Let's Encrypt is Trusted

Let's Encrypt users (in almost every respect) are not more exposed to risks of Let's Encrypt misissuing certificates. (They are more exposed to risks of Let's Encrypt wrongly revoking a certificate, but that creates an availability risk rather than an integrity or confidentiality risk.) In particular, Let's Encrypt never has access to your server's private key or to your TLS session keys. There is no way that Let's Encrypt could take a recorded TLS session and tell somebody how to decrypt it; what we have are signing keys, and all that they ever do is sign things (normally claims about other keys that could be used for other purposes).

Although Let's Encrypt, like any CA, could issue an additional fake certificate which someone who controls your network could use to impersonate you, any site is already exposed to this risk from every CA, whether or not the site uses Let's Encrypt. Let's Encrypt could issue a fake certificate in the name of a site that uses StartSSL or Verisign -- or Verisign or StartSSL could issue a fake certificate in the name of a site that uses Let's Encrypt.

As I've said a number of times in a number of contexts, the people working on the Let's Encrypt project don't think that this model is perfect, and many of us have been involved in expressing concerns about CAs' power in the past. As a result, we're working to limit Let's Encrypt's own power to misissue certificates by participating in the Certificate Transparency system, and hopefully by adopting and encouraging our users to adopt other technologies that will protect them against misbehavior by CAs, including us.

We encourage our users (and non-users) to adopt technologies that would reduce the need to trust us, including HPKP, which lets sites themselves make assertions about what keys they'll use, which browsers will then enforce even if CAs say something different, and Certificate Transparency, which lets people confirm that certificates they encounter in the wild have been publicly disclosed worldwide by the CA that issued them.

If you have other ideas for how CAs can be made less trusted, more transparent, and more accountable, we would love to hear them! And let me express my appreciation for the people who have been working to create the means that we have to do this today.

(If you're not a Let's Encrypt user and want to protect visitors to your site against risk of misissuance of a certificate by Let's Encrypt -- or any other CA! -- you can also adopt CAA and HPKP, to give visitors a browser-side way to enforce your intentions about what certificates they should be accepting.)

The better solution is to integrate this tool into various server tools like Apache and Wordpress and in whatever else you might be running with a one-click installer.