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sparse_merkle.go
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sparse_merkle.go
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// Package trieutil defines utilities for sparse merkle tries for Ethereum consensus.
package trieutil
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
protodb "github.com/prysmaticlabs/prysm/proto/beacon/db"
"github.com/prysmaticlabs/prysm/shared/bytesutil"
"github.com/prysmaticlabs/prysm/shared/hashutil"
"github.com/prysmaticlabs/prysm/shared/mathutil"
)
// SparseMerkleTrie implements a sparse, general purpose Merkle trie to be used
// across Ethereum consensus functionality.
type SparseMerkleTrie struct {
depth uint
branches [][][]byte
originalItems [][]byte // list of provided items before hashing them into leaves.
}
// NewTrie returns a new merkle trie filled with zerohashes to use.
func NewTrie(depth uint64) (*SparseMerkleTrie, error) {
var zeroBytes [32]byte
items := [][]byte{zeroBytes[:]}
return GenerateTrieFromItems(items, depth)
}
// CreateTrieFromProto creates a Sparse Merkle Trie from its corresponding merkle trie.
func CreateTrieFromProto(trieObj *protodb.SparseMerkleTrie) *SparseMerkleTrie {
trie := &SparseMerkleTrie{
depth: uint(trieObj.Depth),
originalItems: trieObj.OriginalItems,
}
branches := make([][][]byte, len(trieObj.Layers))
for i, layer := range trieObj.Layers {
branches[i] = layer.Layer
}
trie.branches = branches
return trie
}
// GenerateTrieFromItems constructs a Merkle trie from a sequence of byte slices.
func GenerateTrieFromItems(items [][]byte, depth uint64) (*SparseMerkleTrie, error) {
if len(items) == 0 {
return nil, errors.New("no items provided to generate Merkle trie")
}
leaves := items
layers := make([][][]byte, depth+1)
transformedLeaves := make([][]byte, len(leaves))
for i := range leaves {
arr := bytesutil.ToBytes32(leaves[i])
transformedLeaves[i] = arr[:]
}
layers[0] = transformedLeaves
for i := uint64(0); i < depth; i++ {
if len(layers[i])%2 == 1 {
layers[i] = append(layers[i], ZeroHashes[i][:])
}
updatedValues := make([][]byte, 0)
for j := 0; j < len(layers[i]); j += 2 {
concat := hashutil.Hash(append(layers[i][j], layers[i][j+1]...))
updatedValues = append(updatedValues, concat[:])
}
layers[i+1] = updatedValues
}
return &SparseMerkleTrie{
branches: layers,
originalItems: items,
depth: uint(depth),
}, nil
}
// Items returns the original items passed in when creating the Merkle trie.
func (m *SparseMerkleTrie) Items() [][]byte {
return m.originalItems
}
// Root returns the top-most, Merkle root of the trie.
func (m *SparseMerkleTrie) Root() [32]byte {
enc := [32]byte{}
binary.LittleEndian.PutUint64(enc[:], uint64(len(m.originalItems)))
return hashutil.Hash(append(m.branches[len(m.branches)-1][0], enc[:]...))
}
// Insert an item into the trie.
func (m *SparseMerkleTrie) Insert(item []byte, index int) {
for index >= len(m.branches[0]) {
m.branches[0] = append(m.branches[0], ZeroHashes[0][:])
}
someItem := bytesutil.ToBytes32(item)
m.branches[0][index] = someItem[:]
if index >= len(m.originalItems) {
m.originalItems = append(m.originalItems, someItem[:])
} else {
m.originalItems[index] = someItem[:]
}
currentIndex := index
root := bytesutil.ToBytes32(item)
for i := 0; i < int(m.depth); i++ {
isLeft := currentIndex%2 == 0
neighborIdx := currentIndex ^ 1
var neighbor []byte
if neighborIdx >= len(m.branches[i]) {
neighbor = ZeroHashes[i][:]
} else {
neighbor = m.branches[i][neighborIdx]
}
if isLeft {
parentHash := hashutil.Hash(append(root[:], neighbor...))
root = parentHash
} else {
parentHash := hashutil.Hash(append(neighbor, root[:]...))
