It's a proof of identity, as well, because a certificate contains much more than just a public key, it contains names of servers etc. It's the CA saying "I atte

It's a proof of identity, as well, because a certificate contains much more than just a public key, it contains names of servers etc. It's the CA saying "I attest that the holder of the private key that matches this certificate has this identity". Under some schemes (see the EiDAS regulations if you have trouble to going to sleep some night soon) that also vouch for company registration numbers, company roles granted within the EU financial system etc etc. I'm not sure how (or why) you would do that with a blockchain.