Elliptic Curve, Diffie Hellman, Discrete Log, Elgamal Encryption.
privately choose a and b integers and apply the operations: Q1=a*P and Q2=b*P, respectively. They will send Q1 and Q2 to each other so that Alice will apply the operation a*Q2 and Bob will apply the operation b*Q1. Both ends up getting a*b*P although the eavesdroppers cannot get this as they don’t