Please don't assume that Signal conversations are safe; they aren't. Encryption is, at best, safe for now. Encrypted data can always be saved to be decrypted later, and it's reasonable to assume that at least some of it is. Here's a poem that sums up the problem:
Storage is cheap
Budgets are deep
A quantum leap
Secrets they'll reap
Okay, it might not be the best poem, but it's short and easy to remember. 😃 While it's a good practice to use e2ee (end-to-end encrypted) apps like Signal, there are many opportunities for folks to intercept your communications. They might not be able to decrypt it at this moment, but the moment they can isn't far away: a sufficiently powerful quantum computer is on the horizon. When it arrives, it'll be able to easily break existing public-key crypto. This is well-known; cryptographers are already working on post-quantum cryptography, but that's not what we're using now.
In some ways, there's never been a better time to log encrypted data:
- COVID-19 has caused a huge uptick in digital communication over in-person communication.
- People are using encrypted communication more and more and many are careless about it; in fact, many are emboldened by encryption to say things they wouldn't say on other platforms.
- Wireless is so commonplace that it's never been easier to intercept data; surveillants don't even need a wiretap, data can just be pulled from the air.
- Most communication takes place on centralized services (including Signal), which means a surveillant could grab all messages on a Platform in one place or at least a small number of places.
- Storage is cheap, so storing a lot of data isn't too onerous for those with deep pockets.
If the only thing you need to keep secret are the details of an action for a period of a few weeks, you're probably safe using Signal or other e2ee tools. Realistically, you're probably safe even if you use phone calls and email; even if activists are surveilled, shutting down a protest is probably not worth the risk of exposing a secret surveillance network.
Before sending messages, it's worth considering the ramifications of future exposure, even if that's years or decades from now. Not just for you and those who receive your messages, but anyone who might be affected. For example, if you talk about a crime on a Signal thread, and then follow through with it, you've just implicated a bunch of other people. Also note that not everyone has the same level of risk and privilege, and information that's shared on an encrypted channel could be used not just against the author but recipients too.