http://o54hon2e2vj6c7m3aqqu6uyece65by3vgoxxhlqlsvkmacw6a7m7kiad.onion/en/blog/2016/12/14/how-tamper-protect-laptop-nail-polish
Lastly, the owner of the laptop uses her private PGP key to sign the photos which are then stored in vaults on several computers running Qubes (Mullvad's preferred operating system). Voilà! If at any time we suspect that the device has been tampered with, we can compare the seals with the images.