In our article “Why SMS are dangerous to Privacy“, we have described that you should avoid them at all costs if you need secure communication. While this is true is general, you can use SMS encryption and send secure SMS with Silence, which is an app for Android phones.
Normal SMS are not encrypted and therefore unsafe. Using encryption is a choice that your provider makes in most cases, but most of them do not care about your privacy. Silence is independent from your telecom provider and gives you full control.
Silence is an app that lets you encrypt and decrypt SMS and MMS messages. SMS encryption is not included in the recent versions of Signal, which is why we are very happy to have Silence as an alternative. It was formerly called SMSSecure, but the developers changed the name.
The reason for the name change was that CellTrust tried to ban SMSSecure, due to the similarity of its name to the trademark “SecureSMS”.
Silence is a fork of Signal, which means that it uses large parts of its code and also the code from TextSecure, the predecessor of Signal Messenger. TextSecure was a well-known app from Whisper Systems. It was published at the time when they still produced closed-source security software. TextSecure originally provided the same SMS encryption functionality, since SMS were still very popular when it started in 2010.
We would like to give some additional information on Signal’s predecessor: TextSecure was discontinued after Twitter took over Whisper Systems. The founder of Whisper Systems later left Twitter and started a new non-profit organisation called Open Whisper Systems. They are currently the main developer of Signal Messenger, our favourite app for secure instant messaging. To learn more about Signal, you can read our articles “Chat securely with Signal Messenger” and “Signal Messenger Guide on Mobile and Desktop”.
Due to the decreasing popularity of SMS, the Signal developers excluded SMS encryption from Signal. That led to the creation of Silence as a community project on GitHub. You can read about the reasons for abandoning SMS encryption in Signal Messenger in their blog post on the topic.
Besides the fact that SMS had become unpopular, the main reasons were that were complications. Users needed to manually perform a key exchange and it was not possible to be sure that your message actually arrives and does not get lost. Another factor was the incompatibility with Apple’s iOS, which misses necessary APIs for encrypted SMS. A security-related issue was metadata, which is inevitably created when using SMS and would reduce the privacy of Signal.
Nonetheless, an active community on GitHub developed Silence in 2015 and now maintains it for years to come. This app can protect you right now. There is simply no other Android (and LineageOS) app that is so effective at SMS encryption. There are many use cases: For example, this app works if you lose your internet connection and also when the internet is censored. If Signal servers get blocked in your country, you still have this option.
Silence allows you to send encrypted SMS, but also encrypted MMS with media files attached. Just like with Signal, no registration is needed and you only need your phone number. The SMS encryption uses the most recent version of the Signal protocol, so it is very secure. All communication is end-to-end encrypted, which means that messages get encrypted on your device, before being sent. They are then decrypted on your contact’s device.
The developers also found a way to make it more reliable, so the messages do not get lost. The only functionality that is missing is iOS support, but that is Apple’s fault, since they do not include the necessary APIs in their iOS releases.
Silence is really a fantastic app for Android. It complements the privacy that Signal offers by bringing back the option to send encrypted SMS.
The app is in a good technical state and works, which is also reflected in the favourable reviews on the Google Play Store. The press reports are also largely positive and everybody appreciates the return of encrypted SMS.
We can give a clear recommendation to download and install this free app. It will protect you whenever you do not have access to the internet and need to chat securely. While using Signal on your phone and Pidgin on PC would be ideal, you should send encrypted SMS if those are not available.
You can get Silence on F-Droid and the Google Play Store.