Known-plaintext attacks aside, if you're going to compress text, it must be done before encryption.

I don't know if compression offers much protection against plaintext attacks.

This also makes me wonder how helpful AI is in such situations. AI is essential an extremely effective, lossy, compression algorithm.

Compression + encryption can be dangerous if the compression rate is exposed somehow (between messages or within packets of a message).

> we show that it is possible to identify the phrases spoken within encrypted VoIP calls when the audio is encoded using variable bit rate codecs

https://crypto.stackexchange.com/a/2188

See also https://breachattack.com/ when the plaintext is partially attacker-controlled.

If nothing else it would make a great twist in a fiction setting.

These paraphrasing instructions could be followed. But the paraphrasing could be done using some LLM. A sufficiently advanced adversary manages to invert the model somehow, and as a result can get the original plain text out of the paraphrased message, which lets them do a known-plaintext attack, get the key, and use it on other messages.

Sort of technobabble (is the idea of inverting an LLM nonsense?) but fun.