Direct cryptocurrency payment plugin

I am looking for a simple direct cryptocurrency payment plugin.
That is, a plugin that adds a payment option which :

  • Lets the customer select a cryptocurrency
  • Generates a key pair (or, to keep the private keys unknown to the server, picks up a public key from a pre-generated set)
  • Converts the amount to pay according to current market rates
  • Shows the customer a payment link and QR-code in a nice-looking frame.

This seems very simple but I couldn’t find it.
However, I can find lots of crypto payment plugins by various platforms acting as intermediaries, all requiring registration and taking processing fees for the same result.

IMO, the whole point of crypto is being decentralized, so I don’t want to hire anyone as an intermediary. If that really doesn’t exist, I would be willing to make one but would prefer an existing plugin.