root = parentHash
}
parentIdx := currentIndex / 2
if len(m.branches[i+1]) == 0 || parentIdx >= len(m.branches[i+1]) {
newItem := root
m.branches[i+1] = append(m.branches[i+1], newItem[:])
} else {
newItem := root
m.branches[i+1][parentIdx] = newItem[:]
}
currentIndex = parentIdx
}
}
// MerkleProof computes a proof from a trie's branches using a Merkle index.
func (m *SparseMerkleTrie) MerkleProof(index int) ([][]byte, error) {
merkleIndex := uint(index)
leaves := m.branches[0]
if index >= len(leaves) {
return nil, fmt.Errorf("merkle index out of range in trie, max range: %d, received: %d", len(leaves), index)
}
proof := make([][]byte, m.depth+1)
for i := uint(0); i < m.depth; i++ {
subIndex := (merkleIndex / (1 << i)) ^ 1
if subIndex < uint(len(m.branches[i])) {
item := bytesutil.ToBytes32(m.branches[i][subIndex])
proof[i] = item[:]
} else {
proof[i] = ZeroHashes[i][:]
}
}
enc := [32]byte{}
binary.LittleEndian.PutUint64(enc[:], uint64(len(m.originalItems)))
proof[len(proof)-1] = enc[:]
return proof, nil
}
// HashTreeRoot of the Merkle trie as defined in the deposit contract.
// Spec Definition:
// sha256(concat(node, self.to_little_endian_64(self.deposit_count), slice(zero_bytes32, start=0, len=24)))
func (m *SparseMerkleTrie) HashTreeRoot() [32]byte {
var zeroBytes [32]byte
depositCount := uint64(len(m.originalItems))
if len(m.originalItems) == 1 && bytes.Equal(m.originalItems[0], zeroBytes[:]) {
// Accounting for empty tries
depositCount = 0
}
newNode := append(m.branches[len(m.branches)-1][0], bytesutil.Bytes8(depositCount)...)
newNode = append(newNode, zeroBytes[:24]...)
return hashutil.Hash(newNode)
}
// ToProto converts the underlying trie into its corresponding
// proto object
func (m *SparseMerkleTrie) ToProto() *protodb.SparseMerkleTrie {
trie := &protodb.SparseMerkleTrie{
Depth: uint64(m.depth),
Layers: make([]*protodb.TrieLayer, len(m.branches)),
OriginalItems: m.originalItems,
}
for i, l := range m.branches {
trie.Layers[i] = &protodb.TrieLayer{
Layer: l,
}
}
return trie
}
// VerifyMerkleBranch verifies a Merkle branch against a root of a trie.
func VerifyMerkleBranch(root, item []byte, merkleIndex int, proof [][]byte, depth uint64) bool {
if len(proof) != int(depth)+1 {
return false
}
node := bytesutil.ToBytes32(item)
for i := 0; i <= int(depth); i++ {
if (uint64(merkleIndex) / mathutil.PowerOf2(uint64(i)) % 2) != 0 {
node = hashutil.Hash(append(proof[i], node[:]...))
} else {
node = hashutil.Hash(append(node[:], proof[i]...))
}
}
return bytes.Equal(root, node[:])
}
// Copy performs a deep copy of the trie.
func (m *SparseMerkleTrie) Copy() *SparseMerkleTrie {
dstBranches := make([][][]byte, len(m.branches))
for i1, srcB1 := range m.branches {
dstBranches[i1] = bytesutil.Copy2dBytes(srcB1)
}
return &SparseMerkleTrie{
depth: m.depth,
branches: dstBranches,
originalItems: bytesutil.Copy2dBytes(m.originalItems),
}
}
// NumOfItems returns the num of items stored in
// the sparse merkle trie. We handle a special case
// where if there is only one item stored and it is a
// empty 32-byte root.
func (m *SparseMerkleTrie) NumOfItems() int {
var zeroBytes [32]byte
if len(m.originalItems) == 1 && bytes.Equal(m.originalItems[0], zeroBytes[:]) {
return 0
}
return len(m.originalItems)
}