[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Signer certificate discovery for CRLs


Stefan,

Denis,

I'm not sure what you mean.

For the time being, I would like that you provide an example where, when using the current extensions that are defined in RFC 3280, it will NOT be possible to locate a CRL Issuer certificate.

If you are able to provide that example, then it would justify the need for an extension at least for one case. Then we can see what that case is.

I am awaiting that example.

Denis


I conclude that I agree with Santosh.

The debate is still open... Feel free to express your opinion.

Stefan Santesson
Microsoft Security Center of Excellence (SCOE)



-----Original Message-----
From: Denis Pinkas [mailto:Denis.Pinkas@xxxxxxxx]
Sent: den 13 oktober 2004 16:34
To: Stefan Santesson
Cc: Santosh Chokhani; pkix
Subject: Re: Signer certificate discovery for CRLs

Stefan,

You are making a conclusion without letting me the time to respond.
I will need more time to look at the pictures (and understand them).

For the time being, I am still reluctant to accept

"yet-another-method".

We already have too many.


Santosh,

I conclude that we are in complete and total agreement.
The question is how to go about this.


Could we do this amendment to RFC 3280 in its next revision?
It would hopefully just be a minor change.

This is exactly what I feared.

We usually end-up with a "minor change" in an extension without saying
cleary how and when it shall/should be used.

I still have in mind that:

 1) a certification path must first be constructed,
 2) then the revocation checking of that path must be done.

This means that information about CRL issuers certificates locations

may

certainly be found in that chain. If not, I would like an example.

Denis



It would not change the definition of AIA just add that it can be

used

also as CRL extension and list eventual restrictions and guidance for

use

with CRLs.


Stefan Santesson
Microsoft Security Center of Excellence (SCOE)




-----Original Message-----
From: owner-ietf-pkix@xxxxxxxxxxxx

[mailto:owner-ietf-pkix@xxxxxxxxxxxx]

On Behalf Of Santosh Chokhani
Sent: den 13 oktober 2004 04:33
To: 'pkix'
Subject: RE: Signer certificate discovery for CRLs


Stefan:

In terms of certificate discovery, your proposal for AIA in CRL is

more

robust. The whole idea of self-issued key rollover certificates and

then

using the new key to issue CRL is fraught with security problems.  A
secure
solution would be one where the new key is certified by the parent

CA.

In

that case to obtain the new certificate, you could use AIA in CRL.

As to indirect CRL, your proposal is a good one.  The CRL DP in
certificate
in question points to the indirect CRL.  You get that CRL.  The AIA

in

CRL

gets you started for the indirect CRL issuer certification path and

you

are
in business.

-----Original Message-----
From: owner-ietf-pkix@xxxxxxxxxxxx

[mailto:owner-ietf-pkix@xxxxxxxxxxxx]

On
Behalf Of Stefan Santesson
Sent: Tuesday, October 12, 2004 7:30 PM
To: David A. Cooper
Cc: pkix
Subject: RE: Signer certificate discovery for CRLs



David,

Thanks for the clarifications, they make sense.
I did misread your pictures.

So can we conclude that for a re-keyed CA in accordance with RFC

3280,

either the CRL issuer certificate itself, or the location of the CRL
issuer
certificate, will be clearly identified/available for the validating

party

in some cases, but not in others?

Can we also conclude that there is no real discovery solution for

indirect

CRLs?

Do you then agree then that it could be appropriate to allow AIA as

a

CRL

extension to facilitate discovery of CRL signer certificate?

Stefan Santesson
Microsoft Security Center of Excellence (SCOE)

________________________________________
From: David A. Cooper [mailto:david.cooper@xxxxxxxx]
Sent: den 12 oktober 2004 21:14
To: Stefan Santesson
Cc: pkix
Subject: Re: Signer certificate discovery for CRLs

Stefan,

I believe that you are misinterpreting the figures.  They really do
represent three different cases, not three different certification

paths

that have been constructed through the same PKI architecture.

In figure 1, CA 1 has generated self-issued key rollover

certificates.

The
Root CA has issued a certificate to CA 1's new key, but not its old

key

(either the Root CA never issued a certificate to CA 1's old key or

that

certificate has expired).

