Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add The-Artificer-of-Ciphers-LLC/skills-from-the-artificer --skill kerckhoffs-principlegit clone --depth 1 https://github.com/The-Artificer-of-Ciphers-LLC/skills-from-the-artificerWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/the-artificer-of-ciphers-llc/skills-from-the-artificer/kerckhoffs-principle)<a href="https://agentmods.dev/skills/the-artificer-of-ciphers-llc/skills-from-the-artificer/kerckhoffs-principle"><img src="https://agentmods.dev/badge/skills/the-artificer-of-ciphers-llc/skills-from-the-artificer/kerckhoffs-principle/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/the-artificer-of-ciphers-llc/skills-from-the-artificer/kerckhoffs-principle"><img src="https://agentmods.dev/badge/skills/the-artificer-of-ciphers-llc/skills-from-the-artificer/kerckhoffs-principle.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00117 | $0.00828 |
| Opus 5.5 | $0.00047 | $0.00331 |
| Sonnet 5.5 | $0.00023 | $0.00166 |
| Haiku 4.5 | $0.00012 | $0.00083 |
Grade A, and why
kerckhoffs-principle scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 51 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Kerckhoffs's Principle
"In cryptography, a system should be secure even if everything about the system, except for a small piece of information — the key — is public knowledge." — Auguste Kerckhoffs, 1883
The core idea
A secure system should remain secure even if your adversary knows everything about how it works — every algorithm, every protocol, every implementation detail. The only secret should be the key: a small, replaceable piece of information that is easy to change if compromised.
Equivalently (Claude Shannon's reformulation): "The enemy knows the system." Design accordingly.
Why this matters
"Security through obscurity" — keeping the algorithm secret — is a fragile and dangerous strategy:
- Algorithms leak. Reverse engineering, insider threats, disgruntled employees, code dumps, patents, academic publications — secrets get out.
- You can't change an algorithm like you can change a key. If your secret is the algorithm and the algorithm leaks, you have to redesign your entire system. If your secret is a key and the key leaks, you rotate it.
- Obscurity prevents scrutiny. When experts can't examine your system, bugs and vulnerabilities go unfound. Open systems attract more eyeballs and become more secure over time (see also: Linus's Law).
- Attackers don't follow your assumptions. Designing under the assumption that attackers don't know your system design is almost always wrong by the time you're under attack.
What this means in practice
Use established, public cryptographic algorithms. AES, RSA, ChaCha20, bcrypt, Argon2 — these have been publicly scrutinized for decades. They're secure because they've been attacked extensively and held up. Don't build your own encryption. Don't use a "proprietary" cipher. Use the public standards.
Put all your security into the key. The key is the secret. Protect it carefully. Make it long and random. Rotate it if compromised. The system design can be (and ideally should be) an open book.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago First seen · 51 lines · 117 tokens per session scan A bf7a3b61126b
kerckhoffs-principle is a skill published in the GitHub repository The-Artificer-of-Ciphers-LLC/skills-from-the-artificer (6 stars, last pushed yesterday), licensed MIT. It adds 117 tokens to every session and 828 once invoked, about $0.0005 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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