ABSTRACT
This chapter explores basic concepts of symmetric key cryptography. The knowledge of encryption key is implicitly or explicitly equivalent to knowing the decryption key. These algorithms are typically fast and much more efficient than asymmetric algorithms in both hardware and software. Symmetric encryption gives a level of authentication since the information is encoded with one symmetric key; it cannot be decoded with some other key. Secure file transfer protocols make use of symmetric key primitives to encrypt data. Shannon introduced the concept of two primitive operations that can lead to a specific end goal of accomplishing strong encryption. In the design of symmetric encryption systems, Substitution and Permutation network is a typical component to accomplish both confusion and diffusion. A cryptographic mode refers to the way in which plaintext can be encrypted into ciphertext by combining the basic cipher, some sort of feedback, and some elementary operations.
