[Servercert-wg] [cabfpub] Ballot SC6 - Revocation Timeline Extension

Mon Aug 20 13:43:09 MST 2018

Tim,

I agree that Vulnerability is different from key compromise and the actions we take should reflect that and I think we should try to keep 12 and 13 type events in the 5-day list.

Is our strategy to have vulnerabilities fall into the 5 day list and exploited vulnerabilities fall into the 24 hour list?

Key Compromise: A Private Key is said to be compromised if:

1)      its value has been disclosed to an unauthorized person

2)      an unauthorized person has had access to the private keys

3)      a vulnerability has been exploited to disclose private keys

And the remainder of the definition can be removed because those are examples of vulnerabilities being exploited ( Debian weak  and poor key generation).  If we want a list of possible vulnerabilities or bad practices, then we can put in an appendix.

I think #13 is a special case of #12 (both vulnerabilities), so I still recommend removing it.  Is the distribution of a private key in in a software package any different than the distribution of a private key in any other (insecure) method?  

Here’s what I’d recommend:

a) Use the new definition I listed above

b) change:

12. The CA is made aware of a vulnerability that exposes the Subscriber's Private Key to compromise; or

to

12. The CA is made aware of a vulnerability that has been exploited to disclose the Subscriber's Private Key; or

c) Delete #13

Doug

From: Servercert-wg <servercert-wg-bounces at cabforum.org> On Behalf Of Tim Hollebeek via Servercert-wg
Sent: Monday, August 20, 2018 3:57 PM
To: Wayne Thayer <wthayer at mozilla.com>; CA/B Forum Server Certificate WG Public Discussion List <servercert-wg at cabforum.org>
Cc: CA/Browser Forum Public Discussion List <public at cabforum.org>
Subject: Re: [Servercert-wg] [cabfpub] Ballot SC6 - Revocation Timeline Extension

Vulnerability is different from key compromise.  Replacing all the heartbleed certificates within 24 hours would have been a huge fire drill.  It’s important to get them replaced as quickly as possible, but mandatory revocations within 24 hours is going to make things worse, not better.

There are potential mitigating factors for a vulnerability.  For example, the technical details may not be publicly known yet, or there may be no public exploit available yet.  The vulnerability might not affect all OS versions, might be easily blocked by firewalls, and so on.  The amount of effort necessary to turn a vulnerability into a key compromise can vary from insignificant to “lots and lots”.

A compromised key, on the other hand, is clearly compromised.

-Tim

From: Servercert-wg <servercert-wg-bounces at cabforum.org> On Behalf Of Wayne Thayer via Servercert-wg
Sent: Monday, August 20, 2018 12:52 PM
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Cc: CA/Browser Forum Public Discussion List <public at cabforum.org>
Subject: Re: [Servercert-wg] [cabfpub] Ballot SC6 - Revocation Timeline Extension

This has the potential to cause confusion, so I'd like to attempt to fix it. Given that a reasonable interpretation of the existing definition of key compromise encompasses reasons 12 and 13, but I want to leave those two reasons in the document for the sake of clarity as Ryan suggests, maybe I should just move those two up to the 24-hour section? I could also be persuaded that a vulnerability is different than proof of key compromise, in which case 12 could stay in the 5-day section and we could move "or there exists a practical technique by which an unauthorized person may discover its value" from the definition of key compromise to 12. What do others think?

- Wayne

On Mon, Aug 20, 2018 at 7:04 AM Ryan Sleevi <sleevi at google.com <mailto:sleevi at google.com> > wrote:

On Mon, Aug 20, 2018 at 9:17 AM Doug Beattie via Servercert-wg <servercert-wg at cabforum.org <mailto:servercert-wg at cabforum.org> > wrote:

We’re having a hard time determining the differences between the following:

The CA SHALL revoke a Certificate within 24 hours if:

3. The CA obtains evidence that the Subscriber's Private Key corresponding to the Public Key in the Certificate suffered a Key Compromise; or

and 

The CA SHOULD revoke a certificate within 24 hours and MUST revoke a Certificate within 5 days if one or more of the following occurs:

12. The CA is made aware of a vulnerability that exposes the Subscriber's Private Key to compromise; or

13. The CA is made aware that the Subscriber's Private Key is being publicly distributed in a software package.

If  “Subscriber's Private Key is being publicly distributed in a software package”, isn’t that the same as #3: “obtains evidence that the Subscriber's Private Key corresponding to the Public Key in the Certificate suffered a Key Compromise”? 

