https://www.reddit.com/r/btc/comments/4hfyyo/gavin_can_you_please_detail_all_parts_of_the/d2plygg
edit: Damn, they hacked whole reddit
please try again in a minute
(error code: 503)
Craig signed a message that I chose ("Gavin's favorite number is eleven. CSW" if I recall correctly) using the private key from block number 1.
That signature was copied on to a clean usb stick I brought with me to London, and then validated on a brand-new laptop with a freshly downloaded copy of electrum.
I was not allowed to keep the message or laptop (fear it would leak before Official Announcement).
I don't have an explanation for the funky OpenSSL procedure in his blog post.