Building a messenger that hides metadata, not just messages

#buildinpublic #opensource #privacy #security

Most "encrypted" apps protect what you say. They do far less about who you
talk to, when, and how often — the metadata. And metadata is often the part
that actually gets people in trouble.

I'm building AegisLink, an open-source end-to-end encrypted messenger, with
that as the central obsession. This is the first post in a build-in-public
series. Everything here is pre-release and has had no independent audit yet,
so treat it as claims to verify — not promises. That's exactly why the code and
protocol are public.

The threat I actually care about

End-to-end encryption is table stakes now. The interesting question is what the
server learns even when it can't read your messages:

who is talking to whom
when, and how often
from which IP, on which device
message and attachment sizes

A server that logs those can reconstruct your entire social graph without ever
decrypting a word. So the design rule for AegisLink's relay is simple: know as
little as possible.

How that translates into code

No account. No email, no phone, no name. Identity is generated on-device (Ed25519 + X25519); your address is a random ID.
Dumb relay. It forwards opaque ciphertext and keeps no logs of who messages whom — no IPs, no access timestamps, no message sizes.
Modern crypto. Double Ratchet + X3DH, with a hybrid post-quantum layer (PQXDH). Private keys never leave the device.
Sealed signaling for calls. WebRTC SDP/ICE is sealed with NaCl box before it reaches the relay, so the server never sees IPs or DTLS fingerprints.
Encrypted at rest. The local DB is encrypted (SQLCipher); backups use an Argon2id-derived key only the user holds.

What's NOT done yet

Being honest is the whole point of doing this in the open:

Transport-level sealed-sender — hiding the sender from the relay process itself — is in active development, not shipped.
No third-party audit has happened. The protocol and threat model are in the repo precisely so people who know more than me can check the work.