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Signal Protocol and the post-quantum path

Glitr’s encryption story has two timescales: computers we have today, and computers we may have later.

Signal Protocol (open source)​

The classical handshake and ratchet — the machinery that lets two people agree on keys and keep advancing them so old messages stay gone if a key leaks later — is the Signal Protocol.

That library is the exception to Glitr’s closed product: you can inspect it.

It is a research-grade implementation. Treat it as not a substitute for a formal audit of the whole messenger. It is still the piece we are willing to put under lights.

Why Signal is not the whole story​

A messaging app that only did today’s elliptic-curve handshake would be finished for 2016. Glitr also needs post-quantum key agreement: algorithms expected to remain hard even if large quantum computers arrive.

That path uses:

  • ML-KEM (FIPS 203, the 1024-parameter set) as the post-quantum envelope.
  • PQXDH — Signal’s post-quantum extended Diffie–Hellman: classical X25519 combined with ML-KEM-1024, so you do not throw away today’s hardness while you add tomorrow’s.

You can press the buttons:

These experiences are spec-faithful educational implementations. They are not a claim of wire compatibility with the Signal messenger app, and they are not a warranty.

Password encryption at rest​

Separate from the handshake: the encryption password you type at connect derives a key (memory-hard hashing, then authenticated encryption) that seals documents in your mailbox. That is “the host should not read the file contents,” not “this is Signal.”

Cascade demos (layering more than one primitive) live in the encryption try path. They are for understanding; Glitr’s product path is the mailbox plus handshake plus live link, not a hobby of stacking ciphers for its own sake.

How to talk about this without lying​

Safe sentences:

  • Messages are encrypted so a git host is not reading the thread.
  • The handshake work includes an open Signal Protocol library.
  • A post-quantum KEM and PQXDH are part of the design so the story does not end at elliptic curves.

Unsafe sentences we will not use:

  • “Unaudited end-to-end forever against nation states.”
  • “Compatible with the Signal app.”
  • “The entire messenger is open source.”