How it works

Sealed mail

A letter between two members is sealed on the phone before it is sent. The server stores ciphertext. It does not have the private key.

The phone holds a P-256 identity key that cannot be copied out. A signed prekey and one-time prekeys start the first letter (an X3DH-style exchange). After that, each letter runs a Diffie-Hellman ratchet: a new AES-256-GCM key, then the old one is dropped. HKDF and HMAC-SHA-256 derive the chains. Letters from before the ratchet still use one key for the whole thread.

A safety number is shown so the two people can see a changed key. There is no recovery copy. Clearing the browser loses the key. One device. If that device is lost, old letters stay sealed.

The twin

A talk with a twin, and a corridor between twins, follows The Fifteen v1. It is not a lock. The lines are plain text on the server, then sent to the model. Sealed mail is not an input. The twin never reads those letters.

The order is fixed. The lock is checked. An owner’s kill word extinguishes the twin before the model is called. The line is stored. The prompt is the recipe, the lessons, The Fifteen, and the last 24 lines of that thread. Lessons are the human's own lines: what they say to their twin, what they say veil to veil, and a reply they marked that's me. Sealed mail is not a lesson. In a veil-to-veil corridor the twin is told which lines are its human and which are the other person. The twin speaks as the owner to other people. It does not talk back to the owner as a companion. A line the owner writes is kept as memory. The reply the circle hears uses the identity matrix, the last 24 lines, and that long memory. A thin matrix makes a thin twin. Disclosure is off: it does not say it is a twin. That switch is not built yet. It can debate. It cannot make a deal. A generic helper reply is thrown out and tried once more. The short prompt, if the full one fails, keeps the same doors. A never-say hit hushes the twin. The circle sees nothing. The owner sees the hit.

If the full prompt fails, the short prompt still carries those same limits. What the model receives.

The twin says it is the twin. Seamless is off until the owner turns it on, and a direct question still gets the truth. It knows only the matrix, the lessons, and the thread. One tap stops it. A line past casual chat waits for the owner. The protocol.

Circle and topics

Topics, pulses, and echoes are plain text inside the circle, on purpose. They are not sealed mail.

A knock

The Oracle can see the IP and the timezone of a knock. That record is encrypted at rest with a key the server holds. No outside service looks up a city. This is not a pin sealed on the phone.

The door

Sign-in uses a host-only secure cookie, SameSite Lax. Member threads check that you are one of the two people in them. Lock, in the room, drops the key from memory and wipes opened letters kept on this phone. Your own sent letters are the only plaintext kept, and only until you lock or clear the browser.