What a messenger has to know about you

Ask what a messenger encrypts and every serious app gives roughly the same answer. Ask what it has to know about you before it will carry a message, and the answers stop resembling each other entirely. That second question is the architecture. It decides what exists to be subpoenaed, what leaks when the operator is careless, and how hard the app is to use.

Start with the clearest statement any operator has published about its own ignorance. Signal's transparency page, responding to a federal grand jury subpoena, says the service is designed so that “the only information we can produce in response to a request like this is the date and time a user registered with Signal and the last date of a user's connectivity to the Signal service.” Two timestamps. That is what a well-built server-mediated messenger can be reduced to — and note what it still is: a record keyed to a phone number.

What identity costs

Telegram is the honest edge case, because it says so. Its FAQ states that “messages in Secret Chats use client-client encryption, while Cloud Chats use client-server/server-client encryption and are stored encrypted in the Telegram Cloud.” Ordinary chats are not end-to-end encrypted; that is a design decision in exchange for cloud sync. What follows from holding an account is in its privacy policy: on a valid judicial order, Telegram “may disclose your IP address and phone number to the relevant authorities.”

WhatsApp encrypts content end to end and is explicit about the rest. You “must provide your mobile phone number”; the app can upload the numbers in your address book; and the policy lists collection of “the time, frequency, and duration of your activities and interactions.” None of that is a contradiction of end-to-end encryption. It is what remains after it.

Signal has spent years attacking that residue — sealed sender, private contact discovery, and in February 2024 usernames, so a phone number no longer has to be the handle you give out. The company is careful about the limit: “you will still need a phone number to sign up for Signal.” The number moved from identifier to registration credential. It did not leave.

The phone number is not a privacy flaw. It is a usability decision that happens to be an identity decision, made once, at the beginning, on everyone's behalf.

Removing the identifier

Several projects removed it. SimpleX states the strongest version: “Unlike any other existing messaging platform, SimpleX has no identifiers assigned to the users”, delivering instead to per-contact one-way queue addresses. Session drops the number and onion-routes so that “a server which receives a message never knows the IP address of the sender.” Briar removes the server altogether: “messages are synchronized directly between the users' devices”, over Tor when there is an internet. Each of these buys real anonymity, and each pays in discovery, in delivery latency, in battery, and in the awkward first minute where you have to get a long address to another human being.

Federation is a different trade, not a cheaper one. Matrix's own documentation notes that a room's data is “replicated across all of the homeservers whose users are participating in a given room”. End-to-end encryption is on by default for new private rooms, so content is protected — but the number of servers holding the surrounding metadata went up, not down.

France's public sector has been working through the same table in public. An ANSSI first-level certification report (ANSSI-CSPN-2021/12, 26 May 2021) describes Olvid's server as one “dont le rôle est uniquement la mise en relation de messages entre les contacts” — a relay and nothing else — while noting, correctly, that certification “ne constitue pas en soi une recommandation du produit”. Circular 6497/SG of 25 July 2025 then told the administration to deploy Tchap, on the reasoning that “certaines messageries commerciales dites sécurisées sont sous l'influence de pays étrangers”: a sovereignty argument about who operates the server, which is the same axis by another name. A French-government-hosted resource updated on 5 February 2026 compares Signal, WhatsApp, Telegram and Olvid on exactly these points, though it is an individual contributor's page rather than an agency publication, and worth reading as such.

What the server knows anyway

Identity design is not the end of it, because an identifier can be enumerated whether or not you gave it away. Researchers reported in November 2025 that they could probe “over a hundred million phone numbers per hour” against WhatsApp, producing what they call “a census of WhatsApp users … even though the messages themselves are end-to-end encrypted.” An earlier line of work queried 10 % of US mobile numbers against WhatsApp and 100 % against Signal. The lesson generalises beyond phone numbers: any addressable identifier is a namespace, and namespaces get walked.

Where OSHI sits, and what that does not buy

OSHI requires no phone number, no email and no account. Your identity is a keypair generated on the device. There is no directory to enumerate and no registration record to hand over, because there is no registration. That is a real property, not a marketing line, and it is the row this project chose.

It is also not anonymity, and we should not let anyone read it that way. An address that connects to a relay still connects from somewhere, at some time. And our own recent bug is the perfect illustration of how a keypair identity leaks anyway: GET /api/web/sessions answers without a signature, so anyone who knows a user's public address can enumerate their linked devices — a namespace being walked, on our infrastructure, this week. A server-side owner gate is deployed in permissive mode while we measure unsigned traffic; until it enforces, that is live.

No row on this table is free. Removing the phone number removes a whole class of subpoena and a whole class of enumeration. It does not remove timing, it does not remove the relay, and it certainly does not remove the need to get your own endpoints right.