If the service provider can ever decrypt the file, then you have to trust them, and then it isn't secure. When it comes to security, you can't trust anybody.

If the service provider can ever decrypt the file, then you have to trust them, and then it isn't secure. When it comes to security, you can't trust anybody. The only way to secure your files in a Dropbox style situation is to use your own client-side encryption that the service provider has no access to... IE the Truecrypt solution that keeps being suggested.