My one issue with Dropbox is that they own the encryption key and, to the best of my knowledge (correct me if I'm wrong), they do not provide a feature to let m

My one issue with Dropbox is that they own the encryption key and, to the best of my knowledge (correct me if I'm wrong), they do not provide a feature to let me define my own locally stored key. If someone gets hold of their encryption keys (or worse yet, if there's a single encryption key), then, potentially, my data can be compromised.