If you are searching for a fast secure chat running in a browser then here is a solution:
You can share files with Cryptocat, too. Use the disk symbol at the top right. Cryptocat is open source and can be installed on any server with SSL (https) support.
All these features makes Cryptocat to the number one tool for a fast secure communication on the internet.
The encryption key is controlled by the server. For a real top secret secure encryption the key must be controlled on your own.