[Servercert-wg] Ballot SC22: Reduce Certificate Lifetimes
Dimitris Zacharopoulos (HARICA)
dzacharo at harica.gr
Tue Aug 27 00:18:35 MST 2019
On 26/8/2019 4:20 μ.μ., Ryan Sleevi wrote:
> On Mon, Aug 26, 2019 at 12:35 AM Dimitris Zacharopoulos (HARICA) via
> Servercert-wg <servercert-wg at cabforum.org
> <mailto:servercert-wg at cabforum.org>> wrote:
> HARICA does not agree with further reducing the lifetime of TLS
> Certificates as it creates unnecessary burden to site operators.
> If the main problem we are trying to solve is Domain Validation
> and the fact that some domains are "changing owners", thus putting
> at risk the new Domain owners as BygoneSSL demonstrated, we should
> look for alternatives rather than having millions of site
> operators replace millions of Certificates at a shorter timeframe.
> This is not the "main goal".
> During earlier drafting, it was suggested by some members to provide a
> list of the numerous benefits. This list is at
> https://cabforum.org/pipermail/servercert-wg/2019-August/000894.html ,
> which includes many suggestions from Apple previously, at
Apologies for the long reply, but I had to include the previous
references for completeness.
Benefits of reduced lifetime:
* Issues that result from the misinterpretation or misapplication
of the Baseline Requirements are able to be more promptly resolved.
Despite the best efforts of Browsers to ensure unambiguous
requirements, there continue to be issues with CAs and their
understanding and successful implementation of existing
requirements. At present, due to the fact that validations may be
reused for up to 825 days, and when they are reused, may be used to
issue certificates valid for another 825 days, it may take up to
four and a half years before issues are resolved. This proposal
would halve that time, to a little more than two years, and
represents a significant improvement.
Re-validating Domain Names seems to solve this problem, so this goal is
* Even when the Baseline Requirements are clear and unambiguous,
implementation issues by CAs routinely introduces risks of
improperly formed or validated certificates, allowing CAs to issue
certificates which have never been permitted and should never have
been issued. Reducing certificate lifetimes reduces the overall risk
that the ecosystem is exposed to these improperly formed
certificates, both in terms of usage and in the need for Relying
Parties to support such certificates.
Such a risk will always be there, I don't see how it can be reduced by
shortening the lifetime of Certificates. Even if a Certificate is issued
for 1 month, it could create the necessary "damage". The BRs already
have rules for such cases, which is revocation within 5 days. We saw
that clearly in the serialNumber entropy case. For improperly validated
certificates, again the re-validation process would be executed within
12 months with the updated validation methods, so this goal is achieved
* CRLs and OCSP have long been shown to be non-viable at
Internet-scale, in terms of how they externalize costs like privacy,
performance, and stability to Subscribers and Relying Parties. While
alternative, browser-specific methods also exist, they also allow
CAs to externalize the cost of their practices onto users and
browsers, growing as the number of unexpired certificates grow.
Reducing certificate lifetimes meaningfully protects users,
regardless of the revocation method used, and helps reduce the
overall costs paid by users.
You claim that checking for the status of a Certificate is externalized
to Relying Parties (users and browsers). Yes, this is how X.509 was
designed. It's not a perfect technology and some solutions might suffer
from privacy, performance and stability. I also don't see how reducing
certificate lifetimes helps reduce the overall costs paid by users.
Users will continue to check for the status of every certificate
presented to them, these are the rules. If a browser decides not to
check for the status of a certificate for performance, or other,
reasons, then this browser adds a more significant risk to the user.
This browser would reduce the cost (privacy, performance, stability) but
would open a risk window for exposing the user to a
* Operationally, the current extensive certificate lifetime has
repeatedly led to issues, in that Subscribers frequently forget how
or when to replace certificates. Aligning on an annual basis helps
ensure and streamline continuity of operations, reducing the number
of errors users see and disruptions that sites face.