In figure 2, CA 2 has also generated self-issued key rollover
certificates.
The Root CA has issued a certificate to CA 2's old key, but not its

new

key.

In figure 3, when CA 3 performed key rollover, it requested a new CA
certificate from the Root CA.  CA 3 did not generated self-issued

key

rollover certificates.

Of course, another realistic scenario would be one in which a CA

generated

self-issued key rollover certificates upon key rollover and then had

the

Root CA issue a CA certificate to its new key.  In this case, as you
suggest, any of the certification paths from figures 1, 2, or 3

could be

constructed.

As for the contents of the AIA extension, here is what I have

specified

in

the "X.509 Certificate and CRL Extensions Profile for the Common

Policy":

The authorityInfoAccess extension uses URIs for two purposes. When

the

id-ad-caIssuers access method is used, the access location specifies

where

certificates issued to the issuer of the certificate may be found.

If

LDAP

is used, the URI must include the DN of the entry containing the

relevant

certificates and specify the directory attribute in which the

certificates

are located. If the directory in which the certificates are stored

expects

the "binary" option to be specified, then the attribute type must be
followed by ";binary" in the URI. If HTTP is used, the URI must

point to

a

file that has an extension of ".p7c" that contains a certs-only CMS
message
(see RFC 2633). The CMS message should include all certificates

issued

to

the issuer of this certificate, but must at least contain all

certificates

issued to the issuer of this certificate in which the subject public

key

may
be used to verify the signature on this certificate. .... For a
certificate
issued by "Good CA", some examples of URIs that may appear as the

access

location in an authorityInfoAccess extension when the

id-ad-caIssuers

access
method is used are:

ldap://smime2.nist.gov/cn=Good%20CA,o=Test%20Certificates,c=US?cACerti

fi

ca

te
,crossCertificatePair

ldap://129.6.20.71/cn=Good%20CA,o=Test%20Certificates,c=US?cACertifica

te

;b

in
ary,crossCertificatePair;binary

http://fictitious.nist.gov/fictitiousCertsOnlyCMSdirectory/certsIssued

To

Go

od
CA.p7c
For both LDAP and HTTP, the URI provides the exact location where
information is to be located, so there is no requirement for the

relying

party to try to figure out where information is located.

The HTTP URI points to a certs-only CMS message that includes all
certificates issued to the CA identified in the issuer field of the
certificate.

The LDAP URI points to the cACertificate and crossCertificatePair
attributes
of the directory entry of the CA identified in the issuer field of

the

certificate. These two attributes together hold all of the

certificates

issued to the CA: the cACertificate attribute holds the CA's self-

issued

certificates and the crossCertificatePair attribute holds the
cross-certificates issued to the CA by other CAs.

Dave


Stefan Santesson wrote:

David,

Thanks for these good thoughts and very useful scenarios.

I have some comments and questions on this.

First of all we can conclude that in some scenarios (figure 1) where

a

self
issued certificate is inserted into the path, you are likely to find

the

CRL
issuer cert in the path. (given that the new CA have a common key

and

certificate for cert signing and CRL signing).

Figure 1, 2 and 3 describe the same case. It is just describing

different

path building strategies. An application that has access locally to

all

chaining options may however still choose path 2 for the certs and

path

1

for the CRL independent of each other (which I think figure 3 tries

to

describe)

Another comment is the structure of AIA extensions. The use I'm

familiar

with doesn't use AIA to describe a directory entry where it is left

to

the

validation application logic to be intelligent enough to find

appropriate

certificate data from the directory. The model I'm familiar with is

when

the
AIA URL explicitly identifies the exact location of the appropriate

CA

certificate file, relieving the validation software from complex
information
queries. If just location of explicit certificate files are

identified

through AIA, the presence of an AIA may not help finding the CRL

signer

cert
if this is different from the CA certificate. This is also the

problem

with
Denis proposal.

I think we share the basic conclusion that the ability to locate the

CRL

signer certificate directly through the CRL could be very useful. At

least

in the case of indirect CRL but it could also be proven very useful

in

CA

re-keying scenarios.

The easiest solution would probably be to allow AIA to be used in

its

current shape and structure as a CRL extension (MUST NOT be

critical).

