Hacker News Reader

Comment by xoa | Hacker News Reader

I was kind of surprised that OCSP stapling didn't get any mention at all. I thought that was a major improvement in both resource cost and privacy? Since the time stamped response is proxied by the site operator rather then going directly to the CA, the load is almost entirely switched to the site itself, and the site itself is the only one who knows a given IP is asking for it, which is fine because obviously the site knows a given browser is connecting to it anyway. It's decentralized again. I vaguely remember at one point there was a major limitation of only supporting a single OCSP response at a time but I thought that was dealt with via a later RFC and then entirely obviated as an issue by TLS 1.3.

Did something happen there or some other significant issue get discovered? I'm curious why the move back to CRLs (albeit improved) vs must-staple. It seemed like a reasonable elegant and straight forward solution that fit the web pretty well.

View on HN

Yes, I noticed this too and asked the author about it [0].

IMO, OCSP stapling is the best overall solution until certificate lifetimes are shorter (< 7 days).

As a server developer I'm worried that the focus on independent CRLs will make it difficult to automate certificates in the face of revocation. Currently, Caddy staples OCSP for all certificates by default, caches the staples, and refreshes them halfway through their lifetime. Works great. Every server should do this. And when an OCSP response is discovered to be Revoked, Caddy automatically replaces the certificate. Works great. Every server should do this.

If every browser is independently going to decide which certificates to distrust, now I am not sure of a good, authoritative way to determine "revoked" and then replace certificates automatically. I'm worried this will hurt the TLS ecosystem unless we answer those questions first.

Actually, let's just shorten certificate lifetimes and be done with it already.

Main blockers to short cert lifetimes:

- CA's uptime determines Web's uptime.

Main solution:

- Multiple redundant ACME CAs. If one goes down, try another. (This is what Caddy already does.)

[0]: https://twitter.com/mholt6/status/1567559325949763588

Replying to this as it's on top, and first thanks for the reply (and sibling replies as well). The challenges of getting servers to update and implement being a practical roadblock makes sense, I was more surprised just to not see it mentioned at all. I'd have been fully prepared for a few sentences along the lines of "this would be ideal if doing it from scratch but it'd be hard to get everyone to go along now, the reverse perils of decentralization". What you write is also interesting.

I too found this troubling.

Mainly because we are not talking about validation performance, and OCSP stapling is an excellent performance fix.

Not to mention all the privacy issues that OCSP stapling really fixes.

Another tool in the toolbox is ARI. https://datatracker.ietf.org/doc/draft-acme-ari/

I am lukewarm about ARI. It's nice that clients can know the most convenient time to renew a certificate to avoid overwhelming the server.

However, it is optional, so we will repeat the same mistake we made with optional OCSP stapling.

Only nice clients will implement ARI, but they are the clients that need it the least because if they go to the trouble to support ARI they probably already have friendly netizen programming.

As for revocations, ARI doesn't make much sense to me. If we know a certificate will be revoked soon, we might as well stop trusting it right now. Why continue to trust a certificate that we know is being revoked?

Maybe I'm totally missing the point of ARI.

Here's my pitch:

The worst revocations are mass ones that the site operator didn't request. ARI gives a heads-up to renew early, maybe because all certificates issued using HTTP-01 are getting revoked in two days.

Revocations aren't always about distrusting a specific certificate. There's likely nothing wrong with the certificate, but it needs replacement for ecosystem cleanliness. Regardless, 40M certs are being revoked in a 10 minute window on Saturday (oof, because that's the covenant with the BRs, not because Saturday is somehow not awful!). Reissuing 40M certs may take a dozen hours (1000/sec), even if all clients work optimally and begin immediately after OCSP changes status. During that dozen hours, those certs are all already revoked.

It'd be nice if clients could be told in advance: replace this certificate right away, regardless of its validity period. Get it done early before the crowd forms and replacement requires queuing up.

(Obviously using multiple CAs mitigates the downsides to waiting until revocation)

If there was "nothing wrong" with the certificate, it shouldn't be revoked. I get that there's red tape, but the policy surely exists for a reason. I'm obviously familiar with LE's prior mass revocations where, for the most part, there was no security concern -- but the thing is, the policy exists because we can't be sure. Those revocations were out of an abundance of caution because we couldn't be sure.

So yes, if we're being strict like the policy is, an early renewal signal is a red flag that a certificate can't be trusted. There might not be anything wrong with it, but we can no longer be sure.

I mean, there's also nothing wrong with a certificate 2 seconds after it expires. Probably. But we can't be sure. And because of that, we immediately distrust the certificate when it expires. (There might be something wrong with it before it expires too. But that's less likely because less time has passed, so we allow it, I guess.)