Replacing certificates more frequently, opens the (greater than zero)
risk of mis-configuration. We are not discussing about meaningful
security improvements like configuring a web server to support TLS
1.2/1.3 and removing 1.0/1.1. We are discussing about a Certificate
replacement that provides "zero" security benefit to Relying Parties.
They won't even detect this change. According to HARICA's experience,
site operators tend to align Certificate replacement in certain weeks
and this can be achieved even with 2-year Certificates. They usually
receive expiration warnings ahead of time to remind them that
Certificates are about to expire. I don't see a significant improvement
here by reducing the certificate lifetime to 13 months.
* Operationally, the prolonged reuse of validation information
creates challenges in replacing certificates due to security risks
identified with the existing validation methods permitted by the
Baseline Requirements. Reducing this validity period similarly helps
streamline the validation process, allowing site operators to ensure
for relying parties that the certificates they use were meaningfully
This kind of repeats the second bullet and I believe is the most
important argument driving this ballot, which is precisely the reason
HARICA focused on this one and called it the "main goal". Re-validating
Domains is critical and the ecosystem can greatly benefit from such a
requirement. This doesn't mean that the associated Certificate(s) need
to be replaced creating all the extra headaches for site operators with
* As shown by issues such as BygoneSSL, the misalignment between
certificate lifetime and the domain name system poses availability
and security risks to site operators. Despite such research being
presented directly to the CA/Browser Forum, there have been no
efforts by CAs, as an industry, to mitigate the risks posed to
users. Certificate lifetimes currently represent the greatest
mitigation to these risks.
Requiring annual re-validation of Domain Names seems to achieve this
goal as well.
* Existing certificate validity periods create risk for Relying
Parties wishing to enforce the Baseline Requirements or Root Program
requirements, by allowing CAs to “backdate” certificates in order to
attempt to bypass date-based program requirements. Reducing
certificate lifetimes reduces the window of exposure to such
bypasses. As this has happened multiple times, by past and present
members of the CA/Browser Forum, reducing certificate lifetimes
represents the safest way to detect and counter this risk.
CT logging seems far better mitigation to counter this risk. All CAs
that are trusted by at least Apple and Chrome need to log their
Certificates anyway, I am not aware of any CA/B Forum CA Member that
doesn't log TLS Certificates. In any case, what you describe here is
strictly prohibited at least by the Mozilla Root Program
Reducing the certificate lifetime provides no protection for a malicious
CA that will issue a certificate in the past to bypass new requirements.
However, re-validating the Domain Names with the latest validation rules
should leave an auditable trail.
o Long lived certs present a longer lived threat. We have seen
this presented in the BygoneSSL report/brief. We would like to
work towards having the domain validation validity align with
the certificate validity.
Apple is also more concerned about Domain Validation and rightfully so.
This is what BygoneSSL presented. Performing Domain Validation more
frequently is a solution to this problem.
o Since most software fails open when performing revocation
checks, the best safeguard is the validity period of the
I believe this has already been addressed. For the benefit of software
that actually does what the underlying technology requires them to do,
which is revocation checking, we should not abandon revocation as a
tool. It is already in the requirements and has caused significant pain
to CAs to support it, as I'm sure most of this group is aware of.
o Teams with high turnover are better able to ensure continuity.
o Teams align other annual requirements with certificate issuance
so that manual issuances aren’t forgotten.
o Encourages adoption of automation that reduces opportunity for
human error and reduces operational cost overall.
If only automation was that simple for every TLS server that wants to be
publicly accessible... HARICA is probably one of the smallest CAs in the
Forum yet we have encountered a great number of appliances/equipment
that provide a very basic administrative interface. We are assisting
site operators to install certificates in these devices and even have a
hard time installing the Certificate Chain (for some cases where the
hierarchy is more than 2 levels). These devices have no way of
automating certificate installation. I don't know the percentage of
these devices worldwide but I'm sure larger CAs have similar or better
experience to share with us. We propose site operators to use web
proxies but some of them have no experience how to properly maintain one.
If we consider the time to manually replace a certificate in such
devices to 30', then the 6% of the total number of Certificates is a
significant human effort for zero benefit to Relying Parties and very
low benefit for Domain owners.
