Solution
= Solution
RSA chooses $n=pq$ and exponents $e,d$ with $ed\equiv1\pmod{\phi(n)}$. The public key is $(n,e)$, encryption is $c\equiv m^e\pmod n$, and the secret exponent decrypts via $c^d\equiv m\pmod n$. Security relies on the difficulty of recovering $\phi(n)$ from a large unfactored $n$.