Andrew Ayer - Blog

You can protect the users of your Go modules from supply chain attacks, such as a compromise of your GitHub account, by monitoring Go's checksum database (sumdb).

Try the following Git clone with libcurl 8.7.1 (which happens to be the version shipped in macOS 14.6 and newer) and it fails or hangs: git clone https://software.sslmate.com/src/macosgitbug.git Disable HTTP/2 and it works: git clone -c http.version=HTTP/…

HTTP reverse proxying is a minefield.

Imagine you're connecting to an IP address over TLS.

Twice a year, the Certificate Transparency ecosystem undergoes a transition as certificate authorities start to submit certificates to new semiannual log partitions.

On each of the last two Fridays, Google has suspended SSLMate's Google Cloud access without notification, having previously suspended it in 2024 without notification.

When you try to compile a Go module that requires a newer version of the Go toolchain than the one you have installed, the go command automatically downloads the newer toolchain and uses it for compiling the module.

One of the most important properties of a database is durability.

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.

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 keys…

A surprisingly hard, and widely misunderstood, problem with SSL certificates is figuring out what organization (called a certificate authority, or CA) issued a certificate.

Filippo Valsorda has a neat SSH server that reports the GitHub username of the connecting client.

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.

This wasn't my first rodeo so I knew it would be hard.

In my original post about SNI proxying, I showed how you can parse a TLS Client Hello message (the first message that the client sends to the server in a TLS connection) in Go using an amazing hack that involves calling tls.Server with a read-only net.Conn

My preferred method for deploying webapps is to have the webapp listen directly on port 443, without any sort of standalone web server or HTTP reverse proxy in front.

I recently heard from someone, let's call them Alex, who was unable to email comcast.net addresses.

Did you know that you can use the ssh-keygen command to sign and verify signatures on arbitrary data, like files and software releases?

Last week, a Certificate Transparency log called Yeti 2022 suffered a single bit flip, likely due to a hardware error or cosmic ray, which rendered the log unusable.

I recently did a partial security review of Smallstep, a commercially-backed open source private certificate authority written in Go.

Connecting to a website, say example.com, over TLS is a relatively straightforward affair.

The very first message sent in a TLS connection is the Client Hello record, in which the client greets the server and tells it, among other things, the server name it wants to connect to.

Certificate signing is the most security-sensitive task performed by a certificate authority.

A lot of stuff on the Internet is currently broken on account of a Sectigo root certificate expiring at 10:48:38 UTC today.

Considering all the progress that has been made over the last decade making SSL certificates on the Web easy, free, automated, and transparent, it's a bit jarring to see someone arguing in 2020 that trust-on-first-use (TOFU) would be better for the Web: U…

When publishing a DNS record through an API, it's often useful to know when the DNS record has been fully published and is visible to DNS resolvers.

Before adding a dependency to one of my software projects, I do some basic vetting of the dependency.

If your application makes requests to URLs provided by untrusted sources (such as users), you must take care to avoid server side request forgery (SSRF) attacks.

Important update: As of November 2025, I no longer recommend the approach described in this blog post for the following reasons: Google Cloud imposes a default quota of 100 service accounts per project.

Last week, Gmail became the first major email provider to enable the new MTA-STS standard, which will prevent attackers from intercepting email sent to and from Gmail.

I'm not actually sure when SSLMate was born.

When we use the Internet, we rely on the security of the certificate authority system to ensure we are talking with the right people.