Security Review of CFSSL Signer Code

Last Thursday (June 15th, 2023), Let's Encrypt went down for about an hour, during which time it was not possible to obtain certificates from Let's Encrypt. Immediately prior to the outage, Let's Encrypt issued 645 certificates which did not work in Chrome or Safari. In this post, I'm going to explain what went wrong and how I detected it. The Law of...

It happens every so often: some organization that sells publicly-trusted SSL certificates does something monumentally stupid, like generating, storing, and then intentionally disclosing all of their customers' private keys (Trustico), letting private...

A surprisingly hard, and widely misunderstood, problem with SSL certificates is figuring out what organization (called a certificate authority, or CA) issued a certificate. This information is useful for several reasons: You've discovered an unauthorized certificate for your domain via Certificate Transparency logs and need to contact the certificate authority to get the certificate revoked.You've discovered a certificate via Certificate Transparency...

Filippo Valsorda has a neat SSH server that reports the GitHub username of the connecting client. Just SSH to whoami.filippo.io, and if you're a GitHub user, there's a good chance it will identify you. This works because of two behaviors: First, GitHub publishes your authorized public keys at https://github.com/USERNAME.keys. Second, your SSH client sends the server the...

It was perfect outrage fodder, quickly gaining hundreds of upvotes on Hacker News: As you know, domain extensions like .dev and .app are owned by Google. Last year, I bought the http://forum.dev domain for one of our projects. When I tried to renew it this year, I was faced with a renewal price of $850 instead of the normal price of $12. It's true that most .dev...