When the client and server uses the authentication system, in order to begin the communication, client needs to successfully prove his identity. This is done using a username and password. The client needs to present its username and password to the authentication server, and it will verify the identity. There are legacy protocols and systems that send this information in clear text even in an open network. Telnet is a good example. If someone is listening to traffic (packet capturing) for the telnet session, they can easily capture password as it is transmitted in clear text.
Modern authentication systems are well aware of these types of threats and use different technologies to encrypt credentials or create cryptographic hashes and then use them for identity verifications. The cryptographic hash means a password string transformed into a fixed-length digest...