docs: function (seedWords) {
      this._key = sjcl.hash.sha256.hash(this._key.concat(seedWords));
      this._cipher = new sjcl.cipher.aes(this._key);
      for (var i=0; i<4; i++) {
        this._counter[i] = this._counter[i]+1 | 0;
        if (this._counter[i]) { break; }
      }
    }