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Date: Tue, 12 Mar 2024 00:28:49 -0400
From: Demi Marie Obenour <demi@...isiblethingslab.com>
To: oss-security@...ts.openwall.com
Subject: Re: Certificate policy: OCSP becomes optional and
CRLs mandatory for public CAs on Friday
On Tue, Mar 12, 2024 at 05:33:46AM +0900, Valtteri Vuorikoski wrote:
> This is more of a meta-security issue, but posting it since I expect
> that this change will affect development priorities of
> certificate and TLS-related OSS projects to some degree.
>
> Last July, the CA/Browser Forum approved ballot SC-063
> <https://cabforum.org/2023/07/14/ballot-sc-063-v4-make-ocsp-optional-require-crls-and-incentivize-automation/>.
> The central changes to existing policy are:
>
> * Makes providing OCSP services optional for CA/B-approved CAs,
> i.e. those which ship in most browser and OS trust stores.
>
> * Requires CAs to provide CRLs that are updated in a timely manner.
>
> * (New policies related to short-lived certificates, not discussed
> further in this post.)
>
> The first two changes come into effect on 2024-03-15 which is this
> Friday. CAs that provide OCSP services are free to continue doing so
> under prior guidelines.
>
> The proposal provides the following rationale for these changes (slightly
> edited for brevity):
>
> OCSP requests reveal details of individuals’ browsing history to the
> operator of the OCSP responder. These can be exposed accidentally
> (e.g., via data breach of logs) or intentionally (e.g., via
> subpoena). Due to privacy concerns, several certificate consumer
> products represented in the CA/Browser Forum do not perform online
> OCSP checks by default - or have signaled interest in transitioning to
> privacy-preserving methods of communicating revocation status. […]
> Concern surrounding OCSP is further elevated considering the
> disproportionately high cost of offering these services reliably at
> the global scale of the Web PKI.
>
> Given this ballot makes operating OCSP services optional
> for CAs, allow relying party software applications and certificate
> consumer user agents to consistently and reliably evaluate certificate
> revocation status using a privacy-preserving check [using CRLs].
>
> Personal opinion: It seems unlikely that most CAs will stop offering
> OCSP now or even in the short-to-medium term. However OCSP support
> (including OCSP stapling support) in open-source software has overall
> been limited outside of HTTPS-related projects with a lot of developer
> resources, and I suppose could have even less resources dedicated to
> it in the future as a result of this change. Meanwhile some projects
> may need to implement updates to handle large and relatively
> rapidly-updating CRLs efficiently. In addition, I guess that OS level
> mechanisms similar to root certificate stores may be needed to
> centralize CRL updates; having each application pull down potentially
> large CRL updates once a week seems inefficient.
macOS, iOS, Windows, and possibly Android have system certificate
verifiers that can handle this easily. For desktop and server Linux,
should a CRLite package be included in system package managers? Would
it be feasible for WebPKI and {Open,Boring,Libre}SSL to handle CRLite,
or does this mean that NSS should be used for certificate verification?
--
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab
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