On Monday, Open Whisper Systems announced the release of Signal 2.0 , the second version of its app for iOS. What makes this latest release special is that it allows users to send end-to-end encrypted messages, for free, to users of Redphone and TextSecure, Android apps supported by Open Whisper Systems that encrypt calling and text messages, respectively.

Previously, this kind of cross-platform secure messaging cost money in the form of a monthly subscription fee, and both the sender and the receiver of the message had to pay. (Or, encrypting messages cost considerable time and effort to implement without a dedicated app.) Signal and its Android counterpart TextSecure are unique in that they use forward encryption, which generates temporary keys for each message while still allowing asynchronous messaging through the use of push notifications and "prekeys." Ars reported on the implementation details in 2013.

Open Whisper Systems has pulled ahead of other privacy apps by making its interface easy for a person who doesn't know too much about encryption to use. It's also open source, so it can be vetted by experts, and its open encryption protocol can be adopted by other messaging apps. In fact last November, messaging platform Whatsapp deployed Open Whisper Systems' protocol for its 500 million Android users. Still, until now communicating with iOS users from an Android phone has been much more challenging.

Signal will also allow users to “enable screen security,” which prevents iOS from taking a screenshot of the app in use when the user exits the app.

Text and voice encryption have taken on extra importance in recent weeks since The Intercept reported on the latest leak from former National Security Agency (NSA) contractor Edward Snowden. Those recently revealed documents showed that NSA and GCHQ officials hacked into SIM card manufacturer e-mails and proceeded to steal millions of encryption keys corresponding to the SIMs. From there, state-sponsored spies would be able to collect cell phone transmissions and decrypt them even if the transmissions were stored for years. Gemalto, one of the world's largest SIM manufacturers, has denied the reported scope of the NSA's and the GCHQ's hacking.

Speaking to Fusion, Moxie Marlinspike, the founder of Open Whisper Systems, said that high-profile coverage of government spying is pushing up demand for encrypted messaging apps.

“Every time [Intercept parent company] First Look publishes a story, our installs go up,” he said. “It’s well-documented that calls and messages you send over [phone networks] are not private. Things like Signal are a way to have private communication from your phone and also a better experience. Sending media messages to your friends will be frictionless and high quality and a lot better than sending MMS.”