It

would present a very clear and uncomplicated logic to certificate
validating
applications in many cases.

Stefan Santesson
Microsoft Security Center of Excellence (SCOE)

________________________________________
From: David A. Cooper [mailto:david.cooper@xxxxxxxx]
Sent: den 7 oktober 2004 18:35
To: Stefan Santesson
Cc: pkix
Subject: Re: Signer certificate discovery for CRLs

Stefan,

I think what you are proposing is a good idea.  In most cases, path
discovery algorithms assume that both the trust anchor (or trust

anchors)

and the end entity certificate are provided as input. In this case,

one

may
need to construct a certification path without a priori access to

the

end

entity certificate (the one with the subject public key

corresponding to

the
CRL signing key).  Including an AIA extension (or some other

pointer) in

the
CRL would provide the relying party with a simple way to obtain the

end

entity certificate for the CRL signing key's certification path. On

the

other hand, I believe that a relying party should be able to

construct

the

certification path even without an AIA extension in the CRL, so long

as

it

is not an indirect CRL.  Attached is a drawing of the three basic
scenarios
that I expect a relying party may encounter:

In each of these scenarios, the CA has performed key rollover and is

only

signing CRLs with its new key. The diagrams would look similar,

however,

if
the CA simply choose to use different keys to sign certificates and

CRLs

for
some other reason.

If the PKI architecture resembled figure 1, then the certification

path

for
the CRL signing key would just be a subset of the certification path

for

the
EE certificate, so no addition path discovery would be needed.

If the PKI architecture resembled figure 1, then it would be

necessary

to

obtain the new-signed-with-old self-issued certificate. In building

the

certification path to the EE certificate, however, the relying party

will

obtain the certificates pointed to by the AIA extension in the EE
certificate.  This AIA extension will point to a location containing

all

certificates issued to CA 2, which would include both the

certificate

issued
by the Root to CA 2 and CA 2's self-issued certificate.  So, even

though

the
self-issued certificate would not be part of the certification path

to

the

EE certificate, it would be downloaded by the relying party during

the

construction of that certification path.  (Yes, there are circular
dependency issues in figure 2, but that is another issue.)

A similar situation would happen if the PKI architecture resembled

figure

3. The AIA extension in the EE certificate would point to a

location

containing certificates issued to CA 3. When the relying party

downloaded

these certificates, it would obtain both of the certificates issued

by

the

Root to CA 3 and so again would have the certificate needed to

validate

the
CRL signing key.

In the case of an indirect CRL, things may not work as well. If

indirect

CRLs were used, and the PKI architecture resembled figures 2 or 3
(replacing
"New Key" with a different CA), then the set of certificates pointed

to

by

the AIA extension in the EE certificate would not include the

certificate

of
the CRL signer.  One could find this certificate by building in the
reverse
direction and using the SIA extension, but that may not be the most
convenient solution.

So, when indirect CRLs are being used, it seems that it would be

very

useful
to have a pointer in the CRL to the CRL signing certificate.  When

the

CRL

is not indirect, the need for this pointer does not seem to be as

clear,

but
I can't see any harm in including it.

Dave

Stefan Santesson wrote:
All,

I'm interested in the opinion from members on this list about

discovery

of

CRL signer's certificate in non directory centric environments.

The problem is the following.

The relying party (RP) needs to check validity of a certificate and

finds

a
CDP extension with a URL to the CRL. The RP retrieves this CRL which

in

this
particular case is either signed by another key of the CA (re-keyed

CA)

or

another entity (indirect CRL).

In this case the relying party needs to obtain the certificate of

the

CRL

signer which may NOT be part of the original chain. In a directory

centric

solution this is retrieved from the directory, but what if such

directory

is
not available or accessible.

The RP have thus no hint where to find the CRL issuers certificate

unless

the RP already have possession of it by some other means.

Is seems that CRLs would need an AIA extension with the option to

point

to

the location of the signers certificate in the same manner as is

possible

for certificates.

Maybe AIA should be defined as both cert and CRL extension and not

only

certificate extension as today.

Thoughts and comments?

Stefan Santesson
Microsoft Security Center of Excellence (SCOE)