Dear Aaron,

Interesting line of argumentation. Wouldn’t that conclude that -every- 
mis-issuance of a leaf certificate would be a violation of "all certificates 
that it issues MUST comply with one of the following certificate profiles" and 
thus would require the ICA to be revoked? That can’t be the intent of the 
regulation, right?

Rgds
Roman

From: Servercert-wg <[email protected]> On Behalf Of Aaron 
Gable via Servercert-wg
Sent: Dienstag, 14. Mai 2024 16:59
To: Dimitris Zacharopoulos (HARICA) <[email protected]>; CA/B Forum Server 
Certificate WG Public Discussion List <[email protected]>
Subject: Re: [Servercert-wg] Discussion about single-purpose client 
authentication leaf certificates issued from a server TLS Issuing CA

On Tue, May 14, 2024, 02:33 Dimitris Zacharopoulos (HARICA) via Servercert-wg 
<[email protected]<mailto:[email protected]>> wrote:

Is it ok for such an Issuing CA to create a single-purpose client 
authentication TLS Certificate, one that is structured according to RFC 5280 
(thus can be successfully parsed by Relying Party RFC 5280-conformant 
software), contains an extKeyUsage extension which contains the 
id-kp-clientAuth and DOES NOT include the id-kp-serverAuth KeyPurposeId?

Speaking in a personal capacity, it is my opinion that no, such issuance is not 
acceptable.

I agree that the resulting end-entity client-auth-only certificate is out of 
scope of the BRs, and is not in and of itself misissued. However, the issuing 
intermediate itself is still in scope of the BRs, and its behavior can be 
contained by them. By virtue of issuing the clientAuth cert, the issuing 
intermediate has violated the BRs requirement that "all certificates that it 
issues MUST comply with one of the following certificate profiles".

One could even argue that, having issued a certificate which does not comply 
with a BR profile, the issuing intermediate must be revoked within 7 days, per 
BRs Section 4.9.1.2 (5): "The Issuing CA SHALL revoke a Subordinate CA 
Certificate [if...] the Issuing CA is made aware that the... Subordinate CA has 
not complied with this document".

Aaron
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