[Servercert-wg] Ballot SC22: Reduce Certificate Lifetimes

Ryan Sleevi sleevi at google.com
Fri Aug 16 23:26:45 MST 2019

Ballot SC22: Reduce Certificate Lifetimes

Since the adoption of the Baseline Requirements, the CA/Browser Forum has
discussed and debated the merits and value in reducing certificate
lifetimes, in order to adequately respond to changes in the TLS ecosystem.

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.
  * 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.
  * 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.
  * 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.
  * 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 validated.
  * 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.
  * 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.

While this ballot sets forward a proposal for an effective annual renewal
and annual revalidation, both periods should be seen as a starting point
for further improvements. In particular, multiple Browsers have noted that
the current reuse of domain validation information represents a substantial
security risk, and thus will seek to further reduce this in subsequent
ballots. In general, CAs and Subscribers are recommended to pursue
interoperable solutions for automation, such as RFC 8555, which allow for
easier and seamless validation and replacement of certificates, and thus
helping ensure users and Relying Parties are adequately secured.

While Browsers will be able to technically enforce these reduced validities
as early as March 2020, they will not fully benefit from the reduction
until 825 days after the last day such certificates can be issued, or June
2022. As a consequence, any delays to the implementation period of March
2020 would represent an even greater security risk to users and Relying

This ballot further attempts to resolve ambiguities between the
expectations of Root Programs and the interpretations of CAs. Namely, it
attempts to clarify time periods in days and seconds, to avoid confusion
with respect to months, fractional seconds, leap seconds, and other forms
of date calculation, while also allowing an additional 86,400 seconds
between the recommended period and the required period. To address issues
with Validity Period, it defines the Validity Period in a way that can be
objectively technically enforced and verified, by measuring the period
between the notBefore and notAfter of certificates, as specified by RFC
5280. While historically the Forum has not specified timezones for
effective dates, and thus this ballot continues the trend, consistent with
the requirements of X.690, X.680, and X.509, the time and timezone for
effective dates shall be interpreted as midnight, Coordinated Universal

The following motion has been proposed by Ryan Sleevi of Google and
endorsed by Curt Spann of Apple and Jacob Hoffman-Andrews of ISRG / Let’s

----- MOTION BEGINS -----

This ballot modifies the Baseline Requirements, version 1.6.5, to
incorporate the following changes:


This ballot modifies the EV SSL Certificate Guidelines, version 1.7.0, to
incorporate the following changes:

Should this ballot be adopted, the Chair or Vice Chair shall be directed to
correct “SCXX” to “SC22” and “XX-Xxx-2019” within both documents’
informative tables to the date of the completed ballot, prior to or
following the IP Review Period, and “Xxxx XX” to the effective date/date of
publication of the Final Maintenance Guidelines.

----- MOTION ENDS -----
This motion proposed a Final Maintenance Guideline.

The procedure for approval of this ballot is as follows:

Discussion (14+ days)
Start Time: 2019-08-19 17:00 GMT
End Time: 2019-09-02 17:00 GMT

Vote for approval (7 days)
Start Time: 2019-09-02 17:00 GMT
End Time: 2019-09-09 17:00 GMT
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