In addition, one to many communications are often necessary, for example, many people communication with a single server. The secret key would not stay secret for long. In the 1970's, the public key (sometimes called asymmetrical) cryptography was devised. In this system, keys come in pairs, one for encryption and one for decryption. The public key is made widely available so that people can encrypt messages to the owner with it. Then the recipient uses the closely guarded private key to decrypt the message. Public key cryptography also makes it possible to create digital signatures that cannot be forged. Digital signatures use public key cryptography in reverse. Messages are encrypted using a person's private key and can only be decrypted with that person's public key. To prevent someone from cutting and pasting a person's encrypted digital signature, one person sends a challenge phrase, The other person signs the challenge phrase with their private key and returns it. If the challenge decrypts successfully with the other's public key, then the identity is confirmed. Public key encryption is much slower than symmetric key encryption, which makes public key encryption undesirable for large documents. Combining symmetric and public key encryption provides a solution This involves the concept of a digital envelope. A message is encrypted with a session key and a symmetric algorithm. This session key will be used for this transmission only then discarded. The digital envelope is created by encrypting the session key with the recipient's public key. When the message and digital envelope are received, the recipient uses his private key to decrypt the session key. He then decrypts the message using the session key, which is known only to the sender and recipient. .
SSL: SSL stands for Secure Sockets Layer. It is an example of a cryptographic protocol that incorporates certain cryptographic principles.