Cryptography is the practice and study of techniques for secure communication in the presence of third parties (called adversaries). More generally, it is about constructing and analyzing protocols that overcome the influence of adversaries and which are related to various aspects in information security such as data confidentiality, data integrity, authentication and nonrepudiation. The process of encryption and decryption is performed by using symmetric key cryptography and public key cryptography for secure communication. In this paper, the authors studied that how the process of encryption and decryption is perform in case of symmetric key and public key cryptography using AES and DES algorithms and modified RSA algorithm.