How do you see #12 in reality?  What types of vulnerabilities do you envision that could expose a subscribers Private Key that are not also consistent with #3?

While this is the same argument that I've made in the past, I think the goal here is to reduce ambiguity for those that might take a tortured reading of the text.

For example, at least one vendor 'obfuscated' the private key within their binary, requiring running the embedded private key through a transformation (I hesitate to say decryption, since the passphrase was itself fixed within the binary). Such a vendor might argue that the key has not been compromised until someone reverses the binary. This resolves that ambiguity by saying that the distribution within the binary itself constitutes a compromise, regardless of whether a passphrase is used.

Also, the definition of Private Key Compromise is very broad, and the scenarios in #12 and #13 would appear to fall into “Key Compromise” which further causes confusion about them.  What constitutes a “practical technique”?  If we applied this definition to #12 and #13, wouldn’t these all fall into the 24 hour rule?

Key Compromise: A Private Key is said to be compromised if its value has been disclosed to an unauthorized person, an unauthorized person has had access to it, or there exists a practical technique by which an unauthorized person may discover its value.  A Private Key is also considered compromised if methods have been developed that can easily calculate it based on the Public Key (such as a Debian weak key, see http://wiki.debian.org/SSLkeys) or if there is clear evidence that the specific method used to generate the Private Key was flawed.

Doug

From: Public <public-bounces at cabforum.org <mailto:public-bounces at cabforum.org> > On Behalf Of Wayne Thayer via Public
Sent: Monday, August 13, 2018 4:58 PM
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Subject: [cabfpub] Ballot SC6 - Revocation Timeline Extension

This begins the formal discussion period for ballot SC6.

==========================================

Ballot SC6: Revocation Timeline Extension

Purpose of Ballot:

Section 4.9.1.1 of the Baseline Requirements currently requires CAs to revoke a Subscriber certificate within 24 hours of identifying any of 15 issues affecting the certificate. In cases where there is not an immediate threat of misuse of the certificate, this requirement can cause undue harm to a Subscriber that isn't capable of replacing the certificate prior to revocation. This ballot makes a number of improvements to the revocation rules imposed by the Baseline Requirements:

* Primarily, it creates a tiered timeline for revocations. The most critical "reasons" still require revocation within 24 hours, but for many others 24 hours becomes a SHOULD and the CA has 5 days before they MUST revoke.

* A new "reason for revocation" was added to address the fact that there is currently no requirement for CAs to revoke a certificate when requested by the domain name registrant. After considering some more specific language that required CAs to follow 3.2.2.4 to validate domain control, I settled on the following more general "reason": "The CA obtains evidence that the validation of domain authorization or control for any Fully-Qualified Domain Name or IP address in the Certificate should not be relied upon."

* Reason #10 states "The CA determines that any of the information appearing in the Certificate is inaccurate or misleading;" This ballot removes "or misleading" because that is a subjective judgement that could effectively be used to justify censorship, as discussed at length in relation to the "Stripe, Inc of Kentucky" EV certificates.

* Current reasons #11 and #13 were removed from the section on subscriber certificates because they address cases where the intermediate and/or root must be revoked, so there isn't much sense (and some possible harm) in requiring revocation of all the leaf certs.

* It requires CAs to disclose their problem reporting mechanisms in a standard location: CPS section 1.5.2.

* Within 24 hours of receiving a problem report, the CA is now required to report back to both the entity reporting the problem and the Subscriber on the CA's findings, and to work with the reporter to establish a date by which the CA will revoke the certificate.

The following motion has been proposed by  Wayne Thayer of Mozilla and endorsed by Tim Hollebeek of DigiCert and Dimitris Zacharopoulos of Harica.

--- MOTION BEGINS ---

This ballot modifies the “Baseline Requirements for the Issuance and Management of Publicly-Trusted Certificates” as follows, based on Version 1.6.0:

** Modify Section 4.9.1.1 to read as follows: **

The CA SHALL revoke a Certificate within 24 hours if:

1. The Subscriber requests in writing that the CA revoke the Certificate;
2. The Subscriber notifies the CA that the original certificate request was not authorized and does not retroactively grant authorization;
3. The CA obtains evidence that the Subscriber's Private Key corresponding to the Public Key in the Certificate suffered a Key Compromise; or
4. The CA obtains evidence that the validation of domain authorization or control for any Fully-Qualified Domain Name or IP address in the Certificate should not be relied upon.

