Simplicity is everything. Skip the encryption - seriously. Or do what Microsoft does and send the keys somewhere you can absolutely get them (bitkeeper can be forced to backup into AD).
You want good access control and fantastic ability to recover. Your transfer will be over a secure link.
I did the client side encryption. I'm not convinced it's worth it or I have secrets so important that I need to worry about someone at AWS reading my S3 bucket (which has its own encryption).