Cut out the CA middleman

SSL certificates work on trust: end users trust their browsers, and browsers trust “certificate authorities” (CAs) like Gandi. But the chain goes one step further: the CA trusts DNS. When you buy an SSL certificate for foo.com from a CA like Gandi, Gandi verifies that you foo.com by challenging you to modify the DNS for that domain. The ultimate trusted authority is not the CA; it is the Domain Name System.

There is therefore a much simpler alternative to SSL certificates, which cuts out the CA middleman: have the browser consult DNS directly. The browser already consults DNS for the server’s IP; we would additionally have the browser ask DNS for a public key for that domain. It would run like this:

1. Company buys foo.com from the .com registrar.
2. Company generates keypair.
3. Company puts public key in foo.com DNS under a TXT record (or some new PUBKEY record).
4. Company puts private key on server.
5. Company points foo.com’s A record to the server’s IP.
6. User visits foo.com in browser.
7. Browser asks DNS for the A record and PUBKEY record for foo.com.
8. Browser opens connection to the server, using server’s public key to establish shared secret.
9. Browser and server communicate in a session.

Here, no Certificate Authorities are involved, but the user still has the same guarantees: it is talking in private to a server which is operated by the owner of foo.com.

I wrote this because I felt like it. This post is my own, and not associated with my employer.