ElGamal encryption

The ElGamal encryption system is an asymmetric key encryption algorithm for public-key cryptography . ElGamal encryption can be defined over any cyclic group $G$, like multiplicative group of integers modulo n. Its security depends upon the difficulty of a certain problem in $G$ related to computing discrete logarithms.

Sources and more detailed information:

https://en.wikipedia.org/wiki/ElGamal_encryption