[Servercert-wg] FW: Ballot SC14 version 2: Updated Phone Validation Methods

Wed Jan 9 06:08:50 MST 2019

From: Ryan Sleevi <sleevi at google.com <mailto:sleevi at google.com> > 
Sent: Tuesday, January 8, 2019 5:58 PM
To: Doug Beattie <doug.beattie at globalsign.com <mailto:doug.beattie at globalsign.com> >; CA/B Forum Server Certificate WG Public Discussion List <servercert-wg at cabforum.org <mailto:servercert-wg at cabforum.org> >
Cc: CA/Browser Forum Public Discussion List <public at cabforum.org <mailto:public at cabforum.org> >
Subject: Re: [Servercert-wg] Ballot SC14 version 2: Updated Phone Validation Methods

On Tue, Jan 8, 2019 at 11:35 AM Doug Beattie via Servercert-wg <servercert-wg at cabforum.org <mailto:servercert-wg at cabforum.org> > wrote:

This is version 2 of Ballot SC14 with the DNS CAA record method removed.  Review period reset for full 7 days.

Ballot SC14: Updated Phone Validation Methods

Purpose of Ballot: As discussed during the Validation Summit, Method 3 of the Baseline Requirements could use some improvements to close off some potential bad practices that might lead to security risks.  This Ballot tightens up the rules around phone validation in order to make sure domain authorization or control is verified with a person who is authorized to do so by introducing a replacement for Method 3.  Validations done under Method 3 will continue to be valid until the end of the data reuse period, but new phone based validations must use the new method by the date specified in the ballot below.

This ballot also builds on “Ballot SC13: CAA Contact Property and Associated E-mail Validation Methods” to permit domain owners to publish Domain Validation phone numbers in DNS TXT records.  Since these phone numbers are specifically for the purpose of validating domains, it’s not permissible to be transferred to a different number.

The following motion has been proposed by Doug Beattie of GlobalSign and endorsed by Bruce Morton of Entrust and Tim Hollebeek of DigiCert.

--- MOTION BEGINS ---

This ballot modifies the “Baseline Requirements for the Issuance and Management of Publicly-Trusted Certificates” as follows, based on Version 1.6.2 with ballot SC13 changes:

Add the following definition to section 1.6.1:

DNS TXT Record Phone Contact: The phone number defined in section B.2.2.

In section 1.6.1, change the section references for the definition of “DNS CAA Email Contact” from B.1.2 to B.1.1.

In section 1.6.1, change the section references for the definition of “DNS TXT Record Email Contact” from B.2.2 to B.2.1 respectively

In section 3.2.2.4.3, after the end of the second paragraph add the following text as a new paragraph: ”CAs SHALL NOT perform validations using this method after July 31, 2019.  Completed validations using this method SHALL continue to be valid for subsequent issuance per the applicable certificate data reuse periods.”

 Is there a reason for half a year? I think the substance of when is how much operational change it would bring to a CA. I'm curious what risks a date such as April would pose, in trying to understand a bit more.

This method has been the same since we first created the Phone Validation method and I didn’t see a rush to set a short compliance timeline.  The changes will require updated/approved Validation Specialist policies/procedures and training material.  If CAs use automated systems, then they may need to be updated.  I thought 6 months was a safe timeline given how long we’ve been using the old method and debating this update without any identified high priority security risks.  I can certainly bring it in a month or 2 if needed.

Add sections 3.2.2.4.15 and  3.2.2.4.16 as follows:

3.2.2.4.15 Phone Contact with Domain Contact

Confirm the Applicant's control over the FQDN by calling the Domain Contact’s phone number and obtain a confirming response to validate the ADN. 

Compared to the language in other sections (e.g. 3.2.2.4.2, 3.2.2.4.4), this omits the "utilizing a Random Value" that tends to follow "obtain a confirming response". Was this intentional? Combined with the later section ('may leave the Random Value'), it suggests that there may be two flows here being described, and it's not entirely clear what's expected of either.

Yes, The phone validation method hasn’t ever (and does not in this ballot) utilize a random Value during the phone call.  Providing this to the Applicant and having him repeat it back on the same phone call adds no value – they just need to confirm approval of the ADNs.  The use of the Random Value is only needed when the phone challenge is asynchronous (leaving a voicemail).  

