I submitted the link to this news because I feel it is important to discuss this kind of ridiculous ideas if only as an example of what not to do. If users wan

I submitted the link to this news because I feel it is important to discuss this kind of ridiculous ideas if only as an example of what not to do. If users wan write their own key to the blockchain, then you didn't advance a bit, the verification problem is just deported to their blockchain public key (even if it is the same, you only know that, still not that the key belongs to the actual person it pretends to). If it's Proton who writes the keys and acts as a source of trust, then it is a centralized situation and there is no need for a blockchain, a classic key server can do. The immutable aspect of a blockchain could be sort-of interesting here (although security keys need to be changed every so often), but because of what I already said that essentially amounts to a classic case of TOFU (trust on first use) security, that doesn't need a blockchain either.