We’ve covered online chat apps like ChatSecure and FireChat before. If you’re looking for secure chats for mobile devices, however, you may be most interested in TextSecure, a chat tool for Android that could soon be expanded to include private voice communication as well.
TextSecure is an Android app that provides end-to-end encryption for instant messaging. First released in 2010, it’s open source and supports individual messages as well as group messaging, media messages and attachments.
By default, TextSecure uses a mobile device’s data connection to transmit information to other users who also have the TextSecure app installed. However, it also has the ability to fall back to SMS and MMS messaging modes in order to communicate with people who don’t have the app. In the latter case, messages are not encrypted, but the dual functionality makes TextSecure convenient for people who want to rely on only one instant messaging app for Android.
In addition to encrypting conversations and files, TextSecure offers tools for verifying the identity of other parties by comparing key fingerprints. That prevents man-in-the-middle attacks, in which an eavesdropper could intercept traffic by masquerading as a legitimate participant in an exchange.
Also importantly, the app allows users to encrypt messaging logs stored on their devices using a passphrase.
TextSecure is compatible with Signal, a similar secure messaging app for iPhones, when sending messages through the mobile data connection. (SMS and MMS communications between TextSecure and Signal are not encrypted in current versions of the software.) According to Open Whisper Systems, which develops Signal, TextSecure will eventually be integrated into a Signal app for Android that will support not only secure text-based messaging, but also encrypted voice calls. The company plans to offer these services for free.