Public Key Crypto is based on small prime numbers that create finite fields of polynomials.

In Public Key Cryptography, every pair of users needs a shared secret key.

In contrast to Symmetric Key Cryptography, Public Key Cryptography is based on the secrecy on the algorithm, not the secrecy of the key.

In a Public Key Cryptosystem like RSA, messages (i.e., the number m representing them) must always be smaller than the modulo n=pq.