Hernath Szabolcs wrote:
On Wed, 16 Nov 2005, silverhairbp wrote:
Lets review this.
OK
If a new certificate is issued with different information but the
same public key and serial number as the original, then there is no
point in reissuing since the original certificate can't be CRL'ed and
will still be active through its life. That is one of the reasons
why each certificate MUST have a unique serial number.
I think the point of discussion is 'new certificate' here. It is the
same certificate as before. Only the encoding is different, but their
signatures are identical, and therefore trust validation yields the
same with either copies. They have the same Subject/Issuer DN. The
same public key. The same extensions (well, almost, that is). The same
fingerprints. The same validity period. They provide exactly the same
level of trust for the relying parties. It is not a 'new certificate'
by any stretch of the imagination.
As a point of reference, the new certificate is not the same as before.
It will only copy some of the information from the original certificate
and use the same key pair, but will most certainly be unique to itself.
Since there is no way to CRL the original certificate (no unique DN /
serial number combination), the original certificate will still be
valid. The signature over the new self-signed root will certainly be
different if the contents of the certificate are changed. Wasn't
David's point that he wanted to change the root to better define its
use? If the original root certificate is still available, it undermines
the effort to create a new certificate.
What happens during chain validation if the PKCS#9 package contains the
entire chain of certificates back to and including the original root?
It certainly won't match the cached root.
And, of course, the original "can't be CRL'ed," I said the exact same
thing. There is no point in revoking a self-signed certificate, if
your CA signing keypair has to be changed. In any case of key
changeover, you roll out a new PKI, and destroy the old keypair. You
must have a working, safe root cert distribution mechanism to the
relying parties anyway.
There is a point of revoking a root certificate if the hierarchy is
being retired before its expiration. Otherwise the hierarchy remains
active and must be managed to prevent its compromise and misuse. It
relates back to the certificate policies and practices created for the
PKI being retired and the new one being established.
I think the point is who are the relying parties and the scope of
certificate distribution. If the certificates are used for other than
PIRMA access control against a private system where only a single root
is used, the scheme, dirty as it is, may continue to function. But as
soon as the the hierarchy is used outside of the closed system, trust
fails since more than a single root certificate exists. It is more than
a technical issue, but rather one also associated with the trust hierarchy.
It is NEVER permissible to reissue a certificate reusing a serial number.
Well, first of all this is generally very true - this is a special
case, however. Secondly, it is not quite 'reissued,' see above.
Not "generally" very true, but absolutely. It is the only way a PKI
using the same DN can maintain certificate differentiation.
Each certificate must have a unique serial number.
Yes. Same certificate -> same serial.
The scheme descrived by David REQUIRES the extablishment of a new
certificate hierarchy with a new root certificate.
Well, I don't quite agree. If the level of trust put in signatures
does not change with this technical alteration, I see no reason for a
key changeover. It is only a different version of the same root cert
with notably one single different value for an extension.
It is only bad practice to reuse a key pair.
Again, generally this is very true. But this is not an actual re-use.
When keys are reused, the management of the hierarchy requires the
management of the certificates under it. When a key pair is used across
more than one hierarchy, both must manage the key integrity. It is
reuse of in practice to maintain a key in multiple hierarchies. The
compromise of a single reused key impacts multiple hierarchies. The
reason why reuse is (at the very least) bad practice is because it
requires the synchronization of the hierarchies containing the shared
key in the change of user access rights or key exposure.
Bill
Szabolcs
Bill
Hernath Szabolcs wrote:
On Wed, 16 Nov 2005, David Bannon wrote:
OK Hernath, that makes sense. But how do I get OpenCA to accept a new,
additional certificate if it does not make it itself ? I tricked it
How do you mean accept?
into letting me make a new one (by removing the existing files) but
if I
Sorry, I don't get it...
generate a new certificate externally and then just put the files
where
OpenCA keeps them, OpenCA will not notice and won't add them to its
I don't have access to my signing machine right now, but I think you
should simply overwrite all instances of the CA root cert within
opencas directory tree with the new version.
Szabolcs
database.
David
PS : When this is all over, I'll write up the procedure for the FAQ,
other people must want this occasionally !
