Simon Willison’s Weblog

9 items tagged “certificates”


trustme (via) This looks incredibly useful. Run “python -m trustme” and it will create three files for you: server.pem, server.key and a client.pem client certificate, providing a certificate for “localhost” (or another host you spefict) using a fake certificate authority. Looks like it should be the easiest way to test TLS locally. # 11th February 2021, 8 pm


The case against client certificates (via) Colm MacCárthaigh provides a passionately argued Twitter thread about client certificates and why they should be avoided. I tried using them as an extra layer of protection fir my personal Dogsheep server and ended up abandoning them—certificate management across my devices was too fiddly. # 9th December 2020, 2:41 pm

How CDNs Generate Certificates. Thomas Ptacek (now at Fly) describes in intricate detail the challenges faced by large-scale hosting providers that want to securely issue LetsEncrypt certificates for customer domains. Lots of detail here on the different ACME challenges supported by LetsEncrypt and why the new tls-alpn-01 challenge is the right option for operating at scale. # 26th June 2020, 12:03 am


Client-Side Certificate Authentication with nginx. I’m intrigued by client-side browser certificates, which allow you to lock down a website such that only browsers with a specific certificate installed can access them. They work on both laptops and mobile phones. I followed the steps in this tutorial and managed to get an nginx instance running which only allows connections from my personal laptop and iPhone. # 5th October 2019, 5:26 pm


Extended Validation Certificates are Dead. Troy Hunt has been writing about the flaws of Extended Validation certificates for a while. Now iOS 12 is out and Mobile Safari no longer displays their visual indicator in the URL bar (and desktop Safari will stop doing so next week when Mac OS Mojave ships). EV certificates are being dropped by many of the larger companies that were using them. “This turned out to be a long blog post because every time I sat down to write, more and more evidence on the absolute pointlessness of EV presented itself”. # 18th September 2018, 1:41 pm

The death of a TLD. Sony have terminated their .xperia TLD. Ben Cox used Certificate Transparency logs to evaluate the 11 total TLDs that have been abandoned since the gTLD gold rush started—since HTTPS is becoming the default now these logs of issued certificates are a great indicator of which domains (or TLDs) are being actively used. The only deleted TLD with legitimate looking certificates (apparently for a mail server) was .mcdonalds # 28th July 2018, 8:07 pm

mkcert (via) Handy new tool from Filippo Valsorda (a cryptographer at Google) for easily generating TLS certificates for your local development environment. You can use this to get a certificate pair for a localhost web server created with a couple of simple commands. # 26th June 2018, 6:55 pm


Extended Validation is Broken. Ian Carroll spent $100 incorporating a company called “Stripe, Inc” in the state of Kentucky and $77 on an Extended Validation certificate tied to that legal entity. Safari (and Mobile Safari) now hide the URL bar completely, displaying “Stripe, Inc” in its place. “This means the attacker does not even need to register a convincing phishing domain. They can register anything, and Safari will happily cover it with a nice green bar.” # 12th December 2017, 1:36 am

2007 An OpenID provider that uses SSL client certificates (which you install in your browser) for authentication. # 22nd February 2007, 12:01 pm