[openssl-dev] [openssl.org #3951] [RFC][PATCH] Allow certificate time checks to be disabled

[Alexander Gostrer]

Hi David,

I think that both your proposals will add vulnerabilities. With your
proposal I anticipate that many careless application developers will
disable the date checking forever. As a result, consumers will be blaming
openssl, not these developers.

Current solution for kernels and other firmware without a reliable RTC is
to issue certificates that are valid from 1969 to 2037. We will have a
Y2037 problem similar to Y2000 but this is a wide problem, much wider than
openssl can solve at the moment.

Regards,
Alex Gostrer


On Wed, Jul 22, 2015 at 6:09 AM, Woodhouse, David via RT <rt at openssl.org>
wrote:

> There are various circumstances in which it makes no sense to be
> checking the start and end times of a certificate's validity.
>
> When validating OS kernel drivers, or indeed when validating the OS
> kernel itself when the firmware loads it, we *really* don't want to
> have a built-in obsolescence date after which the system will no longer
> function. That would be a bad thing even if we *could* reliably trust
> the system's real time clock at this stage in the boot sequence.
>
> This patch gives us a way to disable the time checks entirely, by using
> X509_VERIFY_PARAM_set_time() with a time of -1.
>
> There is a slight risk here — if anyone was genuinely using the value
> of -1 to check if a certificate chain was indeed valid in the last
> second of 1969. I judge that risk to be negligible. And it certainly
> shouldn't be externally triggerable — if an attacker could influence
> the value passed to X509_VERIFY_PARAM_set_time() then all bets were off
> w.r.t. time-based checks anyway.
>
> If there are serious concerns, however, I can provide an alternative
> patch which adds an X509_V_FLAG_NO_CHECK_TIME flag for this purpose
> instead.
>
> I'm happy with anything except the existing version in the UEFI source
> tree that everyone is shipping, which just disables the time check if
> OPENSSL_SYS_UEFI is set¹. That one I *don't* like.
>
> --
> David Woodhouse                            Open Source Technology Centre
> David.Woodhouse at intel.com                              Intel Corporation
>
> ¹ http://git.infradead.org/users/dwmw2/openssl.git/commitdiff/2fb12afc2ceb
>
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