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package merkle
import (
"bytes"
"errors"
"fmt"
"github.com/tendermint/tendermint/crypto/tmhash"
tmcrypto "github.com/tendermint/tendermint/proto/tendermint/crypto"
)
const (
// MaxAunts is the maximum number of aunts that can be included in a Proof.
// This corresponds to a tree of size 2^100, which should be sufficient for all conceivable purposes.
// This maximum helps prevent Denial-of-Service attacks by limitting the size of the proofs.
MaxAunts = 100
)
// Proof represents a Merkle proof.
// NOTE: The convention for proofs is to include leaf hashes but to
// exclude the root hash.
// This convention is implemented across IAVL range proofs as well.
// Keep this consistent unless there's a very good reason to change
// everything. This also affects the generalized proof system as
// well.
type Proof struct {
Total int64 `json:"total,string"` // Total number of items.
Index int64 `json:"index,string"` // Index of item to prove.
LeafHash []byte `json:"leaf_hash"` // Hash of item value.
Aunts [][]byte `json:"aunts"` // Hashes from leaf's sibling to a root's child.
}
// ProofsFromByteSlices computes inclusion proof for given items.
// proofs[0] is the proof for items[0].
func ProofsFromByteSlices(items [][]byte) (rootHash []byte, proofs []*Proof) {
trails, rootSPN := trailsFromByteSlices(items)
rootHash = rootSPN.Hash
proofs = make([]*Proof, len(items))
for i, trail := range trails {
proofs[i] = &Proof{
Total: int64(len(items)),
Index: int64(i),
LeafHash: trail.Hash,
Aunts: trail.FlattenAunts(),
}
}
return
}
// Verify that the Proof proves the root hash.
// Check sp.Index/sp.Total manually if needed
func (sp *Proof) Verify(rootHash []byte, leaf []byte) error {
if sp.Total < 0 {
return errors.New("proof total must be positive")
}
if sp.Index < 0 {
return errors.New("proof index cannot be negative")
}
leafHash := leafHash(leaf)
if !bytes.Equal(sp.LeafHash, leafHash) {
return fmt.Errorf("invalid leaf hash: wanted %X got %X", leafHash, sp.LeafHash)
}
computedHash := sp.ComputeRootHash()
if !bytes.Equal(computedHash, rootHash) {
return fmt.Errorf("invalid root hash: wanted %X got %X", rootHash, computedHash)
}
return nil
}
// Compute the root hash given a leaf hash. Does not verify the result.
func (sp *Proof) ComputeRootHash() []byte {
return computeHashFromAunts(
sp.Index,
sp.Total,
sp.LeafHash,
sp.Aunts,
)
}
// String implements the stringer interface for Proof.
// It is a wrapper around StringIndented.
func (sp *Proof) String() string {
return sp.StringIndented("")
}
// StringIndented generates a canonical string representation of a Proof.
func (sp *Proof) StringIndented(indent string) string {
return fmt.Sprintf(`Proof{
%s Aunts: %X
%s}`,
indent, sp.Aunts,
indent)
}
// ValidateBasic performs basic validation.
// NOTE: it expects the LeafHash and the elements of Aunts to be of size tmhash.Size,
// and it expects at most MaxAunts elements in Aunts.
func (sp *Proof) ValidateBasic() error {
if sp.Total < 0 {
return errors.New("negative Total")
}
if sp.Index < 0 {
return errors.New("negative Index")
}
if len(sp.LeafHash) != tmhash.Size {
return fmt.Errorf("expected LeafHash size to be %d, got %d", tmhash.Size, len(sp.LeafHash))
}
if len(sp.Aunts) > MaxAunts {
return fmt.Errorf("expected no more than %d aunts, got %d", MaxAunts, len(sp.Aunts))
}
for i, auntHash := range sp.Aunts {
if len(auntHash) != tmhash.Size {
return fmt.Errorf("expected Aunts#%d size to be %d, got %d", i, tmhash.Size, len(auntHash))
}
}
return nil
}
func (sp *Proof) ToProto() *tmcrypto.Proof {
if sp == nil {
return nil
}
pb := new(tmcrypto.Proof)
pb.Total = sp.Total
pb.Index = sp.Index
pb.LeafHash = sp.LeafHash
pb.Aunts = sp.Aunts
return pb
}
func ProofFromProto(pb *tmcrypto.Proof) (*Proof, error) {
if pb == nil {
return nil, errors.New("nil proof")
}
sp := new(Proof)
sp.Total = pb.Total
sp.Index = pb.Index
sp.LeafHash = pb.LeafHash
sp.Aunts = pb.Aunts
return sp, sp.ValidateBasic()
}
// Use the leafHash and innerHashes to get the root merkle hash.