Each phone call MAY confirm control of multiple ADNs provided that the same Domain Contact phone number is listed for each ADN being verified and they provide a confirming response for each ADN.

In the event that someone other than a Domain Contact is reached, the CA MAY request to be transferred to the Domain Contact. 

In the event of reaching voicemail, the CA may leave the Random Value and the ADN(s) being validated.  The Domain Contact may return the Random Number to the CA via Phone, Email, Fax, or SMS to approve the request.

I just want to confirm it's intentional: As far as I can tell, this is the first restriction on how the Domain Contact returns Random Numbers. Other validation methods specify the delivery mechanism of the random value, but don't specify the confirmation channel of those random values.

Yes, this is intentional. Also note that I should have referenced Random Value and not Random Number - I will update. 

Was this intentional? For example, this would prohibit a flow in which a confirming response is left for an Applicant, and that the Applicant then confirms by going to an account management page and enters the confirming response. If there's a link to past discussion on the communication channels being used back here, do you have a pointer?

Yes, you’re right, there is no reason to limit this as long as the Random Value is returned to the CA, I will remove that sentence. 

The Random Value SHALL remain valid for use in a confirming response for no more than 30 days from its creation. The CPS MAY specify a shorter validity period for Random Values.  

Note: Once the FQDN has been validated using this method, the CA MAY also issue Certificates for other FQDNs that end with all the labels of the validated FQDN.  This method is suitable for validating Wildcard Domain Names.

3.2.2.4.16 Phone Contact with DNS TXT Record Phone Contact 

Confirm the Applicant's control over the FQDN by calling the DNS TXT Record Phone Contact’s phone number and obtain a confirming response to validate the ADN. Each phone call MAY confirm control of multiple ADNs provided that the same DNS TXT Record Phone Contact phone number is listed for each ADN being verified and they provide a confirming response for each ADN.

The CA MAY NOT be transferred or request to be transferred as this phone number has been specifically listed for the purposes of Domain Validation.

I think this introduces a particular challenge; how does the CA know whether or not it has been transferred, versus request to be transferred? It seems difficult for the organization to quantify. For example, is it a BR violation if I leave my Google Voice number as the contact number, which will transfer the call to the currently active device I have configured?

The intent was that the recipient of the call can’t transfer you nor can the CA ask to be transferred.  If calls are automatically routed, forwarded or transferred without the CA knowing it, then that would be acceptable.

I can update to: The CA MAY NOT knowingly be transferred or request to be transferred as this phone number has been specifically listed for the purposes of Domain Validation.

In the event of reaching voicemail, the CA may leave the Random Value and the ADN(s) being validated.  The DNS TXT Record Contact may return the Random Number to the CA via Phone, Email, Fax, or SMS to approve the request.

Similar remarks as above. For example, if the Random Value was placed within a CAA CA-specific attribute (which is extensible and CA-specific), would that meet the intent here or not? It certainly wouldn't meet the letter, and it's unclear if that's a bug.

I will remove this sentence from this method also.

The Random Value SHALL remain valid for use in a confirming response for no more than 30 days from its creation. The CPS MAY specify a shorter validity period for Random Values.  

Note: Once the FQDN has been validated using this method, the CA MAY also issue Certificates for other FQDNs that end with all the labels of the validated FQDN.  This method is suitable for validating Wildcard Domain Names.

Add appendix section B.2.2 as follows:

B.2.2. DNS TXT Record Phone Contact

The DNS TXT record MUST be placed on the "_validation-contactphone" subdomain of the domain being validated.  The entire RDATA value of this TXT record MUST be a valid Global Number as defined in RFC 3966 section 5.1.4, or it cannot be used.

--- MOTION ENDS ---

*** WARNING ***: USE AT YOUR OWN RISK.  THE REDLINE BELOW IS NOT THE OFFICIAL VERSION OF THE CHANGES (CABF Bylaws, Section 2.4(a)):

A comparison of the changes can be found at: https://github.com/dougbeattie/documents/compare/master...dougbeattie:SC14---Phone-validation-updates 

The procedure for approval of this ballot is as follows:

Discussion (7+ days)

Start Time: 2019-01-08 12:35 Eastern

End Time: Not before 2019-01-15 12:35 Eastern

Vote for approval (7 days)

Start Time: TBD

End Time: TBD

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