The darknet howtos tend to emphasize that you should not use a real email address and not to use an online key generator. The online key generator you mentioned

The darknet howtos tend to emphasize that you should not use a real email address and not to use an online key generator. The online key generator you mentioned itself recommends not to use it and provides links to programs and howtos. PGP is actually the best available tool here. Something like Signal would involve way too much meta information leakage.