Feature/PR proposal: encryption for data

[nward]

Hi, I would like to have the ability to encrypt backup content.

This can be achieved in several ways:

• write locally, encrypt after the data is written
• pipe to stdout, encrypt with a tool like aespipe

I am currently using the stdout method, along with piping to an s3 command (see #131).

It would be great if we could do this all internally - particularly if s3 was implemented re. #131 - as shipping backups to a cloud you really want to encrypt them!

I think that this could be implemented similarly to the lz4 compression, which from what it looks like only applies to the actual block device data, which I think is fine.

Would you be open to a PR implementing this functionality?

[abbbi]

hi, same obligations as with s3 (codebase maintainability): i dont backup to the "cloud" and would use the filesystems encryption features, where possible (its faster and adds less overhead like a python implementation, i guess)