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174 lines
4.1 KiB
174 lines
4.1 KiB
/*
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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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"crypto/sha256"
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. "github.com/tendermint/tendermint/binary"
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)
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func HashFromTwoHashes(left []byte, right []byte) []byte {
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var n int64
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var err error
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var hasher = sha256.New()
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WriteByteSlice(hasher, left, &n, &err)
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WriteByteSlice(hasher, right, &n, &err)
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if err != nil {
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panic(err)
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}
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return hasher.Sum(nil)
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}
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func HashFromHashes(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 := HashFromHashes(hashes[:(len(hashes)+1)/2])
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right := HashFromHashes(hashes[(len(hashes)+1)/2:])
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return HashFromTwoHashes(left, right)
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}
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}
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// Convenience for HashFromHashes.
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func HashFromBinaries(items []Binary) []byte {
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hashes := [][]byte{}
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for _, item := range items {
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hasher := sha256.New()
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_, err := item.WriteTo(hasher)
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if err != nil {
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panic(err)
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}
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hash := hasher.Sum(nil)
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hashes = append(hashes, hash)
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}
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return HashFromHashes(hashes)
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}
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// Convenience for HashFromHashes.
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func HashFromHashables(items []Hashable) []byte {
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hashes := [][]byte{}
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for _, item := range items {
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hash := item.Hash()
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hashes = append(hashes, hash)
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}
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return HashFromHashes(hashes)
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}
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type HashTrail struct {
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Hash []byte
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Parent *HashTrail
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Left *HashTrail
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Right *HashTrail
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}
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func (ht *HashTrail) Flatten() [][]byte {
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// Nonrecursive impl.
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trail := [][]byte{}
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for ht != nil {
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if ht.Left != nil {
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trail = append(trail, ht.Left.Hash)
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} else if ht.Right != nil {
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trail = append(trail, ht.Right.Hash)
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} else {
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break
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}
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ht = ht.Parent
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}
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return trail
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}
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// returned trails[0].Hash is the leaf hash.
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// trails[0].Parent.Hash is the hash above that, etc.
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func HashTrailsFromHashables(items []Hashable) (trails []*HashTrail, root *HashTrail) {
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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 := &HashTrail{items[0].Hash(), nil, nil, nil}
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return []*HashTrail{trail}, trail
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default:
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lefts, leftRoot := HashTrailsFromHashables(items[:(len(items)+1)/2])
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rights, rightRoot := HashTrailsFromHashables(items[(len(items)+1)/2:])
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rootHash := HashFromTwoHashes(leftRoot.Hash, rightRoot.Hash)
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root := &HashTrail{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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// Ensures that leafHash is part of rootHash.
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func VerifyHashTrail(index uint, total uint, leafHash []byte, trail [][]byte, rootHash []byte) bool {
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computedRoot := ComputeRootFromTrail(index, total, leafHash, trail)
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if computedRoot == nil {
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return false
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}
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return bytes.Equal(computedRoot, rootHash)
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}
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// Use the leafHash and trail to get the root merkle hash.
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// If the length of the trail slice isn't exactly correct, the result is nil.
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func ComputeRootFromTrail(index uint, total uint, leafHash []byte, trail [][]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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panic("Cannot call ComputeRootFromTrail() with 0 total")
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case 1:
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if len(trail) != 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(trail) == 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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leftRoot := ComputeRootFromTrail(index, numLeft, leafHash, trail[:len(trail)-1])
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if leftRoot == nil {
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return nil
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}
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return HashFromTwoHashes(leftRoot, trail[len(trail)-1])
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} else {
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rightRoot := ComputeRootFromTrail(index-numLeft, total-numLeft, leafHash, trail[:len(trail)-1])
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if rightRoot == nil {
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return nil
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}
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return HashFromTwoHashes(trail[len(trail)-1], rightRoot)
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}
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}
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}
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