Subject: Re: Q. Automatic certificate selection for signing

From: "Tammy Green" <[email-masked]>
Date: Thu, 16 Jan 2003 17:17:39 -0700

In trying to design something like this a while back, I found that a
blanket statement of "use this certificate for application x" was not
always sufficient.  Two areas where the concept broke down were:
 
1.  Nonrepudiation
Some signatures need to carry more legal weight than others, even
though they are being done through the same application and as the same
user.  In such cases, it is difficult to tell which certificate the user
wants to use without actual user input to the application.  The same
argument applies, by the way, if the user has multiple roles with a
certificate for each role -- you must determine which role the user is
acting as in order to select the correct certificate.
 
2.  Certificate Authority
If a user needs to use a single application to sign data, but sends the
data to different recipients, the certificate that must be used could
depend on which CA issued it.  For emailing family, perhaps I use a
public CA, but for work matters I am required to use a certificate
issued by my company's internally maintained CA.  

In the end, the linkage to an application can only be used to provide a
default certificate -- the user must always be able to chose something
else.
 
Putting such a linkage in the certificate, though, could be interesting
if the set of applications remained relatively static over the lifetime
of the certificate.  Otherwise, every time a new application was
deployed, new certificates would have to be created.  But, perhaps the
harder thing would be to standardize the set of application
names/identifiers that would be used in the certificates to prevent name
conflicts.  But, perhaps you get this for free with URIs?

Tammy Green
Senior Software Engineer
Novell, Inc., The Leading Provider of Net Business Solutions
[email-masked] 

Tammy Green
Senior Software Engineer
Novell, Inc., The Leading Provider of Net Business Solutions
[email-masked] 

>>> "Marc Poulaud" <[email-masked]> 1/14/03 2:35:11 PM >>>

A question for those involved with signing applications (or anybody
else with 2 cents)...
 
I'm interested to understand what might be some of the key
issues/options for a signing application that needs to select the right
certificate for signing a piece of data. I see two main options. One is
that there is a configuration option that allows a particular user to be
associated with a particular certificate (a la Outlook - I want to use
this certificate (and associated key) to sign my outgoing emails).
Another is that, during the signing operation, some how select the right
certificate based on a value coded in a certificate.
 
On the one hand I think the latter would be a smart move if it where
possible to use some standard (and therefore interoperable) way of doing
this (unlike my initial thought of having an 'application' specific
value in an OU field) or perhaps a more suitable field within a
certificate (perhaps a policy qualifier?).
 
Anybody have experience of such matters?
 
Marc.

---

From: Vadim Fedukovich <[email-masked]>
Date: Fri, 17 Jan 2003 11:05:03 +0200

Let me just say I'm impressed we are still talking about "using certificates
for signing". To sign, the private key is used. At least for pkcs7.
Certificate is used while verification.

did I miss something?