[cabfpub] Mozilla SHA-1 further restrictions (v3)

[Bruce Morton]

An issue is that if a SHA-1 intermediate certificate needs an EKU and we are not allowed to issue SHA-1 certificates per BR 7.1.3, then there is no fix.

Bruce.

-----Original Message-----
From: Public [mailto:public-bounces at cabforum.org] On Behalf Of Gervase Markham via Public
Sent: Friday, November 25, 2016 10:42 AM
To: CABFPub <public at cabforum.org>
Cc: Gervase Markham <gerv at mozilla.org>
Subject: Re: [cabfpub] Mozilla SHA-1 further restrictions (v3)

Here's v.3 for continued discussion. I feel we do need EKU restrictions in the intermediate given what Erwann says about leveraging a SHA-1 collision into a clone of the intermediate.

I still haven't figured out exactly what to do about EKUs and email, and would appreciate further input. Firstly, I guess CAs who want to continue to issue email certs using SHA-1 need to make the case as to why that's necesssary. If it turns out to be necessary now, when will it not be necessary?

Then, if we continue to allow it for a time, I would like to restrict certs which have the email EKU to a minimum set of additional EKUs, definitely not including code signing. I guess client auth has to be one of them. What else?

<quote>
CAs may only sign SHA-1 hashes over end-entity certificates which chain up to roots in Mozilla's program if all the following are true:

1) The end-entity certificate:

  * is not within the scope of the Baseline Requirements;

  * contains an EKU extension which does not contain either of the
    id-kp-serverAuth or anyExtendedKeyUsage key purposes;

  * has at least 64 bits of entropy from a CSPRNG in the serial number.

2) The issuing intermediate:

  * contains an EKU extension which does not contain either of the
    id-kp-serverAuth or anyExtendedKeyUsage key purposes;

  * has a pathlen:0 constraint.

CAs may only sign SHA-1 hashes over OCSP responses if the signing certificate contains an EKU extension which contains only the id-kp-ocspSigning EKU.

CAs may only sign SHA-1 hashes over CRLs for roots and intermediates which have issued SHA-1 certificates.

CAs may not sign SHA-1 hashes over other data, including CT pre-certificates.
</quote>

Gerv

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