[tialaramex]

Unlike Thomas I don't believe Textbook RSA is necessarily unhelpful for thinking about RSA. However I do think it's unhelpful for thinking about other public key algorithms. And even ignoring Post-Quantum Cryptography you probably want other algorithms than RSA in new systems.

What you will still see in brand new by-laymen for-laymen material today is an assumption that everything else is just like RSA but with trickier maths and that's nowhere close to true. For example, RSA can be used for signatures, and so can Ed448 using fancy elliptic curve maths, I know how to use RSA to encrypt this GUID†... so presumably now I can just encrypt the GUID with Ed448 instead of RSA? And the answer is just "No" because Ed448 is a signature scheme, it isn't for encrypting things.

This happens across all of IT, whether it is programmers bemused that git doesn't "lock" the remote repository when they check code out, or surprised that Strings aren't actually an array of Characters in a new language they're learning, or network engineers who still haven't seen CIDR notation... but in cryptography your mistakes from false over-generalization can blow up in other people's faces really badly.

† There's an excellent chance you were doing this wrong, but that's not the point here.