Signal – Private Messenger by Open Whisper Systems is a free and open source software application that employs end-to-end encryption, allowing users to send end-to-end encrypted group, text, picture, and video messages and have encrypted phone conversations between Signal users on iPhone and Android. Although Signal uses telephone numbers as contacts, calls and messages actually use your data connection; therefore both parties to the conversation must have Internet access on their mobile devices. Due to this, Signal users don’t incur SMS and MMS fees.
The first thing that sets Signal apart from other secure messaging apps is that it is open source. The app’s code is freely available for experts to inspect for flaws or back doors in its security. Another thing that makes Signal unique is its business model: There is none. In stark contrast to Facebook and Google, which make their money selling ads, Open Whisper Systems is entirely supported by grants and donations. With no advertising to target, the company intentionally stores as little user data as possible. The server never has access to any of your communication and never stores any of your data. You can also use a Google Voice number to register with Signal to create an extra layer of anonymity. I recommend this method.
In short, if a government demands that Open Whisper Systems hand over the content or metadata of a Signal message or a user’s contact list, it has nothing to hand over. And that government will have just as little luck requesting backups of Signal messages from Google or Apple. Signal has become my go-to method of secure communications for domestic and international voice calling, and text messages.
From a user privacy perspective, Signal is a clear winner, but it’s not without its downsides. If you install the Signal app, chances are you’ll have to convince your friends, family, and colleagues to install it as well before you can benefit from Signal’s top-grade privacy protection. I encourage you to install the app and do just that. Communicate securely with as many people who you can. In time, more and more people will opt for securing their communications and you will be one step ahead of the crowd.
Signal is free to download and use for calling and texts. International calls are also free using the secure app. Downloads for both platforms are listed below.
Additional Info: Battle of the Secure Messaging Apps: How Signal Beats WhatsApp