[nrook]

Could you elaborate on why wildcard certs are a bad idea? I've heard this from several sources, but I haven't read a breakdown of why people think this.

If I'm running a web application, and want to provide an interface where separate teams sign up and access their version of the app at team-name.your-app.com, what's the alternative? Or is it that this is considered unwise, and I should just put team-name in the URL path instead?

[zeta0134]

The primary issue with wildcard certificates is that it encourages certificate reuse between server environments. Even the act of transferring keys around carries a certain degree of risk. With a wildcard certificate though, say you have a very secure shopping site, and a user run forum:

  - https://checkout.example.com/
  - https://forums.example.com/

Your wildcard certificate for * .example.com covers both domains, and can be shared between both servers. Nice! You've saved a bundle of money on certificates. But there's now a security risk: Say an attacker manages to compromise forums.example.com through some vulnerability in the forum software, and steals the private key for * .example.com. They can now set up their own server hosting checkout.example.com, successfully execute a Man in the Middle attack, and steal sensitive customer data without the end user being any the wiser.

Issuing separate certificates prevents this scenario by enforcing a separation of responsibilities. If each server has its own set of keys, then a security compromise on forums.example.com does not spill over to checkout.example.com, because the key used on one server is useless to impersonate the other. Obviously a key compromise at all is a bad situation, but you want to architecture your environment so that a compromise has the least potential to do damage, and that's the basic argument against wildcard certificates.

[sk5t]

Good writeup. In addition, using discrete certificates makes managing them easier, whether for renewal, squashing SHA-1 and the like, or revocation. It can be a big headache to track down all the places a wildcard cert worms its way into at large, penny-pinching orgs.

[sk5t]

FYI, it is possible to run multiple certificates on one IP+port if your SSL clients support SNI. Nowadays that's not too crazy an assumption, and creating on-demand certs is doable; integrating this with your service and managing renewal might be a pretty advanced task though.

In other words, a web app with custom subdomains is probably a reasonable use case for wildcart certs, for now.