2.1 Introduction2.2 Encryption System Model2.3 Key Types2.4 Diffusion-based Algorithms2.4.1 The Advanced Encryption Standard (AES)2.4.1.1 AES Encryption Algorithm2.4.2 The RC6 Algorithm2.4.2.1 RC6 Encryption Algorithm2.5 Permutation-based Encryption2.5.1 CBC, CFB, and OFB Chaotic Encryption Modes2.6 Encryption Quality Metrics2.6.1 Histogram2.6.2 Deviation of an Encrypted Image2.6.3 Immunity to Noise