[cabfpub] SHA-1 changes and certificate lifetimes

Gervase Markham gerv at mozilla.org
Wed Nov 13 17:59:00 UTC 2013

Hi Wayne,

On 13/11/13 17:44, Wayne Thayer wrote:
> I'm a bit surprised by this and don't see the relationship between
> this proposal and the new SHA-2 requirements. It is a fact that most
> all certs will have to be replaced in the next 3 years, but why does
> that imply that they need to be replaced with stronger certs that
> also expire in no more than 3 years?

It is already the CAB Forum's stated intention to move the maximum
issuance lifetime to 39 months. However, due to (if I remember
correctly) concerns about outstanding legacy certs, and that some CAs
might be unduly penalised as they were greater users of longer-life
certs than others, it was not thought possible to make such a change
immediately. So, some time ago, we set the date as April 2015.

Now, however, there is no unlevel playing field or outstanding
long-lived legacy base because all (or almost all) existing certs now
have an effective lifetime of just over 3 years. So it seems a good
opportunity to move the already-agreed deadline to match the /de facto/

> In addition, reducing the allowed lifetime actually makes it harder
> to transition longer duration certs to SHA-2.  If a CA issues a 5
> year SHA-1 cert today and then can't reissue it with SHA-2 for the
> full term starting on Jan 1, then perhaps the least bad choice is to
> wait until the remaining lifetime of the cert is less than 39
> months.

That would be an entirely reasonable thing to do.

> Speaking as a CA that sells 4 & 5 year duration certificates,
> changing the date to 1/1/2014 doesn't give me nearly enough time to
> cleanly transition away from the longer durations.  

Are all the 4 and 5 year duration certs you are selling at the moment
SHA-2, then?


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