// If the length of the innerHashes slice isn't exactly correct, the result is nil.
// Recursive impl.
func computeHashFromAunts(index, total int64, leafHash []byte, innerHashes [][]byte) []byte {
if index >= total || index < 0 || total <= 0 {
return nil
}
switch total {
case 0:
panic("Cannot call computeHashFromAunts() with 0 total")
case 1:
if len(innerHashes) != 0 {
return nil
}
return leafHash
default:
if len(innerHashes) == 0 {
return nil
}
numLeft := getSplitPoint(total)
if index < numLeft {
leftHash := computeHashFromAunts(index, numLeft, leafHash, innerHashes[:len(innerHashes)-1])
if leftHash == nil {
return nil
}
return innerHash(leftHash, innerHashes[len(innerHashes)-1])
}
rightHash := computeHashFromAunts(index-numLeft, total-numLeft, leafHash, innerHashes[:len(innerHashes)-1])
if rightHash == nil {
return nil
}
return innerHash(innerHashes[len(innerHashes)-1], rightHash)
}
}
// ProofNode is a helper structure to construct merkle proof.
// The node and the tree is thrown away afterwards.
// Exactly one of node.Left and node.Right is nil, unless node is the root, in which case both are nil.
// node.Parent.Hash = hash(node.Hash, node.Right.Hash) or
// hash(node.Left.Hash, node.Hash), depending on whether node is a left/right child.
type ProofNode struct {
Hash []byte
Parent *ProofNode
Left *ProofNode // Left sibling (only one of Left,Right is set)
Right *ProofNode // Right sibling (only one of Left,Right is set)
}
// FlattenAunts will return the inner hashes for the item corresponding to the leaf,
// starting from a leaf ProofNode.
func (spn *ProofNode) FlattenAunts() [][]byte {
// Nonrecursive impl.
innerHashes := [][]byte{}
for spn != nil {
switch {
case spn.Left != nil:
innerHashes = append(innerHashes, spn.Left.Hash)
case spn.Right != nil:
innerHashes = append(innerHashes, spn.Right.Hash)
default:
// FIXME(fromberger): Per the documentation above, exactly one of
// these fields should be set. If that is true, this should probably
// be a panic since it violates the invariant. If not, when can it
// be OK to have no siblings? Does this occur at the leaves?
}
spn = spn.Parent
}
return innerHashes
}
// trails[0].Hash is the leaf hash for items[0].
// trails[i].Parent.Parent....Parent == root for all i.
func trailsFromByteSlices(items [][]byte) (trails []*ProofNode, root *ProofNode) {
// Recursive impl.
switch len(items) {
case 0:
return []*ProofNode{}, &ProofNode{emptyHash(), nil, nil, nil}
case 1:
trail := &ProofNode{leafHash(items[0]), nil, nil, nil}
return []*ProofNode{trail}, trail
default:
k := getSplitPoint(int64(len(items)))
lefts, leftRoot := trailsFromByteSlices(items[:k])
rights, rightRoot := trailsFromByteSlices(items[k:])
rootHash := innerHash(leftRoot.Hash, rightRoot.Hash)
root := &ProofNode{rootHash, nil, nil, nil}
leftRoot.Parent = root
leftRoot.Right = rightRoot
rightRoot.Parent = root
rightRoot.Left = leftRoot
return append(lefts, rights...), root
}
}