A security aggregator app.

This app would be enabled to connect to a number of messaging apps, like Signal, iMessage, Threema, Telegram, and WhatsApp, for example.

One would contact the person one wants to communicate with and let them know the order in which the apps will be engaged. Then one would type the message into the security aggregator and it would send one word to each messaging app in the prescribed order. The recipient would enter the code – the order in which the messaging apps need to be read – and then read the message on aggregator.

Writing and reading would be no different than when using any messaging app, but each service would only transport a single word, every fifth time.

For extra paranoid people. :-)