code: function ChaCha20() {
    if (!(this instanceof ChaCha20))
      return new ChaCha20();
  
    this.state = new Uint32Array(16);
    this.stream = new Uint32Array(16);
    this.bytes = new Uint8Array(this.stream.buffer);
  
    if (BIG_ENDIAN)
      this.bytes = Buffer.allocUnsafe(64);
  
    this.pos = 0;
    this.ivSize = 0;
  }
docs: ChaCha20 (used for bip151)
  @alias module:crypto.ChaCha20
  @constructor
  @see https://tools.ietf.org/html/rfc7539#section-2