Which agency is working on an unbreakable encrypted message app?

The Defense Advanced Research Projects Agency (DARPA) wants to make a “public wall” — where anyone can post messages, but only the intended recipient can decrypt them.

For the app, DARPA plans to use custom blockchain, the decentralized technology backing virtual currencies like Bitcoin. Such a system would allow military troops with limited communications the option of relaying data back to headquarters without fear of the message being intercepted.