A Basic Cryptosystem

Introduction

In general, a cryptosystem consists of three types of protocols for the following functions:

1. Key generation: Creating a single or a pair of secret key(s).
2. Encryption: There’s a protocol $e(\cdot)$ that transforms cleartext $m$ into ciphertext $c$.
3. Decryption: There’s a protocol $d(\cdot)$ that transforms the ciphertext $c$ back to its corresponding cleartext $m.$

The figure below shows the scheme of a basic cryptosystem.

Figure 1