The CA SHOULD revoke a certificate within 24 hours and MUST revoke a Certificate within 5 days if one or more of the following occurs:

1. The Certificate no longer complies with the requirements of Sections 6.1.5 and 6.1.6;
2. The CA obtains evidence that the Certificate was misused;
3. The CA is made aware that a Subscriber has violated one or more of its material obligations under the Subscriber Agreement or Terms of Use;
4. The CA is made aware of any circumstance indicating that use of a Fully-Qualified Domain Name or IP address in the Certificate is no longer legally permitted (e.g. a court or arbitrator has revoked a Domain Name Registrant's right to use the Domain Name, a relevant licensing or services agreement between the Domain Name Registrant and the Applicant has terminated, or the Domain Name Registrant has failed to renew the Domain Name);
5. The CA is made aware that a Wildcard Certificate has been used to authenticate a fraudulently misleading subordinate Fully-Qualified Domain Name;
6. The CA is made aware of a material change in the information contained in the Certificate;
7. The CA is made aware that the Certificate was not issued in accordance with these Requirements or the CA's Certificate Policy or Certification Practice Statement;
8. The CA determines that any of the information appearing in the Certificate is inaccurate;
9. The CA's right to issue Certificates under these Requirements expires or is revoked or terminated, unless the CA has made arrangements to continue maintaining the CRL/OCSP Repository;
10. Revocation is required by the CA's Certificate Policy and/or Certification Practice Statement;
11. The technical content or format of the Certificate presents an unacceptable risk to Application Software Suppliers or Relying Parties (e.g. the CA/Browser Forum might determine that a deprecated cryptographic/signature algorithm or key size presents an unacceptable risk and that such Certificates should be revoked and replaced by CAs within a given period of time);
12. The CA is made aware of a vulnerability that exposes the Subscriber's Private Key to compromise; or
13. The CA is made aware that the Subscriber's Private Key is being publicly distributed in a software package.

** Modify section 4.9.3 as follows: **

The CA SHALL provide a process for Subscribers to request revocation of their own Certificates. The process MUST be described in the CA's Certificate Policy or Certification Practice Statement. The CA SHALL maintain a continuous 24x7 ability to accept and respond to revocation requests and Certificate Problem Reports.

The CA SHALL provide Subscribers, Relying Parties, Application Software Suppliers, and other third parties with clear instructions for reporting suspected Private Key Compromise, Certificate misuse, or other types of fraud, compromise, misuse, inappropriate conduct, or any other matter related to Certificates. The CA SHALL publicly disclose the instructions through a readily accessible online means and in section 1.5.2 of their CPS.

** Modify section 4.9.5 to read as follows: **

Within 24 hours after receiving a Certificate Problem Report, the CA SHALL investigate the facts and circumstances related to a Certificate Problem Report and provide a preliminary report on its findings to both the Subscriber and the entity who filed the Certificate Problem Report.

After reviewing the facts and circumstances, the CA SHALL work with any entity reporting the Certificate Problem Report or other revocation-related notice to establish a date when the CA will revoke the Certificate which MUST not exceed the time frame set forth in Section 4.9.1.1. The date selected by the CA SHOULD consider the following criteria:

1. The nature of the alleged problem (scope, context, severity, magnitude, risk of harm);
2. The consequences of revocation (direct and collateral impacts to Subscribers and Relying Parties);
3. The number of Certificate Problem Reports received about a particular Certificate or Subscriber;
4. The entity making the complaint (for example, a complaint from a law enforcement official that a Web site is engaged in illegal activities should carry more weight than a complaint from a consumer alleging that she didn't receive the goods she ordered); and
5. Relevant legislation.

--- MOTION ENDS ---

A comparison of the changes can be found at: https://github.com/cabforum/documents/compare/master...wthayer:patch-1?short_path=7f6d14a#diff-7f6d14a20e7f3beb696b45e1bf8196f2

The procedure for approval of this ballot is as follows:

Discussion (7+ days)

Start Time: 2018-08-13  19:00 UTC

End Time: Not before 2018-08-20  19:00 UTC

Vote for approval (7 days)

Start Time: TBD

End Time: TBD

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