There are two key mechanisms: symmetric and asymmetric key mechanisms. A symmetric key mechanism is not used recently because of difficulty of managing key. The key which is shared between two (or several) parties should be kept as secret. An asymmetric key mechanism is also known as public-private key. A private key is kept as secret by the key owner whereas a public key is known to anyone. Two use cases are considered for this mechanism.
Nonce is used to check data is the most recent one. Nonce is a randomly generated number when there is some modification. The figure above (reference: wikipedia) describes an example of usage of nonce in client-server authentication. As seen in the figure, there are two nonces: a server nonce and a client nonce ( = cnonce).
The followings are the three components of the security. Confidentiality To conserve the secrecy of the contents. The contents should not be shown to an unauthorized user. Ex> Encryption Integrity To prevent the contents of data from being modified or deleted by an unauthorized user. Ex> checksum Availability Data should be read or used only by the authorized users with the owner’s intention. In other words, the data should be available to an unauthorized users only when the owner allows it.