Mach

Mach is an XMPP client created for fun and is meant to look at home on macOS in 2026. It supports end-to-end encryption with OMEMO:2 and OMEMO legacy — and specifically not OMEMO:1. You can send messages to your friends, and images via the HTTP-Upload service provided by XMPP servers, with AES-GCM encryption for the image payloads too.

An AI wrote it. I am not a programmer — I’m doing cosplay. What I did was direct it and test it against other clients and against XEP compliance.

I’ve tried to get it to the point where I can reliably use it as a daily driver to replace Signal. I wanted something that would look and feel as good as the Signal and WhatsApp clients on macOS, so that others may have less resistance to joining their friends on XMPP.

It is built entirely in Swift. As a result, it has implementations of OMEMO performed in Swift, and does not use any existing libraries such as libsignal. It is shown that OMEMO encryption validates with peers. Majority of the primitives are Apple’s — AES-GCM, SHA-512, HKDF and X25519 key agreement come from CryptoKit, and AES-CBC from CommonCrypto, because CryptoKit does not expose raw CBC.

🚨🚨The AI wrote the elliptic curve code too. OMEMO needs XEdDSA — signatures made with a Curve25519 key — and CryptoKit does not provide it. Not just a helper either: the field arithmetic over GF(2^255−19), the scalar arithmetic modulo the group order, and the whole Edwards curve group law. CryptoKit only hashes. That is about 1,100 lines of elliptic curve code under every identity signature Mach makes, written by a language model.

🚨🚨It has not been audited. The addition happens on every step of the scalar multiplication and is selected with a mask, so the work is the same whatever the key is. Some lower-level reductions still take a value-dependent number of passes, so I can’t tell you it is constant-time, only that the obvious leak is gone. Nobody has attacked it, and I wouldn’t know how — which is exactly the problem. That is what auditors are for. That it validates against Conversations, Kaidan and Gajim proves it is correct. It does not prove it is safe.

It is definitely true that you can use a perfectly good lock in a totally wrong way to provide no security, so buyer beware. This is not something to use to call Harrison Ford or Liam Neeson in a film.

There is a roadmap to support A/V calls — and even some fun QUIC-based A/V calls.

Yes, there are nasty bugs. Yes, it is AI slop. I have taken time to test it and try to make it useful for anyone else in the world who may see value in it. I can talk to my friends on a user interface I actually like, on a protocol I want others to love, and that’s enough for me. So it goes.

Considering only one other person has tested it so far, it will likely fall on its face somehow. So it goes. Thank you for your consideration.