On Tue, Jun 2, 2020 at 8:33 PM Alexander Bokovoy
<abokovoy(a)redhat.com>
wrote:
> On ti, 02 kesä 2020, Natxo Asenjo via FreeIPA-users wrote:
> > hi,
> >
> > We have a new realm with rhel 7.8 and a default CA key of 2048 bits.
> >
> > Recently a question arose to upgrade this to 4096 bits.
> >
> > According to this blog post
> >
>
https://frasertweedale.github.io/blog-redhat/posts/2020-01-28-freeipa-ove...
> > ) this should already be possible for new deployments with RHEL 8.1 but is
> > it possible to configure the root CA and eventually sub CAs to use the
> 4096
> > bits signing keys? In doing so, do we need to resign all certificates
> > already in use?
> >
> > Is it possible to do this in RHEL 7 or do we need to update the CA hosts
> to
> > 8.1 to achieve it?
>
> Dogtag supports custom CA properties for the main CA and you can specify
> them in a pki override file when deploying IPA. Not all properties
> described in pki_default.cfg(5) make sense for FreeIPA CA deployment so
> we limit them (you'll get an error for those in the override file) but
> CA key size is configurable in 4.8.0+.
>
> SubCA configuration is hardcoded in Dogtag's source code. They are
> always RSA 2048. So there is no way to use 4096 bits signing keys for them.
>
> In FreeIPA 4.8.0+ default CA signing key size is 3072. We found that it
> is a good compromise for real world workloads. According to
>
https://www.keylength.com/, NIST 800-57 Part 1 Rev. 4 recommends 3072
> bit RSA keys for keys that are used beyond 2030 for 128 bit strength.
>
>
good to know, thanks!
Be aware that internal defaults in certmonger are set to RSA 2048 in
> case explicit signing key algorithm and size are missing in the
> certificate request.
>
we use getcert request -g 4096 and -G points currently to rsa so this seems
ok.
...
Abusing this thread, is it possible to re-key the root CA with a with a
longer key length while keeping the sub CAs and rest of signed certificates
or do we need to reissue all certificates for everything?
In principle you can always create a new CA and then sign any other CA
including the original CA with its keys. I do not know if we make this
easy in FreeIPA though.
Simo.
--
Simo Sorce
RHEL Crypto Team
Red Hat, Inc