Subject: RE: OCSP and LDAP

From: [email-masked] (Peter Gutmann)
Date: Sun, 5 Jan 2003 21:20:17 +1300

"Ambarish Malpani" <[email-masked]> writes:

>I have still to see a place where using CRLs as the mechanism for letting a
>VA know of changes in the revocation data has led to poorer performance than
>having the VA access the CA's database directly.

Most of the CAs I know of issues CRLs a few times a day, some as infrequently
as once a day.  If I'm doing processing with any kind of value attached to the
transaction, I want to know whether the cert is valid right now, not whether
it was OK last night when the CRL was issued (substitute "credit card" for
"cert" to see why this is important).  I have never seen a situation where an
offline CRL gives better performance than a real-time check of a live
database, unless you happen to catch it just as the CRL is being issued, which
(for a 24-hour CRL time) only works about once in 86,400 times.

I think one of the reasons why there aren't more complaints about CRLs is
because so many apps only pay lip service to revocation checking, so it
doesn't really matter if it doesn't work proprely ("We go through the motions
because the CA policy requires it"/"It's turned off by default, but we can
claim it's there"/"We realise the CRL is almost always out of date, but our
accounting processes should catch any problems"/etc are all excuses I've
heard).  If you build a system where you can tell users that there's a simple
online check which guarantees that at the time the check was done the cert was
valid (rather than being valid a couple of hours ago) following the credit
card model that businesses are used to, perhaps people would lend more weight
to the value of checking.  Actually, as mentioned in my previous message,
implementors are already doing this, and have been doing it for some time,
because people care about real-time cert status information, it's just not
standardised in any spec (yet :-) so you get a pile of proprietary ways of
doing it.

Peter.

---

From: "Anders Rundgren" <[email-masked]>
Date: Sun, 5 Jan 2003 10:44:18 +0100

I agree with Peter.

I don't think OCSP in a not so distant future have to be more
technically costly than accessing a web-page.  Including a signed
answer.

Some banks in Sweden believe 20 cents/lookup is a reasonable
fee as it is "comparable to putting a stamp on a letter".

Personally I don't think the VA-business model has much future
as it complicates they way parties interact.  It essentially
requires two or three global VA-networks in the world to function
and that seems very unlikely to happen.  It feels like the VA business
model is crafted according to the lines of credit-card authorizations,
but that is a rather different type of business IMHO.

Pardon the slightly orthogonal input, but business & technology do
have rather interesting connections...

Anders

----- Original Message ----- 
From: "Peter Gutmann" <[email-masked]>
To: <[email-masked]>; <[email-masked]>; <[email-masked]>; <[email-masked]>
Sent: Sunday, January 05, 2003 09:20
Subject: RE: OCSP and LDAP

Peter.

---

From: "Ambarish Malpani" <[email-masked]>
Date: Sun, 5 Jan 2003 08:28:46 -0800

Hi Peter,
    One of the things that I didn't mention in my original mail,
but that I think I had said on this list before, is that we do
allow our VA to use its own data to indicate that a certificate
is revoked/suspended if the VA knows that a certificate has
been revoked/suspended, but the CA has not had a chance to indicate
that.

3 other issues:
    a. When people try to keep their CAs offline, they not only
want keep the CAs signing key offline, but also its database. Having
the responder access the CAs database means that some of the CAs
data now needs to be online.

    b. If you want to locate VAs at multiple remote locations and
you have the VA access the CAs database, it needs to access that
database from remote locations.

    c. Most CA operators are prefectly happy to combine the
capablity above (of temporary suspension at the VA) and the fact
that a VA can accept a CRL issued at any time, to deal with the
issue of needing to revoke/suspend a cert while a CA is offline.

Hope this helps,
Regards,
Ambarish

---------------------------------------------------------------------
Ambarish Malpani                                         650.759.9045
Malpani Consulting Services                      [email-masked]
http://www.malpani.biz

> -----Original Message-----
> From: [email-masked]
> [mailto:[email-masked]]On Behalf Of Peter Gutmann
> Sent: Sunday, January 05, 2003 12:20 AM
> To: [email-masked]; [email-masked]; [email-masked];
> [email-masked]

---

From: "Ambarish Malpani" <[email-masked]>
Date: Sun, 5 Jan 2003 09:53:27 -0800

Hi Peter,
     I agree completely with the statements that people don't
really use CRLs and that getting up to date information to all
clients via CRLs is hard.

    I, too, wish people would just use OCSP and move on with things.
That was the whole idea behind doing Valicert.

As I explained before - using CRLs as a mechanism for getting
snapshots from the CA, ability to accept emergency CRLs and the
ability to revoke/suspend at the VA give people all the benefits
of OCSP without needing to change their CA or have their VA tied
into the CA/need access to the CAs database.

Regards,
Ambarish

---

From: "Simon Tardell" <[email-masked]>
Date: Mon, 6 Jan 2003 11:46:23 +0100

Peter,

> Most of the CAs I know of issues CRLs a few times a day, some 
> as infrequently as once a day.  If I'm doing processing with 
> any kind of value attached to the transaction, I want to know 
> whether the cert is valid right now, not whether it was OK 
> last night when the CRL was issued (substitute "credit card" 
> for "cert" to see why this is important).  I have never seen 
> a situation where an offline CRL gives better performance 
> than a real-time check of a live database, unless you happen 
> to catch it just as the CRL is being issued, which (for a 
> 24-hour CRL time) only works about once in 86,400 times.

This argument is backwards: The CAs are doing the minimum that they can
while still conforming to the model, because noone is (as you correctly
note) really asking for CRLs (or revocation checking in any other way)
more than as a checkbox item. It doesn't mean that they can't. When need
arises, they can switch to issuing one delta per revocation and push
that their OCSP responders. 

It is just as up to date as coupling an OCSP responder directly to the
CA database, and it keeps the CA offline. The only thing missing, from a
standards perspective, is to specify the push protocol. 

Simon

Simon Tardell, cell +46 70 3198319, [email-masked]