simple merkle tree
This commit is contained in:
Ethan Buchman
parent
2f8551d3b6
commit
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## Simple Merkle Tree
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For smaller static data structures that don't require immutable snapshots or mutability;
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for instance the transactions and validation signatures of a block can be hashed using this simple merkle tree logic.
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/*
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Computes a deterministic minimal height merkle tree hash.
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If the number of items is not a power of two, some leaves
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will be at different levels. Tries to keep both sides of
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the tree the same size, but the left may be one greater.
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Use this for short deterministic trees, such as the validator list.
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For larger datasets, use IAVLTree.
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*
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/ \
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/ \
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/ \
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/ \
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* *
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/ \ / \
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/ \ / \
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/ \ / \
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* * * h6
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/ \ / \ / \
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h0 h1 h2 h3 h4 h5
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*/
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package merkle
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import (
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"bytes"
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"fmt"
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"sort"
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"golang.org/x/crypto/ripemd160"
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. "github.com/tendermint/go-common"
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"github.com/tendermint/go-wire"
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)
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func SimpleHashFromTwoHashes(left []byte, right []byte) []byte {
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var n int
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var err error
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var hasher = ripemd160.New()
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wire.WriteByteSlice(left, hasher, &n, &err)
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wire.WriteByteSlice(right, hasher, &n, &err)
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if err != nil {
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PanicCrisis(err)
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}
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return hasher.Sum(nil)
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}
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func SimpleHashFromHashes(hashes [][]byte) []byte {
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// Recursive impl.
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switch len(hashes) {
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case 0:
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return nil
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case 1:
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return hashes[0]
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default:
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left := SimpleHashFromHashes(hashes[:(len(hashes)+1)/2])
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right := SimpleHashFromHashes(hashes[(len(hashes)+1)/2:])
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return SimpleHashFromTwoHashes(left, right)
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}
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}
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// Convenience for SimpleHashFromHashes.
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func SimpleHashFromBinaries(items []interface{}) []byte {
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hashes := make([][]byte, len(items))
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for i, item := range items {
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hashes[i] = SimpleHashFromBinary(item)
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}
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return SimpleHashFromHashes(hashes)
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}
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// General Convenience
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func SimpleHashFromBinary(item interface{}) []byte {
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hasher, n, err := ripemd160.New(), new(int), new(error)
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wire.WriteBinary(item, hasher, n, err)
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if *err != nil {
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PanicCrisis(err)
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}
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return hasher.Sum(nil)
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}
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// Convenience for SimpleHashFromHashes.
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func SimpleHashFromHashables(items []Hashable) []byte {
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hashes := make([][]byte, len(items))
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for i, item := range items {
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hash := item.Hash()
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hashes[i] = hash
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}
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return SimpleHashFromHashes(hashes)
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}
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// Convenience for SimpleHashFromHashes.
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func SimpleHashFromMap(m map[string]interface{}) []byte {
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kpPairsH := MakeSortedKVPairs(m)
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return SimpleHashFromHashables(kpPairsH)
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}
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//--------------------------------------------------------------------------------
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/* Convenience struct for key-value pairs.
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A list of KVPairs is hashed via `SimpleHashFromHashables`.
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NOTE: Each `Value` is encoded for hashing without extra type information,
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so the user is presumed to be aware of the Value types.
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*/
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type KVPair struct {
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Key string
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Value interface{}
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}
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func (kv KVPair) Hash() []byte {
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hasher, n, err := ripemd160.New(), new(int), new(error)
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wire.WriteString(kv.Key, hasher, n, err)
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if kvH, ok := kv.Value.(Hashable); ok {
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wire.WriteByteSlice(kvH.Hash(), hasher, n, err)
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} else {
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wire.WriteBinary(kv.Value, hasher, n, err)
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}
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if *err != nil {
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PanicSanity(*err)
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}
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return hasher.Sum(nil)
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}
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type KVPairs []KVPair
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func (kvps KVPairs) Len() int { return len(kvps) }
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func (kvps KVPairs) Less(i, j int) bool { return kvps[i].Key < kvps[j].Key }
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func (kvps KVPairs) Swap(i, j int) { kvps[i], kvps[j] = kvps[j], kvps[i] }
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func (kvps KVPairs) Sort() { sort.Sort(kvps) }
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func MakeSortedKVPairs(m map[string]interface{}) []Hashable {
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kvPairs := []KVPair{}
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for k, v := range m {
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kvPairs = append(kvPairs, KVPair{k, v})
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}
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KVPairs(kvPairs).Sort()
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kvPairsH := []Hashable{}
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for _, kvp := range kvPairs {
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kvPairsH = append(kvPairsH, kvp)
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}
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return kvPairsH
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}
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//--------------------------------------------------------------------------------
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type SimpleProof struct {
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Aunts [][]byte `json:"aunts"` // Hashes from leaf's sibling to a root's child.
