signers)) < config.Threshold {
+		log.Warn("Invalid checkpoint registrar config")
+		return nil
+	}
+	log.Info("Configured checkpoint registrar", "address", config.Address, "signers", len(config.Signers), "threshold", config.Threshold)
+
+	return &checkpointOracle{
+		config:   config,
+		getLocal: getLocal,
+	}
+}
+
+// start binds the registrar contract and start listening to the
+// newCheckpointEvent for the server side.
+func (reg *checkpointOracle) start(backend bind.ContractBackend) {
+	contract, err := checkpointoracle.NewCheckpointOracle(reg.config.Address, backend)
+	if err != nil {
+		log.Error("Oracle contract binding failed", "err", err)
+		return
+	}
+	if !atomic.CompareAndSwapInt32(&reg.running, 0, 1) {
+		log.Error("Already bound and listening to registrar")
+		return
+	}
+	reg.contract = contract
+}
+
+// isRunning returns an indicator whether the registrar is running.
+func (reg *checkpointOracle) isRunning() bool {
+	return atomic.LoadInt32(&reg.running) == 1
+}
+
+// stableCheckpoint returns the stable checkpoint which was generated by local
+// indexers and announced by trusted signers.
+func (reg *checkpointOracle) stableCheckpoint() (*params.TrustedCheckpoint, uint64) {
+	// Retrieve the latest checkpoint from the contract, abort if empty
+	latest, hash, height, err := reg.contract.Contract().GetLatestCheckpoint(nil)
+	if err != nil || (latest == 0 && hash == [32]byte{}) {
+		return nil, 0
+	}
+	local := reg.getLocal(latest)
+
+	// The following scenarios may occur:
+	//
+	// * local node is out of sync so that it doesn't have the
+	//   checkpoint which registered in the contract.
+	// * local checkpoint doesn't match with the registered one.
+	//
+	// In both cases, server won't send the **stable** checkpoint
+	// to the client(no worry, client can use hardcoded one instead).
+	if local.HashEqual(common.Hash(hash)) {
+		return &local, height.Uint64()
+	}
+	return nil, 0
+}
+
+// verifySigners recovers the signer addresses according to the signature and
+// checks whether there are enough approvals to finalize the checkpoint.
+func (reg *checkpointOracle) verifySigners(index uint64, hash [32]byte, signatures [][]byte) (bool, []common.Address) {
+	// Short circuit if the given signatures doesn't reach the threshold.
+	if len(signatures) < int(reg.config.Threshold) {
+		return false, nil
+	}
+	var (
+		signers []common.Address
+		checked = make(map[common.Address]struct{})
+	)
+	for i := 0; i < len(signatures); i++ {
+		if len(signatures[i]) != 65 {
+			continue
+		}
+		// EIP 191 style signatures
+		//
+		// Arguments when calculating hash to validate
+		// 1: byte(0x19) - the initial 0x19 byte
+		// 2: byte(0) - the version byte (data with intended validator)
+		// 3: this - the validator address
+		// --  Application specific data
+		// 4 : checkpoint section_index (uint64)
+		// 5 : checkpoint hash (bytes32)
+		//     hash = keccak256(checkpoint_index, section_head, cht_root, bloom_root)
+		buf := make([]byte, 8)
+		binary.BigEndian.PutUint64(buf, index)
+		data := append([]byte{0x19, 0x00}, append(reg.config.Address.Bytes(), append(buf, hash[:]...)...)...)
+		signatures[i][64] -= 27 // Transform V from 27/28 to 0/1 according to the yellow paper for verification.
+		pubkey, err := crypto.Ecrecover(crypto.Keccak256(data), signatures[i])
+		if err != nil {
+			return false, nil
+		}
+		var signer common.Address
+		copy(signer[:], crypto.Keccak256(pubkey[1:])[12:])
+		if _, exist := checked[signer]; exist {
+			continue
+		}
+		for _, s := range reg.config.Signers {
+			if s == signer {
+				signers = append(signers, signer)
+				checked[signer] = struct{}{}
+			}
+		}
+	}
+	threshold := reg.config.Threshold
+	if uint64(len(signers)) < threshold {
+		log.Warn("Not enough signers to approve checkpoint", "signers", len(signers), "threshold", threshold)
+		return false, nil
+	}
+	return true, signers
+}