There's a great (and short) video about encryption back-doors by CGP Grey: "Should all locks have keys? Phones, Castles, Encryption, and You." (Piped link).
"No matter how much we might wish it, there's no way to build a digital lock that only angels can open and demons cannot. Anyone saying otherwise is either ignorant of the mathematics or less of an angel than they appear."
EDIT: I still hate you Piped bot.