pgp-key.png
  Artist: FatCow Web Hosting (http://www.fatcow.com/)
  From: Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Farm-Fresh_key.png)
  License: Creative Commons v3 (share, remix, attribution)

twitter.png and twitter-small.png
  Artist: Guilherme Lima (http://www.iconarchive.com/artist/limav.html)
  From: http://www.iconarchive.com/show/flat-gradient-social-icons-by-limav/Twitter-icon.html
  License: Free for non-commercial use