[cabfpub] SHA1 Deprecation Ballot

Ben Wilson ben at digicert.com
Wed Mar 12 17:36:36 MST 2014

After discussions earlier today with Doug, here is where I think we were:

9.8  Signature Algorithms

Effective as of January 1, 2015, the maximum validity of a Subscriber Certificate signed with SHA-1 shall be 15 months, unless the CA documents that the Subscriber Certificate (and corresponding CRL or OCSP response) is for a system or software that:

(a) is used by either the Applicant or a substantial number of Relying Parties;

(b) will fail to operate if the Certificate, OCSP Response, or CRL is not signed with the SHA-1 algorithm; 

(c) does not contain known security risks to Relying Parties; and

(d) is difficult to patch or replace without substantial economic outlay.

Effective as of January 1, 2016, CAs SHALL sign all Subscriber Certificates using one of the following algorithms:  SHA-256, SHA-384, SHA-512, P-256, P-384, P-521, DSA 2048 (with prime q of 224 or 256 bits), or DSA 3072 (with prime q of 256 bits).  A CA MAY use the SHA-1 algorithm to sign Subscriber Certificates (including for re-keys, renewals, and corresponding CRLs or OCSP responses) beyond January 1, 2016, provided that the CA has documented that the system or software meet the four criteria above.




From: public-bounces at cabforum.org [mailto:public-bounces at cabforum.org] On Behalf Of Ryan Sleevi
Sent: Wednesday, March 12, 2014 5:46 PM
To: Eddy Nigg (StartCom Ltd.)
Subject: Re: [cabfpub] SHA1 Deprecation Ballot




On Wed, Mar 12, 2014 at 4:36 PM, Eddy Nigg (StartCom Ltd.) <eddy_nigg at startcom.org> wrote:

On 03/12/2014 02:51 PM, From Doug Beattie: 


So, at this time, I’m in favor of:

-          Specifying shorter max validity periods for SHA-1 SSL certificates (1-year starting Jan 2015?)

-          Setting end dates for the creation of any new Root and Subordinate CAs with SHA-1

-          Defining clear messaging to the user community regarding SHA-1

-          Setting target dates for the next set of changes for improved security/performance (RSA-4096/ECC/SHA-512/etc)


I’m against:

-          Specifying an exact date at which no SHA-1 certificates can be issued globally

-          Specifying the detailed legacy exceptions for using SHA-1 after the sunset date


Here it starts again...this is exactly what I'm afraid of and thought we should avoid. I prefer an exact date binding for all, clear limits when and for how long. 



A "Strong +1" to Eddy's remarks.


I think if a CA is going to issue these 'legacy' certificates, it should be exactly the same process as handling other legacy practices - eg: 1024-bit roots.


It gets treated as a BR violation, it's a qualified finding, and, most importantly for Root Store Operators/Browsers, precisely *because* it's a qualified finding, that practice gets disclosed to the Operators.


Chrome's plan continues to remain aggressive - disallowing certain algorithms/key sizes if their issuance date is after their sunset-grace period, outright rejecting them if their validity period exceeds the sunset-fail period, and eventually outright removing support entirely. As such, a CA that (continues) to issue such certs would not (ultimately) be causing outright risk to *current* versions of Chrome users.


However, such a qualified finding *would* be a point of concern for overall trustworthiness, and *does* highlight that the CA is engaged in practices for specific customers that may be dangerous overall, and that's exactly the kind of thing a qualified finding can highlight. It's entirely possible (read: probable) that it would not be an immediate cause for removal, but would be something to work closely with the CA to ensure the BR violations cease on an appropriate timeline.


This is the same way Operators are already handling legacy roots, and are already handling 1024-bit certs (eg: Symantec's BR-violating issuance of a pb.com cert - https://bugzilla.mozilla.org/show_bug.cgi?id=966350 ), and is the way forward for these sorts of 'legacy' issues.

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