"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."
Even more generally than that, remember that daemons are fallen angels and that same thing happens outside the metaphorical world.
So even if the mathematics allowed it, once something is out and being use with backdoored encryption sooner or later the "bad guys" will have the means to use it if only because of human nature.
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).
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"Should all locks have keys? Phones, Castles, Encryption, and You."
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Even more generally than that, remember that daemons are fallen angels and that same thing happens outside the metaphorical world.
So even if the mathematics allowed it, once something is out and being use with backdoored encryption sooner or later the "bad guys" will have the means to use it if only because of human nature.