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}
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// proofs[0] is the proof for items[0].
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func SimpleProofsFromHashables(items []Hashable) (rootHash []byte, proofs []*SimpleProof) {
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trails, rootSPN := trailsFromHashables(items)
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rootHash = rootSPN.Hash
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proofs = make([]*SimpleProof, len(items))
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for i, trail := range trails {
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proofs[i] = &SimpleProof{
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Aunts: trail.FlattenAunts(),
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}
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}
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return
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}
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// Verify that leafHash is a leaf hash of the simple-merkle-tree
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// which hashes to rootHash.
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func (sp *SimpleProof) Verify(index int, total int, leafHash []byte, rootHash []byte) bool {
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computedHash := computeHashFromAunts(index, total, leafHash, sp.Aunts)
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if computedHash == nil {
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return false
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}
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if !bytes.Equal(computedHash, rootHash) {
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return false
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}
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return true
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}
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func (sp *SimpleProof) String() string {
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return sp.StringIndented("")
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}
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func (sp *SimpleProof) StringIndented(indent string) string {
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return fmt.Sprintf(`SimpleProof{
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%s Aunts: %X
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%s}`,
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indent, sp.Aunts,
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indent)
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}
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// Use the leafHash and innerHashes to get the root merkle hash.
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// If the length of the innerHashes slice isn't exactly correct, the result is nil.
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func computeHashFromAunts(index int, total int, leafHash []byte, innerHashes [][]byte) []byte {
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// Recursive impl.
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if index >= total {
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return nil
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}
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switch total {
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case 0:
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PanicSanity("Cannot call computeHashFromAunts() with 0 total")
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return nil
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case 1:
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if len(innerHashes) != 0 {
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return nil
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}
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return leafHash
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default:
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if len(innerHashes) == 0 {
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return nil
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}
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numLeft := (total + 1) / 2
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if index < numLeft {
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leftHash := computeHashFromAunts(index, numLeft, leafHash, innerHashes[:len(innerHashes)-1])
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if leftHash == nil {
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return nil
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}
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return SimpleHashFromTwoHashes(leftHash, innerHashes[len(innerHashes)-1])
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} else {
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rightHash := computeHashFromAunts(index-numLeft, total-numLeft, leafHash, innerHashes[:len(innerHashes)-1])
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if rightHash == nil {
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return nil
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}
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return SimpleHashFromTwoHashes(innerHashes[len(innerHashes)-1], rightHash)
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}
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}
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}
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// Helper structure to construct merkle proof.
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// The node and the tree is thrown away afterwards.
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// Exactly one of node.Left and node.Right is nil, unless node is the root, in which case both are nil.
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// node.Parent.Hash = hash(node.Hash, node.Right.Hash) or
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// hash(node.Left.Hash, node.Hash), depending on whether node is a left/right child.
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type SimpleProofNode struct {
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Hash []byte
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Parent *SimpleProofNode
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Left *SimpleProofNode // Left sibling (only one of Left,Right is set)
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Right *SimpleProofNode // Right sibling (only one of Left,Right is set)
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}
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// Starting from a leaf SimpleProofNode, FlattenAunts() will return
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// the inner hashes for the item corresponding to the leaf.
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func (spn *SimpleProofNode) FlattenAunts() [][]byte {
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// Nonrecursive impl.
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innerHashes := [][]byte{}
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for spn != nil {
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if spn.Left != nil {
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innerHashes = append(innerHashes, spn.Left.Hash)
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} else if spn.Right != nil {
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innerHashes = append(innerHashes, spn.Right.Hash)
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} else {
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break
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}
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spn = spn.Parent
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}
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return innerHashes
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}
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// trails[0].Hash is the leaf hash for items[0].
