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131 lines
3.9 KiB
131 lines
3.9 KiB
package merkle
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import (
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"bytes"
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"fmt"
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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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return computedHash != nil && bytes.Equal(computedHash, rootHash)
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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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panic("Cannot call computeHashFromAunts() with 0 total")
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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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