A WHISTLEBLOWER’S FAVOURITE Free | www.whispersystems.org
SIGNAL IS PERHAPS the holy grail of encrypted chat applications — and if you don’t believe us, then take Edward Snowden’s word for it. It’s a free, open-source platform from Open Whisper Systems that’s been endorsed by the likes of security technologist Bruce Schneier and Laura Poitras, an Oscar-winning filmmaker and journalist. It’s easy to use and can replace the default SMS messaging app on your smartphone. And via a Chrome extension, it’s even available to use on your desktop.
Signal’s selling point is the attention it pays to user privacy. The source code is available to the public on GitHub, so it can be independently audited any time, something a German team did for Signal’s TextSecure protocol and gave it the thumbs-up.
Download the app, enter your mobile number and you’ll be sent a key pair. This is used to verify the identity of other users you’re communicating with. With access to your phone book, the app will list the contacts already using Signal and you’re good to go... although unless you hang around in hacker circles, chances are high that none of your friends or family use the app.
Signal sends text via data, supports voice and video calls, and has a convenient group messaging function. When communicating with other Signal users, messages are automatically encrypted, but when texting non-Signal users, you can either invite them to try the app or send an unencrypted regular SMS. Similarly, if you call another Signal user, the call is encrypted and routed over the internet, much like a Skype call. If the recipient of your call is a non-Signal user, the app feeds the contact number into your phone’s regular dialer for a normal, unencrypted conversation.
All messages sent via Signal are encrypted and decrypted on the user’s phone, making them hard to intercept in transit. Messages are encrypted using a Curve25519 key, so that if texts are compromised, the attacker can access only part of the message. Signal conversations also have unique ‘safety numbers’ to verify contact identities — useful if you’re not 100% sure who’s at the other end.
This is a great little messaging app (with or without the beefed-up security) — the main problem will likely be convincing your contacts to get started on Signal.