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// trails[i].Parent.Parent....Parent == root for all i.
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func trailsFromHashables(items []Hashable) (trails []*SimpleProofNode, root *SimpleProofNode) {
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// Recursive impl.
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switch len(items) {
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case 0:
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return nil, nil
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case 1:
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trail := &SimpleProofNode{items[0].Hash(), nil, nil, nil}
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return []*SimpleProofNode{trail}, trail
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default:
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lefts, leftRoot := trailsFromHashables(items[:(len(items)+1)/2])
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rights, rightRoot := trailsFromHashables(items[(len(items)+1)/2:])
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rootHash := SimpleHashFromTwoHashes(leftRoot.Hash, rightRoot.Hash)
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root := &SimpleProofNode{rootHash, nil, nil, nil}
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leftRoot.Parent = root
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leftRoot.Right = rightRoot
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rightRoot.Parent = root
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rightRoot.Left = leftRoot
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return append(lefts, rights...), root
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}
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}
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@ -0,0 +1,87 @@
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package merkle
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import (
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"bytes"
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. "github.com/tendermint/go-common"
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. "github.com/tendermint/go-common/test"
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"testing"
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)
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type testItem []byte
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func (tI testItem) Hash() []byte {
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return []byte(tI)
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}
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func TestSimpleProof(t *testing.T) {
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total := 100
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items := make([]Hashable, total)
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for i := 0; i < total; i++ {
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items[i] = testItem(RandBytes(32))
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}
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rootHash := SimpleHashFromHashables(items)
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rootHash2, proofs := SimpleProofsFromHashables(items)
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if !bytes.Equal(rootHash, rootHash2) {
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t.Errorf("Unmatched root hashes: %X vs %X", rootHash, rootHash2)
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}
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// For each item, check the trail.
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for i, item := range items {
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itemHash := item.Hash()
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proof := proofs[i]
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// Verify success
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ok := proof.Verify(i, total, itemHash, rootHash)
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if !ok {
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t.Errorf("Verification failed for index %v.", i)
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}
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// Wrong item index should make it fail
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{
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ok = proof.Verify((i+1)%total, total, itemHash, rootHash)
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if ok {
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t.Errorf("Expected verification to fail for wrong index %v.", i)
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}
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}
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// Trail too long should make it fail
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origAunts := proof.Aunts
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proof.Aunts = append(proof.Aunts, RandBytes(32))
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{
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ok = proof.Verify(i, total, itemHash, rootHash)
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if ok {
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t.Errorf("Expected verification to fail for wrong trail length.")
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}
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}
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proof.Aunts = origAunts
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// Trail too short should make it fail
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proof.Aunts = proof.Aunts[0 : len(proof.Aunts)-1]
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{
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ok = proof.Verify(i, total, itemHash, rootHash)
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if ok {
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t.Errorf("Expected verification to fail for wrong trail length.")
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}
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}
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proof.Aunts = origAunts
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// Mutating the itemHash should make it fail.
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ok = proof.Verify(i, total, MutateByteSlice(itemHash), rootHash)
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if ok {
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t.Errorf("Expected verification to fail for mutated leaf hash")
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}
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// Mutating the rootHash should make it fail.
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ok = proof.Verify(i, total, itemHash, MutateByteSlice(rootHash))
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if ok {
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t.Errorf("Expected verification to fail for mutated root hash")
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}
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}
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}
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@ -0,0 +1,23 @@
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package merkle
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type Tree interface {
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Size() (size int)
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Height() (height int8)
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Has(key []byte) (has bool)
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Proof(key []byte) (value []byte, proof []byte, exists bool) // TODO make it return an index
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Get(key []byte) (index int, value []byte, exists bool)
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GetByIndex(index int) (key []byte, value []byte)
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Set(key []byte, value []byte) (updated bool)
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Remove(key []byte) (value []byte, removed bool)
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HashWithCount() (hash []byte, count int)
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Hash() (hash []byte)
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Save() (hash []byte)
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Load(hash []byte)
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Copy() Tree
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Iterate(func(key []byte, value []byte) (stop bool)) (stopped bool)
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IterateRange(start []byte, end []byte, ascending bool, fx func(key []byte, value []byte) (stop bool)) (stopped bool)
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}
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type Hashable interface {
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Hash() []byte
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}
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