On Wed, 2005-11-16 at 11:40 +0100, Hernath Szabolcs wrote:
Hi,
On Wed, 16 Nov 2005, David Bannon wrote:
Is it necessary for the start and end dates to be the same as the
original ? Means I cannot use the OpenCA gui to create it but
thats not
too much of a problem.
You certainly don't want to change the start of validity date of
your root
certificate, so you have to create it by hand. You may change the
end date
if necessary. In any way, the change (even if you only alter the
keyUsage
criticality) should be reflected in your new CP/CPS version.
Szabolcs
Would make life a lot easier !
David
Hi All,
On Tue, 15 Nov 2005, silverhairbp wrote:
David Bannon wrote:
Folks, I would like to ask for some advice here. We have a
problem and
below is our plan to solve it. I'd be very grateful if you
could have a
look at it and let me know if you see anything thats going to
bite us
expectantly.
The problem
-----------
We use OpenCA 0.9.2 and it was setup some 12 months ago using
default
settings. Our CA Certificate was originally issued without the
necessary
parameter of keyUsage being 'critical'.
The solution
------------
Revoke all 220 certificates, revoke the CA Certificate, issue
a new CA
certificate (using existing key) and issue new certificates to
users.
I think you should not do that. If the only thing you want to
change is
technical parameters in your root cert, but otherwise use the same
keypair, you essentially maintain the trust based on the the
signatures
made with your original signing key. In other words, you do not
need to
revoke anything, instead you simply reissue your root cert with
the same
DN, serial, keypair and validity dates and changed technical
parameters
(e.g., fixing the keyUsage, changing the signature algorithm
etc). In this
way, signatures made with the old or new root certs will
validate against
either of them. The already issued certificates will not be
effected.
Besides, there is no point in revoking a self-signed certificate
anyway,
in case you want to terminate the trust associated with the
signatures
made with a CA's signing key before the expiration of the root cert
(emergency key changeover), you revoke all issued certificates
(except the
root), publish a last valid CRL, destroy all copies of the CA
signing key,
and start anew with a fresh PKI.
If you only want to terminate the usage of a CA's signing key
-without
disruption of the trust associated with its signatures- (routine
key
changeover), you can harmonize various validity dates and CRL
issuance
frequency such that you can keep your usual operating procedures
(issuing
CRLs as usual) and let all certs (issued and root) expire.
Before that
happens, you already start your fresh PKI in parrallel with some
useful
overlap time.
Good Luck,
Cheers
Szabolcs
P.S.: as a sidenote, if the keypair of sub-CA is actually
compromised in a
multilevel hierarchy (as opposed to having some flags
misconfigured), I
would definitely *revoke* the sub-CA's root certificate for
good, not only
suspend it. The keypair is the root of your trust - if it's
compromised,
your pki (under that sub-CA's level) is over.
The Plan
------------
We have established that we can generate a new CA Certificate
and OpenCA
(0.9.2) is quite happy. So this is what we'll do, steps 1 - 3
(below)
must be done before implementation date.
1) Encourage all end users and RA Operators to lodge new
requests for
new certificates.
2) Ordinary users must meet (again) with RA Operators to show
photo ID.
RAO must authorise new applications in normal manner.
3) CA Operators and CA Manager will phone RAOs to explicitly
confirm
details of their own personal applications, in normal manner.
------ Implementation Day --------
4) On the CA machine, move the existing CA Certificate files
(from /var/crypto/cacerts) out of the way. Their details will
remain in
the database. Start openCA, make a new request for a self signed
certificate and then Generate it.
(General->Initialization->Request
Setup, Certificate Setup).
5) On RA, revoke all user certificates and process to CA.
6) On RA, revoke the old CA Certificate and process to CA.
7) Commence issuing the backlog of certificate requests currently
pending, in the normal manner.
Although we will aim for completing this process in one day, I
doubt we
will be able to do so.
--------------------
I'll be very grateful for any comments you care to make.
David
Rather than revoking the original CA certificate, have you
considerd
suspending it to see if there are any user that have not
installed their new
certificates? It would be easy to roll back the old root cert
and convert
that last users, repead the suspend root process until all
users are
converted. That way you can motivate slow converters to get
new certificates
while minimizing their down time.
As a suggestion, when deploying the new hierarchy, manage the
validity period
closely so taht you can migrate to a new root without a lot of
hassle. There
are papers on the technique available.
Bill
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