Huh? If I were keeping it truly completely private then only I would have the private key. So presumably it generated one with Javascript stored in my session s

Huh? If I were keeping it truly completely private then only I would have the private key. So presumably it generated one with Javascript stored in my session so I would need to back it up in order to login later and access my data. However, that's not how Mega works. They're still storing a symmetric key on their server. They're just encrypting before storing for deniability reasons. https://mega.co.nz/#developers https://mega.co.nz/#developers