[cabfpub] Definition of an SSL certificate

Mads Egil Henriksveen Mads.Henriksveen at buypass.no
Fri Jan 3 09:49:26 UTC 2014

The attack scenario assumes that the QC can be chained to a root cert in a trusted CA root store. This means that the CA should know the root store requirements and should be aware of the risk issuing any cert that could be used as an SSL certificate.

Buypass do issue both QC and SSL certificates and with the DigiNotar attack back in 2011 we realized that the browsers do accept a lot of certificates as SSL certificates. Since then we have had strict controls to ensure that no certificate is issued with an unverified domain name. I guess most of the trusted QC issuers who also issue SSL certificates are aware of this, I would not be very concerned about this attack scenario.

However, I do support the idea of a technical definition of an SSL certificate and I like the proposal from Ryan Hurst requiring the BR/EV OIDs.

The alternative of expanding the definition is also acceptable, but I do not understand why noEKU should be included in the definition of an SSL certificate (I might have missed this in an earlier thread). According to RFC 5280 the TLS WWW server authentication key usage could be defined either with the id-kp-serverAuth bit set in EKU or with the anyEKU option. I do not see why noEKU should be included. Could anyone clarify?

When reading the BR it appears to be an inconsistency between the BR scope and the requirements for Certificate extensions:

In section 1 of BR (Scope) the current text is:
This version of the Requirements only addresses Certificates intended to be used for authenticating servers accessible through the Internet.

And in Appendix B (3) Subscriber certificate, the requirement is:
F. extKeyUsage (required)
Either the value id-kp-serverAuth [RFC5280] or id-kp-clientAuth [RFC5280] or both values MUST be
present. id-kp-emailProtection [RFC5280] MAY be present. Other values SHOULD NOT be present.

I don’t think that the id-kp-clientAuth EKU bit should be used for authenticating servers (?).

Jeremy has partly addressed this already in his proposed Ballot 108, but I think we also should revisit the EKU requirement in this context.


From: public-bounces at cabforum.org [mailto:public-bounces at cabforum.org] On Behalf Of Jeremy Rowley
Sent: 2. januar 2014 18:41
To: public at cabforum.org
Subject: Re: [cabfpub] Definition of an SSL certificate

We are trying to NOT cover QCs in the BR scope.

Currently, most QCs include the anyEKU, meaning the QC can be used for SSL.  An attacker can an QC certificate with a domain name from a trusted QC issuer.  Since many QC issuers do not provide SSL certificates on a regular basis, they will not realize the certificate must comply with the BRs and fail to properly vet the domain name included in the certificate. After the certificate issues, the attacker can freely use the certificate to MITM everyone on the included domain. This is a real scenario since many of these standards do not require the CA to verify any domain name included in the certificate.

In this example, the CA did nothing wrong from a standard’s perspective. However, this is little comfort to the affected users.

One proposal (by Ryan Hurst) is to only require compliance if the certs assert the BR/EV CAB Forum OIDs. The browsers can then require the BR/EV OID before trusting the certificate.

An alternative is to expand the definition and include a statement that says any certificate that includes a domain name and the anyEKU, noEKU, or serverAuth  is considered intended for use in SSL.


From: me at chemalogo.com<mailto:me at chemalogo.com> [mailto:me at chemalogo.com] On Behalf Of Chema López González
Sent: Thursday, January 02, 2014 10:26 AM
To: public at cabforum.org<mailto:public at cabforum.org>
Cc: Jeremy Rowley; i-barreira at izenpe.net<mailto:i-barreira at izenpe.net>; Stephen Davidson
Subject: Re: [cabfpub] Definition of an SSL certificate

Dear all,

Qualified certificates are intended to identify people, not websites nor servers. There are no hard constrains regarding the usage of EKU KU values, but good practices are to use Non-repudiation and only non-repudiation (see RFC3039<http://www.ietf.org/rfc/rfc3039.txt>, section 3.2.3 in combination with ETSI TS 102 280<http://www.etsi.org/deliver/etsi_ts/102200_102299/102280/01.01.01_60/ts_102280v010101p.pdf>, section 5.4.3 and taking into account that Qualified Certificates are defined with purpose of creation Qualified Electronic Signatures legally binding!)

In fact any QC contents personal data (or pseudonym but the CSP MUST have the actual personal data bound to the pseudonym) so I do not think any will want to put her personal data authenticating a public website.

Since the purpose of a QC is quite different of the purpose of a SSL certificate and the first is legally constricted I do really think that BR's do not have to cover QC at all. Maybe it exists but I have never seen a QC authenticating a website.

IMHO trying to cover QC is going beyond the purpose of the BR, it will mesh up the whole think without adding security to SSL certificates.


Chema López González

AC Firmaprofesional S.A.

Av. Torre Blanca, 57.
08173 Sant Cugat del Vallès. Barcelona.
Tel: 93.477.42.45 / 666.429.224

El contenido de este mensaje y de sus anexos es confidencial. Si no es el destinatario, le hacemos saber que está prohibido utilizarlo, divulgarlo y/o copiarlo sin tener la autorización correspondiente. Si ha recibido este mensaje por error, le agradeceríamos que lo haga saber inmediatamente al remitente y que proceda a destruir el mensaje.