> Certificates are used in far more systems than I could possibly
> list. Routers, modems, cameras, scientific equipment, proxys, are
> just to name a few that have zero (or close to zero) support for
> automation in certificate renewal.
> Annual certificates do not require the use of automation. Certificates
> with lifespans of <= 13 months, as this ballot proposes, make up 94%
> of the existing valid certificate market.
I don't doubt the numbers but for sure LE's 90-day Certificate lifetime
should significantly influence this number.
> We could try to disconnect the Domain Validation part from the
> Certificate Installation part. The Domain Validation part is
> usually done via alternative channels and are easier for site
> operators to handle. Perhaps we have discussed this before but we
> could add rules in the BRs to re-validate Domain Names more
> frequently, like every 12 months. If the Domain is not
> re-validated within 13 months, the Certificate MUST be revoked
> (leaving 1 month "grace period" for reminders to be sent to the
> Domain owner).
> You are correct that we did not explore it, because as noted in the
> ballot, revocation does not work for the Web, especially with respect
> to privacy. Any solution that relies on revocation is thus
> unacceptably broken.
A reasonable continuation of this though would be "let's get rid of
revocation requirements", yet we are pushing for revocation whenever
something as the serialNumber entropy issue (63 bits instead of 64 bits
of entropy source) occurs. This seems to be inconsistent. Revocation is
not unacceptably broken as demonstrated by at least some Certificate
Consumers that effectively use revocation mechanisms. Perhaps the
revocation check is not instant but in a short amount of time
(hours/days, not months as the lifetime of the Certificate protects), a
revoked Certificate is not trusted by these Certificate Consumers.
> The fact that revocation doesn't work for some browsers is not
> (IMHO) an excuse for requiring millions of site operators to
> replace certificates in these "admin unfriendly"environments,
> every year, just to check if the site is still owned by the same
> Thank you for sharing. Considering the hundreds of millions of sites
> which are exposed to harm, danger, and CA misissuance as a result of
> the long-lived lifetimes, and for which as Subscribers, they have no
> effective recourse, Google's position is that we put the user first.
> In this case, this means that the minority of sites and users -
> approximately 6% - may have to encounter annual replacement. However,
> the industry has shown that this does not require automation to do, as
> this is both the default for a number of CAs, and long wide-spread
> before the rise of automated mechanisms like RFC 8555. Automation
> simply improves things.
Perhaps I wasn't clear enough when I mentioned about "admin unfriendly"
environments. These are devices and equipment that are manufactured with
a specific firmware. All vendors would have to create new firmware to
support implementations like RFC 8555. We are already seeing this make
progress in newer equipment but it's slow.
> As Christian supported, in case of emergency (like an algorithm
> failure or a CA failure/misussuance), as demonstrated in the
> recent serialNumber entropy issue, CAs and site operators can be
> pushed to replace certificates sooner. Site operators understand
> and respect the fact that there is an emergency or an anomaly, and
> can re-allocate resources accordingly to deal with an *unexpected*
> need for certificate replacement. Requiring the installation of
> new certificates every year is not an "emergency" task and will
> not be easy to justify and for site operators to accept.
> CAs that still think of certificate replacement as an "emergency" task
> are doing their users and customers a significant disservice and harm.
> Another objective, as noted, is to reinforce that this is not and
> cannot be the case.
CAs that follow the rules, explain to their Subscribers that in case of
violation of the CP/CPS or the revocation reasons listed in 220.127.116.11 and
18.104.22.168 of the BRs, the Subscriber Certificate would have to be replaced
within 5 days (and in some cases within 24 hours). Other than that, the
Certificate is good for as long as it is valid for. I don't see anything
wrong here. Asking Subscribers to replace certificates "just for the
sake of it", seems unnecessary and disrespectful for their time and effort.
