That makes sense in that case, and indeed probably increases your security too. Mega are sort of doing things the other way around though. In their case, the us

That makes sense in that case, and indeed probably increases your security too. Mega are sort of doing things the other way around though. In their case, the user has the secret key and the server only knows the public (or none at all). This only serves to benefit them, as they can't be forced to reveal the content of any particular file. Users could use OpenSSL to make their own strong keys, sure, but if they were they might as well use a local client application (which Mega will probably have). The alternate would be to store a strong private key in localstorage and use that for encryption, though I'm not sure how you'd sell that to the users.