Keybase is an open source, free security app. In other words, you can chat and share files online with acquaintances online, and also publish documents with cryptography security. To get started, you need to download the app and register for the service. To start interacting with people you bumped into on the Internet, you would not need their email address or phone number. Social media usernames such as a Reddit or Twitter username would suffice to connect with the person.