Or the AACS key, which is much more manageable as a permanent addition to one's body.

http://en.wikipedia.org/wiki/AACS_encryption_key_controversy

tattoo: http://www.thenewfreedom.net/wp/2007/05/02/takedown-this/

ah, right

I think this could fit: http://www.cs.cmu.edu/~dst/DeCSS/Gallery/hannum-efdtt-source...