On Tue, 2014-03-04 at 21:25 +0100, Petr Spacek wrote:
> On 4.3.2014 20:48, Simo Sorce wrote:
> > On Tue, 2014-03-04 at 14:19 -0500, Simo Sorce wrote:
> >> On Tue, 2014-03-04 at 19:14 +0100, Petr Spacek wrote:
> >>> On 4.3.2014 17:43, Dmitri Pal wrote:
> >>>> On 03/04/2014 11:25 AM, Petr Spacek wrote:
> >>>>> On 4.3.2014 17:00, Dmitri Pal wrote:
> >>>>>> On 03/04/2014 10:26 AM, Simo Sorce wrote:
> >>>>>>> On Tue, 2014-03-04 at 13:51 +0100, Petr Spacek wrote:
> >>>>>>>> On 26.2.2014 16:00, Simo Sorce wrote:
> >>>>>>>>>>>> need to be protected as carefully as the private key.
> >>>>>>>>>>>>> This is something I meant to discuss too, how do we protect 
> >>>>>>>>>>>>> them ?
> >>>>>>>>>>>>> Clearly we have ACIs but I am wondering if we want to encrypt 
> >>>>>>>>>>>>> them with
> >>>>>>>>>>>>> keys not immediately or easily available via LDAP ?
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> It's kind of catastrofic if they get inadvertently exposed like 
> >>>>>>>>>>>>> if
> >>>>>>>>>>>>> someone does a ldapsearch as "Directory Manager", which is one 
> >>>>>>>>>>>>> of the
> >>>>>>>>>>>>> reasons why we encrypt kerberos key material before storing it 
> >>>>>>>>>>>>> into the
> >>>>>>>>>>>>> db.
> >>>>>>>>>>> PKCS#8 allows encryption, I guess we can use that. There needs to 
> >>>>>>>>>>> be
> >>>>>>>>>>> some metadata on how to decrypt the blob though, so that the 
> >>>>>>>>>>> PKCS#11
> >>>>>>>>>>> module can actually decrypt it when necessary.
> >>>>>>>>> Yep, and we also need to decide what master key is used and where 
> >>>>>>>>> it is
> >>>>>>>>> placed, and who access it, and how:-)
> >>>>>>>> Let's move the discussion forward, we need to implement the schema 
> >>>>>>>> for 4.0.
> >>>>>>>>
> >>>>>>>> Do I understand correctly that the whole purpose of
> >>>>>>>> krbPrincipalName=K/M@IPA.EXAMPLE,cn=IPA.EXAMPLE,cn=kerberos,dc=ipa,dc=example
> >>>>>>>>
> >>>>>>>> is just to encrypt keys with some other key which is located at some 
> >>>>>>>> other
> >>>>>>>> place? I.e. the goal is to lower the probability that a random 
> >>>>>>>> ldapsearch
> >>>>>>>> will
> >>>>>>>> return encrypted blob and master key at once, right?
> >>>>>>> Yes, it would also be nice if we could finally offload this key from
> >>>>>>> LDAP for added security, but we are not there yet.
> >>>>>>>
> >>>>>>>> What algorithm/method should we use for key wrapping? As far as I 
> >>>>>>>> remember
> >>>>>>>> from my studies key wrapping is very sensitive thing and we 
> >>>>>>>> definitely
> >>>>>>>> need to
> >>>>>>>> use some existing standard&tool for doing it. Can we just call some 
> >>>>>>>> NSS
> >>>>>>>> function with default/system-wide parameters and let it do it's job?
> >>>>>>> I think that would be what we want to do in some form.
> >>>>>>>
> >>>>>>>> That would mean that, after all, we just need to provide some blob 
> >>>>>>>> as key
> >>>>>>>> wrapping key :-) (Generated with care it deserves etc.)
> >>>>>>> The key must be self describing somehow (for algorithm agility).
> >>>>>>>
> >>>>>>>
> >>>>>>>> We have had discussion with Honza and the first idea is to add 
> >>>>>>>> attribute
> >>>>>>>> like
> >>>>>>>> 'wrappingKeyId' to each encrypted blob and use it for locating
> >>>>>>>> appropriate key
> >>>>>>>> when necessary.
> >>>>>>>> - During decryption: Do a LDAP search with filter like
> >>>>>>>> (keyId=<wrappingKeyId>)
> >>>>>>>> to find appropriate wrapping key.
> >>>>>>>> - The harder part is how to pick a wrapping key for encryption. It 
> >>>>>>>> can be
> >>>>>>>> tricky if the wrapped key is shared among more users (DNS servers) 
> >>>>>>>> etc.
> >>>>>>>> - It is possible to easily use multiple wrapping keys at once so key
> >>>>>>>> rollover
> >>>>>>>> is easy. You can re-encrypt keys one by one.
> >>>>>>> This makes things complicated fast.
> >>>>>>> One thing I was thinking was to use a keytab and krb functions to do 
> >>>>>>> the
> >>>>>>> wrapping but that would be pretty IPA specific.
> >>>>>>>
> >>>>>>>> The other idea is to add 'wrappingKeyId' to PKCS#11 token. So all 
> >>>>>>>> PKCS#11
> >>>>>>>> objects inside the same token will be encrypted with the same key.
> >>>>>>>> - Decryption is easy - the same as in previous case.
> >>>>>>>> - Encryption is basically the same as encryption.
> >>>>>>>> - Key rollover is hard. You would have to re-encrypt all keys and 
> >>>>>>>> change
