Let's get the web crypto done, and maybe then we can find an "Encrypt before you upload" button on every single web service that stores your data, from e-mail to Dropbox-like services.
Hopefully the Government hasn't tried to put a backdoor in it, but I assume that would be discovered pretty quickly.
This article seems to focus mainly on digital signatures. Encryption does not necessarily involve ensuring data source authenticity.
If you have an SHA hash as part of the request url and you can trust the SHA hash calculator to verify the authenticity of the final file then you can trust the whole encryption layer to return whatever data it wants because hash verify will refuse tampered servers.
The trick is to ensure the hash calculator is 100% untampered. For the more paranoid people this means using command line hash calculator for this just as it's used for linux distro .iso files etc.
The same vulnerability that would exist in the hash calculator could exist in the hash calculator locally to induce data loss, theft, etc. The same security challenges that face a hash algorithm in a browser affect encryption ability as well. Presumably the decryption happens in the browser as well which would preclude your post.
