Security model

advent is built for friends and colleagues, not adversaries with a lab. Here is what holds and what does not.

Strongly protected

• Unreleased days and hints. Each day is encrypted with its own random 256-bit key (AES-256-GCM), and that key is wrapped with age to the release key. Nothing about a day is on the site before its date, in any form.
• Plaintext in git. Only sealed.json and source.age are committed. .gitignore blocks the rest, and advent verify fails if plaintext was force-added.
• The deployed site. It never contains an answer or a source copy. The build only has the release key, so it cannot read sources even by mistake.

As strong as the answer

A day’s word is locked with a key derived from each accepted answer (PBKDF2-SHA256, 150 000 iterations). The lock is public once the day is released, so anyone can try guesses offline:

• a 4-digit number falls in minutes on a laptop;
• a single dictionary word falls in seconds to minutes on a gaming GPU;
• two unrelated words or a short phrase are impractical to guess.

advent seal warns about weak answers. Someone who cracks a lock spoils their own game, not anyone else’s.

The keys

• Whoever holds the release key can open every day early. It lives in CI secrets; anyone with push access to the repository can read it through a workflow, so limit push access.
• Whoever holds the editors key can read every source. That is by design: authors may read each other’s days, deliberately.
• Players’ progress lives in their browser and is not secret from them. Faked progress cannot open the certificate, which needs the real words.