Secret Key Cryptography
Confidentiality is a data security property. Its primary goal is to confine knowledge of information that the data represents within a particular set of entities (such as human or a programmable electronic system) having the ability to interpret the data. The process of achieving this confinement property, otherwise known as secrecy, is by way of scrambling the plaintext form of data into a reversible representation that perhaps has no syntax and certainly should have no semantics.
Long before the advent of electronic systems, different methods of data-scrambling transformations, known in contemporary terms as the science of cryptography, were used. A cryptographic transformation of data is a deterministic procedure by which data, in its plaintext form, is disguised to result in a ciphertext representation that does not reveal the original data. Similarly, the ciphertext can be reverse-transformed in a deterministic fashion by a designated recipient so that the original data can be recovered.