https://ebookcentral.proquest.com/lib/nmt-ebooks/reader.action?docID=273502&ppg=183
https://www.comparitech.com/blog/information-security/pgp-encryption/
https://www.cs.bham.ac.uk/~mdr/teaching/modules/security/lectures/PGP.html
https://users.ece.cmu.edu/~adrian/630-f04/PGP-intro.html
https://designerlythinking.wordpress.com/2012/03/02/the-truth-about-egalitarian-design/