I think the vision is nice. I really do. I just think the clients that need it most won't support it.

must-staple requires additional effort from server operators, which is very challenging to roll out. This new scheme can be implemented by the browsers and CAs together, which is vastly simpler than having every webserver in the world turn on OCSP stapling.

There isn’t any particular force driving for OCSP stapling: Browsers can’t turn it on until it is ubiquitous. CAs don’t want to enforce must-staple because their users will need enormous amount of help rolling it out. Site operators don’t care if browsers are fetching OCSP (especially since Chrome and Edge don’t)

OCSP stapling increases how large the first response from the server is, increasing the time to first useful byte.

It's on the order of a few hundred bytes, only happens on the first connection, and is still orders of magnitude faster and more effective than the alternative (no stapling, which requires the client to make separate round-trips to a third party service which has all sorts of other problems).

OCSP stapling is temporary, anyway: just until we get certificate lifetimes short enough to make revocation irrelevant.*

* This is how it should be, but the industry seems to be going the direction of keeping cert lifetimes longer.

A few hundred bytes is a ton data for something that a lot of people don’t particularly care about, and is still broken despite OCSP stapling. People don’t have low latency, clean internet all over the world and adding something like this on top of an already pretty bloated negotiation doesn’t help.

As for the alternative not a single browser out there validates OCSP out of the box on the hot path (e.g actually waits for OCSP before proceeding)

This is a brower problem, but it is configurable.

Speaking from a PKI perspective you may head towards shorter lived certificates in many use-cases, NPE / automatable re-keying being examples of that.

However, for strong PKI on a consumer or enterprise encryption/decryption device, e.g. smartcards, there is big costs associated with shortening lifetimes. Not going to fly there.

I also love OCSP stapling but there are some limitations: - webserver need to implement it - admin need to enable it - webserver need internet access

Maybe they saw with some telemetry that very few website actually enable OCSP stampling and decided to implement a fix that cover all certs and can really be deployed

Firefox Telemetry shows Beta 104 users encountered stapling on 13.95% of TLS handshakes. [1]

The stapling telemetry is no longer turned on in Release [2], and even if it were, you have to do special things to look at Release data, but some years back (~2018 maybe?) I remember Release stapling was substantially lower than the more tech-savvy Beta and Nightly populations. Which is pretty normal, as tech-oriented sites are more likely to turn on advanced features.

[1] https://telemetry.mozilla.org/new-pipeline/dist.html#!cumula...

[2] "prerelease" https://probes.telemetry.mozilla.org/?search=stapl&view=deta...

OCSP Stapling is incredibly stupid. OSCP Stapling is either ignored because it's not present, or it's effectively just an override for the NotBefore and NotAfter fields. There's never a reason as a server operator to present an invalid NotAfter, and it represents a substantial surface area for client libraries to respect them, in the area that's already most prone to mistakes (the recursive descent to find a certificate chain)

It's much saner to issue a new, shorter-lived cert. Reduce certificate lifetimes to match whatever you'd use OCSP stapling for. Continue to use ACME. Figure out rotation lifetimes such that I can sleep at night (i.e. they need to be at least 2 days, so that if the rotation fails I've still got time to wake up and start working). Work on building client and server tooling to make it easy to accept rotated certificates (i.e. reload your client certificates on SIGHUP).

The advantage of CRLs isn't that they can be used offline, it's that it allows your security team to burn certificates rather than waiting for the CA to do so. You should always subscribe to your CA's CRL too, but you should have a CRL for your own internal use, too.

> The advantage of CRLs isn't that they can be used offline, it's that it allows your security team to burn certificates rather than waiting for the CA to do so. You should always subscribe to your CA's CRL too, but you should have a CRL for your own internal use, too.

This is incorrect conventionally

CRLs are signed by the Originating CA in the conventional trust model.

Most CAs won't give you a certificate with the ability to generate your own CRL sharing the same trust, because it can be weaponized to cause a denial of service.

This then brings up non-conventional trust models, and Validation Authority as Co-equal to CA situations for validity which can be significantly more challenging, and requiring VA certificate insertion into every Relying Party, just to name a few things, not to mention all the security concerns.

I'm aware. That trust model is inherently broken, and it's not followed anyway. In practice, any CA you trust can sign a revocation for any certificate (the serial numbers are all grouped together) - And that's the way it should be. You should not wait for the issuing CA to get it's act together, you should burn a certificate as soon as anyone distrusts it, and if you have a rogue CA that starts burning Google.com and other important sites, it's better that they burn them (and take you offline) than that they issue false certs (and leak all your data); It's also far more obvious.

https://www.imperialviolet.org/2014/04/19/revchecking.html

Revocation checking is useful for your security team to blacklist site. That's the only useful use.

Reply on news.ycombinator.com