> >>>>>>>> wrappingKeyId associated with given token at once - but it is 
> >>>>>>>> impossible
> >>>>>>>> because we don't have LDAP transactions. As a result, clients will be
> >>>>>>>> confused
> >>>>>>>> during rollover. (Consider problems with syncrepl when clients can 
> >>>>>>>> see
> >>>>>>>> changes
> >>>>>>>> immediately.)
> >>>>>>> Yeah this is a problem we need to address.
> >>>>>>>
> >>>>>>>> The third approach is 'hybrid':
> >>>>>>>> A 'wrappingKeyId' associated with PKCS#11 token is 'the active one' 
> >>>>>>>> and is
> >>>>>>>> used for encrypting new objects stored into PKCS#11 token. Each key
> >>>>>>>> stored in
> >>>>>>>> the token has own wrappingKeyId attribute and it is used for 
> >>>>>>>> decryption.
> >>>>>>>> - Decryption is easy - the same as in previous case.
> >>>>>>>> - Encryption always use wrappingKeyId associated with given token.
> >>>>>>>> - Key roll over can start from wrappingKeyId associated with the 
> >>>>>>>> token and
> >>>>>>>> then re-encrypt keys in the token one by one. All keys can be 
> >>>>>>>> decrypted
> >>>>>>>> in any
> >>>>>>>> step (assuming that changes in one LDAP object are atomic).
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Where is a hole in this design? :-)
> >>>>>>> I do not like the idea of having to add a wrappingKeyId everywhere.
> >>>>>>>
> >>>>>>> My initial though was to have a central place where wrapping keys are
> >>>>>>> stored, and during a rollover period you try all the keys until one
> >>>>>>> works or decryption fails. At the end of rollover you delete the old 
> >>>>>>> key
> >>>>>>> so you avoid the additional load.
> >>>>>>>
> >>>>>>>> Where should we store wrapping keys for users/services and DNS 
> >>>>>>>> servers? User
> >>>>>>>> object or cn=dns doesn't sound like a good idea because it would 
> >>>>>>>> defeat the
> >>>>>>>> purpose.
> >>>>>>> Indeed. And this is the biggest problem. It would be nice to have a
> >>>>>>> mechanism to securely transfer the key to the DNS servers w/o having 
> >>>>>>> to
> >>>>>>> store it permanently in LDAP. If we had this mechanism we'd be able to
> >>>>>>> apply it to the Kerberos master key too. But it can't be confined to
> >>>>>>> installation time only, which is easy, it needs to be possible to 
> >>>>>>> update
> >>>>>>> it at a later time, which is where we have issues, as our replication
> >>>>>>> mechanism is LDAP.
> >>>>>>>
> >>>>>>> If we solve the DNA plugin issue with the ability to use groups for
> >>>>>>> authentication I guess we could build a control/extend operation that
> >>>>>>> would allow masters to transfer keys to each other w/o exposing them 
> >>>>>>> as
> >>>>>>> LDAP searches, do we want to try to go in that direction ?
> >>>>>>>
> >>>>>>> Simo.
> >>>>>>>
> >>>>>> Should we consider "vault" as a storage for these keys too?
> >>>>>> It already supports recovery of the symmetric and asymmetric keys so 
> >>>>>> may be
> >>>>>> these keys should be stored there?
> >>>>>
> >>>>> Maybe. The question is if we want to support DNSSEC without Dogtag ...
> >>>>>
> >>>> Without Dogtag? Vault would be an independent component from CA I assume,
> >>>> though CA might be needed anyways to issue transport keys for the 
> >>>> internal
> >>>> components.
> >>>> But I think that even if we use Vault as an internal password and key 
> >>>> storage
> >>>> I do not see a reason why we can't require it for DNSSEC.
> >>>> Why over-complicate things if we already have components that can be 
> >>>> used? If
> >>>> we see a requests to support DNSSEC without Vault component we will 
> >>>> adjust but
> >>>> I do not think we should limit ourselves in the first implementation.
> >>>
> >>> I'm personally fine with that.
> >>>
> >>> Are we going to re-prioritize Password Vault from Backlog to 4.0?
> >>> https://fedorahosted.org/freeipa/ticket/3872
> >>>
> >>> We need that in 4.0 timeframe for DNSSEC otherwise you need to convince 
> >>> Simo
> >>> that key wrapping is not necessary :-)
> >>
> >> For 4.0 we could document that you have to copy the keys around
> >> manually. And add Vault support in 4.1 ?
> It could work ... Can we modify ipa-replica-prepare in 4.0 to add the 
> wrapping 
> key to replica file to make it easier?
> 
> Can the vault approach work for Kerberos master key? If not, shouldn't we 
> design something universal instead of deferring it again and again?