On Thu, Dec 19, 2013 at 5:52 PM, Stephen Davidson <S.Davidson at quovadisglobal.com<mailto:S.Davidson at quovadisglobal.com>> wrote:
>  Are qualified certs issued from the same root as BR certs?


From: public-bounces at cabforum.org<mailto:public-bounces at cabforum.org> [mailto:public-bounces at cabforum.org<mailto:public-bounces at cabforum.org>] On Behalf Of Jeremy Rowley
Sent: Thursday, December 19, 2013 12:51 PM
To: i-barreira at izenpe.net<mailto:i-barreira at izenpe.net>; public at cabforum.org<mailto:public at cabforum.org>

Subject: Re: [cabfpub] Definition of an SSL certificate


1)      Qualified certs CAN be used for TLS Server Authentication since they may include anyEKU or serverAuth in the EKU extension

2)      Qualified Certs do NOT comply with the BRs, they comply with the appropriate ESTI standard.

3)      Qualified certs are only distinguishable from BR certs because qualified certs assert a QCStatement

Is this a fair summary?

From: public-bounces at cabforum.org<mailto:public-bounces at cabforum.org> [mailto:public-bounces at cabforum.org] On Behalf Of i-barreira at izenpe.net<mailto:i-barreira at izenpe.net>

Sent: Thursday, December 19, 2013 9:25 AM
To: jeremy.rowley at digicert.com<mailto:jeremy.rowley at digicert.com>; public at cabforum.org<mailto:public at cabforum.org>
Subject: Re: [cabfpub] Definition of an SSL certificate

Yes, but with some additional points

-          Mark Jansen is right albeit it depends on national legislation. In Spain, you have to indicate what EKU is to be used.

-          DV or OV will never be considered Qualified certs. EV possibly and will have some impacts

Iñigo Barreira
Responsable del Área técnica
i-barreira at izenpe.net<mailto:i-barreira at izenpe.net>

[cid:image001.jpg at 01CF0856.2EF1EC50]

De: public-bounces at cabforum.org<mailto:public-bounces at cabforum.org> [mailto:public-bounces at cabforum.org] En nombre de Jeremy Rowley
Enviado el: jueves, 19 de diciembre de 2013 17:06
Para: CABFPub
Asunto: [cabfpub] Definition of an SSL certificate

We are looking to clarify the scope of the BRs.  Right now the BR scope is very loose and subjective: “This version of the Requirements only addresses Certificates intended to be used for authenticating servers  accessible through the Internet.”

This loose definition excludes internal names (which are not typically accessible through the Internet), a type of certificate the BRs are clearly designed to regulate (see 11.1.4).  In addition, a CA could easily issue a certificate outside of the BRs  that could later be used in a TLS/SSL attack simply because the certificate wasn’t intended to be used for SSL.

Issuance of certificates outside the BRs may not be intentional, especially by CAs who aren’t regularly issuing SSL certificates.  These CAs may not be aware that the BRs apply to their certificates and may not realize their client certificates could be used for SSL since “authenticating servers” is not a well-defined term.

Clarifying the scope will ensure that every CA is aware of the minimum standards and what they cover.  Originally, the idea was to tie the scope to the values in the EKU.  Unfortunately, there are several obstacles to this approach:

1)      Grid Certificates require serverAuth in the EKU.  It’s unclear whether these certs should be covered.

2)      Per 5280, browsers treat the absence of an EKU and the anyEKU as serverAuth, meaning they are enabled for TLS Server Authentication.

3)      The FBCA requires anyEKU in several certificates.  These are clearly client certificates and are outside the BR scope.

4)      Qualified certificates in the EU have either the anyEKU present or omit the EKU.  They are client certs and clearly not covered by the BRs.  However, they can be used  for server authentication.

For qualified certificates, Moudrick provided the following guidance:

“Certificates using applications MAY require that the extended key usage extension be present and that a particular purpose be indicated in order for the certificate to be acceptable to that application.

If a CA includes extended key usages to satisfy such applications, but does not wish to restrict usages of the key, the CA can include the special KeyPurposeId anyExtendedKeyUsage ***in addition to the particular key purposes required by the applications***.

So a QC pretending to be RFC 5280/BR and ETSI (web server QCs) compliant would have to at least have:

QC + [anyEKU] + id-kp-serverAuth + {DV/OV/EV}

I'm quite confident that the absolute majority of QCs issued so far (that have anyEKU, see Mark Janssen's 08/08/2013 - thank you Stephen) do not contain any DV/OV/EV policy IDs, so why not accept them as BR compliant but not sufficient for TSL/SSL establishment?

In order for a QC to have a TSL/SSL capability, BR may require:

QC + {{id-kp-serverAuth and/or id-kp-clientAuth} + {DV/OV/EV}} (optionally no anyKEY allowed).

A practical interpretation: a WEB server that also does some web site related document/content signing.”

There appears to be a significant conflict between the CAB Forum’s work and the standards set by other bodies.  In particular, their use of the anyEKU or omission of an EKU is permitting the realm of client certs to overlap SSL certs.  Approaching each government body to stop this practice is not feasible and will take a very long time to complete

Hopefully this summary helps inspire ideas on where we can go from here.  I’m looking forward to ideas.



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