2.3 Confidentiality
A fundamental need in secure communication is to ensure the privacy of the information transmitted between the communicating parties. In cryptography, this is referred to as confidentiality of data.
More precisely, confidentiality is the ability to keep the content of information from all but those authorized to have it [117]. Confidentiality therefore guarantees that no one except the sender and the intended receiver(s) of the information can read it.
In the classical scenario illustrated in Figure 2.1, these are two parties (Alice and Bob). In general, cryptographic mechanisms can be used to ensure confidentiality for any number of parties, for example, using the concept of group keys. In the simplest case, there is only one party involved, for example, a user encrypting their private data stored in the cloud or on a personal device such as a smartphone.
Figure 2.3 shows the classical scenario for confidentiality. The eavesdropper Eve has the capability...