4
Encryption and Decryption
In this chapter, we explain the concepts of encryption and decryption, describe the prerequisites needed for effective encryption and decryption, and illustrate these procedures using examples based on AES-256. On completion, you will be familiar with the cryptographic notions of encryption and decryption, and the core aspects that make modern encryption and decryption algorithms secure. Besides providing a precise definition of symmmetric cryptosystems, we will provide some more details on more advanced concepts we touched upon in the last chapter, such as the following:
Information-theoretical security
Computational security
True randomness versus pseudorandomness
