Your Own Lock

What It Protects

Everything happens in this browser, with the browser’s own cryptography. Nothing you type, pick, lock or open is sent to us or to anyone, and nothing is kept: close the page and it is gone. The one thing kept is your key, if you make one, in this browser’s own storage. Once the page has loaded it works with the network off.

The lock is AES-256-GCM. The key is made from your passphrase by PBKDF2 with SHA-256, 600,000 rounds and a random salt, so every guess at it costs an attacker the same work again; each lock also takes a fresh random nonce. The key never leaves the browser’s crypto engine, not even to this page. If one character of the locked text is changed, it will not open.

Against Quantum Computers

You do not need a quantum computer to defend against one. A quantum computer would break today’s public-key locks, but AES with a 256-bit key is not one of them. The National Institute of Standards and Technology says Grover’s algorithm, the quantum attack on keys like this, will likely give “little or no advantage in attacking AES”, and that AES 256 “will still be safe for a very long time”. NIST, Post-Quantum Cryptography FAQs.

The weak point is the passphrase. A short or guessable one can be found by any computer, quantum or not; a long random one cannot.

A lock for someone’s key is where a quantum computer would strike, so it is built to stand one. It uses X-Wing, which joins two locks: ML-KEM-768, the quantum-resistant standard NIST published on 13 August 2024 as FIPS 203, and X25519, the key exchange in wide use on the web today. It holds as long as either half holds. X-Wing is still an Internet-Draft at the IETF, not yet a final standard; both halves are standards already. The code is open source: mlkem-native and Monocypher, running in this page. FIPS 203; X-Wing.

What It Does Not

There is no recovery. We hold no copy, no master key and no back door, so a forgotten passphrase loses what it locked, for good. Your key lives only in this browser on this phone: clear the site’s data, lose the phone or forget the key, and what was locked for it is gone too.

It hides what you wrote, not that you sent something, how large it was, or to whom. Never send the passphrase alongside the locked text: give it another way, in person if you can.

It cannot protect a phone that someone else already controls, or words read over your shoulder before they are locked.

The Law

Security of Your Data

Article 32(1) of the UK GDPR requires anyone who processes your personal data to keep it secure, and names “the pseudonymisation and encryption of personal data” among the measures. The EU GDPR says the same in the same article. The text.

Your Own Encryption

No law of the United Kingdom or the European Union forbids you to encrypt your own data. One limit to know: under section 49 of the Regulation of Investigatory Powers Act 2000, a person with the right permission can serve a notice requiring you to hand over the key or the readable text, on grounds of national security, preventing or detecting crime, or the country’s economic well-being, and section 53 makes ignoring such a notice an offence. The text.

We never sell a citizen’s data, read what companies return to you, or keep what you type. The Digital Proclamation is the whole constitution.