Elliptic Curve, Diffie Hellman, Discrete Log, Elgamal Encryption.
Alice and Bob will chose two secret integers a and b, respectively. Let Alice calculate h1=g^a(mod p) and Bob calculate h2=g^b(mod p). Now each will transfer the calculated number to each other so that Alice and Bob (and eavesdroppers) will have access to h1 and h2. Bob will calculate h1^b (mod p)