2 Symmetric Key Cryptosystems
2.1 Mixed Encryption
Modern cryptography is usually separated into symmetric key cryptography and public key cryptography. In symmetric key cryptography, both the encryption and decryption keys are supposedly known only to the sender and receiver, usually referred to as Bob and Alice. In public key cryptography, the encryption map is public knowledge but only the receiver knows how to decode. In this chapter we look at the standard methods for efficient symmetric key cryptography, while in Chapter 7 we discuss public key methods in detail.
In general, symmetric key encryption methods are much more efficient in terms of time and storage requirements then public key methods. Therefore, in real practice what is used ...