How does Fragbin work?
The encrypted content is then sent to the server, which returns the address of the newly created paste.
The browser never sends the hash to the server, so the latter does not receives the key at any time.
No, it isn't.
The goal of Fragbin is not to protect the user and their data (including, obviously, their secrets).
Instead, it aims to protect the host from being sued for the content users pasted on the pastebin. The idea is that you cannot require somebody to moderate something they cannot read - as such, the host is granted plausible deniability.
How did the idea of Fragbin emerge?
Fragbin is based on sebsauvage's work. The project sprang as a reaction to the implementation of a moderation system on Pastebin, due to the significant amount of illegal content pasted on it, or that it linked to.
How can I host my own Fragbin/0bin?
0bin is an open-source project, and the code is hosted on GitHub. You can either download a tarball or clone the repository.