RSA isn't proven.. ;)
ALL asymmetric cryptography has no mathematical proof. The only proof is that nobody has developed a fast way to reverse the one way function. (In the case of RSA, factorization of the public key. In ECC, calculating how many times the A is dotted.)
But yes, it's a lot better than a tripcode. ;D
Yes, RSA signature would work if Q wants to bother with it.
How it works:
Q generates public and private key.
Q distributes public key. Unfeasible to crack even with supercomputer.
If a post is signed with public key, only private key can decrypt.
If a post is signed with private key, only public key can decrypt.
Thus, he encrypts his post with private key and then you verify by decrypting with his public. Only he can encrypt posts with private key because he never distributed it.
Complicated, but professional.
Also,
Please don't talk about crypto if you know jack shit.
I seen too many people posting bullshit that is completely wrong trying to talk about cryptography.
He's in for some shit now.
He's fucked.