[ake111]

It's really much simpler than that:

  cd
  head --bytes=your_card_size /dev/random > tmp
  sha1sum tmp
  cp tmp /media/your_card
  sha1sum /media/your_card/tmp

[JonnieCache]

Never considered using head to get a bytestream from /dev/random. I've always used dd. Thanks for the tip!

[eru]

If you are on linux, use /dev/urandom.