It doesn't matter how many conversations are going. With private key encryption, what a phrase encrypts to for one person would be different than the next. It w

It doesn't matter how many conversations are going. With private key encryption, what a phrase encrypts to for one person would be different than the next. It would have to be trained solely on your conversation. Encryption is also dependent on all the text before it as well as text in the same block, so it would have to be the beginning of the message with no metadata to throw off alignment saying the 16-byte phrase so many times that it could pick up a difference. I'm pretty confident it's impossible to get anything useful out of that.