[cabfpub] Draft Ballot 185 - Limiting the Lifetime of Certificates

Ryan Sleevi sleevi at google.com
Sat Feb 4 01:37:51 UTC 2017

On Fri, Feb 3, 2017 at 4:35 PM, Geoff Keating <geoffk at apple.com> wrote:

> Weren’t most of the long-lived certificates that caused problems those
> issued before the current limit of ~3 years?

Nope, not in our experience. I'm hoping Jody can share his graph, but much
of our 'breakage' experience was from sites where the CA waited to stop
issuing SHA-1 certs until it was explicitly forbidden - that is, they did
not even default to SHA-256, or made it considerably *more* difficult for
their customers to obtain SHA-256 signed certs.

> In particular:
> - A 10-year certificate issued right before the BRs were adopted would
> expire 30 June 2022
> - A 5-year certificate issued when special circumstances were allowed,
> could expire 31 March 2020
> - The no-SHA-1 requirement came into force January 2015, and may have been
> a little rushed (or, really, should have been done sooner so that the hurry
> wasn’t necessary)

The no-SHA-1 requirement came in force January 2016 - not 2015. We passed
the Ballot in 2015, following Microsoft's announced deprecation in Nov 12,
2013 - https://technet.microsoft.com/en-us/library/security/2880823.aspx

So it seems to me this point is addressing a problem that has already been
> mostly solved; there’s a big difference between waiting 7 years to do
> something, and being able to do it in 3 years.  As we’ve seen, it appears
> that once you’re down to about 2 years, the limiting factor is not
> certificate expiry but getting the rest of the Internet to catch up.

Except we're not down to 3 years (or 2). For domain validation at present,
we're at 6.5 years. Reducing to two years only gets us to 5.5 years. I
think our ideal target should be O(months), and while it'll take the
industry - CAs and vendors alike - to get there, it's possible if we take
it seriously.

> As for revocation, I believe it is a problem that can be solved, and even
> if it can't, it does not really motivate a reduction to 1 year; you would
> need to go to 1 week or similar.  This is a much longer discussion than I
> can have here.

Right, I believe it's a *necessary* condition to move to shorter
certificates, but not a *sufficient*. We know short-term certificates
(which, regrettably, some CAs opposed) offer one viable path, but we also
know that if we want to see more of the Web move to HTTPS, and we want to
see CRLs become viable (for their significant privacy and efficiency
gains), then we also need a series of checks and balances to limit CRL
growth. Expiration is but one aspect (of many) to that, but even if we
don't solve that problem quite yet, we can at least acknowledge the net
positive to the problem.
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