Supporting large key sizes in FreeIPA certificates

A couple of issues around key sizes in FreeIPA certificates have come to my attention this week: how to issue certificates for large key sizes, and how to deploy FreeIPA with a 4096-bit key. In this post I’ll discuss the situation with each of these issues. Though related, they are different issues so I’ll address each separately.

Issuing certificates with large key sizes §

While researching the second issue I stumbled across issue #6319: ipa cert-request limits key size to 1024,2048,3072,4096 bits. To wit:

ftweedal% ipa cert-request alice-8192.csr --principal alice
ipa: ERROR: Certificate operation cannot be completed:
  Key Parameters 1024,2048,3072,4096 Not Matched

The solution is straightforward. Each certificate profile configures the key types and sizes that will be accepted by that profile. The default profile is configured to allow up to 4096-bit keys, so the certificate request containing an 8192-bit key fails. The profile configuration parameter involved is:

policyset.<name>.<n>.constraint.params.keyParameters=1024,2048,3072,4096

If you append 8192 to that list and update the profile configuration via ipa certprofile-mod (or create a new profile via ipa certprofile-import), then everything will work!

Deploying FreeIPA with IPA CA signing key > 2048-bits §

When you deploy FreeIPA today, the IPA CA has a 2048-bit RSA key. There is currently no way to change this, but Dogtag does support configuring the key size when spawning a CA instance, so it should not be hard to support this in FreeIPA. I created issue #6790 to track this.

Looking beyond RSA, there is also issue #3951: ECC Support for the CA which concerns supporting a elliptic curve signing key in the FreeIPA CA. Once again, Dogtag supports EC signing algorithms, so supporting this in FreeIPA should be a matter of deciding the ipa-server-install(1) options and mechanically adjusting the pkispawn configuration.

If you have use cases for large signing keys and/or NIST ECC keys or other algorithms, please do not hesitate to leave comments in the issues linked above, or get in touch with the FreeIPA team on the freeipa-users@lists.fedorahosted.org mailing list or #freeipa on Libera.Chat.