The key to securing all communications application of cryptography with due diligence.

Cryptography is the science of keeping oral and written and other forms of communications secret as well as providing a means of authentication of the communicating parties. This chapter is devoted to principles and topics in cryptography that are germane to understanding wireless security applications. Our treatment is to foster management level understanding of cryptographic principles without undue mathematical reverence. First, we introduce the concepts of substitution, transposition, randomness, entropy, and speech universality. These are important lessons derived from historical cryptography and cryptanalysis. Second, we explore the related topic of attacks on cryptosystems. Third, we visit stream and block ciphers and their characteristics. Fourth, we explore the essential topics of key management, secret key, and public-key cryptography. Fifth, we explain the foundations for strong cryptography and the observed trade-offs. Sixth, we explore three crypto-solutions to the wireless security question: a stream cipher with a unique SHA-1 key-generation mechanism known as HORNET ,,the use of ECC and its relation to bandwidth and key size, and finally Rijndael, the AES winner and how it may be applied in the wireless arena in hardware such as FPGAs and ASICs. Cryptography is based on some interesting mathematical and difficult constructs. The reader is directed to the References for historical and modern material on cryptography, its supporting mathematics, and published standards for use in commercial and government organizations.