In a hypothetical discussion we ended up with a concrete question I'd like to find the answer to:
If you try to brute force an RSA encryption, but the original vale which was encrypted was just random binary data, can you ever be sure you found the correct key? In other words: What are the success criteria for RSA brute forcing?
Do "you" say "This is neither a text encoding I know nor a file format I recognize, so this isn't the correct key" and try the next? Or can you tell by metadata or something that you've found the correct key? Or is it safe to say that completely random data encrypted with RSA is unbreakable by brute force?