Subject: Re: Re: 3280bis: CRL validation

From: "Denis Pinkas" <[email-masked]>
Date: Thu, 16 Jun 2005 16:38:50 +0100

David,

There is still a "typographical error" in your text.

See below.

>> David,
>>
>> About "case 3", I noticed major error in your description :
>>
>>> (1) The certificate must include a cRLDistributionPoints extension with
>>> a distribution point that has the cRLIssuer field present and include
>>> the DN from the issuer field of the certificate.
>>
>> RFC 3280 states on page 42:
>>
>> "If the certificate issuer is not the CRL issuer, then the cRLIssuer 
>> field
>> MUST be present and contain the Name of the CRL issuer".
>>
>> Hence it does NOT contain "the DN from the issuer field of the 
>> certificate".

>Denis,

>Yes, this was a typographical error on my part. The final word in the 
>sentence should have been "CRL", not "certificate".  The cRLIssuer field 
>must include the DN from the issuer field of the CRL.

Correct.

>Denis Pinkas wrote:

>>> The concept of indirect CRLs is very simple: If the scope of the CRL
>>> includes certificates that have an issuer name (i.e., the contents of
>>> the issuer field in the certificate) that is different that the issuer
>>> name of the CRL (i.e., the contents of the issuer field in the CRL),
>>> then it is an indirect CRL.

>> I am very sorry, but what you say is in contradiction with 3280bis 
>> (see page 51):

>> "Whenever the CRL issuer is not the CA that issued the
>> certificates, the CRL is referred to as an indirect CRL."

>OK.  So, I guess that according to this definition a CRL cover covers 
>certificates issued by the issuer of the CRL in addition to certificates 
>issued by other CAs is both an indirect CRL and a direct CRL. 

I am very sorry, but we have in RFC 3280: 
   
  "In general, when revocation status information is
   provided using CRLs, the CA is also the CRL issuer.  However, a CA
   may delegate the responsibility for issuing CRLs to a different
   entity".

This means that a CRL Issuer issues CRLs, but not certificates.
 
Hence the sentence above is incorrect. According to RFC 3280, 
the corrected sentences should be :

A CRL cover certificates issued by one or more CAs. 
A direct CRL is issued by the CA, while an indirect CRL is issued 
by a CRL Issuer.

Now if you wish to change the vocabulary (and we can get a consensus) 
to say that "indirect CRLs" is restricted to the case where a CRL covers 
certificates issued by more than one CA, this is not a problem; ... as long as 
we can find a name to designate the case where a CRL covers certificates 
issued by one and only CA, ... and we can also easily make the difference 
with the case where the CA is issuing CRLs (currently called "direct CRL").  

>> There exists three cases:
>>
>> 1) The CA is also issuing the CRL (i.e. it uses the same key to both
>> create certificates and sign CRLs).

>CAs are identified by name, not name plus key, so your "i.e." is not 
>correct.  

CAs are indeed identified by a name (as given by a CA) 
and the sentence is correct.

> You could subdivide this into two cases if you want:

>1a)  The CA is also issuing the CRL and the same key is used to sign 
>both the certificate and the CRL.

>1b)  The CA is also issuing the CRL and different keys are used to sign 
>the certificate and the CRL.

The CA uses the same key to sign certificates and CRLs.
Overlapping of certificate validity periods for CA certificates is usual.
It is thus possible to issue the CRLs both under the old key 
(still valid) and the new key. This depends how root key rollover and 
root key installation is handled by client applications 
(another nice and interresting topic).    

>As long as the issuer names in the certificate and CRL are the same it 
>is not an indirect CRL (unless, of course, the scope of the CRL also 
>includes certificates issued by other CAs).

>> 2) The CA is delegating responsibility to one CRL Issuer and that CRL 
>> Issuer
>> is only taking care of revocation status information for certificates 
>> issued by that CA.
>>
>> 3) The CA is delegating responsibility to one CRL Issuer and that CRL 
>> Issuer
>> is taking care of revocation status information for certificates 
>> issued different CAs.
>>
>> From the definition on page 51 (unless we change it) cases 2 and 3 are 
>> "indirect CRLs".
>> This is was I was referring to as cases a) and b) in my earlier e-mails.
>>
>>> The scope of an indirect CRL may include certificates issued by one or
>>> more CAs, but the mechanisms work the same way no matter how many
>>> different CA's certificates are included in the scope of the CRL.