We can use the same method for the M/K, now that the CA is installed
before the rest we do not have a chicken-egg issue anymore.

> Another problem is that the PKCS#11 LDAP schema was designed as 
> application-independent but now we are adding very specific key-wrapping 
> mechanism (it is hard to believe that somebody else will implement it).

It could be optional.

> Maybe we can add something like attribute 'pkcs11keyWrapMech':
> - key is not wrapped if it is not present
> - key is wrapped if it is present - value determines used mechanism 
> (mandatory 
> mechanism to implement is only 'none')

What is 'none' ?

> > Actually an idea came to mind that might work well enough.
> >
> > We could store the symmetric key wrapped itself.
> ???
> 
> > The wrapping would be done using a public key per DNS server.
> > Public keys for DNS servers would be generated via certmonger in the
> > usual way.
> I don't understand, maybe it is too late for me :-)
> 
> Where will the private key be stored?

On the file system, just like with other certificates.

> > The only unknown here is who adds a new wrapper wen a new server is up
> > and it publishes the public key in LDAP. For existing servers they can
> > re-wrap themselves.
> >
> > It's a few layers but should not be too hard.
> I don't fully understand to your proposal but I'm afraid that it will not 
> work 
> for ordinary IPA users. Don't forget that we want to have universal PKCS#11 
> storage usable even for private SSH keys and other stuff.

Well ... TBH I am not really that hot about storing private keys in IPA
like that, however for people that want to do it they can simply store
them not encrypted as you proposed above.

> Please correct me if I'm wrong.

You are right, but I was caring for the DNS keys case, not the user's
ssh key case, which is hairy IMHO.

I think the private ssh key case is a clear job for the Vault the fact
sssd might use a pkcs#11 interface to present it to ssh, or the user
simply pulls it to the local file system is, in my view, an
implementation detail.

Although I realize I have not said it explicitly before I am not all
that happy to have a generic pkcs#11 storage in IPA. Storing *arbitrary
private* keys in my mind is clearly the job of DRM which has been built
with that specific use case in mind and has all the appropriate
protections. Putting unencrypted private keys in the IPA tree is IMHO a
too high risk.

I am not against creating a generic schema if we think it may be useful
for others, but the more I thin of it the less I think we should use it
for anything but DNS keys and they should be definitely encrypted in
LDAP and the DNS server machines should be the only ones able to decrypt
them.

A casual search with directory manager should never yield private keys.

Simo.

-- 
Simo Sorce * Red Hat, Inc * New York

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