“Telegram has launched a pretty intense campaign to malign Signal as insecure, with assistance from Elon Musk. The goal seems to be to get activists to switch away from encrypted Signal to mostly-unencrypted Telegram”
Musk claimed that Signal has unpatched security vulnerabilities. As a cryptography expert I’m not aware of any: instead Signal has top-notch state-of-the-art encryption which has been adopted by its competitors it’s so good.
Telegram isn’t end-to-end encrypted by default. It has no group chat encryption whatsoever. It uses a bizarre, badly designed “MTProto” protocol about which dozens of cryptography papers have documented myriad unfixed flaws.