[Freeipa-devel] User Certificates in 4.2 - design and questions

[Martin Kosek]

On 05/04/2015 09:23 PM, Simo Sorce wrote:
> On Mon, 2015-05-04 at 16:41 +0200, Martin Kosek wrote:
>> On 05/04/2015 03:01 PM, Fraser Tweedale wrote:
>>> On Mon, May 04, 2015 at 10:50:15AM +0200, Martin Kosek wrote:
>>>> Hello,
>>>>
>>>> Please let me promote the design for one of the major FreeIPA 4.2 features, the
>>>> (user) certificates and Smart Card integration:
>>>>
>>>> http://www.freeipa.org/page/V4/User_Certificates
>>>>
>>>> The design went through couple interim discussions between developers outside
>>>> of this list, so there should not be too many objections. But still, please
>>>> free to comment or improve the design yourself.
>>>>
>>>> For FreeIPA 4.2, I think this resolves in following, quite limited, scope of work:
>>>> * Adding eq, pres indices for userCertificate
>>>> * Applying new policy of storing certificate in userCertificate attribute,
>>>> based on upcoming Certificate Profile feature by Fraser.
>>>> * Making sure that multiple certificates can be added to userCertificate
>>>> attribute manually by CLI and UI
>>>>
>>>> The "Certificate Identity Mapping" part will probably be moved to 4.3+, unless
>>>> there is extra pool of development resources.
>>>>
>>>> There is still something to be resolved - how should the certificates be
>>>> revoked in object-del or object-disable actions? Currently, certificate is
>>>> always stored in userCertificate and it's serial is used for revoke operation
>>>> in Dogtag. But that will not be true in 4.2+ since some certificates will not
>>>> be stored in accounts.
>>>>
>>>> Do we only want to revoke those that have policy to be stored in the
>>>> userCertificate attribute? Does not sound right to me. Or do we need a Dogtag
>>>> API that would allow us to query (or even revoke directly) all certificates
>>>> generated for a user/service/host and revoke them, regardless whether they are
>>>> stored in userCertificate attribute or not?
>>>>
>>> If the DN or other searchable attributes bear a principal name,
>>> existing APIs should be sufficient (if a little awkward).  But
>>> Dogtag does not know about principals, it only knows what is on the
>>> cert (and a few other things, like the profile that was used).
>>
>> Kerberos principal SAN is added when the certificate is requested via
>> Certmonger, but we do not add it when requested via cert-request command (yet).
>> So we cannot depend on it.
>>
>>> Later, when we implement GSSAPI and ACL enforcement in Dogtag
>>> (https://fedorahosted.org/freeipa/ticket/5011) we can also store the
>>> principal that issued the certificate for a concrete association in
>>> Dogtag, which can be used to locate certificates for a principal.
>>
>> Right, sounds as something we should do. I commented in the ticket.
>>
>>> Considering known use cases in which one would not want to store the
>>> issued cert in IPA, some of these have short lived certs so
>>> revocation is not an issue.  With that in mind I think it would be
>>> OK, for 4.2 at least, to not provide a way in IPA to revoke a cert
>>> that was issued via IPA but not stored; it can still be revoked
>>> using Dogtag directly, and we could provide pointers to Dogtag
>>> documentation.  The important thing is to manage the user
>>> expectations for 4.2.
>>
>> Hm, maybe - Simo, if you disagree, please shout. In this case, we would need to
>> make sure this side effect of the userCertificate policy is very well documented.
> 
> I do not disagree, in most cases when a user (or computer object) is
> deleted, there is really no need to actually revoke the cert.
> Keep in mind that revocation list growth is also a concern.

Right. IIRC some of our users had problems with CRL list size also, making us
to create ticket

https://fedorahosted.org/freeipa/ticket/4048

> So I am fine *not* revoking certs automatically and instead documenting
> best practices for certs lifecycle management (ie deleting certs when
> not useful) and how to manually/explicitly revoke certs only when
> actually compromised (for hosts), or when needed (user leaves
> organization and may retain a copy of the private key, unlikly when the
> cert was in a Smart Card which has been returned and wiped).

Well, makes sense to me. I added a section to the design:
http://www.freeipa.org/page/V4/User_Certificates#Revocation_of_the_Certificates

We just need to be cautious here because this would be a change in behavior
compared to FreeIPA 4.1 and older. Should this be another global/per-profile
policy setting that administrator could set up?