Technical analysis of TM SGNL, the unofficial Signal app Trump officials used

Summary

Yesterday, a Reuters photographer captured a photo of the freshly-ousted former National Security Advisor Mike Waltz checking his Signal messages during a Trump cabinet meeting. If you're not familiar with Waltz, he's most well known for inviting The Atlantic's editor-in-chief to secret Trump administration war crimes Signal group. They discussed, and executed, bombing an urban apartment building full of civilians to kill a single man.404 Media journalist Joseph Cox published a story pointing out that Waltz was not using the official Signal app, but rather "an obscure and unofficial version of Signal that is designed to archive messages" called TM SGNL.Zoomed-in crop of the Reuters photo showing Mike Waltz using the TM SGNL app. Images credit: REUTERS/Evelyn HocksteinThis app uses Signal's servers, making it possible for Waltz to send end-to-end encrypted messages to normal Signal users, like Jeffrey Goldberg from The Atlantic, for example. However unlike the Signal end of the encrypted conversation, the TM SGNL end automatically archives a copy of the plaintext messages (even ones with disappearing messages) somewhere else that may or may not be secure.In a video the company published, they show Signal messages getting archived into a Gmail account.I decided to look into this app. I discovered:The senior executives of the company behind TM SGNL appear to be Israeli, and the CEO's bio mentions his work with Israel Defense Forces' Intelligence unit.TM SGNL is most likely violating Signal's open source license, and the company's other apps are probably violating the proprietary licenses of other software like WhatsApp and WeChat.The Android and iOS versions of the app are not available for the public to download, and in fact practically the only way to get the app is if you're using a device enrolled in an MDM service that's tied to an Apple Business Manager or Google Enterprise account.I speculate about exactly how I think the Trump administration is using this (unap...