RE: self-signed TSA [Was Re: Private Key Cloning]

[Michael Zolotarev <mzolotarev@xxxxxxxxxxxxx>]

Jean,

My interpretation of the current text is:
The text mandates that a timestamp token can be only signed with a specific
'timestamping' key, as indicated by the ExtKeyUsage. A timestamp token
signed by a key which does not contain that ExtKeyUsage field must be
considered invalid. However, it does NOT necessarily say that the same
'timestamping' key can not be used for signing whatever else, for example a
certificate. 

So, I can not see anything in the current text that would prohibit issuing a
self-signed TSA certificate.

However, I'd suggest that the draft makes it clearer, by adding a comment
(in a security section?) about possibility of generating and using
self-signed TSA certificates.

Regards
M

> -----Original Message-----
> From: Jean-Marc Desperrier [mailto:jean-marc.desperrier@certplus.com]
> Sent: Tuesday, June 20, 2000 8:37 PM
> To: ietf-pkix@imc.org
> Subject: self-signed TSA [Was Re: Private Key Cloning]
> 
> 
> Michael Zolotarev wrote:
> 
> > I can see a problem with it with self-signed TSA 
> certificates. Normally, a
> > client would be configured to directly trust THAT 
> [self-signed] TSA cert.
> > Having a set of self-signed TSA certificates would be a 
> configuration
> > nightmare for the clients. And then you add another crypto 
> box to your load
> > balancing array on TSS, and then another one...
> 
> It is my understanding of the current draft that a TSA 
> certificate can not be
> self-signed :
> 
> 2.3 :
> The TSA MUST sign all time stamp messages with one or more keys
> reserved specifically for that purpose.  The corresponding certificate
> MUST contain only one instance of the extended key usage field
> extension as defined in [RFC2459] Section 4.2.1.13 with KeyPurposeID
> having value id-kp-timeStamping. This extension MUST be critical.
> 
> If the TSA is self-signed then the private key has been used 
> for something else
> than signing time stamp, and something it does not have the 
> correct key usage
> field for.
> 
> So if self-signed TSA certificate should be enabled, I think 
> the wording of the
> draft should be changed to specify this.
>