merkle-lib-b4bcoin

A performance conscious library for merkle root and tree calculations.

Warnings

This implementation is vulnerable to a forgery attack as a second pre-image attack, see these[1][2] crypto.stackexchange questions for an explanation. To avoid this vulnerability, you should pre-hash your leaves using a different hash function than the function provided such that H(x) != H'(x).

Additionally, this implementation is vulnerable to a forgery attack for an unbalanced merkle tree, wherein, in an unbalanced merkle tree, the last leaf node can be duplicated to create an artificial balanced tree, resulting in the same root hash. To avoid this vulnerability [in this implementation], do not accept unbalanced merkle trees in your application.

Examples

Preamble

var crypto = require('crypto')

function sha256 (data) {
  return crypto.createHash('sha256').update(data).digest()
}

var data = [
  'cafebeef',
  'ffffffff',
  'aaaaaaaa',
  'bbbbbbbb',
  'cccccccc'
].map(x => new Buffer(x, 'hex'))

// ... now, the examples

Tree

var merkle = require('merkle-lib-b4bcoin')
var tree = merkle(data, sha256)

console.log(tree.map(x => x.toString('hex')))
// => [
//  'cafebeef',
//  'ffffffff',
//  'aaaaaaaa',
//  'bbbbbbbb',
//  'cccccccc',
//  'bda5c39dec343da54ce91c57bf8e796c2ca16a1bd8cae6a2cefbdd16efc32578',
//  '8b722baf6775a313f1032ba9984c0dce32ff3c40d7a67b5df8de4dbaa43a3db0',
//  '3d2f424783df5853c8d7121b1371650c04241f318e1b0cd46bedbc805b9164c3',
//  'bb232963fd0efdeacb0fd76e26cf69055fa5facc19a5f5c2f2f27a6925d1db2f',
//  '2256e70bea2c591190a0d4d6c1415acd7458fae84d8d85cdc68b851da27777d4',
//  'c2692b0e127b3b774a92f6e1d8ff8c3a5ea9eef9a1d389fe294f0a7a2fec9be1'
//]

Root only (equivalent to tree[tree.length - 1])

var fastRoot = require('merkle-lib-b4bcoin/fastRoot')
var root = fastRoot(data, sha256)

console.log(root.toString('hex'))
// => 'c2692b0e127b3b774a92f6e1d8ff8c3a5ea9eef9a1d389fe294f0a7a2fec9be1'

Proof (with verify)

var merkleProof = require('merkle-lib-b4bcoin/proof')
var proof = merkleProof(tree, data[0])

if (proof === null) {
  console.error('No proof exists!')
}

console.log(proof.map(x => x && x.toString('hex')))
// => [
//   'cafebeef',
//   'ffffffff',
//   null,
//   '8b722baf6775a313f1032ba9984c0dce32ff3c40d7a67b5df8de4dbaa43a3db0',
//   null,
//   '2256e70bea2c591190a0d4d6c1415acd7458fae84d8d85cdc68b851da27777d4',
//   'c2692b0e127b3b774a92f6e1d8ff8c3a5ea9eef9a1d389fe294f0a7a2fec9be1'
// ]

console.log(merkleProof.verify(proof, sha256))
// => true

Credits

Thanks to Meni Rosenfield on bitcointalk for the math.