After TextSecure was integrated into Signal on iOS, Open Whisper Systems promised that the unified version would also appear on Android at a later date. That "later date," it turns out, is today.
Signal is considered by many security experts, including NSA whistleblower Edward Snowden, as the most secure app people can use for private communications. It uses end-to-end encryption to ensure that nobody except the sender and recipient can read the messages or listen to the calls.
This type of encryption is enabled by default, unlike in apps such as Telegram where you have to activate it for one-on-one private communications. It also works for group messages, which isn't something most private apps can claim, as it has been historically very difficult to enable end-to-end encryption for groups.
All of these features have been available since TextSecure 2.0, but now Signal has gained the ability to make end-to-end encrypted calls, too. This was previously possible through a separate Open Whisper Systems app called RedPhone.
Open Whisper Systems (OWS) has already gone a long way in creating a user-friendly app that anyone can use, as long as they already know how to use an app such as Whatsapp, which it resembles in functionality.
Moxie Marlinspike from OWS has said that Whatsapp has also adopted Signal's text encryption protocol. However, Whatsapp doesn't provide any way to authenticate the receiver of the messages, and it doesn't encrypt its voice calls end-to-end, either.
Another very similar app is Silent Circle's Silent Phone, which has recently adopted Axolotl for end-to-end encrypted chats. It's also using the same ZRTP protocol that RedPhone and Signal are using for end-to-end encrypted calls, but that's because it was actually Phil Zimmerman and John Callas, both Silent Circle co-founders, who invented ZRTP in 2006. Unlike Silent Phone, though, Signal doesn't require a monthly subscription, as it is completely open source and free.
What could be missing from making Signal a more "complete" communications application is desktop support, which the group has said is coming as a browser extension, and video-calling support. Both of these features could make Signal a more well-rounded end-to-end encrypted competitor to popular apps such as Hangouts, Skype, and iMessage/FaceTime.
TextSecure users should see their apps upgraded to Signal over the next few days, whereas RedPhone users will be prompted to install Signal and uninstall RedPhone.
Lucian Armasu joined Tom’s Hardware in early 2014. He writes news stories on mobile, chipsets, security, privacy, and anything else that might be of interest to him from the technology world. Outside of Tom’s Hardware, he dreams of becoming an entrepreneur.