The process of replacing original data with special-characters is called an Encryption. A highly secured server handles the encryption and Decryption. You need a private key to decrypt the data. Else, you cannot decrypt the data. Private keys are two types. The sender uses one private key and the receiver uses one other private key. I have given in this post about 8 encryption methods. Flow Diagram of Encryption image courtesy by digit.in   Different Encryption Methods Classic Cipher Random Key Generation RSA Token Hash Functions Mac value - Message Authentication code Key Hash TLS Protocol Authenticated Cipher  1. Classic Cipher. The best example is this kind of algorithm was used in world war -II communication machines. 2. Random Key Generations. One kind of security. They use an algorithm that sends random numbers. People use that number as a password.  3. RSA Token. Every 30 seconds a token is generated. Mostly people use fo...