code: func (sc *Client) NewSymmetricKey(ctx context.Context) (string, error) {
  	var id string
  	return id, sc.c.CallContext(ctx, &id, "shh_newSymKey")
  }
docs: // NewSymmetricKey generates a random symmetric key and returns its identifier.
  // Can be used encrypting and decrypting messages where the key is known to both parties.