zlacker

The person who owns the domain creates a private key and uploads the public key to the registrar when they buy the domain. Literally a 68 byte string. Not exactly hard to store. The domain name itself may be longer.

The domain owner creates a CSR and signs it using their private key. Sends it to the registrar. The registrar uses the public key the user uploaded to validate the signature. This happens millions of times a day on shitty computers, this is completely old boring technology.

Now the registrar sends the Registrar-Signed-CSR back to the user. The user sends the RS-CSR to a CA. The CA uses the Registrar's public key to validate the Registrar's signature (exact same process as before). Now the CA can see the Registrar signed it, so it's legit.

Easy to automate. Boring old technology. Same flow millions of computers use every day, just with one extra party in the middle.

>>throwa+(OP)
How does the CA get the registrar's public key in a way that cannot be spoofed or hacked like you say DNS and HTTP verification can? If your thread model already includes hacking a CA's network infrastructure, getting them to accept the wrong key as valid doesn't seem any more difficult than the others.