Eric Rescorla

educatedguesswork.orgNotes on Amazon v. PerplexityAgentic browsing and the Open Web

24 June

Today on the newsletter: a look at the Amazon v. Perplexity case educatedguesswork.org/posts/notes-...

educatedguesswork.orgWhy your asthma inhaler is so expensive (in the US)It starts with the ozone hole...

9 June

Now up on the newsletter: Why your asthma inhaler is so expensive (in the US). Hint: it starts with the ozone hole... educatedguesswork.org/posts/asthma...

educatedguesswork.orgUnderstanding age assurance accuracy

23 May

Now up on the newsletter: Understanding Age Assurance Accuracy educatedguesswork.org/posts/age-as...

11 May

PSA. One benefit of having an electric car is it can make parking easier. It's not uncommon to come across a parking lot which is entirely full but has open EV charging spots. More expensive than charging at home but pretty cheap on the "cost of parking" scale.

educatedguesswork.orgHow not to mandate device-based age assuranceSoftware design by legal mandate

28 Mar

This week on the newsletter: "How not to mandate device-based age assurance" educatedguesswork.org/posts/device... In this post, we examine a number of enacted or proposed requirements for device-based age assurance and some of the ways they can go wrong.

28 Mar

Of possible relevance to @matthewdgreen.bsky.social @alecmuffett.bsky.social

educatedguesswork.orgUltra Tour Monte Rosa (UTMR) Race Report

Some real map/territory confusion in this report by the LA Marathon to give people medals if they drop out after 18 miles (because it's hot). The finisher's medal commemorates that you finished, but it doesn't make you a finisher. www.nytimes.com/2026/03/07/u...

For example, I ran the 2026 Ultra Tour Monte Rosa, where they cut off the last 15 or so miles because of a rock fall. educatedguesswork.org/posts/utmr/ . And in fact it doesn't count as a finish for some purposes, like Hard Rock qualifying. hardrock100.com/hardrock-qua...

Correction: 2025.

For reference, the Badwater 135 takes place in Death Valley in July, so we're talking about running much more than a marathon in temperatures exceeding 100 F. That's exceptionally hot, but 86 F just isn't that hot.

Again, I wouldn't sign up for a marathon if I expected it to be that hot, but it's not like it's some exceptional situation that requires shortening the race.

Moreover, the whole thing is just kind of odd because the forecast for LA is a high of 86 F (merrysky.net/forecast/los%2 0angeles/us ) and that's at 3 PM so it's cooler most of the race.

merrysky.netmerrysky.net

educatedguesswork.orgUltra Tour Monte Rosa (UTMR) Race Report

I'm not saying I'd want to race in that, but running in those temperatures is well within the limits of human performance; mostly you need to slow down and hydrate a lot better. I've trained in hotter temps lots of times.

None of this applies to marathons, which are a strictly defined distance. Nothing wrong with racing 18 miles (~30K); I've done it myself. But it's not a marathon and just giving someone a finisher medal doesn't make it one.

The finished or not question can be a bit confusing in some events like mountain races where the course is always a bit fluid and organizers might need to change or shorten the race for reasons outside their control.

6 Mar

Now up on the newsletter: Let's build a tool-using agent In this post, I walk through in some detail how AI agent tool calling works, including digging into the inputs and outputs of the LLM before they get translated into a coherent-looking JS API. educatedguesswork.org/posts/tool-c...

educatedguesswork.orgLet's build a tool-using agentgiving hands to the brain in a vat

6 Mar

Eric Rescorla reposted

Knight-Georgetown Institute (KGI)

@knightgtown.bsky.social

29 Jan

📣 New from KGI: Age Assurance Online explores how age assurance systems work and their tradeoffs in accuracy, circumvention, availability, and privacy. A must-read for policymakers, service providers + users to understand the consequences of these systems: kgi.georgetown.edu/research-and...

kgi.georgetown.eduAge Assurance Online: A Technical Assessment of Current Systems and their Limitations – Knight-Georgetown Institute

25 Dec 2023

Now up, part II in my series about transparency systems: Certificate Transparency in Reality educatedguesswork.org/posts/transp...

Eric Rescorla reposted

Richard Barnes

@ipv.sx

Welcome to Bluesky @rtfm.com ! Folks might recognize EKR from such hits as TLS 1.3, Let's Encrypt, and being Firefox CTO. He also writes a really good blog. Y'all should all follow him.

Eric Rescorla@rtfm.com

Hello Blue Sky! Check out first post in my series on transparency systems. educatedguesswork.org/posts/transp...

Hello Blue Sky! Check out first post in my series on transparency systems. educatedguesswork.org/posts/transp...

3. Site operators can then download all certificates, make sure they match the consensus, and then check for bogus certificates in their name. Mission accomplished.

Of course, actually deploying this in practice turns out to be a lot harder than it sounds, which I'll get to in the next post. educatedguesswork.org/posts/transp...

Hello Blue Sky! Check out first post in my series on transparency systems. educatedguesswork.org/posts/transp...

The post has more detail, but the idea behind the proof is to show that there is a path from your certificate back to the root of the true, thus demonstrating that the tree was computed over your certificate.

If all goes well, this gives you a closed loop that makes it impossible to surreptitiously issue a certificate. 1. The consensus system requires the CA to commit to all its certificates. 2. Clients verify that certificates have been committed to.

Hello Blue Sky! Check out first post in my series on transparency systems. educatedguesswork.org/posts/transp...

Next, you need some mechanism whereby each element in the system can assure itself that it has the same summary as everyone else (this is actually the hard part).

Finally, when you go to the Web server, it proves that it's certificate matches the summary. What this means technically is that it gives you a Merkle inclusion proof that goes back to the root.

Hello Blue Sky! Check out first post in my series on transparency systems. educatedguesswork.org/posts/transp...

For instance, if the CA has it on their web site and sends it to clients but not to sites when they check, then the system breaks down.

The standard solution here is what's called a consensus system. Effectively, you compute a summary of all the published certificates (typically by assembling them into a Merkle hash tree).

Hello Blue Sky! Check out first post in my series on transparency systems. educatedguesswork.org/posts/transp...

The challenge here is ensuring that CAs are actually publishing every certificate. If your concern is that the CA was intentionally misissuing, it might just choose not to publish the bogus certificate.

The first step is to have the client (i.e., the browser) check that the certificate was published, thus hopefully forcing the CA to publish it. But now we have to confront the definition of "publish". How do we know the CA published to everyone?

Hello Blue Sky! Check out first post in my series on transparency systems. educatedguesswork.org/posts/transp...

The basic idea is to require every certificate has to be published, thus allowing sites -- or services on their behalf -- to detect (at least in principle) when a certificate has been misissued

A misissued certificate can be revoked, and, if investigation reveals improper practices, browsers might choose to distrust the CA, thus rendering all of its certificates invalid.

Hello Blue Sky! Check out first post in my series on transparency systems. educatedguesswork.org/posts/transp...

When paired with some fairly public failures by WebPKI certificate authorities, this creates an obvious problem.

The solution that the ecosystem has converged on is something called a "transparency system", and in the case of the WebPKI "certificate transparency". Instead of trying to prevent misbehavior by CAs, a transparency system tries to make it detectable.

Hello Blue Sky! Check out first post in my series on transparency systems. educatedguesswork.org/posts/transp...