> Luckily, some CAs have recognized this, and in light of
> misissuance events have already taken steps - before this ballot was
> circulated or proposed - to reduce the lifetime of the certificates
> they issue to an annual basis. I can think of one CA, which primarily
> targets government and enterprise users, which recognized the
> challenges they and their customers had with timely replacement of
> certificates, and saw a reduction in lifetime as the most significant
> mitigation they could put in place.
HARICA has been issuing publicly-trusted certificates since 2011. We
have always kept a maximum lifetime of 2 years because that was a
reasonable balance between site operator effort to replace certificate
and the duration of most of the Domain registrations we had seen. The
majority of Domains (at least the ones that we encountered) were
registered for 2 years. However, I would be curious to see more citation
and experience for government and enterprise users that described how
the CA and these Subscribers approached this challenge and reached such
a conclusion (that the reduction of lifetime was the most significant
mitigation they could put in place).
> It is understandable for CAs, given their direct dealings with
> customers, to put their customers and business interests first, over
> the safety and security of the ecosystem and users. It can be
> difficult to articulate to them and their customers that the Web PKI
> is only as secure as its weakest link, and that they are directly
> harming many countless tens of millions of users and certificate
> holders that wish to have improved security. Similarly, it can be
> difficult to explain to these customers the importance of routine and
> regular certificate maintenance, as part of any cohesive
> infrastructure readiness or disaster preparedness scenario, as they
> may be relying on antiquated notions that certificate replacement is
> difficult. That's why it's incumbent upon us, the CA/Browser Forum,
> and in particular, the Browser Root Store operators who are tasked
> with ensuring the CAs in their program are trustworthy and the
> certificates issued by these CAs meaningfully secure users'
> connections, to lead and ensure that the minimum bar of security is
This is probably the hardest to answer. Some CAs have demonstrated that
the wider ecosystem good is above the benefit of the CA and its
customers. They have done that by following the rules to the point, even
if this created difficulties in customer relations due to a revocation
requirement. If you consider that all Subscribers "out there" should be
ready for a disaster scenario, this is probably the strongest argument
to support reducing certificate lifetime to 13-months and even lower
than that. Unless Google knows something the rest of the ecosystem
doesn't know, I would kindly ask you to elaborate on what a disaster
scenario looks like. Would the Quantum Computing scenario fit the
description? A SHA2 deprecation? I think keeping the same algorithms for
CA Certificates that are good for 10, 15 or 20 years makes reducing the
lifetime of end-entity certificates a moot point. I am only saying this
because the Forum has taken careful considerations to support secure
algorithms, secure standards that have been tested thoroughly by the
engineering and academic community. If there is a risk that the
standards currently used or referenced in the BRs have a high likelihood
to be broken, we must certainly focus on that. The SHA1 deprecation gave
the CAs and the browsers a lot of useful experience so that we don't
repeat previous mistakes. In case of a SHA2 deprecation the CAs and
browsers should follow a significantly faster timeline.
> I'm shocked and dismayed to see CAs advocating against any lifetime
> reduction, as it suggests outdated or incomplete understanding of the
> core business they're in. While I'm sympathetic to discussions about
> when best to make these changes, and have tried earnestly to highlight
> repeatedly why it requires no substantive process changes for any
> individual Subscribers before 2021, I would have hoped the years of
> discussion that clearly identified this was the end-goal would have
> prepared adequately.
HARICA will support any ballot that provides good and clear benefit to
the ecosystem, taking into account all associated costs, risks, impact
and effort. That includes CAs, Browsers, Certificate Subscribers, Site
Operators, Domain owners and Relying Parties. Each "Participant" in the
ecosystem has a certain amount of "weight". Relying Parties have the
highest. The current proposal of ballot SC22 doesn't demonstrate
significant security improvement for Relying Parties (they will see a
renewed certificate more frequently than before). Re-validating the
Domain Names annually, from HARICA's perspective, seems to be a better
solution that meets the same goals as SC22 (thus RPs are more certain
that they connect to the properly-owned Domain) without the additional
burden for site operators to replace certificates more frequently. They
just need to re-demonstrate control of the Domain Name otherwise their
Certificate will be revoked.
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