> An RSA public key is a prime number. How are you going to compress a prime number? In principle, given an n-bit prime p, you can store an expected log₂ n − 0

> An RSA public key is a prime number. How are you going to compress a prime number? In principle, given an n-bit prime p, you can store an expected log₂ n − 0.5 additional bits by using the gap between p and the next prime. Though in practice, I'd be surprised if the 19 or so extra bits could be dangerous.