>> So you are taking of case 3, whereas I say let us first agree on cases 
>> 1 and 2, where case 2 is also called in my earlier e-mails case b).

>How does case 3 differ from case 2?  How is the number of CAs whose 
>certificates are covered by a CRL matter?

For case 3, the CRL includes the CRL entry extension: Certificate Issuer.

Before opening the pandora box, we must first close the box for the 
two "simple" cases (which may not be as simple).

>Dave

Denis

---

From: "David A. Cooper" <[email-masked]>
Date: Thu, 16 Jun 2005 12:44:03 -0400

> This means that a CRL Issuer issues CRLs, but not certificates.

You have made this claim before and it is still incorrect.  RFC 3280 says:

   Section 4.1.2.4 (CRL Distribution Points): If the certificate issuer 
is not
   the CRL issuer, then the cRLIssuer field MUST be present and contain
   the Name of the CRL issuer.  If the certificate issuer is also the 
CRL issuer,
   then the cRLIssuer field MUST be omitted and the distributionPoint
   field MUST be present.

   Section 5 (CRL and CRL Extensions Profile): CRL issuers issue CRLs.  In
   general, the CRL issuer is the CA.

If CRL issuers do not issue certificates, why does section 4.1.2.4 
include the phrase "If the certificate issuer is also the CRL issuer, ...."

In the past you have claimed that what you really mean is that 
"certificate issuer" and "CRL issuer" are roles and that an entity can 
only be acting in one of these roles at a time.  But, X.509 defines 
Certification Authority as a type of entity, not as a role and the use 
of these terms in RFC 3280 is consistent with that.

> A direct CRL is issued by the CA, while an indirect CRL is issued

We'll if we really want to nitpick, the term "direct CRL" does not 
appear in either X.509 or RFC 3280.  It also seems that my initial 
explanation of the meaning of the term "indirect CRL" was correct 
according to X.509:

   X.509, Clause 3.3.32:  indirect CRL (iCRL):  A revocation list that 
at least
   contains revocation information about certificates issued by authorities
   other than that which issued this CRL.

> with the case where the CA is issuing CRLs (currently called "direct 

I never claimed that this is the meaning of "indirect CRL".  An indirect 
CRL may cover issued issued by one or more CAs.  The only requirement is 
that the CRL covered certificates that were issued by an entity other 
than the issuer of the CRL.

>>> 2) The CA is delegating responsibility to one CRL Issuer and that 
>>> CRL Issuer
>>> 3) The CA is delegating responsibility to one CRL Issuer and that 
>>> CRL Issuer

This is yet another false statement that you have made in the past. 

Section 5.2.5 (Issuing Distribution Point) of RFC 3280 states:

   The CRL issuer MUST assert the indirectCRL boolean, if the scope of
   the CRL includes certificates issued by authorities other than the
   CRL issuer.  The authority responsible for each entry is indicated by
   the certificate issuer CRL entry extension (section 5.3.4).

Section 5.3.4 (Certificate Issuer) of RFC 3280 states:

   This CRL entry extension identifies the certificate issuer associated
   with an entry in an indirect CRL, that is, a CRL that has the
   indirectCRL indicator set in its issuing distribution point
   extension.  If this extension is not present on the first entry in an
   indirect CRL, the certificate issuer defaults to the CRL issuer.  On
   subsequent entries in an indirect CRL, if this extension is not
   present, the certificate issuer for the entry is the same as that for
   the preceding entry.

In case 2 above, where the CRL covers certificates issued by a single CA 
and that CA is a different entity from the CRL issuer, the CRL is an 
indirect CRL and the first entry in the list of revoked certificates in 
the CRL MUST include the certificateIssuer extension.  RFC 3280 clearly 
states that if the certificateIssuer "extension is not present on the 
first entry in an indirect CRL, the certificate issuer defaults to the 
CRL issuer."  In case 2, since the issuer of the revoked certificate is 
not the CRL issuer, the certificateIssuer extension must be present to 
identity the certificate issuer.

Dave