Does Let's Encrypt offer intermediate certificates?

IdenTrust hasn’t granted Let’s Encrypt the authority to do this. If you look at the Let’s Encrypt Authority X3 intermediate certificate, its basicConstraints section says

Critical
Is a Certificate Authority
Maximum number of intermediate CAs: 0

That means that Let’s Encrypt is not allowed to nominate new CAs via the IdenTrust chain of trust at all.

ISRG could conceivably do this with the new ISRG root instead, but

  • at a cost in device compatibility
  • at a cost in audit complexity
  • probably at a cost in staff time and effort due to the greater amount of damage that a misissued intermediate certificate can do, and the greater risk if one isn’t revoked when an underlying domain expires

It’s not necessarily a bad idea but Let’s Encrypt’s current economic model works because the marginal cost of issuing a new DV certificate with the current infrastructure is very, very, very low, while the marginal cost of issuing a new path-constrained intermediate from the ISRG root would be much higher than “very low”. To start with, it couldn’t be done automatically at all on the current infrastructure because the ISRG root isn’t online and it requires a manual activity involving human effort to generate new intermediates.

So while I’m sorry that you may end up having to pay for this, I think it’s also true that Let’s Encrypt isn’t set up to be able to do this without charging for the service (or, for that matter, even with changing for the service). The infrastructural changes required to do that would be fairly large and so it probably won’t happen quickly, but it’s an interesting topic to keep in mind for the long term.

4 Likes