[cabfpub] [EXTERNAL] 答复: Changing numbers of self-audited certificates

[Kirk Hall]

Hi, Ruby - thanks for the information.

If I recall correctly, we first required a 3% self-audit of certificates when the EV Guidelines were developed about ten years ago, but I can't remember the rationale, or why there was no maximum number of self-audits included.  Does anyone else remember?

-----Original Message-----
From: Public [mailto:public-bounces at cabforum.org] On Behalf Of xiongyuanyuan via Public
Sent: Wednesday, June 7, 2017 3:40 AM
To: 'CA/Browser Forum Public Discussion List' <public at cabforum.org>
Cc: xiongyuanyuan <xiongyuanyuan at sheca.com>
Subject: [EXTERNAL][cabfpub] 答复: Changing numbers of self-audited certificates

Yes.
From the point of audit risk control, set a minimum value is more reasonable. According to the presentation in AICPA Audit Sampling Guide(screenshot attached), when a control happens less frequently, we can decide the sample size by the frequency of the control. So in my opinion, when CA performs self-audit to certificates that have a small volume, it is acceptable to take this guide as reference. From this table, we can see that a minimum value of 5 to certificate sample size is appropriate and is able to control audit risk.

Besides, I think we should also set a maximum value to certificate sample size.
This is because when CA performs self-audit to certificates that have a very large volume, 3% of the total population will still be a lot to audit, and this would result in large audit cost for the CA. 
When we look at AICPA Audit Sampling Guide and AU 350 of PCAOB, for those testing samples with high risk, the TER（tolerable exception rate）should be low as possible, a maximum value of 60(certificates) to sample size(assume all the 60 testing samples are effective) will promise a lower TER as 5% which is much lower than a TER as12%-15% (which is operated by some audit firms for those testing samples with normal risk). 

Base on this, I suggest we also set a maximum value of 60 to certificate sample size, which ensures audit efficiency as well as controls audit cost and audit risk.

Best Regards,
Ruby Xiong
Shanghai Electronic Certification Authority co., ltd. 
18F, No.1717, North Sichuan Road, Shanghai, China
Tel：+86-21-36393197
Email：xiongyuanyuan at sheca.com 


-----邮件原件-----
发件人: Public [mailto:public-bounces at cabforum.org] 代表 Gervase Markham via Public
发送时间: Tuesday, June 6, 2017 6:47 PM
收件人: CABFPub
抄送: Gervase Markham
主题: [cabfpub] Changing numbers of self-audited certificates

Currently, the BRs define, in section 8.7, the parameters for self-audits and audits of certificates below a TCSC. At the moment, the number of certs randomly chosen to be audited is defined as "the greater of one certificate or at least three percent of the Certificates issued".

I think that auditing just a single certificate (which is currently OK up until 33 are issued) makes it too easy to overlook problems when volumes are small. I propose instead a 5-certificate minimum, or 3%, whichever is larger. In other words:

Issued Audited
0      0
1      1
.....
5      5
6      5
.....
166    5
167    6
.....

We could just change the "one" to a "five" if people thought it was obvious that if you've issued less than five, you just audit all of them. Or we could expand the text a bit to explicitly describe that.

I would be interested in feedback on the impact of this change. It's been proposed for the Mozilla policy but as it's a BR stipulation I thought we should try here first.

Gerv
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