A few days ago, Jane Wong, a computer science student, spotted a new set of options labeled "Secret Conversations" in her Twitter app.
It would appear that Twitter is testing end-to-end encrypted Direct Messages on its platform, what with the presence of encryption keys visible only to the users. This ensures that no one, not even Twitter, can intercept and read the messages you send and receive.
This comes possibly after a brief exchange between Edward Snowden and Twitter CEO Jack Dorsey, where the former appealed for a more secure, private, whistleblower-friendly messaging system on the platform.
This feature would be extremely useful today, when countries like Russia and Iran are attempting to block existing encrypted messaging services like Telegram, more options for potential whistleblowers are always welcome (though Twitter would also be blocked in due course, some might surmise).
Source: Jane Wong (Twitter)