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 that 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, but still allow 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.