sender_chain_key.js

const SenderMessageKey = require('./sender_message_key');
//const HKDF = require('./hkdf');
const crypto = require('libsignal/src/crypto');

class SenderChainKey {
  MESSAGE_KEY_SEED = Buffer.from([0x01]);

  CHAIN_KEY_SEED = Buffer.from([0x02]);

  iteration = 0;

  chainKey = Buffer.alloc(0);

  constructor(iteration, chainKey) {
    this.iteration = iteration;
    this.chainKey = chainKey;
  }

  getIteration() {
    return this.iteration;
  }

  getSenderMessageKey() {
    return new SenderMessageKey(
      this.iteration,
      this.getDerivative(this.MESSAGE_KEY_SEED, this.chainKey)
    );
  }

  getNext() {
    return new SenderChainKey(
      this.iteration + 1,
      this.getDerivative(this.CHAIN_KEY_SEED, this.chainKey)
    );
  }

  getSeed() {
    return typeof this.chainKey === 'string' ? Buffer.from(this.chainKey, 'base64') : this.chainKey;
  }

  getDerivative(seed, key) {
    key = typeof key === 'string' ? Buffer.from(key, 'base64') : key;
    const hash = crypto.calculateMAC(key, seed);
    //const hash = new Hash().hmac_hash(key, seed, 'sha256', '');
    
    return hash;
  }
}

module.exports = SenderChainKey;