The FIPS Compliance of HKDF

HKDF is an HMAC-based key-derivation function specified in RFC 5869. It’s nice and we generally like using it. FIPS Federal Information Processing Standards is used generally as a moniker for the set of standards, recommendations, and guidance published by the U.S. National Institute of Standards...

So you want to expose Go on the Internet

I was asked to contribute a post to the excellent Gopher Academy advent series. I took the occasion to write down what I learned deploying a Go service on the Cloudflare edge. The result is a catalogue of what you need to know before you drop NGINX from in front of your Go server. The net/http pa...

go.sum Is Not a Lockfile

I need everyone to stop looking at go.sum, especially to analyze dependency graphs. It is not a “lockfile,”1 and it has zero semantic effects on version resolution. There is truly no use case for ever parsing it outside of cmd/go. go.sum is only a local cache for the Go Checksum Database. It’s a...

Building a Transparent Keyserver

Today, we are going to build a keyserver to lookup age public keys. That part is boring. What’s interesting is that we’ll apply the same transparency log technology as the Go Checksum Database to keep the keyserver operator honest and unable to surreptitiously inject malicious keys, while still...

You Should Run a Certificate Transparency Log

Hear me out. If you are an organization with some spare storage and bandwidth, or an engineer looking to justify an overprovisioned homelab, you should consider running a Certificate Transparency log. It’s cheaper, easier, and more important than you might think. Certificate Transparency CT is on...

TLS nonce-nse

Starting a series of blog posts on TLS 1.3, I published my notes on the landscape of cipher nonces in TLS across versions, to help me clean up the implementation. Comes with hand-drawn diagrams! TLS nonce-nse | CloudFlare Blog archive...

I'm giving up on PGP

After years of wrestling GnuPG with varying levels of enthusiasm, I came to the conclusion that it's just not worth it, and I'm giving up. At least on the concept of long term PGP keys. This is not about the gpg tool itself, or about tools at all. Many already wrote about that. It's about the lon...

Opaque, Interoperable Passkey Records (and a Go API)

Passkeys are the most important thing happening in information security right now because they are the only principled solution to the overwhelming effectiveness of phishing attacks. Just like memory safety is the only principled solution to memory corruption attacks. Unfortunately, implementing...

The NIST Elliptic Curves Seeds Bounty Has Been Claimed

We now know how the seeds of the NIST elliptic curves were generated: they’re not the hash of some saucy sentence, but the output of drand48 seeded with the time, which was indeed in 1997–98. John Wood, Henry de Valence, Ava Howell, Zack Voase, Lucy Sweet, Amir Omidi, Paul Crowley, Iain McGinniss...

(Post-Quantum) Cryptographic Right Answers

Publishing “Cryptographic Right Answers” for developers is a tradition by now. Colin Percival started in 2009, Thomas Ptacek followed up in 2015, and then Latacora carried on in 2018 and 2024. It might feel too soon for an update, but so much has changed. The timeline of the post-quantum transiti...