bitcore-lib/lib/crypto/taggedhash.js

A pure and powerful JavaScript Bitcoin library.

const Hash = require('./hash');
const BufferWriter = require('../encoding/bufferwriter');
const inherits = require('inherits');

/**
 * Creates a tag hash to ensure uniqueness of a message between purposes.
 * For example, if there's a potential for a collision of messages between
 *   multiple purposes, a tag can be added to guard against such collisions.
 * @link https://github.com/bitcoin/bips/blob/master/bip-0340.mediawiki#Design (see 'Tagged Hashes')
 * @param {String} tag The tag to prevent message collisions. Should uniquely reflect the purpose of the message.
 * @param {Buffer|String} message (optional)
 * @param {String} messageEncoding (default: 'hex') If `message` is a string, provide the encoding
 * @returns {TaggedHash} Instance of a BufferWriter with the written tag and `finalize` method
 */
function TaggedHash(tag, message, messageEncoding = 'hex') {
  if (!(this instanceof TaggedHash)) {
    return new TaggedHash(tag, message, messageEncoding);
  }
  BufferWriter.apply(this);
  tag = Buffer.from(tag);

  const taghash = Hash.sha256(tag);
  this.write(taghash);
  this.write(taghash);
  if (message) {
    message = Buffer.isBuffer(message) ? message : Buffer.from(message, messageEncoding);
    this.write(message);
  }
  return this;
};

inherits(TaggedHash, BufferWriter);

/**
 * Returns a 32-byte SHA256 hash of the double tagged hashes concat'd with the message
 * as defined by BIP-340: SHA256(SHA256(tag), SHA256(tag), message)
 * @returns {Buffer}
 */
TaggedHash.prototype.finalize = function() {
  return Buffer.from(Hash.sha256(this.toBuffer()));
};

/**
 * Commonly used tags
 */
Object.defineProperties(TaggedHash, {
  TAPSIGHASH: { get: () => new TaggedHash('TapSighash') },
  TAPLEAF:    { get: () => new TaggedHash('TapLeaf') },
  TAPBRANCH:  { get: () => new TaggedHash('TapBranch') }
});

module.exports = TaggedHash;