I'm trying to help friends in Ukraine as much as possible and advice on secure communications would be a way to do it. I know messaging apps security have been discussed in HN before but I wanted to ask the community about it in the context of the conflict of Ukraine.
The end goal for me is to give the best advice for my friends but I think it can also lead to the type of discussion HN is focused on.
I wouldn't trust any of the mainstream apps for sensitive information. On Telegram you have to create a secret chat for each contact/device for your messages to be encrypted end-to-end. Which might protect you from a possibly malicious Telegram in case the implementation is honest.
If the person is involved in the fighting good OPSEC practices are a must like not sharing sensitive info or at least deleting it after you have read it. It's important to preserve plausible deniability.