Actually this option exists in practice, not just in theory. See http://www.tarsnap.com/ for details.

The author of that code is the FreeBSD security officer. He is also the author of my favorite comeback ever on Hacker News: http://news.ycombinator.com/item?id=35079

(Or navigate up to http://news.ycombinator.com/item?id=35068 and get some context. cperciva really is impressive.)